MYE Technical Manual 1942
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vke
HYE TECHNICAL,
. MAN nAL
MALLORY
.
Published by
P. R. MALLORY &
~O.,
Indianapolis, Indiana
IN~.
OUR SINCERE APPRECIATION TO YOUI
* ThuS do we ackn~wledge a special debt of gratitude for'generous, spontaneous, willing
help, ~nd permission to use articles, charts, and other information without which it would have been impossible
to make this MYE Technical Manual complete.
Air-King Products Co., Inc.
Alliance Manufacturing Company
Automatic Radio Manufacturing Co., Inc.
Belmont Radio Corporation
Brush Development Co.
Bryan Davis Publishing Co.
Buick Motor Co.
Capehart Division of Farnsworth
Television & Radio Corp.
Clough-Brengle Co.
Colonial Radio Corporation
Communications
Crosley Radio Corporation
Crowe Name Plate & Manufacturing Co.
Delco Appliance Division,
General Motors Sales Corporation
Delco Radio Division,
General Motors Corporation
Detrola Corporation
Electrical Research Laboratories, Inc.
Electronics
Emerson Radio & Phonograph
Corporation
Fada Radio and Phonograph Corporation
Fairbanks, Morse & Co.
Farnsworth Radio & Television Co.
Ford Motor Co.
Galvin Manufacturing Corporation
General Electric Co.
General Household Utilities Company
General Radio Co.
Gilfillan Bros., Inc.
Herbert Horn Radio Co.
Hickok Electrical Instrument Co.
Howard Radio Company
Hudson Motor Car Co.
Jensen Radio Manufacturing Co., Inc.
Ken-Rad Tube & Lamp Corporation
Magnavox Co., Inc.
McGraw-Hill Book Co., Inc.
Meissner Mfg. Co., In!!.
Midwest Radio Corp.
Mission Bell Radio Mfg. Co., Inc.
Noblitt-Sparks Industries, Incorporated
Pacific Radio Corporation
Pacific Radio Exchange, Inc.
Packard Bell Radio Company
Packard Motor Car Co.
Peter Plln Radio Corp.
Philco Radio & Television Corp.
For years it has been the Mallory-Yaxley pledge to retain
leadership in furnishing constructive, helpful information and
assistance to the radio service and engineering professionsand to make that information worthy of its confidence. In
this, the MYE Technical Manual, there is ample evidence of
the continuance of this pledge.
Radio Products Corporation
Radiotron Division of RCA Mfg. Co.
Raytheon Production Corp.
RCA Manufacturing Company, Inc.
Radio Engineering Handbook, by Keith
Henney (Copyright McGraw-Hill Book
Co., Inc.)
Radio Manufacturers Association
Sears-Roebuck & Co.
The Spar's-Withington Company
Stewart-Warner Corporation
Stromberg-Carlson Telephone
Manufacturing Company
Sylvania Electric Products, Inc.
Trav-Ier Radio & Television Corporation
Triplett Electric Instrument Co.
Troy Radio & Television Co.
United American Bosch Corporation
Utah Radio Products Company
Warwick Manufacturing'Co.
Webster Company
Wells-Garduer & Co.
W.lcox-Gay Corporation
Zenith Radio Corporation
In dedicating the MYE Technical Manual to the radio and
electronic industries, we are also dedicating it to those who
have made it possible.
You are always welcome at the Mallory factory, where you
may review and witness the continued research and development work-an activity which warrants your 100% confidence.
Reproduction or use, without express permissi;on, of editorial or pictorial content, in any manner, is prohibited,
No patent liability is assumed with respect to the use 01 the in/ormation contained herein,
Copyright 1942 by P. R. Mallory & Co" Inc., Indianapolis, Indiana, U. S. A.
Copyright under International Copyright Union
All rights reserved under Inter.American Copyright Union'{191O}, by P. R. Mallory & Co., Inc.
F Gurth Printing
PRINTED IN U. S. A.
· . . Up to This Time
N
one of our friends-evidently a
mation you could get to keep apace. So we brought
newcomer in the radio service field-wrote us
out the first complete Auto Radio Manual with quar-
for some help. "I knew you made parts, both original
and replacement," he said, "but how long have you
terly supplements to k~ep it up-to-date. The demand
for this book was terrific. Many of you still treasure it,
been is~uing technical literature ?"
even though it has been supplanted by more complete
When? It started a chain .of memories that ran
back eight years when vibrators were new and myste-
and up-to-date guides.
OT LONG AGO
rious; and service men needed information and help
That same year we gave you a greatly improved
and more complete Volume Control Manual-con-
to make repairs. Like every subsequent publication,
the Manual we issued then had a definite"purpose ...
cise, accurate and practical. It was widely imitated
filled a definite need of the industry.
announced thirty new replacement volume controls
but never quite equaled. More important to you, we
That same year, 1934, saw another help produced
that would service 98 % of the 3,200 set models then
in answer to your insistent calls for aid. The publication of a complete manu~l on replacement volume
in existence. Only four of the new controls would service 1938 models. It was the first move towards stand-
controls had been attempted but never before accom-
ardization of replacement controls.
plished. It became a reality with the issuance of the
Yaxley Replacement Volume Control Manual.
In 1935, we had not fully made up our minds
You have told us again and again that the time a-nd
money it has saved you is incalculable.
whether to issue further publications ... but you de-
In 1936, we introduced standardization of condensers with the announcement of 69 units for seryic-"
cided for us. Automobile radio was gaining ground
ing 100% of all radio sets using dry electrolytics.
with seven league boots, and you needed all the infor-
Over and above the many constructional features for
3
THE
MYE
TECHNICAL
universal replacement was an extra featur~the new
Mallory Condenser Service and Replacement Manual,
which gave in Qetail the universal app,lication ,of these
condenser~ in everyday service work. To guide our
planning, we had solicited your aid through personal
calls and extensive questionnaires. From a detailed
analysis of your problems, we made possible the first
practical system of condenser servicing.
But, in spite of the progress you had helped us
make, we were still dissatisfied. Too many of yo"\!
complained of the growing number of "guides," the
endless job of looking through dozens of books to get
the "dope'; you needed. A bright idea suddenly struck/
us. Why not lump all of our separate manuals into
one complete book-a book where you could find on
one page and on one line all the information you '
nee,ded for replacing controls, condensers and vibrators ? We could also put in the I.F. peaks of all makes
and models, the complete tube complement, perhaps
a reference to the transformer circuit. So, we started
to work.
In May, 1937" after months of almost insurmountable compilation and production problems, we
brought out the First Edition of the Mallory-Yaxley
Radio Service Encyclopedia. (You nicknamed it the
"M.Y.E.") Used daily by tens of thousands, this 'book
prompted your world wide testimony as to itJl indis-
MANUAL
pensable value. Many enthusiastic letters not only
bear witness to this fact, but als~ guided us in making,
important changes in subs~quent editions; changes
that, made their predecessors obsolete.
The Second Edition "M.Y.E." followed the firstfifteen months later. 'Automatic tuning, with its maze
. of complications to plague the service engineer, was
appearing on all new sets with infinite variations.
From our first-hand experience in the design and application of push-button switches with practically
e,very ma~or set manufacturer, we gave you the first
clear, detailed amdysis of all the systems-'with suggested servicing procedures. It was the hit of the year.
Again, you were profuse in your thanks.
In September, 1939, we presented the Third Edi- .
tion,free,of former ~'frills." It had to be. More new
models of radio receivers had been announced during
the period from March, 1938, to September, ~939,
than in any other comparable period. The listings of
makes and models alone required more than twice the
number of pages that had been devoted to them in the
first edition. It became obvious that it would be an
impossibility to have both listings and general technical information in ~ single volume. The book would
become too big, too bulky and too expensive. We
. had
,
4
,
THE
MYE
TECHNICAL
MANUAL
no choice but to omit the technical articles. However,
Almost a year had elapsed. from the time that the
the listings were made even more valuable by the addi·
twelfth, and final Supplement was mailed to you be-
tion of a number of new features, including a refeience by volume and page number to Rider's Manuals,
fore we issued our next publication ... the 4th Edition M.Y.E. During that year you showered us with
questions. The Engineering Application Section of
our Wholesale Division worked overtime to get you
the right answers-fast. Replacements were becoming
more complicated. Controls, particularly, were the
big headache. The variety of shafts and bushings were
enough to drive you "nuts." We purposely held up
the publication of the Fourth Edition M.Y.E. so that
we could give you thorough and painstaking replacement recommendations ... and also the maximum
universal replacement from the fewest number of indi-
and more complete information on tube cOJ;nplements.
You were grateful, and told us so.
vidual parts.
Although we started early in 1940, the further we
got into the job of gathering samples of original parts,
circuit information and other data that would enable
us to set up accurate recommendations, the more evident it became that we could not hope to publish the
M.Y.E. in 1940. It was September of 1941 before we
could get the Fourth Edition in your hands ... but it
was more valuable to you because of the delay.
There were twice as many pages of set and model
listings as in the Third Edition ... almost 400. We
had to change the shape of the book, too, in order to
New and vital developments in radio continued at a
dizzy pace. Shifts in frequei:lCY assignments for stations in the broadcast band necessitated your help in
the re-setting of automatic tuning receivers. Frequency modulation was coming in. Television, with
totally new complexities for the service man, was on
the threshold. Anticipating your troubles, we ha'stened
the first issue of the Supplemental M.Y.E. Monthly
Technical Service ... a service designed to give you
timely data in an unbiased, accurate and easy-tounderstand manner. As succeeding issues reached you
month after month, you hailed the supplements as
the one convenient, economical source of technical
information. You told us that they kept you abreast of
every current development, that one issue was worth
the price of the whole series.
5
THE
MYE
TECHNICAl.
MANUAl.
accommodate original part numbers on all products.
heat of the all-out defense effort, its progress con-
But this new feature saved you even more time and
tinued apace despite serious curtailments in our.
trouble in finding the correct replacement.
When we issued .the Fourth Edition M.Y.E. last
full-time technical staff as a re.sult of drafts and enlist-
fall, we did not announce a Second Supplemental
. mately 2,000 copies are being distributed to military
Technical Service. There were too many uncertainties
radio instructors. Once you look through the book,
ahead. We were in the midst of mounting defense
you'll understand why.
ments. As further proof of its timeliness, approxi-
activities. The future of the entire radio industry was
We are const~ntly studying your problems, work-
unplcdictable and we hesitated to commit ourselves
ing out new helps for you to meet the restrictions that
on a monthly service that we might have to suspend.
We sounded out a great number of you by personal
war imposes, bringing new ideas to you to make your
work more effective and more profitable.
letter on the idea of bringing the former supplements
We are in business to help ·you. Whether it be the
thoroughly up-to-the-minute, adding timely new ones,
selection of a volume control for a 1928 model re-
and binding the whole works in hard cloth covers.
.Your answers were so overwhelmingly affirmative
ceiver, the procurement of a switch for an aircraft
that we started immediately on the all-important revi-
address system, or any of the countless other problems
sions and new texts.
in service, substitution or procurement ... the recom-
crankshaft balancer, taking the hum from a public
Equally important as the enthusiastic "go-ahead"
mendations of the Mallory Engineering Department
signal were the many fine suggestions on the material
are yours for the asking. Sure, we're busy ... but not,
and subject matter for the new book. These sugges-
too busy to help you out.
We hope you'll find the M.Y.E. Technical Manual
a worthy companion to the other well-read books in
your library. Use it regularly-refer to it, and to the
Fourth Edition M.Y.E., whenever you are stumped.
If the answers aren't there, then write to our Engineering Application Section, Wholesale Division.
tions were all given the most careful consideration,
and wherever possible they have been incorporated to
make the M.Y.E. Technical Manual your book. In
presenting the M.Y.E. Technical Manual, we renew
again the responsibility we accepted eight years agoto provide you with factual, usable, reliable data that
would make your job easier and more profitable.
It is a war-time book in every sense. Begun in the
Remember, "Come hell or high water," we're here
to help you.
P. R. MALLORY & CO., INC.
6
e
THE
MYE
Section' I
TE~HNI~AL
MANUAL
Loud Speaker Design
and Application
MALLORY
7
Section 1 •
THE
MYE
TECHNICAL
MANUAL
LOUDSPEAKERDESIG.N AND APPLICATION
In spite of the fact that the most important part of a radio receiver, P. A.
system, electric phonograph, and similar sound reproducing systems is its
loud speaker, there has heen a dearth of practical technical information on this.
device. We~ave long felt that {l simple, straight forward, factual exposition
of loud speakers would be of real value to the service engineer.
It was with this thought in mind that we asked the Jensen Radio Manufac- .
turing Company, Chicago, Illinois, for' technical data suitable for preparation
of a text on this subject. They generously responded by furnishing this complete treatise, which we believe to be a real contribution to the technIcal literature of radio. We believe you will find this chapter to be both interesting
and valuable.
,
I. General Definitions, Physical
Characteristics
DIAPHRAGM
A loud .speaker is a device for converting audio-frequency electrical power
into acoustical power and radiating it
into a specific region"
The most common . type of loud
speaker is the moving coil or "electrodynamic" type. This type of loud
sp'eaker consists essentially of a radiator
or diaphragm to which is rigidly attached a coil, which in turn is immersed
in a steady magnetic field. This dia·
phragm and coil assembly is suspended
by flexible supports allowing vibration
parallel to the axis of the coil. These
vibrations are the result of passing the
audio-frequency electric current through
SOUND CHAMBER
.
VOICE COIL
Fig.2a
the coil. Figures 1 and 2 illustrate this
type of loud speaker.
Figures la, 11;>, and lc illustrate the
"direct-radiator" type. That is, the loud
speaker is designed in such a way that
when used in conjunction with a suit-
CLAMP
RI G
DUST CAP
ANNULUS
SUSPENSION
CONE
HOUSING
SPIDER
SUS
able "baffle" the diaphragm radiates directly into the surrounding air. In contrast, Figure 2 illustrates the class·in
which the diaphragm is coupled by
means of a "sound chamber" to a "horn"
'. which'in tum radiates into the air. This
latter class of loud speakers will be discussed in a later section.
Figure la illustrates a speaker in
which the magnetic field is supplied by
means of an electromagnet or field coil,
whereas Figures Ib and .lc illustrate
those in which a permanent magnet fulfills this duty.
II. The Magnetic Circuit; Field
Coils and Permanent Magnets
CORE OR - - ' i ? ? l
POLE PIECE
F'I ELD COl L
CASE
F'I ELD COl L
Fig.la
8
".
The operation of the loud speaker
does not depend upon how the magnetic field is supplied, providing this
• Section 1
LOUD SPEAKER DESIGN AND APPLICATION
ANNULUS
PENSION
CLAMP
RIN
TABLE 1
Field Coil Excitation
Power
(watts)
DIAPHRAGM
OR CONE
CONE
HOUSING
~:..-~----
RING
MAGNEr
Fig.lb
field has the required strength. This
latter point should be especially noted
since all further explanation concerning
the action of the moving parts will be
general, that is, the required magnetic
field strength is assumed.
Permanent magnet loud speakers are
generally available having magnetic
field strengths identical to equivalent
models using field coils. This equality
is a result of relatively recent develop·
ments in magnetic alloys. No apprecia.
ble deterioration has been noted in
original samples of magnets made from
these alloys several years ago. Thus
misapprehensions with regard to the
efficiency and stability of permanent
magnet structures need no longer exist.
For a given magnetic structure the
field strength depends on the magnet
weight. ijowever as the magnet weight
varies, the air gap (the region in which
the voice coil is situated) should be altered to give best results. A figure of
merit including all these factors is a
good measure of the effectiveness-i)f the
unit; one such measure is-the magrretic
energy iIi the gap stated in milliops of
ergs. Typical values are 0.19 "for a
~~mall inexpensive 5-inch perm'anent
mag-llet speaker, 1.36 for a good quality
lO-inch speaker and 7.5 for a high
quality 12-inch speaker.
For an electromagnet magnetic structure the field strength depends on the
power dissipated in the coil. The manufacturer specifies the normal power to
be dissipated in the field coil. Table 1
shows the field current or voltage required to dissipate a given power in a
field coil of given resistance. As a rough
guide, field-coil power dissipation
should be approximately equal to the
maximum audio-frequency power:han.
dling capacity of the device.
In choosing a loud speaker for a
given application, the decision as to
permanent magnet or field coil magnetic structures depends on several factors (see section 9). Cost is in many
cases a vital factor. Very small permanent magnet loud speakers cost from
the same to about 10 % more than
equivalent field-coil units. Larger permanent magnet speakers used for public
address and large radio receivers cost
approximately 50 % more than field
coil equivalents, while for very large
magnetic structures, such as used in
large public address installations, theatre work, etc., the permanent magnet
speaker may cost more than twice as
much as the field coil unit.
III. Baffles, Cabinets and Aconstic
Loading Networks
Loud speakers of the direct-radiator
type are invariably mounted on some
form of auxiliary structure. This may
take the form of a cabinet (radio console), a flat plan~ surface with an open-
Field
Resistance
(ohms)
Voltage
Field
Current
(rna)
3
3
3
3
3
500
1000
1500
1800
2500
38.8
54.8
67.2
73.6
86.6
77.5
54.7
44.7
40.8
34.6
4
4
4
4
4
500
1000
1500
1800
2500
44.8
63.3
77.5
85.0
100
89.3
63.1
51.6
47.0
40
6
6
6
6
6
500
1000
1500
1800
2500
54.8
77.5
95
103
122
110
77.5
63.1
58,2
49.1
8
8
8
8
8
500
1000
1500
1800
2500
63.3
89,5
110
120
141
126
89.4
72.7
66.6
56.7
500
70.8
100
122
134
158
141
100
82
74.6
63.3
10
10
10
10
10
~ '" 1500
' 1800
14
14
14
14
14
100015'00
1800
2500
83.8
118
145
159
187
167
119
96.5
81. 7
74.8
26
26
26
26
26
500
1000
1500
1800
2500
114
161
198
216
255
228
162
131
120
102
~OOO
250~
/;iit
ing through which the speaker radiates
(flat baffie) , or some more complex
System of acoustic loading. All of these
P PLATE
POLE PIECE
ICE COIL
LOUD SPEAKER HORN UNIT WITH ANNULAR DIAPH RAGM
Fig.2b
9
r
Section 1 •
H E
MY E r E C H N I CAL
MAN
ANNULUS '
NSION
SPIDER
SUSPENSION
CORE OR
POLE PIECE
VOl
COIL
SLUG
MAGNET
MAGN
CASE.
Fig. Ie
devices may be classed in general as
"baffles." Their primary function is to
acoustically "load" the loud speaker to
allow it to radiate more efficiently. This
improved efficiency usually occurs in
the low frequency range. It is important
to remember that the more "adequate"
the "baffle" the more improved will be
the low-frequency response. It should
be emphasized at this point that a loud
speaker cannot be considered as an iso,lated element because: (1) Any baffle is
definitely a part of the acoustical system; (2) The loud speaker may radiate
into a closed room which has its own
acoustic resonance characteristics reflected into the loud speaker; (3) The
accompanying audio-frequency electri·
cal circuits are definitely a part of the
composite system and must be consid. ered when we discuss the operation of
a loud speaker system.
The simplest type of baffle is a large,
flat surface with an' opening through
which the speaker radiates. However,
the simple flat baffle has the following
disadvantages: (1) Large size for adequate low-frequency response; (2)
Very poor low-f~equency response for
large angles from the speaker axis (that
is, as we approach the plane of the
baffle); (3) Limited acoustical flexibility (that is, limited oppottunity for
modification of response characteristics). The open-back radio console.cabinet has the same inherent disadvantages,
since it resembles a flat baffle. However,
'here a new form of difficulty arises
known as '''cabinet resonance." Cabinet
resonance actually modifies the response
characteristics of the system due to a
standing wave pattern in the, cabinet.
10
This results in emphasis of the 150 to
250 cycle response.
The closed box is an improvement
in that it eliminates the back-side radiation as such. In other words, if the
cabinet is rigid, all the sound at the rear
of the cabinet is due entirely to radiation from the front of the cone. There
is, of course, practically u~iform radiation in all directions at low frequencies. See Figure 3. The back-side radiation from the cone may be absorbed
by a heavy absorbent lining on the
interior of the box.
SOLID LOUD SPEAKER ENCLOSURE
SPEAK(R
UA
L
Still more elaborate acoustical loading I networks are in common use. In
one version a large volume is coupled
to the loud speaker and the acoustic
enolosure resonance is used to increase
low-frequency response. A modification of this method is one in which a
column at the rear of the speaker is
lined with absorbent material so that
the column acts as a long acoustic
'trans:q:tission line. '
Figure 4 shows an especially effective
type of acoustic loading in which a second opening or "port" in the otherwise
complete enclosure is adjacent to the
loud speaker diaphragm and is in effect
another radiator coupled to the loud
speaker diaphragm. This "secondary
radiator" (air in the mouth of the
port) moves with a given amplitude
and phase relative to that of the loud
speaker diaphragm in a ma~mer depending upon the spe~ker design and
dimensions .of the enclosure and opening. This is known as the ":Sass Reflex"
principle and results in considerable
advantage over the whole low-frequency
end of the acoustic spectrum. Only a
relatively small amount of sound absorbing material should be placed inside the enclosure, the object being to
have a very small absorption at low
frequencies. A modification uses a
series of short tubes instead of the simple opening in the enclosure.
It is to be emphasized at this point
that no effective equalization of the
electrical circuits in the driving amplifiers can give the same results as adequate acoustic loading and the subsequent high efficiency of the speaker
itself. This is true because: (1) the
poorly-baffled' loud speaker has inherently more distortion; (2) the highly
fig. 3
The stiffness due to the compression
of the air in the closed box acts as if
the stiffness of the speaker suspension
itself were made greater. Cabinet resonance may also occur and cause trouble
in the closed-box type of baffle if sufficient absorbent material is nbt used or
if the enclosure is not sufficiently large.
The totally closed-caliinet is sometimes
improperly called an "infinite baffle"
although the,behavior of the system is
quite different
ENCLOSURE
ABSORPTION
MATtRIAL
PORT
BASS REFLEX
ENCLOSURE
,
Fig. 4
I
• Section 1
LOUD SPEAKER DESIGN AND APPLICATION
100
S
10
....
b
""'",
horn, which has a straight axis with the
area expanding according to a definite
formula. Figure 6 illustrates this type.
A modification is the case in which the
complete horn is "coiled" or folded to
conserve space.
A second form of horn is known as
the multicell in which the area is
broken up into a number of sub-areas
each expanding individually-that is, a
group of individual cells forming an
array. These indiv.idual cells may be
formed by inserting partitions in a
simple or trumpet horn or they may be
completely separate sub-horns assembled in an array. Figure 7 shows an
example of the latter type.
FREQUENCV:HORN MOUTH
DIAMETER CHART I
V=1129 FEET PER SEC. AT
20° CENT.
)\.
" r\
I'.
""
"'I'..
" ""-
I
50
lOa
500
1M
fREQUENCY (CPS)
Fig.S
equalized amplifier may very likely
have limited overload characteristics
thus introducing considerable amplitude distortion.
IV. Horns and Horn Type
Loud Speakers
A horn is a device which is used to
couple a ,relatively small radiator efficiently to the surrounding air. It is
essentially a tube of varying crosssection, increasing in size from the loud
speaker unit to the open end. Relatively
high efficiencies are attained. Furthermore, the horn is relatively directional
at medium and high frequencies. (Contrary to popular opinion, horns are almost perfectly non-directional at low
frequencies.) The most common type
is the exponential horn in which the
area increases exponentially with distance along the horn. The lowest frequency effectively radiated by a horn
depends, first, on its rate of change
of area, and second, upon its mouth
area; the low-frequency end' of the
"" '"
r--...
5M
10M
Fig. 7
range is often called the horn "acoustic cutoff."
The mouth diameter for a horn of
circular cross-section should be about
one-third of a wavelength at the lowest
frequency to be radiated. This relation
is shown in Figure 5.
There are three common variations
of horns, depending upon their particular function. The most common form
is the simple trumpet, or projector-type
MULTICELLULAR HORN
=
=
=
Throat Area
1.718 in 2
Mouth Area 960 in 2
Cutoff Freq.
200 Cycles
The third form is known as the
folded or re-entrant type horn in which
,the axis along which the area expands
is no 10ng!3r a simple straight Of curved
line. Figure 8 shows one type in which
RE -ENTRANT HORN
Fig. 8
HORN LENGTH 10114
THROAT DIA.
.7.
MOUTH DIA.
12
CUT Off fREQUENCY
Fig.6
IN.
IN.
IN.
800 CYCLES
the area expands as a simple horn for
a short distance and then becomes an
annular area expanding back along the
exterior of the first simple horn section. This type of folding may be carried on even further. Figure 9 shows
a type commonly used with large diaphragm loud speaker! in which the
area expands along two channels each
11
Secti9n 1 •
THE
MYE
TECHNICAL
MANUAL
LOUDSPEAKER
SECTION A-A
r
A
)
WING jA'fLES ~
/
,I
,.,- -, \
\
\
....
'"
/
I
I
\
--"
/
, .....
,\
/
\
\
t
J
I
f-/
LOW FREQUENCY FOLDED HORN
Fig. 9
folded upon itself. Folded and re-entrant horns are used where economy of
space is essentiaL
Horns are often used with direct
radiator speaker!'!, the throat area being
approximately the same size as the
diaphragm, and are sometimes referred
to as "directional baffles." Below the
horn "cutoff" the loud speaker merely
radiates essentially as it would on a flat
baffle of the same area as the horn surface_ Thus small "flares" used in this
way add nothing to the low-frequency
response although they may enhance
the speech-frequency range.
'V. Power-Handling Capacity
Power-handling capacity of a given
loud speaker unit is generally determined by the amount of power that can
be handled by the speaker before an
appreciable amount of distortion is
introduced or by the physical ability of
the voice coil to dissipate a given
amount of power. In most cases, especially where the speaker or speaker system is the high-fidelity type, objectionable distortion will be introduced be12
fore the temperature of the voice coil
has risen to a point where permanent
damage will occur_ However, with the
standard-fidelity type speaker, i.e., one
whose high-freque;ncy response is limited to frequencies below approximately 5,000 cycles, the distortion will
not be as noticeable as in the highfidelity type and it is often possible to
damage the voice coil before distortion
is noticeable. One important fact to
remember is that most manufacturers
rate their speakers as to the amount of
musical or voice power that can be
deliver,ed to the speaker and not the
amount of power at a single frequency.
In the case of a metal diaphragm type
speaker, when used with a horn designed for the speaker; the powerhandling capacity of the unit will vary
with the frequency~ At the lower frequencies where the excursion of the
diaphragm increases as the frequency
deQreases (for constant power input) ",
the limiting factor is the distance that
the diaphragm can move before striking the 'walls of the sound chamber.
Thus, a unit that will handle 20 watts
at 400 cycles will handle only approxi-
mately 10 watts at 200 cycles or only
approximately 5 watts at 100 cycles.
In general, for cone type speakers,
the size of the diaphragm and the voice
coil will determine the physical ability
of the unit to handle power. The power-,
handling capacity of the voice coil is
limited by its operating temperature
rise. Therefore a permanent magnet
speaker of a given cone, voice-coil and
magnet size, having no field coil to
contribute heat, is capable of dissipating more power in the voice coil than
the equivalent field-coil design. See Figure 10. Since no universally recognized
standard method of rathlg power-handling capacity has been set up, some
manufacturers' ratings are highly overoptimistic, while other manufacturers
are ultra-conservative and their ratings
may oftentimes be exceeded by as much
as 100,/0 before the speaker willfail for
physical reasons.
One common misunderstanding is
the belief that a speaker rated at, for
example, 25 watts power-handling capacity and using a large cone, of say 15
to 18 inches diameter, cannot be driven
by a small amplifier satisfactorily. On
the contrary, the more efficient a speaker, regardless of its size, the more souna
output will be delivered by that speaker
for any giveri electrical input power. If
an amplifier is normally used with a
12" speaker having an efficiency of approximately 5,/0, it can also be used
with an 18" speaker having powerhandling capacity of 25 watts or more
and an efficiency of 20%, and what is
more, the sound output from the larger
speaker will be approximately four
times (an increase of 6 db) that obtained from the 12" speaker. In other
words a highly efficient speaker requires less power to drive it to a given
acoustical output than a small inefficient
speaker.
Where a speaker ,system is used in
conjunction with an amplifier having
response-equalization or volume-expansion circuits, it is of the utmost importance that the speaker be capable of
handling the maximum power that may
be delivered by the amplifier. For example, even though the unit may be operated on the average with only 2 watts
of power input, it must be capable of
handling 20 watts or more if the peak
power is increased by 10 db due to ex,
pansion or equalization.
LOUD SPEAKER. DESIGN ANP APPLICATION
• Section 1
hes~tancy of some manufacturers in releasing response curves which are likely
to be misunderstood by the reader. Of
course curves run on the same measur,.- 35
ing equipment under identical test
.-; 90
II:
z
conditions are directly' comparable.
VOICE COIL COPPER TEMPERW
w
0.
ATURE RISE
However, since the room conditions in
u
0.
RATED AUDIO INPUT 400 C.P.S.
the final installation play such an im/
~ 80
FIELD COIL SPEAKER
- 30 8I portant part in the quality of reproducw
PERMANENT
MAGNET
SPEAKER
W
II:
U
tion, it sometimes happens that the
CJ
Z
'W
curves of a particular laboratory show
/
070
~
that
speaker "A" is more desirable than
~
:z
en
- 25 w
speaker "B" from I:\. theoretical standII:
w
point, while actually it may be found
~ 60
~
~
that when the two speakers are comII:
1.1
pared side-by-side under living room
en
W
FIELD COIL COPPER _
20
«
II:
conditions, speaker "B" is audibly
TEMPERATURE RISE _
w
:> 50
II:
more acceptable to the listener than
!(
U
II:
z speaker "A." It is therefore suggested
W
0.
that rather than match a speaker to a
/
r
:E 40
15 z
w'
w given amplifier system and acoustic enr
U
vironment, the amplifier be adapted to
II:
match the speaker to that environment.
W
VOICE COIL COPPER_
30
0.
This can be done by incorporating comTEMPERATURE RISE
V
10
NO AUDIO INPUT pensation circuits (see Figure 15 )
F1E'ID COIL S,PEAKER
either in the form of equalizers or filter
20
'circuits, and adjusting them when the
I
speaker is located in the desired posiTEMPERATURE RISE IN
5
tion and all other conditions are identiLOUDSPEAKERS
10
cal with those under which the system
will be normally operated.
'\
There are several types of measurements made on a loud speaker in order
3
2
to show its frequency response characTIME IN HOURS
teristics. The most common is the ax",.10,
ial response curve run with speaker
mounted in some sort of baffie and the
so critical- that even using the same
microphone located directly in front of
VI. Frequency Characteristics
speaker and microphone, response
t!vJ speaker on its axis (generally 18 to
curves obtained under different condi36 inches from the baffie). A curve obThe frequency response curve of a
tions'may :not be similar. For example,
tained by this method, however, is not
loud speaker shows the sound pressure
the three response curves shown in Figconsidered a complete picture of the
output as frequency is varied. A conure 11 were run by three well known , speaker response since it does not take
stant voltage is applied to the grid cirlaboratories on t;4e same loud speaker.
into consideration the directional charcu~t of the power amplifier which in
Curve No. 1 was run by the manufacacteristics of the loud speaker. This
turn drives the loud speaker under test.
turer under outdoor conditions with a
type of curve sho\ys only what the listenIt is important to recognize that the
single microphone in fixed position in
er will hear when his ear is fairly close
frequency response curve of a loud
line with the speaker axis. Curve No.
to
the speaker and in line with the axis,
speaker is meaningless unless all of the
2 was run by another laboratory using
which condition is seldom if ever realtest conditions including the type of
the indoor rotating microphone methized in actual practice. Another method
room, driving amplifier and measuring
od.
Curve
No.
3
was
run
by
a
third
sometimes
employed is one in which the
system used, are known. It is impractilaboratory
using
the
indoor
multiple
output
of
the
speaker is measured by
cal for the average user to measure the
microphone method. The same speaker
the use of a moving microphone. A
frequency characteristics of a loud
was, used throughout but the results are
third method uses a group of microspeaker since the measuring equipment
radically
different.
For
this
reason,
unphones located at various positions
required is relatively complicated as
less the test method employed is known
through the room. In both of these latcompared to that required, for example,
and the room acoustics al'e also known,
ter methods, the output of the microin measuring the response of an audio
a curve run by one manufacturer canphone or microphones is averaged so
amplifier. Moreover, the acoustics of
not be compared with that run by' anthat the sound radiated by the speaker,
the room and the location of the microother manufacturer. This explains the
both on and off the axis, is taken into
phone and speaker under test, may be
TEM PERATURE RISE IN LOUDSPEAKERS
---
100
V
V
/
V
/
;
I
//V
/'
V
/
V
V--
.....-
I
V
13
Section 1 •
THE
MYE
TECHNICAL
MANUAL
12 IN. DYNAMIC SPEAKER CABINET SPEAKER
+2 0
+1 0
.,..
c::
c::
I-
m
c::
MEAN ENERGY DENSITY
MICROPHONE FACING SPEAKER
CONTINUOUSLY
0
"">
d
.-
'j -I 0
..
~
....
...
,
N
III
~ -2 0
.~
...J
..
..
"
....
..
.....
.'
MEAN ENERGY DENSITY
MICROPHONE REVOLVING ONCE
IN ACH QUADRANT
FREE SPACE
ON AXIS
>
....
..
...J
-3 0
20
3
4
5
6
8
9
1.5
100·
2
1.5
3456789
1M
FREQUENCY IN CYCLES PER SECOND
2.
3
4
5
6
7 8 9
12 14 16
10M
Fig. 11
consideration. Since the output of the
loud speaker at the higher frequencies is
considerably more directional than at the
lower frequencies the multiple or moving microphone method would show less
high frequency output from a given
speaker than an axial response curve of
the same speaker. However, since a multiple microphone curve gives a more
complete picture of the overall efficiency of the speaker at all frequencies, at
many positions within the room, it p~
vi des a more reliable indication of the
actual room performance than the axial
method. The frequency characteristics.
of a speaker are determined not only by
design of the. cone assembly but by the
method of baffiing, the location within
the room and the position of sound absorbent materials and reflecting s~r
faces. Thus speaker "A," having a tone
quality that is considered inferior to
speaker "B" in one particular room,
may sound much. better thal'l speaker
"B" if the location of the speaker within the room or the acoustics of the room
itself are changed.
It can be shown by means of frequency response curves that the frequency
characteristics of a loud speaker do not
vary with the amount of power delivered to the voice coil, assuming that the
speaker is nof overloaded. However,
14
due to well established characteristics
of the human ear, especially at low
sound intensities, the response does apparently change with power input. As
shown in Figure 14, the reduced sensitivity of the ear for low and high
frequencies relative to the middle frequencies at low sound intensities, is responsible for this effect. Therefore, in
listening tests, means should be provided within the amplifier or elsewhere
in the system to compensate for the apparent loss in low-frequency and highfrequency respon~e as the power level is
reduced.
VII. Impedance Matching
Since the required load impedance of
amplifier power tubes is relatively high,
and the impedance of loud speaker
voice coils (the load) is relatively low,
a transformer is generally used to match
these two radically different impedances in order that transfer of power
may be efficiently accomplished. It can
be shown that the ratio of the transformer primary turns to the secondary
, turns 'is the square root of the ratio between the speaker impedance and the
100
1
90
III 80
I
:E
a
z
-
w
~PEbA~C~J 1151~PEAKERII N
INFINITE BAFFLE
70
80
U
Z50
~
~ 40
:E
1---1--'
30
20
0
o
I-- V
20
J
30 40
~
'\
60 80 100
200 300 400 600 800 1M
FREQUENCY IN C.P. S.
Fig. 12
/'"'
2M
V
3M 4M
8M 8MIOM
• Section 1
LOU"D S,PEAKER DESIGN AND APPLICAtION
load impedance required by the output
tubes.
The amount of mismatch between the
, optimum load impedance required by
the tubes (tube manufacturers general.
ly list this value ~ their tube data
sheets) and that presented by the loud
speaker will depend upon the use to
which the system is put. In the case of
triode tubes tl}e load impedance presented by the speaker should be equal
to, or in excess of, the optimum load
resistance required by the tubes in order
to keep tube distortion low. Since the
impedance of a speaker varies with frequency (see Figure 12), the voice coil
impedance is approximately the minimum impedance above the resonant
frequency. In general the matching impedance is the 400 cycle impedance for
a conventional speaker intended to reproduce both high and low frequencies.
VIII. Audio-Frequency Transmission Lines and Transformers
When connecting speakers to an amplifier two factors should be taken into
consideration: First, the power loss,
due to line resistance, between the amplifier and speakers should be held to a
reasonable minimum value, and second,
the loss due to line capacity at the
highest frequency which is to be reproduced must not become appreciable.
Both effects are related to the length of
the line and the impedance at which the
line is operated. In general, if the distance between the amplifier and the
speakers is less than 25 or 30 feet, the
impedance of the connecting line (high
impedance, low impedance, or voice
coil) is not important and the most convenient impedance may be used. When
a distance greater than about 25 or 30
feet separates the amplifier and the
speakers, it is then necessary to take the .
resistance and capacity of the leads into
account.
Lines at J7oice-Callimpedance
The following table (Table 2) of
maximum lengths (2 wires) of voicecoil lines assumes a' maximum line resistance equal to 15% of the voice coil
impedance. This limits the power loss in
the line to about 15% of that delivered
TABLE 2
MAXIMUM LENGTH OF LINE, FEET
WIRE SIZE
(B & S Gauge)
No.
No.
No.
No.
No.
No.
12
14
16
18
20
22
Voice Coil Impedance
4 ohms
6 ohms
8 ohms
10 ohms
190 feet
120 feet
75 feet
47 feet
30 feet
19 feet
288 feet
180 feet
110 feet
70 feet
45 feet
28 feet
385 feet
240 feet
150 feet
95 feet
60 feet
37 feet
480 feet
300 feet
190 feet
118 feet
75 feet
46 feet
to the speakers. The capacity of the
lines is here considered negligible.
In the above table, the voice-coil impedance value is the total impedance on
one transmission line. If a single speaker is connected, then the total impedance .
is the voice coil impedan.ce of the one
speaker; if two 4 ohm speakers in series
are connected, then the total impedance
is 8 ohms and line lengths would be
read in the 8 ohm column. On the other
hand, if two 8 ohm speakers are connected in parallel, the resulting total impedance would be 4 ohms. If more than
two speakers are employed, the total
impedance of the group must be calculated. If the total impedance falls between values used in the table, the line
length can be estimated with sufficient
accuracy for practical purposes.
If the use of Table 2 shows insufficient permissible line length at voice
coil impedance, then the line length can
be increased by working at a higher impedance. For a given transmission line,
the higher the value of operating line
impedance, the lower will be the power
losses due to the resistance of the line.
However, the high-frequency losses in a
line due to the capacity between conductors are greater in a high-impedance
line than in a low-impedance line. A
"500 ohm" line will'usually afford an
acceptable compromise between the resistance losses and the losses due to the
capacity of the leads.
At this point, it might be well to define a "500, ohm" load. A "500 ohm"
load is one whose impedance is approximately (plus or minus 10%) 500 ohms
when measured at the ilmplifier end of
the line and includes all speakers, filters, level controls, and transformers
that may be connected across the line.
In other words, the impedance of the
total "load" including the line must
match that of the 500 ohm output trans-
.
former. This means that in order to connect several speakers together in parallel across a "500 ohm" line, the total
impedance of the "load" must be 500
ohms for all speakers, not individually.
For example: If four speakers with
their individual transformers are all
connected in parallel across a "500
ohm" line, each speaker with its own
transformer must have an impedance
of 2,000 ohms, not 500 ohms. Thus,
with four 2,000 ohm "loads" connected
in parallel, the resulting total impedance would be one-fourth of 2,000 ohms
or 500 ohms. Of course, four speakers
with 500 ohm transformers could be
connected in series-parallel across the
500 ohm line.
For the purpose of computing the
"effective impedance" of a group of
speakers connected in parallel, use the
following equation:
1
111
1
1
Z
Zl
Z4
Z5
-=-+-+-+.:..-+Z2
Zs
or in the special case of 3 impedances
in parallel:
-
Z
= ----------
Where: Z is the effective Impedance of
the circuit
Zl is the Impedance of the first
speaker
Z2 is the Impedance of the second speaker
Zs is the Impedance of the third
speaker
etc.
15
SectiOn 1 •
r
HEM YET E C, H N I CAL
MAN U
A
L
(
This reasoning applies to all types of
loads such as transformers, speakers,
filters and level' controls regardless of
the number used. The effectiv~ parallel
impedance of all the loads together,
when con'nected across' a "500 onm"
line, must be 50'0 ohms. The exception
to this is when a fiIt!:;r or level control,
etc., of the so-called 500 ohm input and
500 ohm output type is used. With a device of this kind the line is thought of
as simply, passing through the device
without its acting as a load. However, if
,two or more of these devices are connected in parallel across the line, they
must be 'considered as separate loads
and are treated accordingly.'
With this fact in mind, we may now
consider the methods of connecting the
amplifier and the "loads" to the line.
This is done by means of "impedance
matching" transformers. The transformers are so designed that, with a
given value of load impedance connected across one w~nding, the impedance measured across the other winding
is the required value. In a large welldesigned transformer, there will be
negligible loss of energy due to this
transformation (usually ab.out 10%).
Thus, a plate-t~-linetransformer is used
to transfer the output of the power
tubes at their inherently high impedance 'to a low-impedance line. For
example: If the plate-to-plate load impedance required for a pair of output
tubes in push-pull is 4,500 ohms, a
plate-to-plate transformer with an impedance ratio of nine to one will be
required in order to match these output
tubes to a 500 ohm line.
In order to keep the loss of the line at
a minimum, the total resistance of the
C Jnductors themselves and their capacity must be limited to reasonable values.
,The total resistance of the line should
not be more than about 5% of the load
and should preferably be less. Thus, if
a pair of No. 14 wires is to be used as a
500 ohm line, the line should not be
more than 5,000 feet long (10,000 feet
of wire, resistance 2.52 ohms per thousand feet) if the allowable. resistance is
not to be exceeded.
Upon this basis the maximum length
of line (2 'fires) for various sizes of
conductor is as follows ~Table 3) :
16
.,''::.
TABLE 3-500 ohm line
WIRE SIZE
(B & S Gauge)
No.
No.
No.
No.
No.
No.
12
14
16
18
20
22
MAXIMUM LENGTH
(R~sistance =
25 ohms)
8,000 feet
5,000 feet
3,100 feet
2,000 feet
1,200 feet
780 feet
The other factor controlling the permissible length of the "500 ohm" line is
the capacity of the leads which causes a
loss (attenuation) of the higher fre-
The transformer must be large enough
to handle the power involved and, with
all the speakers connected in parallel to
the transformer secondary, the primary
impedance must have the required value., Thus, if six speakers each having
6-ohm voice coils are to be connected
in parallel to a 500 ohm line, the resulting parallel impedance, of the voice
coils will be 1 ohm and the correct
transformer to use will be one with a
500 ohm primary and a 1 ohm secondary. If, however, the speakers are separated by more than one-half the allowable distance given in Table 2, or have
TABLE 4-500 ohm line
HIGHEST FREQUENCY DESIRED
MAXIMUM LENGTH
(Loss at highest frequency =3 db)
,
20,000 cycles per
15,000 cycles per
10,000 cycles per
7,500 cycles per
5,000 cycles per
second
second
second
second
second
quencies. Ordinary twisted pair or leadcovered cable has a capacity of approximately 50 mmfd. per foot. On this
basis a "500 ohm" line will be limited
in length to 600 feet if it is desired to
keep the attenuation at 10,000 cps. less
than 3 db at the highest desired frequency. This assumes, of course, that
the resistance losses due to the size of
the wire used fer the line do not exceed
25 ohms (see Table 3). The calculation
of losses at high frequencies takes into
consideration the capacity of the line
and the fact that the impedance of a
dynamic speaker is higher than the
rated value at the higher frequencies.
Thus if it is found necessary to run a
line longer than 600 feet and still reproduce frequencies up to 10,000 cps. without attenuation, it will be necessary to
use an equalizer (preferably within the
amplifier or its input circuit) to compensate for the loss due to the capacity
of the line, or ~o operate at a lower line
impedance.
The choice of transformers at the
load end of the line is dependent upon
the number and type of speakers involvea. If all the speakers have the same
voice-coil impedance at 400 cycles (400
cycles is the usual matching frequency
for dynamic, speakers) and all are
mounted close together, all the voice
coils may be connected in parallel and
through one, transformer to the line.
300
400
600
900
1,200
fee~
feet
feet
fellt
feet
different voice-coil imp~dances, it will
then be necessary to use separate lineto-voice-coil transformets for each
speaker. In this case, the primary impedance of each 'of the transformers
will have to be 3,000 ohms so that when
all' six transformers are connected in
, parallel, the resulting impedance will be
500 ohms.
This brings up the relative merits of
series and parallel connections. The
main objection to the series method of
connections is that, in case of the failure of one unit by open-circuiting, the
entire system becomes inoperative. The
use of series connections of speakers or
transformers is sometimes a practical
necessity, however, as in the case of
matching two 8 ohm voice coil speakers
to a transformer which has only a 16
ohm secondary. Then, of course, the
most econ'omical method is to connect
the voice coils in series.
Phtuing
When more than one speaker is used
in an installation, it is important to
operate all the voice coils "in-phase."
That is, all the diaphragms should move
in the same direction at the same instant. If they are not in-phase, the
sound output will be materially reduced
because the sound from one unit will
cancel that of the other. The mQst simple method of checking the phase of
LOUD SPEAKER DESIGN AND APPLICATION
speakers is to first connect and excite
the fields of all the speakers and then
short out the "bucking coils," if any,
temporarily. Then take a dry cell bat- '
tery (1112 volts) and touch the positive
side of the battery to one voice coil lead
and the negative side to the other voice
coil lead. The cone will "jump" either
in or out at the instant the battery is
connected. Test all the speakers in the
same manner, marking the lead on each
speaker which was connected to the
positive battery terminal when the cone
"jumped" out. For parallel operation,
connect all the leads that went to the
positive side together and all those that
went to the negative side together and
the speakers will be correctly phased.
If series operation is necessary, connect
between unlike terminals in the usual
manner. In order to reverse the phase
of any speaker, simply reverse the voice
coil connections, leaving the field connections the same as they were before.
If it is desired to phase several speakers
each having its own transformer attached, the same procedure as outlined
above is followed except that a battery
. of about 221/2 volts and the primary
leads of the transformer (instead of the
voice coil leads) are used (voice coil
leads are to be attached to transformer
secondary leads, and "bucking coil"
shorted out temporarily) .
IX. Applications
Replacements
When installing a replacement speaker there are several important points to
consider other than the obvious ones of
physical size, transformer impedance
and field coil resistance. Probably the
one least considered is the size of the
field coil. The amount of copper in the
field will have a direct bearing on the
amount of power that can safely be dissipated in the field without overheating
and causing a mechanical failure. It
will also have a decided 'effect upon the
efficiency and performance of the speaker. For example, if the original speaker
(say a 5 inch speaker) had a relatively
large field coil, say 2,500 ohms No. 35
wire (.73 Ibs. of copper) and dissipated
5 watts of power, if would be inviting
trouble to use a replacement speaker
having the smallest possible field coil
of the same resistance just because it is
less expensive. Using the smaller field
would cause the field to run very much
hotter (the original field was probably
hot enough) than advisable which
could easily cause the new field or the
voice coil to fail very soon. On the other
hand if the original field was relatively
small and failure was not due to overheating, there is little to be gained by
going to a large field coil unless, of
course, the power delivered to the new
field coil can be increased accordingly
without upsetting the plate voltages
throughout the receiver. Therefore,
whenever possible, use a replacement
speaker having a field coil of approximately the same physical size as that of
the 'original.
At this point it 'may be well to point
out the improved performance obtainable by replacing the field coil type
speakers supplied originally in the older
A.C.-D.C. sets with a P.M. type speaker.
This change will reduce the drain
on the rectifier tube and possibly improve efficiency. This should only be
done, however, when the original field
coil was connected directly from the
positive high voltage to ground, not
when it was used as a bias resistor or as
a choke in the power supply unless the
original field is replaced by an equivalent fixed resistor.
Oftentime when replacing the original speaker it is desirable to use a larger
speaker where it can be accommodated,
as for example in a 'large console. In
general, increasing the diameter of the
speaker cone will increase the bass response of the system, assuming of
course that the amplifier will pass the
lower frequencies. Here, too, the size of
the field coil must be considered for
there is little to be gained if the original
speaker had six watts in the field and
the larger replacement'requires fifteen
watts of field excitation. True, the lowfrequency response may be improved,
but it could probably be improved just
as much by using a less expensive
speaker with the same larger cone
diameter as the I5-watt speaker but
having 'a smaller field that would be
fully excited with six watts. However, if
means are available for increasing the
field excitation at the same time, then
use the larger field because the output
of the larger field coil speaker will be
greater and there will be less low-frequency distortion due to the increased
• Section 1
damping action of the larger magnet
structure.
The substitution of a larger speaker
than the original, especially in the case
of mIdget receivers, is a subject that
should be considered by every servicp
engineer. The chief objection to midget
sets is their lack of low-frequency response. Obviously with such a small
balRe and speaker the bass response of
the set will suffer. One solution to the
problem is to use a larger speaker in a
separate cabinet or balRe. Substituting a
twelve, fifteen or even eighteen-inch
speaker for the original 4 or 5-inch
speaker is indeed a revelation. Usually
it is only necessary to disconnect the
original transformer and substitute a
larger transformer to match the voice
coil of the new speaker to the output
stage. Leave the field of the original
speaker connected in the circuit in order not to upset the plate voltages and
use a P.M. speaker (or one with its own
power supply) for the new speaker. Increasing the bass response by this
method will increase the hum also, but
this can be reduced to an acceptable
amount by the addition of filter condensers or at the most by the use of a
second "30 henry" choke in the power
supply circuit.
P. A. Installations
The size and type of speaker system
in a P. A. installation should be governed almost entirely by the size, type,
location, audience to be covered, the
type of sound to be reproduced and the
psychological reaction desired of the
audience. This, of course, requires that
each installation be analyzed before the
installation is even started. Accordingly
the analysis of the job should cover the
following points:
INDOORS
Size of auditorium.
Area to be covered.
Dimensions.
Approximate size of audience and location
of same.
Actual volume of the room in cubic feet.
The reverberation time, if known.
Seating capacity.
Type and distribution of absorbing materials.
Location of orchestra or source of pickup.
Desired position of ,speakers and microphones.
Ambient noiSe level.
Type of service.
V oice or music reinforcement.
Remote pickup.
Symphony or jazz orchestra.
Point source illusion.
Fre9uency,characteristics of phonograph
pIckup microphone.
17
Section 1 •
THE
MYE
Amplifier.
Audio power available.
Desired coverage.
PERMISSIBLE COST.
TECHNICAL
MANUAL
ambient noise level outdoors and noise
level as well as the acoustics of the room
indoors will have considerable bearing
on the final choice of speakers. It is al~
ways advisable to have more amplifier
power available than the necessary
minimum as a margin of safety against
distortion. Adequate power-handling
capacity should be available in the installation of loud speakers. Since cost is
often '. of predominating importance it
may be necessary to arrive at some suitable compromise between location and
type of speakers finally used as compared with the ideal choice. Wherever
possible, if it is desirable to create the
illusion of the original source, the
speakers should be mounted in a cluster
and as near the source as possiblegenerally directly overhead. Outdoors,
of course, ~ this requires that higher
powered speakers be used than if the
sound were distributed at low level
throughout the audience but this may
be more desirable than the distracting
effect upon tpe audience of having the
performer in front of them and hearing
his voice coming from behind or over-
QUTDOORS
Area to be covered, in square feet.
Dimensions.
Approximate size and location of audience.
Desired location of microphones and
speakers.
Ambient noise level.
Loudes1;. hoise which system must override.
Type of service.
V oice or music reinforcement_
Remote pickup.
Symphony or jazz orchestra.
Point source illusion.
Frequency characteristics of phonograph
pickup microphone.
Amplifier.
Audio power available.
Desired coverage.
PERMISSIBLE COST.
If these facts are known it then becomes relatively simple to determine
the possible locations and types of
speaker system applicable in view of all
requirements. The amount of audio
power can best be determined by the
size of the audience-if outdoors
roughly 5 watts per thousand square
feet, or ~indoors in accordance with the
data given in Figure 13. Of course, the
1000
800
600
500
400
300
200
~K
.<~K~
III\~
100
80
(I)
II~
A
"')(
60
50
40
~~
I~
z
20
Ir
W
k'<
~~R
~
0..
10
8
V
)(
1'-<'
6
5
4
~
IX .'-'1
L¢X r'.'-' \j
~ ~~
3
~~f
2
~
20
3040
~
~
r
6080100
200
400 600 1M
. 2M 3M 4M 6M
SEATING CAPACITY OF AUDITORIUM
Fig. 13
18
v
lAX Y
.t<5 ~
3: 30
0
1)(
10M
head. Whenever it is necessary that
sound be distributed from some point
other than the point of origin, it is always advisable to operate the speakers
at as low a level as is consistent with
intelligibility.
Where the system is required to reproduce voice only, for example in a
football announcing system, it is not
necessary that frequencies below 150 to
250 cycles be reproduced by the speaker system. This permits the use of either
the new multicellular horns and driving
units or short trumpets. The former are
to be preferred, especially where a
highly efficient speaker system is advisable and where maximum intelligibility
is desired. However, where cost is the
more important factor, trumpets can be
substituted iInless, of course, the number of trumpets required is such that it
would be more economical to use a
multicellular horn.
Where the reproduction of both
music and voice is required, a large
horn, bame, ~or suitable speaker enclosure is of importance in order to reproduce the lower frequencies (see
section 4). Thus, in an installation
where at times only voice will be reproduced and at other times a full orchestra, it may be desirable to use a two-way
system consisting of suitable low-frequency unit and multicellular horn and
unit.' In this way the multicellular highfrequency system could be used where
voice only is being reproduced and the
entire system could be used for the
reproduction of music. This would be
by far the most economical use of all
possible components and at the same
time would result in the most efficient
possible speaker system.
Provision should be made, when using a speaker system outdoors, to prevent exposure to excessive humidity.
This would require that the system itself either be weatherproofed or that
arrangements be made to cover the system during rain or snow storms.
One important factor to keep in mind
is the distance over which sound must
be projected from a given speaker system, since sound energy diminishes
approximately as the square of the distance from the source. In other words,
if a speaker system will lay down the
desired sound power at a distance of
100 feet with an input of 10 watts, 100
times as much power or 1,000 watts will
LOUD SPEAKER DESIGN AND APPLICATION
-I-
_ _ F'tELING
200
~ .-/
/
...... :--..
i
I'---..
\
~ t'-.
-~
r\. ~ t'- ~
'\ ~ ~ ~ ~
~~~
/
r-
L
~ ~ ;:: ;:::;:::
t- ~
--
//
/,
J/ /
/
/
V
91%75°/0
1
50 %
~~
10 0/0
~J ~ ~ 5°
1.,
t'-- ~ ~ 1(/. /'
-
I-
20
/
/ /' 9~ Ofo
--- -- --....... r-')
~ ~ ::::::
20
/
"" -
1\
99 %
100
..............
II::
2 ~
:!lz
.02 ~
Z
!oJ
II::
.002
./
~
If
0 /0
2
10,000 20,000
1000
FREQUENCY IN CYCLES PER SECOND
Fig. 14
be required if the distance is increased
to 1,000 feet. As a result, both the am~
plifier and the speaker system must be
designed to handle the required power.
Phonographs
Recent developments in recording
practice and improvements in phonograph pickups make it definitely worthwhile to provide extended-range loud
speakers for high quality reproduction
of commercial phonograph records. Surface noise '( or "needle scratch") is, of
course, somewhat more noticeable as
the response range of the system is extended into the high frequencies. However, many listeners definitely prefer
the reproduction obtainable with such
equipment over that provided by standard fidelity speakers which usually give
predominant emphasis to the middle
high-frequency region. It is highly desirable to provide means for adjusting
the high-frequency response of the
system, so that fewer "highs" are reproduced when playing old or worn records. It should be remembered that
surface noise covers practically the entire audible frequency range, and it can
be reduced only by restricting the range
which is reproduced. The low-frequency
response of the speaker system should
be good and enclosures of the "Bass
Reflex" type are particularly suitable.
The new Single, Concentric and twoway extended-range loud speakers are
particularly suggested for high-quality
record reproduction.
Since oftentimes phonograph records are reproduced in the home at
much lower volume levels than those at
which they were originally recorded the
frequency characteristics of the human
ear must be taken into consideration. It
is therefore desirable to incorporate
both high and low-frequency compensation circuits (see Figures 14 and 15)
within the amplifier so that the quality
of reproduction may be adjusted in accordance with the level of reproduction,
the acoustics of the room and the listener's preference.
Volume Expansion
• With a properly designed volume expansion circuit the reproduction of
phonograph recordings, especially symphonic, can be made much more realistic since for practical reasons most
symphonic recordings are compressed
when originally recorded~ This compression is generally done automatically in the case of phonograph recordings,
whereas in the case of broadcasting stations the compression is done manually
in accordance with the best judgment
of the operator at the time. Volume expansion is, therefore, not generally used
for the r~production of radio programs
but is considered desirable or even necessary for high quality phonograph reproduction. It must be kept in mind,
• Section 1
however, that when compensation or
volume expansion is used in an amplifier, both the output stage of the amplifier and the speaker system must be
capable .of reproducing the loudest
passage without introducing appreciable distortion. For example, in the ordinary home living room and without
either compensation circuits or volume
expansion; an amplifier having an output of 2 to 4 watts is ample. However, if
compensation ·circuits or volume expansion having 10 db gain are introduced,
the output stage must be capable of delivering 20 to 40 watts power without
introducing distortion.
Custom Built Sets, Television and
Frequency Modulation Receivers
These receivers require a speaker
system having as wide a range of response as is practical, consistent with
the cost and performance desired.
Single diaphragm type speakers are
now available covering the range from
below 60 cycles to 10,000 cycles and
above. For most installations, especially
where cost is important, they will serve
very well. However, in general they are
less efficient than an equivalent sized
standard type speaker and they are
more directional at the higher frequencies than a specially designed tweeter.
This first objection is not too important
because most amplifiers have ample reserve power, but the highly directional
characteristics al}ove 5,000 cycles may
be quite objectionable.
In order to overcome this shortcoming and to provide an even greater frequency range, two-way speaker systems
are recommended. When using two
speakers to cover the audio spectrum it
is possible to design a speaker that will
do a better job of covering its portion
of the band than the single wide-range
speaker: In other words, the larger the
cone, in general, the better the low-frequency response; but the smaller the
cone the less directional t4e highs. This
does not infer that any small cone type
speaker is inherently a good high-frequency speaker. By using a metal
diaphragm high-frequency horn type
speaker a relatively small unit can be
made to reproduce the higher frequencies more efficiently and with less directional effects than a larger wide-.
range speaker. A two-way speaker system also requires a dividing network of
19
· Section 1 •
THE
some sort hut such a system can he
made quite efficient and need not he too
expensive. Thus, where it is desirahle to
MYE
TECHNICAL
MANUAL
fr~quency response, wide angle coverage and efficiency' is required, use a
multiple speaker system.
ohtain as wide a frequency· range ali!
pos;ihle, consistent with lo-w cost, use a
single speaker; and where the utmost in
VARIABLE COMPENSATION CIRCUIT
-
ISOLATE FOR
MINIMUM HUM
I MEG.
L I = CHOKE (30 HEN.)
L2 CHOKE (112 HEN.)
CI =.25 MF'D. TO RESONATE CI RCUIT
AT 60 CYCLES APPROX.
C2=.002 M rD. TO RESONATE CIRCUIT
AT 5000 CYCLES APPROX.
=
+15
O~--+----+----~----
NON-VARIABLE COMPENSATION CIRCUIT
ece
6J7
I MEG
~------------~B+
NOTE-IN ORDER TO PREVENT DISTORTION
THESE CIRCUITS MUST BE OPERATED
AT VERY LOW LEVEL (0.1 V. MAX, INPUT)
+10
DB
o
'---+---i----50
Fig. 15
20
400
F'REQ.
e Section 2
THE
MYE
TECHNICAL MANUAL
Superheterodyne
First Detectors
. and Oscillators
I
I
'
MALLORY
21
Section 2 •
THE
MYE
TECHNICAL
MANUAL
SUPERHETERODYNE FIRST DETECTORS
AND 'OSCILLATORS
A recent Superheterodyne incorporating
modern design practices (RCA 27K)
One of the /irst Superheterodyne
. Receivers (RCA Radiola 28)
Introduction
The heart of a superheterodyne is its
frequency-changer-the first detectoroscillator system which converts the frequency of any incoming signal to the
fixed frequency of an intermediate frequency or long wave R.F. amplifier;
where subsequent stages of amplification build up the signal to the desired
level.
It is the purpose of this article to review the developmenf of the various cirpuits which have been used or proposed
for this application, to point out the advantages and disadvantages of each,
and to give service hints, so. that the
service engineer or radio repairman
can proceed with confidence in making
any required adjustment.
Why the Superheterodyne?
Let us begin by briefly explaining the
advantages of the seemingly roundabout
way employed in superheterodynes for
the amplification and selection of radio
signals, as compared with the direct
method of amplifying the signal at its
original frequency (or tuned radio frequency amplification).
22
The advantages are:
1. Better adjacent channel selectivity
2. Uniform selectivity
3. Better. circuit stability
4. ,Uniform gain at various' frequencies
5. Lower cost for equivalent performance
The advantages listed above arise
directly from the use of a fixed tuned
radio frequency amplifier (I.F.) , operating generally, but not necessarily, at a
lower frequency or a longer wave-length
than the received signal. Precision
adjustment for optimum performance
is made when the receiver is constructed, and these adjustments will retain their correct setting for extended
periods of time. The amplifier constants,
such as the inductance of the coils, the
couplinK of the coils, and the value of
the tuning capacitors, have been selected
to give the best results at the desired
frequency. Physically such an amplifier
can be built with great compactness
since adjustable compression type mica
condensers or .small fixed condensers
'are used for tuning; as compared with
the bulky and exp~nsive air dielectric
, gang tuning condensers required for a
tuned radio frequency amplifier.
Even the least expensive superheterodynes usually have a total of five tuned
circuits contributing to the selectivity
of the receiver-a tuned antenna stage
and two tuned circuits in each I.F. transformer. A comparable T.R.F_ receiver
would have to employ a five-gang variable condenser-a form of construction
so expensive as to limit its use to only
the most expensive sets. Furthermore,
gang condensers are bulky, and require
long leads for connectio~s. This, in
turn, causes coupling between circuits
so that elaborate shielding must be used
to provide isolation and to prevent the
amplifier from oscillating. Such shielding is obviously costly_
When amplification occurs at signal
frequency, the amplifier must be tuned
to the signal, and in conventional engineering practice this is accomplished by
connecting a variable air dielectric capacitor across each inductance. Thus,
the LIC ratio (the ratio of inductance
to capacity) ~aries as the condenser is
adjusted for various frequencies, and
the selectivity characteristics are not
constant with frequency. The changing
LIC ratio varies the Q of the circuit.
The Q of a circuit is the ratio of inductive reactance to resistance and constitutes a figure of merit for a tuned circuit
since the higher the Q, the sharper the
tuning. The effect of variable -capacity
also makes it exceedingly difficult to de-
SUPERHETERODYNE fIRST DETECTORS AND OSCILlATORS
sign R.F. transformers having uniform
gain with frequency, since the gain is a
function of the impedance of the tuned
circuit, which varies with the Q. Even
more difficult is the designing of doubletuned transformers (tuned primarytuned secondary type) since coupling
varies with capacity.
The fixed tuned I.F. amplifier of a
superheterodyne is not open to any of
these objections.
There is another advantage of the
superheterodyne circuit which is inherent to all such receivers using an intermediate frequency lower than the
frequency of the received signal, namely-arithmetical selectivity. Radio stations on the broadcast band are located
with 10 kc. channel spacing. It is highly
desirable for a radio receiver to discriminate against interference from an
adjacent channel. The percentage of
difference between the frequency of the
desired signal and the signal on an
adjacent channel varies with the frequency, thus, at 550 kc. the adjacent
channels are off-resonance by 1.8%. At
1,000 kc. the difference is 1
while
at 1,500 kc. the difference is only
0.66%.
In a superheterodyne the incoming
signal is converted to the frequency of
the I.F. amplifier. An adjacent channel
station is still removed by 10 kc. at the
intermediate frequency. Thus, with
a 465 kc. intermediate frequency
the percentage difference between the
adjacent channels becomes over 2.1%.
This percentage difference is constant
at any portion of the broadcast band.
In this connection it is interesting to
note that the percentage difference in,creases with lower I.F. frequencies.
With a 175 kc. I.F. the adjacent channels are separated by almost 6%, while
at 50 kc. (a value used by some manufacturers in the very early days of the
industry) the percentage difference is
20%.
However, the problems of images
and spurious responses increases rapidly with decreasing I.F. frequency so
that the industry has largely standardized on values near 465 kc. The possible presence of such interference
constitutes the main objection to
the superheterodyne principle, and consequently the subject will be discussed
in a later paragraph.
ro,
How the First Detector·Oscillator
Works
The fundamental operation of the
first detector and oscillator is shown by
the block diagram, Figure 1. The
incoming signal is fed into a vacuum
tube, which may be a diode, triode,
tetrode, pentode, or one of the more
complicated types. The output of a local
oscillator is also fed into this tube,
where the two inputs are combined to
produce the intermediate frequency.
By means of special tubes or special
circuits it. is possible to combine the
oscillator and mixer functions in a single tube-however, the fundamental
operating principles remain the same.
INCOMING
INTERMEDIATE
SIGNAL
rREQLJ[NCY
FIG.
1
The local oscillator of a superheterodyne receiver serves two functions.
First, it provides a frequency which
will combine with the radio-frequency
signal and produce, through detection,
a new radio frequency wave called the
intermediate frequency. For this purpose the local oscillation need only be
of the same order of amplitude as the
signal.
When the signal and the local oscillator voltages are combined in the same
circuit, at a given instant they may be
either opposing or aiding one another.
If the frequency of the signal and
that of the oscillator differ (as is the
case in a superheterodyne receiver),
then the two voltages will be alternately
aiding and opposing each other at a
repetition rate equal to the frequency of
the new signal voltage. This combining
of the two radio-frequency voltages is
called heterodyning, or beating. The
beat frequency, called the intermediate
frequency, is not produced immediately
as a result of combining the two radio
frequencies. There are still only the
9riginal frequencies present but the
envelope of the combined wave is varying in amplitude at the beat frequency
rate. To create the new intermediate
frequency, this wave must pass through
a detector.
• Section 2
The second function of the local
oscillator is to raise the efficiency of
detection. If the incoming signal impressed on the detector is of the order of
1 millivolt and the local oscillator voltage impressed on the detector is of
about the same value, the rectified output would be practically zero. The
amplitude of the voltage impressed on
the detector must be of such a magnitude that the tube characteristic is different for the positive and negative half
cycles of oscillation. Increasing the
local oscillation voltage beyond the
requirements for producing the beat
envelope will result in raising the efficiency of rectification. The amount of
local oscillation required for most efficient conversion of the radio wave into
the intermediate wave .is determined by
the detector tube design and usually
runs between 5 and 15 volts in conventional circuits.
It will be seen from the above discussion that the efficiency of conversion of
a heterodyne detector in a superheterodyne receiver does not follow the customary square-law response as does the
second detector and that no matter how
weak the incoming signal may be, there
is no threshold below which the detector
fails to operate.
The first detector is operated over a
non-linear part of its characteristic. The
local oscillation may be supplied from
a separate tube and impressed on the
grid circuit of the detector through a
coupling in its cathode lead, or it may
be supplied from other tube elements
within the same detector tUbe. Some of
the tube elements may serve the double
purpose of both oscillator and detector.
In this latter case the local oscillations
may not appear in the signal input grid
circuit. They will, however, serve their
purpose of changing the operating
characteristic of the detector by altering the electron flow through the detector part of the tube as the local oscillation swings through its cycle. The
detector tube is, in effect, cut off on the
negative cycles. This is the condition
required for detection. In addition to
serving as a detector and sometimes as
an oscillator, the first detector tube also
acts as an intermediate frequency amplifier since the detection takes place in
the grid circuit. The amplification thus
obtained is approximately one-half the
23
Section 2 •
THE
value which would be obtained if the
tube were used as a conventional intermediate frequency amplifier. This is
due to the fact that the local oscillator
swings over the low gain part of the
MYE
TECHNICAL
MANUAL
tube characteristic on its negative half
cycle.
The first detector and the local oscillator of a superheterodyne receiver
each perform two important functions:
The detector creates and amplifies the
intermediate frequency; the oscillator
raises the efficiency of detection and
combines with the signal to produce the
intermediate frequency signal.
The Desired Signal, Images, and Spurious Responses
The Desired Signal
We have stated that the intermediate
frequency signal is produced by combining the incoming signal with R.F.
energy from a local oscillator. The combining of frequencies for the production of beats or heterodynes follows
simple arithmetic in that the two frequencies are simply added or subtracted. However, there are a number of
practical considerations which prevent
the dismissal of the subject with this
brief statemen't. We believe the matter
can be most easily explained by using
specific examples.
Let us assume that we have a desired
signal of 1,000 kc., and an intermediate
frequency of 465 kc. The conventional
way of producing the LF. frequency is
by operating the oscillator at a higher
frequency than the incoming signal.,.thus:
Oscillator - Signal = Output
1,465 kc.
1,000 kc.
465 kc.
Although the intermediate frequency
could be obtained by operating the
oscillator at a lower frequency than the
signal:
Signal - Oscillator = Output
1,000 kc.
535 kc.
465 kc.
The reason the oscillator is not used
on the low side for broadcast band reception is that a greater tuning range
would be required for the oscillator
than for the antenna or R.F. tuningthus:
Output
Oscillator
Signal
,465 kc.
95kc.
550kc.
465 kc.
1,035 kc.
1,500 kc.
A tuning range of 95 kc. to 1,035 kc.
would be impossible to secure without
band switching.
When using the oscillator on the
"high side" the tuning range of the
oscillator is less than tuning range of
the antenna.
24
Signal
550 kc.
1,500 kc.
Oscillator
1,015 kc.
1,965 kc.
Output
465 kc.
465 kc.
lt will be noticed that while the
antenna frequency tuning range has a
ratio of roughly 3 to 1 between maximum and minimum, the oscillator tuning range is approximately 2 to 1.
To provide the single dial control
required of modern receivers, some
method must be used to restrict the tuning range of the oscillator so that a
uniform separation of the value of the
intermediate frequency is maintained
between the signal tuning and the oscillator tuning. If a 465 kc. intermediate
frequency is used the ,oscillator tuning
must always be 465 kc. removed from
the signal. This cannot he accomplished
by simply using a smaller coil for the
oscillator, the effective tuning capacity
must also be reduced. This may be accomplished by connecting a condenser
in series with the oscillator section of
the tuning condenser to reduce its effective capacity. The series-connected condenser is called the low-frequency pad
and its adjustment is, or should be,
familiar to all servicemen. Another way
of accomplishing the same object is to
use a gang condenser in which the oscillator tuning section has specially
shaped plates of smaller area than the
'plates of the variable condenser sections used to tune the antenna and RF.
stag~s.
It is interesting to note that if the
receiver is designed with the oscillator
operating at a lower frequency than the
signal, the low frequency pad or pads
would be placed in the antenna and R.F.
sections of the circuit. This unorthodox
method of using a "low side" oscillator
would prove of advantage in designing
an ultra-high frequency receiver, since
the oscillator would have greater output and stability when operating at a
lower frequency. The difference between the "low side" or lower frequency
oscillator op~ration and "high side" or
high frequency oscillator operation
amounts to twice the intermediate frequenCY, and with a 465 kc. I.F. the
difference in efficiency would be negligible. However, with a 5 megacycle I.F.
th~ difference in oscillator frequency of
10 mc. between the two methods of operation could result in a considerable
improvement in oscillator performance.
Images and Spurious Responses
We approach the subject of "Images
and Spurious Responses" with some
hesitation, because in this section it is
necessary to point out the essential
defects of the superheterodyne system.
It is difficult to point out how various
forms of interference originate within
the superheterodyne without appearing
to condemn the principle of the receiver. Therefore we wish to st,ate emphatically that the superheterodyne is
truly the king of radio receivers, and
that while various improvements will
undoubtedly occur, the fundamental
design will remain. This fact has been,
recognized for many years.
The difficulty arises in the inability
to give a quantitative analysis of the
intensity of the various unwanted responses of the circuit as compared with
normal interference which .originates in
the turmoil of our broadcast band.
After all, it must be realized that
there are only 95 channels for broadcasting stations in the frequencies lying
between 550 kc. llnd 1,500 kc. and on
these 95 channels are located over 600
broadcasting stations. SatisfactOl;y reception can be obtained only on the few
clear channels; or from local stations
which have sufficient power to over-ride
interference originating from perhaps
a dozen other broadcasting stations
operating on the same wave length. An
• Section 2
SUPERHETERODYNE ',RST DETECTORS AND OSCIUATORS
unwanted whistle or squeal does little
harm when it lands on a channel which
at the location of the receiver is unusable anyway; so that most of the effects
to be described will never be noticed by
the average listener_
So far, we have been discussing the
desired signal. However, many signals
other than the desired signal reach the
first detector, since the selectivity of the
usual input circuits of the average
receiver is anything but perfect. Signals
from the adjacent channels are rejected
by the selectivity of the intermediate
frequency amplifier. However, there
are numerous signals and combinations
of signals that can produce heterodynes
which will pass through the LF. ampli-.
fier. These spurious responses can cause'
annoying interference, and a short
resume of their causes is of interest.
Images
Let us revert to the specific "example
used previously. Assume we have a
standard superheterodyne receiving a
1,000 kc. signal, and using a 465 kc.
I.F_ Then the normal operation of the
receiver is:
Oscillator
Signal
LF.
1,465 kc.
1,000 kc.
465 kc.
However, if a nearby station is operating at 1,930 kc. with sufficient intensity to produce an appreciable signal on
the first detector grid, the resulting signal will be passed by the I.F. Thus:
Undesired}
.
Signal
- ,OscIllator = LF.
1,930 kc.
1,465 kc.
465 kc.
The image is simply the "low side"
oscillator response, and the image is
always removed from the desired signal
by twice the value of the intermediate
frequency.
A corollary of this is that the higher
the intermediate frequency, the farther
the image is removed from the desired
signal. Naturally, the farther the image
is displaced from the signal, the easier
the problem of preselection. With receivers using the old standard 175 kc.
I.F., the image response to frequencies
between 550 kc. and 1,250 kc. was in
the broadcast band (900 kc. to 1,600
kc.), so that the possibility of spurious
response and interference is considerable. This is the reason why 115 kc. has
been largely dropped by the industry;
and why the better class of receivers that
employ this LF. frequency will be found
to use two, three, or even four tuned
circuits before the first detector. With
456 and 465 kc. LF. amplifiers the
image (except for a few channels) falls
outside the broadcast band; furthermore the percentage of difference between the frequency of the desired
signal and the image becomes so large
that the rejection of a single tuned circuit, such as a tuned antenna stage,
becomes adequate for ordinary household reception. The mathematical ratio
of the response of a receiver to a wanted
signal, as compared to the response to
the image, is frequently called the image
ratio, and the greater the ratio, the better the receiver.
Spurious Responses from
Harmonics
The strength of the harmonics
emitted by modern transmitters is very
small'in comparison with the power of
the fundamental wave, and in most
instances the actual harmonics cause little interference. The regulations of the
Federal Communications Commission
take care of this. 'However, strong harmonics of a signal may be generated in
the first detector tube; and the effect
will be exactly the same as if the harmonics originated at the transmitter,
except that the locally generated harmonics will be present only on the
stronger signals.
The production of harmonics by the
first detector generally occurs by reason
of grid rectification, the incoming signal having sufficient 'amplitude to override the grid bias. This effect and its
cure is described on page 10. It is the
purpose of this section to point out the
spurious responses which may result
from the harmonics. Thus the second
harmonic of a 1,000 kc. signal would
be 2,000 kc.; and if the harmonic possessed a reasonable intensity it could be
picked up when the receiver was tuned
to that frequency. In this example, little
harm "would result to the broadcast listener since 2,000 kc. is outside of the
broadcast band. However, second harmonics of stations from 550 to 800 kc.
fall in the broadcast band in fre-
quencies from 1,100 kc. to 1,600 kc. As
an example, the harmonic of a 700 kc.
station could spoil reception from a
1,400 kc. station-the effect would be
the same as two stations on the 1,400 kc.
channel.
Third, and higher harmonics are
occasionally encountered in high frequency reception-their intensity is
usually considerably less than the
intensity of the second harmonic, but
their presence may fool the listener into
believing that he is listening to a distant
short-wave station, when the signal
actually is originating in a local transmitter.
If the harmonics originate at the
transmitter, the harmonics are actual
radiated waves and they will be picked
up by any receiver of adequate sensitivity, regardless of its design. The
effect of generating the harmonics at
the receiver is more pronounced in the
first detector of a superheterodyne than
in other types of rlldio circuits. Proper
circuit design, including the 'use of preselection, provides a satisfactory answer
to the problem. A modern short wave
receiver with one or two stages of tuned
R.F. amplification before the first
detector rarely shows this defect.
Oscillator Harmonics
The oscillator of a superheterodyne
can, and usually does generate an abundance of harmonics. In fact, this effect
was deliberately used in the early
Radiola 2nd Harmonic Superheterodynes, in which the fundamental frequency of the oscillator was one-half
the desired frequency. The purpose was
to prevent interlock because the low
intermediate frequency employed would
normally place the resonant points of
the oscillator and the detector input
coils very close together. The second
and higher harmonics of the oscillator
are capable of beating with an incoming signal, and if the difference in fre·
quency between the two equals the
inteqnediate frequency the resultant
output will pass through the LF. amplifier. As specific examples:
Desired
Oscillator
Signal
I.F.
1,465 kc;
1,000 kc.
465 kG.
2nd Harmonic of 1,465 kc.=2,930
25
Section 2 •
rHE
MYE
rECHNICAL
MANUAL
\
kc. This 2,930 kc. oscillator input can
beat either of two frequencies" to the
I.F. frequency:
2,930 kc. - 2,465 kc. = 465 kc.
. 3,395 kc. - 2,930 kc. = 465 kc.
Heterodynes Between Stations
There is a very good reason why the
even numbered intermediate frequencies of 450, 460, 470, etc. are not gen3rd Harmonic of 1,465 kc. =4,395 kc.
erally
used in broadcast receivers.
4,395 kc. - 3,930 kc. = 465 kc.
Broadcasting stations are located in 10
4,860 kc. - 4,395 kc. = 465 kc.
kc. channels--and if two signals differThese examples will explain why a
ing from: each other in frequency by the
short-wave station will occasionally he
value of the intermediate frequency
tuned in on the broadcast band. The
enter the first detector, they will beat
input of such a station will be greatly
with each other to produce a third sigattenuated because the frequency is far
nal of I.F. value. The result would ,be a
removed from the resonant frequency
continuous backgl'ound jumble of the
of the detector grid tank (input tuning
two stations, regardless of where the
circuit), so that the effect is generally
receiver was tuned. Odd numbered
limited to very close stations. Many
intermediate frequencies are used, such
radio amateurs are blamed for spoil~g
as 465 kc., 456 kc., etc., since broadbroadcast reception when the real troucasting stations are never spaced by
ble"lies in the fact that the broadcast
such an odd' interval. Here is one of the
receiver does not have adequate presestrongest arguments to the serviceman
that his test oscillator should be acculection. Adequate preselection, plus reasonable shielding of exposed grid wires
rate, since a discrepancy of 4 or 5 kc.
will eliminate the trouble, or at least
will align a receiver so as to be susceptireduce the trouble to a negligible value.
ble to interference from inter-station heterodynes. Another point-an intermediate frequency amplifier does not
accept a single frequency-it accepts a
Harmonics Beating Harmonics
bimd of frequencies. Also, while the
unmodulated carrier has, or should
have a single frequency, the modulated
Although seldom actually causing
carrier with its side bands may occupy
trouble in receivers of modern design
the full 10 kc. allotted channel. Conseusing the higher intermediate frequently, in locations where the receiver
quencies and modern mixer tubes, it is
is very dose to two powerful broadcastperfectly possible for the harmonic of a
ing stations separated by an interval
station carrier to beat with the harmonic
approximating the I.F. frequency, say
of the oscillator to a value which will be
460 kc. or 470 kc. with a 465 kc. I.F., a
passed by the intermediate frequency
jumble of the two stations may be heard
amplifier. Because both,harmonics will
all over the dial. Assuming that the
have less amplitude than the fundamenantenna is of reasonable length, and
tal frequencies, such responses are genassuming that the receiver is properly
erally quite weak.
aligned, there is still one remedy left to
the serviceman. .Simply realign the
For those who are interested in a
intermediate
frequency a few kc. higher
pastime let us suggest that instead of
or lower than the specified value. In
working a cross:word puzzle, the reader
the example given above, realignment
try figuring all the various combinaat 475 kc. or 455 kc. will probably cure
tions and permutations by which an
,
the
trouble, and there is sufficient range
oscillator and its harmonics can beat on
in
the
trimmers of most I.F. transforma si~al and its harmonics to produce a
ers to permit this. Realignment of the
signal at intermediate frequency. The
I.F. will also call for readjustment of
practical value of such calculation is
the
gang condenser trimmers and low
doubtful, because the higher the ord~r
frequency
pad. After realignment the
of the harmonic the weaker the amphtude, but the number of such combina- . dial scale may be slightly "off" but this
can not be avoided, and is a small price
tions is amazing, and the read~r will be
to pay for the elimination of the interassured of a full evening of entertainference.
ment.
26
Overall Feed-back
There is one curious form of interference which is fairly common .in
receivers using a 175 kc. intermediate '
frequency, and that is the ·inability to
receive stations on 700 kc., 1,050 kc.,
and 1,400 kc. without a strong whistle
being heard. This whistle nas been
found to originate through overall
feed-back. Some of the R.F. energy at
175 kc. frequency passes from the sec:
ond detector through the output system
of the set and is picked up by the input.
The fourth harmonic of 175 kc. is 700
kc.; the sixth harmonic is. 1,050 kc.;
and the eighth is 1,400 kc. If this disturbance suddenly appears in a receiver
which has previously been free froni the
trouble, one should immediately suspect the failure of the R.F. bypass condenser connected to the plate of the
second detector tube, the opening of the
ground lead between the receiver chassis and the loud-speaker, or the failure
of other R.F. bypass conK8
R.F.
l'~PUT
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The 6L7G construction, designed for
mixer service, uses five grids. The No.1
grid is the R.F. input grid, the No. 2
and No.4 grids are the screen, the No.3
grid the injector grid, and the No.5 grid
,
the suppressor.
The 6J8G construction is identical to
that of the 6L7 except that it has an
additional triode section mounted at the
bottom of the common cathode. The
grid of the triode is tied internally to
the No.3 grid of the heptode.
The 6K8 is of an entirely new construction best shown by the bottom
sketch at the right of the page. ~ single
flat cathode is used with a common No.
1 grid for the oscillator and hexode
section. A flat plate is used for both the
oscillator and hexode. The screen and
R.F. input grids are positioned approximately as shown on the sk~tch. The
shields as shown are placed to give a
suppressor action to the hexode section
thus raising its plate resistance and making p()ssible the use of the screen and
plate at the s~me potential.
The ability of the tube to develop a
current at an intermediate frequency is
given by the conversion conductance,
which by definition is the ratio of an
incremental change in intermediate frequency current to the incremental
change in R.F. signal voltage that produces the current. This conductance in
micro mhos is published on all converters
and its use to calculate stage gain is
analogous to the use of mutual with
R.F. amplifier pentodes. The gain equation for a single tuned load is:
,/
SPACE (IIAI(6E
CAMc/7:zJAlCC COt/Pt.lN6
(DII:.
I
,"
0- ........ ,
~ ..........
SHELL.
• Section 2 .
The above equation involves ':lnly one
other tube characteristic, and that is
plate resistance. Published values of
plate resistance and conversion conductance can therefore be used to calculate
stage gain.
In application there are certain phenomena that alter characteristics or
circuit parameters and th{) results are a '
gain value somewhat different than calculated from published data. These unpublished characteristics are essential
in selecting a tube for a particular
service.
Assuming the use of rated voltage!!
and oscillator grid current there are in
41
Section 2 •
THE
general the following effects that occur
in the several tubes:
1. Degeneration at the R.F. signal
frequency.
2. D.C. current flow in the R.F. signal grid circuit that upsets operating
conditions.
3. Oscillator voItageappears in circuits other than those associated with
the oscillator. This voltage may be in
phase or out of phase with the normal
oscillator voltage and the resulting
plate current at oscillator frequency
may be increased or decreased. As
conversion conductance' and gain are
functions of the plate current, the
measured gain is different from that
calculated.
4. Negative or positive loading in
the signal grid circuit affects. the antenna or interstage gain driving the
converter tube. Calculations are often
upset because of this phenomenon.
To facilitate comparison of the five
converter and mixer tubes, the chart
Figure 15 was prepared. It lists eight
separate plienomena found in the several tubes. In addition, a tabulation of
the more important interelectrode capacitances and of the two characteristics,
plate resistance and conversion conductance, is given.
The first phenomenon, capacity coupling from oscillator to signal grid, is
experienced with all tubes. The capacitance, not shown, is approximately .1
mmfd. for each type. The result of the
coupling is mainly that oscillator voltage appears across the signal grid tuned
circuit. At extremely high frequencies
the impedance of the signal grid circuit
to the oscillator frequency is quite high,
and the magnitude of the voltage becomes high enough to over-ride the bias
and cause grid current. If the voltage
does not produce grid current, the effect
is either to increase or decrease the conversion conductance and conversion
gain. If the voltage is sufficient to cause
grid current to flow, the D.C. current
upsets the operating conditions, with
attendant loss in sensitivity.
The oscillator voltage in the signal
grid return, as a result of capacity coupling, is in phase with the normal oscillator voltage if the qscillator is on the
high side of the resonant frequency of
the tuned circuit in the signal grid cirh:
70
-I-- ~- rI- t--I--
.......
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5-5
I-
r--.
.......
....... r-
r-
5-5
40
~
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00
densers need be no higher than for the
half wave rectifier applications, 150volt working condensers are usually
specified for this type of circuit. Such
condensers are safely rated for all except unusual conditions of extremely
high ripple peaks as might occur with
low capacitance values and 25-cycle
supply lines.
It will be noted that condenser CB
has its cathode connected to the chassis and thus if it is of metal can construction the unit may be directly
mounted on the receiver chassis. Condenser CA, on the other hand, must
have its can insulated from the chassis
and be suitably covered to prevent
accidental contact of any grounded
parts with the can of the condenser.
One side of the power line is connected to the junction of these two
condensers designated as point 0 in
Fig; 4B. Since either side of the power
line circuit may be grounded depending on the direction in which the attachment plug is inserted in the power
outlet, it is evident that care must be
taken in the design of transformerless
sets such as the A.C.-D.C. and doubler tyPes from the standpoint of
shock and fire hazard.
The output condenser of the filter
(C 2 of Fig. 4), must of course be rated
at a value determined by the full output of the doubler less the filter drop
and is usually a 250-volt rated unit.
'-"' - I 0-10
r-... ....... ::::::: ~
rJ)
120
6::::
Fe :;.... I-"'"
~
::::::: I:::-.
160
oI:i
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50
6C
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<{
-- ~p
100
• Section 3
~ 20-20
0
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- -- ....- '-"'
-
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P"
- I 0-10
1-
..-:: ~
..-::; .....
,~
-
SUPPLY SYSTEMS
~
00
00
IDC-LOAD CURRENT IN MILLIAM PERES
100
6A
Of importance from the performance standpoint is the effect of circuit
returns and power line grounding conditions on hum pick-up in the audio
circuits and hum modulation of the
oscillator. Either the metal chassis or
a negative bus wire is made the return
point for the RF, IF and audio grid
circuits as well as their respective
cathode or cathode bias circuits. The
heaters of all these tubes are connected in series with a suitable voltage
dropping resistor across the power
line. In half wave circuits such as are
shown in Figs. 1 and 2 the power line
can readily be connected directly to
55
THE
Section 3 ,.
the return side of the grid circuits
(negative side of filter output), if suitable protective measures are taken to
reduce shock and fIre hazard. In these
circuits the succession of heaters starting from the chassis is usually as follows: Second detector at ground on
chassis, then fIrst detector, if of the
converter type, or oscillator if of the
separate tube type, then in succession
the other heaters in order of the audio
and radio gain until the output tube
and the rectifIer are found at the other
end of the series string. By this
method the D.C. and A.C. differences
of potential between the heaters and
their respective cathodes are kept low
for the tubes most likely to introduce
either audio or carrier modulation
hum.
In the symmetrical doubler circuit
of Fig. 4A it will be seen that there
exists a D.C. voltage difference of half
the B supply voltage Between the
chassis and the fIrst heater of the
series string T 1 and that upon this
D.C. potential difference is superimposed the ripple voltage of CB. Fortunately modern tubes have very low
cathode to heater leakage as well as
improved heater constructions which
keeps this source of hum at a minimum. As mentioned above certain
recent receiver models employing this
type of doubler circuit have departed
from the usual symmetry of capacitance and have made CB twice the
capacitance of CA~ This reduceR the
RF impedance between chassis and
power line, as well as reducing the
ripple voltage between heater and
cathode o( the fIrst tube in the series
string.
FIGURE 7
A
SCHEMATIC
TECHNICAl.
MY E
MANUAl.
COInmon Line
or Series Line Feed Type
of Doubler Circuit
Another general type of voltage
. doubler- circuit has been variously
called the common line, series line feed
type, or half wave doubler, is shown
in Figs. 7A and 7B. This circuit operates in a somewhat different manner
from the one just described and might
be, designated as a voltage addition or
multiplier circuit rather than a doubler circuit. It was proposed prior to
1933 and has found occasional application since that time. It will be noted
that this circuit allows one side of the
power line to be connected directly to
the negative side of the fIlter output
and thus overcomes the difficulty of
a high voltage difference between
heater and cathode of the high gain
tubes at the chassis end of the heater
series string. The circuit is shown in
schematic form in Fig. 7A and in simplifIed form as Fig. 7B. Only the portions of the circuit essential to an explanation of its action have been retained in Fig. 7B.
The operation 'of the circuit may be
explained as follows: Assuming point
1 to be positive with respect to point
2 during the initial half cycle, charging current will flow in the direction
shown by the solid arrows through
rectifier tube T 10 until capacitor CA
assumes a charge equal to the instantamlous potential of the line. During the next half cycle as point 2 becomes'positive with respect to point 1
the charge of condenser CA will add
its potential to that of the line and
current will flow through rectifIer
tube T 2, charging capacitor CB to a
potential equal to the sum of the
charge in CA plus the line peak. The
path of this action is shown by the
dotted arrows. This action would result in a charge of condenser CB of
twice the peak line potential if it were
not for the fact that this condenser
begins discharging through the load
the instant that current starts flowing
through rectifIer tube T 2. A cursory
analysis of this circuit would indicate
that since current seems to flow in
both directions through capacitor CA,
as shown by the solid and dotted arrows, a non-polarized type of electrolytic condenser would be required.
This is not the case and it is possible
to use a standard polarized type in
this position. After the steady operating condition is reached the net
charge, which capacitor CA receives
during the half cycle when T 1 is conductive, balances its discharge on the
succeeding half cycle, since CA acts as
a rese~voir to supply the loss of charge
of CB by current through the load. It
will be seen that the polarity of CA
never reverses and thus a polarized or
common type of electrolytic condenser
may be used.
Fig. 8 shows the general nature of
the voltage and current wave shapes
in this type of doubler circuit. These
are seen to be quite dissimilar to those
encountered in the half wave rectifIer
and symmetrical or full wave doubler
circuits and a word or two of explanation may be in order. The shape of the
pulses for the fITst two cycles are
somewhat conjectural since it is difficult to observe them on the cathode
COMMON LINE OR SERIES LINE FEED TYPE OF DOUBLER CIRCUIT
DIAGRAM
B
......
SIMPLIFIED DIAGRAM OF DOUBLER CIRCUIT
~-x-,~
SOLID _
-
'tHARGING
CURRENT FLOW WHEN
IS POSITiVE
56
Q)
DOTTED --~ --~CHARGI NG
CURRENT FLOW WHEN
IS POSITIVE
®
!
,
HALF
WAVE
AND
DOUBLER
POWER
FIGURE 8 VOLTAGE AND CURRENT WAVE SHAPES IN
COMMON LINE TYPE VOLTAGE DOUBLER
+
/,~'\
!.
/,
\
b~~\--~
I
\
\
I
\
\
--~\-- -+- - --+--- I - - --t
\
I
\
/
\
A
\ .. ..--1
/
\
\
I
\
/
/
' ....../
VOLTAGE ACROSS CA
\
\
,
"
I
SUPPLY SYSTEMS
• Section 3
ray oscillograph without elaborate
transient sweep devices. After the
steady slate operating conditions have
been reached, the charging current
pulses into condenser CA (through T 1)
are of very short duration since it is
only necessary to restore the loss of
voltage occasioned by the transfer of
its charge to CB during the portions
of the succeeding half cycles when T 2
is conductive. The discharge pulses
from CA are of longer duration· since
current not only flows into condenser
CB but also into the load resistor during this time period. A condition of
equilibrium is reached when the area
of the charge pulse is equal to the area
of the discharge pulse and then, due
to the difference in time duration of
the pulses, the current wave may be
quite assymetrical as shown in Fig. SF.
Typical Operating
Characteristics of the Series
Line or Half Wave Doubler
B
c+-
VOLTAGE ACROSS Ce
CURRENT THROUGH T(.
CURRENT THROUGH T2
CURRENT THROUGH CA
Unlike the circuits previously discussed, this doubler has quite dissimilar functions for the two capacitors
CA and CB. CA acts as a reservoir of
energy and adds its charge to the line
during the succeeding cycle. It contributes little to the filtering action
and therefore we need only concern
ourselves with its effect on output and
regulation. CB is similar in its function to the input filter condenser of
the half wave A.C.-D.C. circuit of
Figs. I and 2 except for the higher
working voltages encountered. Unlike
the symmetrical doubler, the voltage
ratings of CA and CB 'need be similar
since CA is never subjected to an instantaneous voltage greater than line
peak plus the ripple voltage shown in
Fig. 9C. The average or D.C. voltage
on CA approaches line peak only for
the conditions of low D.C. load currents and high values of capacitance
in both units. For these reasons it is
evident that CA may, for typical operating conditions at 60 cycles, be
specified as a 150-volt rating, especially if its capacitance is high, i.e.,
30 or 40 mfd. Capacitor CB, on the
other hand, is operating with the full
D.C. output voltage of Fig. 9A plus
the peak ripple shown in Fig. 9E. It
must therefore carry a working volt57
Section 3 •
THE
age rating of 250 or 300 volts, depending on load current and voltage.
In the series of curves shown in
Figs. 9A, B, C, D, E, and F, the"value
of capacitor CB has been fixed at 40
mfd. as being. a representative value
from the standpoints of regulation
and ripple voltage (hum). As previously stated, it will be observed that
the value of the line series condenser
CA has only a minor effect on the
ripple voltage and RMS current conditions of CB. The ripple current in
CB again does not exceed the "rule of
thumb" value of 2.4 times the D.C.
load value discussed for the half wave
rectifier case and consequently this
estimate of working conditions provides a generous safety factor.
The conditions of operation of the
line series condenser as shown in Figs.
9B, C and D distinguishes this general
type of circuit from those previously
discussed. It will be noted that the
RMS ripple current through this unit
as shown in Fig. 9B is much higher
in proportion to the D.C. load current
than for either of the other types of
circuits. The ripple current for low
values of load current is seen to approach a value of 3.2 times the D.C.
current. This value has been chosen
as a, convenient figure which again
provides a generous safety factor when
considering load currents of practical
usefulness such as 50 MA or more. It
will be noted that low values of capactance should not be specified for condenser CA wherein the current exceeds
the value of 10 milliamperes per microfarad previously cited as safe for
the type FP capacitor. Other considerations, such as regulation and output voltage, which would influence
the choice of this capacitance value,
would also result in a capacitor value
which would lie in a safe operating
region as far as ripple voltage and
current are concerned. An upper limit
of capacitance is determined only by
the effect of capacitance on- peak ripple current through . the rectifier as
shown in Fig. 9D. In this instance the
D.C. currentlimitof75 MAisreached
before the peak ripple limit .of 450
milliamperes. As previously stated it
has' become standard practice to employ two rectifier tubes in parallel for
the higher D.C. load current conditions.
58
M YE
TECHNICAL
MANUAL
FIGURE 9 COMMON LINE OR HALf WAVE DOUBLER
TYPICAL CHARACTERISTICS
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T2
CAz
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20
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40
50
60
70
80
90
100
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10
20
30
40
50
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80
90
100
~
50H--!;'~++-H-+-+-+-H-+-+-++-H-+-l
.;
c(
10
20
30
40
50
60
70
~~
80
90
100
98
~
~:::J150H-+-+-++-H~~+-HH-+-+-+-~~-l
00.
~
r- 10MFD
>~
,
~ 100rC~B~=~4~~M~P~D-+-+-H-+~,++-H-+-+-+-H
a~
'U
Jl
50~1_+-1~_+-1~-+~+-~~~~~+-~-+~
I I
0
0
I
I
I I I
10
20
"'-
30
40
50
60
70
80
I-t-I- 5MFD
90 100
IDe-LOAD CURRENT IN MILLIAMPERES
9A
HALF
WAVE
AND
DOUBLER
POWER
Series Line Feed or Half Wave Doubler
with Common Cathode Type Condenser
An interesting variation of the type
of doubler just discussed is the circuit
of Figs. lOA and B. This arrangement
of circuit components makes it possible to combine all of the fIlter capacitors in one common cathode type
unit. The resulting saving of both
space and economy of construction
are obvious. In this case the metal can
of a condenser of the FP type can be
mounted directly on the chassis and
it is not necessary to provide insulation of the conaenser can as in the
case of the high side condenser of the
doublers previously discussed. Since
both CA and CB carry ripple currents
of the magnitudes shown in Figs. 9B
and 9F, the ability of the particular
type of condenser construction to adequately radiate the heat occasioned
by the flow of this ripple current
through the series resistance of the
condensers, should be considered in
the choice of a suitable unit. When
these units both having ratings of 40
mfd. and the D.C. load current does
not exceed 75 MA, it is possible to
combine them with the output fIlter
unit in a single condenser of the type
FP construction.
It will be noted that this circuit
interposes between the heater and
cathode of the frrst tube in the series
string the terminal voltage of condenser CA. Since there is superimposed
FIGURE 10
A
• Section 3
SUPPLY SYSTEMS
upon the average voltage a peak rippleas shown in Fig. 9C it is obvious
that the value of CA should be made
as high as is practicable not only to
keep this ripple at a minimum but
also to provide a low impedance path
between the chassis and the power
line for both radio and audio frequency currents.
Voltage Multiplier Circuit
An interesting extension of the principles involved in the half wave type
doubler circuits of Figs. 7 and 10 is
shown in Fig. 11. In this case the
principle does not stop with a doubling of the voltage but is extended to
cover any desired multiple of the line
voltage. Condenser C 1 operates in the
same manner as condenser CA of
Figs. 7, 8, and 9, and delivers its
charge plus the line peak voltage of
the succeeding cycle to condenser C 2 •
This condenser adds its contribution
of double voltage to the line voltage
on the next half cycle when diodes Dl
and Da' are conductive. This action
continues in chain fashion through
condensers and diodes 3, 4, 5, and 6
in turn. It might at first appear as
though the chain of rectifiers when
conductive would short circuit the
charging action. This is not true be-
cause, once the series of condensers
are charged, current from the individual rectifiers flows for only that
portion of the cycle necessary to restore the loss of charge from the condensers due to current through the
load. Thus, after the steady state
conditions are reached, condenser C 1
is charged almost to line peak, condenser C 2 almost to twice line peak,
etc. It is obvious that condensers C1,
C a, C., and CN, may be combined in
one common cathode unit with proper
attention given to the required voltage ratings of the individual sections.
Similarly condensers C 2, C 4, and C 6
may be combined in another or second
common cathode type single unit.
This circuit has been included here
more for its interest as an extension of
the principles discussed than as a suggested practical power supply system.
Those familiar with the technique of
the art of constructing surge generators for lightning research will recognize similarity of this circuit with the
individual charge and series discharge
methods employed to produce very
high voltages. A practical limitation
of a chain circuit of this type is the
fact that if the tubes have their heaters connected in.a series string across
the power line there will exist dangerously high potential differences between heaters and cathodes of the
rectifier at the high voltage end of the
system. This difficulty of course might
be obviated by the use of heater supply transformers but this would destroy the simplicity of this system.
SERIES LINE FEED DOUBLER WITH COMMON CATHODE CONDENSER
SCHEMATIC DIAGRAM
B
SIMPLlF"lED
DIAGRAM Dr DOUBLER CIRCUIT
+
U S PATENT 2 172 962
CHASSIS
P R MALLORY 8. CO INC.
SOLID ___ CIiARGING CURRENT
f1.0W WHEN
IS POSI1"IVE.
+
I
DC
DC
L
VOLTAGE
DIVIDER
aM
~
FIG. log
01----·---i---'
Frc.2
65
MY E
THE
Section 4 •
TECHNICAL
MANUAL
lated from the base and from each
other, permitting independent circuits.
The two reeds on any vibrator had to
be exactly matched in vibrating frequency .. Each production reed was
matched to a standard on a master oscillator by removing a small portion
of the armature weight. The coil was
still a series type, depending upon
the load current for good amplitude,
the contacts of both pairs were closed
at rest, and the second set of contacts
were used for' mechanically rectifying'
the high-voltage AC instead of using a
rectifier tube. As can be seen in the circuit, Fig. 3, a "phantom-load" resistance
Dual Reed Vibrator
The next step in the development of
vibrators was the addition of it second
vibrating reed and associated spring
and contacts. This "dual·reed" vibrator
is illustrated by the line drawing in illustration No.3, together with the circuit in which it was used. The coil
position was changed, so that the armatures now included on the reed assemblies could swing past the end of the
core, 'instead of being attracted to it as
was the case with the original vibrator.
All of the reeds and springs were insu-
The following reproductions picture the Mallory dual·reed or self-rectifying Elkonode in
two positions; a side view showing the Elkonode with cover and rubber cushion removed, and
a front view with wver and cushion removed. Numbered arrows clearly indicate position of
Elkonode parts involved in installing new contact spring and new reed assemblies.
e
1
s
5
6
cg}
L.OCKING SCREW
1111
I
SCREW-DRIVER SI...OT FOR
AO.JUSTING STOP POST
ENLARGED STOP POST ASSEMBLY
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Coil mounting nut
Coil
Stop-post mounting block
Position contact spring behind
stop-post head
11. Contact points
Air-gap
Rppd counter wf'ights
Stop-post locking-screw
Stop-post
Reed Spring Assm.
Contact Spring Assm.
~
III~
#17005
,.. ~
#A-\70~"'---~_'"T-'lm;oo'
P~~~LQAO
#10746
~A~+--J~srG=T'~~=S=FO='M="~
S,",O~T L'ENGTH
# \
B
8t S
WIRE
o~~~
U!AQ CON-
NEC1.~~~~
A-
IN
~C-
TYPE CH SSIS S- IS GROUNDED A.MO
COHDENseR A,I'tO CHOI
........ 6.6V
6.3;;':.:..
-.j 6.0·:'0/Ju1
- -:b~.x...,
~3
V.lnput
v
0
0
i---I.
160
o
20
---- -
40
d.6 \:...
--
--I-~6.0v.'",~
~
~
TAPS 2 & 4
----80
5
---
~
.
1'--"-'0
.......
--·120
-~
-
@.
...... ~
---
-- ~
!"'-' ... ~.
~-
JAPS 1 & 3
I~
'--
200
I!:
:::>
--r
__
120
1"--_...... ~~6.6"
~"
...........
"'"
6.0" ' ,
~
~, 1--,
g
'-- "
~ 160
o
illustrated ~ the previous photograph.
Fig. 20 shows the tube-rectifying type
with tap·switch, and "A" hot, 'fB" plus,
and "B" minus RF or hash filters. Of
course, the tube.rectifying type is intended primarily where "S" minus is
desired off of ground potential. Fig. 21
shows the self-recti,fying type with tap·
switch aDd RF filters while Fig. 22
shows the same type of power unit for a
single range of voltage output, therefore
not requiring the tap.switch. Fig. 23
shows the interior arrangement of a
dual power unit, with .individual pri.
mary RF filters, fuses, apd output resist·
ance smoothing filter. An individual con·
nection and filter is' provided for the
tube heaters so that they may be con·
trolled separately with the heaters of
the tubes in the amplifier or trans·
mitter.
While the output characteristics and
input loads corresponding to same are
shown in Illustrations Nos. 25, 26, 27, '
circuit diagrams representative of the
three types of Vibrapack power units
are shown in Illustrations Nos: 28, 29,
30 on pages 83 and 84.
t,--
--·240
I-200
MAf'tIUAL
280
280
~
:!
TECHNICAL
60
Vm
3
- :I!<
2
--
11-"'"
100
~
4
~
~
80
-. ~
o
~
-&
~
20
~V
40
>
80
60
100
OUTPUT MILLIAMPERES
FIG. 25A-OPERATING CHARACTERISTICS OF VP·551
where they are unobjectionable. Each
vibrator then assumes its normal por'
tion of the load so that satisfactory vi~rator life is secured; and the combined
power output is amply smooth for any
practical application. This fact has
been amply substantiated in actual servo
ice by the performance records of dual
Vibrapacks types VP-555 and VP·557
which are widely used under heavy load
conditions to operate police mobile
radio +ransmitters, etc.
.
Chassis Construction
Illustrations Nos. 20, 21, 22, show
the methods of assembly and constructio~ for the interior of the Vibliapacks
Operation of Vibrapatks on A.C Lines
\
Fu~ing
380
While all vibrator power units should
be fused for protection to the various
components and the battery, it is essential that dual units be individually fused
with the proper fuse. There are two
reasOns for this. There is an appreciable
amount of resistance to fuse and its
holder. 'The use of ,separate fuses provides additional isolation for the two
halves of the supply through the elimination of ~omnion 'impedance. But a
more important consideration is the
fact that should failure of any component render inoperative one side of a
dual pack, the fuse for the other section
will blow and thus prevent a single
vibrator from assuming the full load of
the entire power supply. It is obvio'us
that a single ~section of a dual power
supply could not supply double output
for an extended period of time without
being damaged.
340
440
"'"
" ~,---......
6.0,,>.
........ f--.. --......
4.?v
1--_
6.31'
t--- "'-'
400
.......
..... "
'" 360
~
"--...... 1"--,
" , ~'
. loev, l'
i'- _..
l'
~ S->~~
. -....:.: ...
.
~
"'~......
- ' " ...........
1 r--.. t
r--::.
~3~
--
t--
280
601'
0/. UI
-~-
TAPS 1 & 3
f
!--"'" --~'6
o
~
20
40
....- ~ ~ --5·4
L-----"
1-~
t::::::- 2i"'" ---60
~...
tAPS 2 & 4
---8
~
•
-~II.~
240
I-
.
.....
1'-_
320
r--~-~
1--- 1- __ ~.7..!:...
220
"-,
r-.....
r-.. ....... ~N·J"
........
.~
-
1--_
a
80
plying an additional primary winding
on the vibrator transformer for con·
nectiop. to U5·volt AC lines has been
suggested, and in some instances d-one.
Considerable discussion has occurred at times regarding the operation
0.£ Vibrapack type of power units on
AC {lower lines.
, The possibility of sup-
80
100
o
20
40
OUTJ>UT MILLIAMPERES
FIG. 25B-QPERATING CHARACTERISTICS OF VP-552
60
--
~
@
--@)
I--'"
80
100
• Section 4
VIBRATORS AND VIBRATOR POWER SUPPLIES
fore the usefulness of the receiver was
gone. In this case a high-voltage AC
. winding was included, controlled by a
two-position switch which also controlled the primary DC circuits simultaneously. The heaters were run from
the battery when on DC operation, and
from a portion of the DC primary when
on AC operation, thus eliminating one
winding. It is also not necessary to remove the vibrator from the socket when
operating in this circuit.
6r---~--~----+----+--~
TAPS 1 & 3
.!SJ-
TAPS 2 & 4
---~-4"----
13 5 1----1----1----+----1----+----- 51---~--_I----+_--_+7""":::....j
!.
~
~
~
4
3
2
---
L--::::: - - -
.,;
"
r-...::;.
I"-... I-- .......~
~ 340
............. !2 .
6.3".
6.0V.,.
5
--1'
~
.......
0
~" .......
.
"""- - - -- --- -- ,---- --- -- - .:::- :::::-r-----
o~
~,
~
420 ..... ,
1- .......
1---...
,220
' .......
_6.!.!::.
v".pu,-_
®
"--r---'-t--_ --.
6.0
5.7
~
---
TAPS 2 & 4
TAPS. 1 & 3
,
----8
--::.. g)....-- --~.
@---
2
;l!;
,--
40
60
80
100
-----~
6
--~-4
~
20
,
r-............ " -
300
260
.......-:: ::---
ill Illus-
The circuit diagram shown
.....-::::
-2 ::;;.-
::::--
20
40
60
®
------®
80
100
OUTPUT. MILLIAMPERES
FIG.
25D-OPERATING CHARACTERISTICS ~F
yP.554
81
Section 4 •
THE
----'-
650
r-
'
d~ rr----
-.......S.;>3~
~,-
-
....
$$0
1--
400
--
MYE
425
1- _ _
375
r- -__
1
--
~
~
=::::
TECHNICAL
I-
~
-~-~l
MANUAL
Vibrator Wave Form
with AC Load
- r-
75 It Inpuf
1---~r---r- r -
r-_
325
Here it' is seen that as soon as the
contacts open, at the bre~k, the load
which is connected to the transformer
drains the power from the circuit beyond the capacity of the timing condenser to supply. This reduces the volt-·
age across the primary to zero, thus
.closing the contacts, at the make, with
the full input voltage across them.
Naturally, this condition is somewhat
detrimental to good vibrator performance and life. An inductive load applied
to the transformer creates a worse condition, and therefore, unless comparatively light, is not a recommended, or
approved, load for a vibrator.powered
inverter. Operation of motors, etc., universally re~mlts in damage to the vibrator unless the inverter is expressly designed for that purpose, because of the
extreme starting load imposed by such
devices.
0
275
;
20
MinimlllTl Starting
---- 20
/
V
~
--~
.
/"
10
vV
.
---- 5
Minimum OuTput
V
Current ~5 MA.
;
50
75
100
125
I~I
014 Tubes 140 MA.
---:15
!
/
/
:IS
V
Cu'''",wUb
150
25
4
~
VI
V
V
,
/"
Minimum Output
~
Current 40 MA.
50
75
125
100
175
150
:ItO
OUTPUT MILLIAMPERES
FIG. 26-0PERATING CHARACTERISTICS OF
tration No_ 33, page 85, gives a satisfactory method of operating one vibrator
power-supply on more than one voltage
input. The percentage voltage range
covered should not be too great, or too
large a per cent of die input current
will be coil current, in as much as the
coil of the vibrator must be wound for
the lowest voltage of operation. This
high current on the highest input voltage has the tendency to unbalance the
primary magnetization characteristic.
The unit shown was dev~loped to provide a power sourde for operating 110volt DC razors from a 6-, 12-, or 32volt battery, using a self-rectifying vibrator. By using a more complicated
switching means, the primary could be
made a series-parallel arrangement for
6- and 12-volt operation, reducing the
transformer slightly, but in this case it
was not felt to be worth the involved
switching required_ Rl and R2 are resistors switched into the coil circuit to
permit operation on the higher voltages, with C4 used to by-pass the AC in
the coil circuit.
Illustrations Nos. 34 and 35, pages 85
and 86, are circuit diagrams for inverters to supply AC output voltage from· a
DC source, usually 110 or 220 volts DC.
The former is a simplified circuit using
the shunt-type of vibrator capable of carrying a medium load, with Rl being the
series coil resistance, (this type of vibrator requires a .coil' of such high
resistance that small enough wire to
attain same in the regular coil·dimensions is not practical), and Ca being the
,82
VP-557
AND
VP-555
AC by-passing condenser. C2 are primary point condensers of very low capacity, and C1 is the timing capacity.
When operating into an AC load, it is
necessary to know the type of load,
(whether' capacitive or inductive), and
its value before being able to accurately
set the values for C1 and C2 , as well as
design the correct transformer. For
operating into a resistance load, similar
to the power-supply of an AC radio receiver, the primary voltage waveform
becomes as shown in Illustration No.
35.
The final circuit diagram of illustra·
tion No. 36, page 86, shows an inverter
, using a larger: separate' driver type of
vibrator, capable of handling higher
powers than the one just described. In
this case the coil requires no added resistance for 110 volts, but does require
same for higher voltages, being Rl in
480
1'.........-...
380
440
340
."
5
0
----r--~V.I.'"
---- --' ----I"--.
---... " ... "
'~
~
'5
_~.o~
...
300
260
220
--
.
--" r--~
-- t-!.l.!!':...,
~
TAPS 1 &
~
...... ,!1.$"
-...:.
....,
"
N
..........
..................
'5
............
5320
'0
!!:gil
...:....
,280
---~~
1----__
./"
J
11
~1I:.....
-
TAPS 2 & 4
---·4
@
3
~ I.---
2
.~ 1 ..--=::
:;;.-
20
k::::::= ---Q)
-
"
---- ------ --- ------- --r
- -...
t---.......... _
240
4
o
~ 360
U~"
85
;>
·. . r
440 I---I--~....::.._.d_--+--I--_l
r-__
I...-
I--~
::::- -
280
I---
~6~
_
---....~
I
_
j
t-..
--. r-....
r-- --
--'I~
__
-~L
j
v.......... C"'p.
I'
r __
I~.!::
3201---+-::::..,,-I-._'"""".:.::...-lh.._
-_
-_
1---l
L36
I---f---
- - -!!t.. f-- __
280
16 0
-.... _ L
·1" tJl
__ 0360.....
51
2<101-r.--_-+---+---F::O"...:.;;:""--=---=1
~
....... ~v
::>.
'--. __
I
r-- ~ ...
,~ 400...........
r"-......J l ) . o - ,
I
'-- ~,:-f-__
I--- I~noui
- -......
CD -_
200
-....~
--~~...............
~I
320
50
RF Interference
Suppression
~~
--.il6 V
. In
r---t-
"i---- +----- ®
1
-
240
""f:-~-::._
32V
28"
-.J
___
1-_ 1- __ _
TAPS 2 & 4
TAPS 1 & 3
1.6,1---+--+---1f---t---+---1.61---+--+----If---b;:-~
.,;
I@ ___
1. 2 1---+---+---!--+~®E""""'1-
~ L21---+---+---!-__.::r;pr".---I
--=:::~ ~~
1--+-_-+~-=-,.......j:-::::"....-.9===---I_
8
4~
o
20
-------~
.81--+-..---:::::--_+-::--,.....,::.'--±.--'=-i---I
_.4~
40
60
80
100
40
20
60
80
100
OUTPUT MILliAMPERES
FIG. 27B-OPERATING CHARACTERISTICS
the diagram. In this circuit a transfonner and switching arrangement is
provided for operation on either no
or 220 volts DC, with C1 being the
timing condenser and C2 the point condensers. Cs and Rs are used across the
driver·contacts to prevent erosion and
transfer. Again, the primary may be
made a series·parallel arrangement
with more involved switching.
Other possible applications will come
to mind of the reader. Among them will
be the operation of neon (and other
luminous gas) tubes as signs, warnings,
etc. This has been done very successfully in the past by means of high leakage inductance types of transformers,
,imilar to the AC types used for the
~ame purposes, wherein the tube is ig'lited by the high induced voltage of the
unloaded secondary but which has its
maximum load current controlled by
leakage strips of transformer iron inserted in the window between the primary and the secondary windings which
'ire wound in separated coils. This type
of construction furnishes magnetic
shunts which limit the output.
OF
VP-F558
ply have been barely touched. What the
future may bring, no one knows. Each
year brings new applications wherein
the vibrator power supply serves better
than any other forms of power conversion equipment. The Mallory Laboratory is always on the alert for new
developments, and progress is governed
only by the necessary economic consideration that the potential market justifies the development expense.
TRANSFO;RM~E:!!R_ _--"-<~--'(;:-D):_--___:=:;f....-~
SWITCH
LEGEND
TRANSFORM
C-I
C-2
SECONDARV LEADS TO BE TWISTED
INTO 4 PAIRS. LEADS OF SAME
LEiTERS TO BE PAIRED
Future Developmeuts
From all this, it will be evident that
the design possibilities and the field of
application for the vibrator pow~r sup-
Perhaps the biggest "bugaboo" or
difficulty in the application of Vibrator
power-supplies to radio receiver operation, even for engineers and designers
experienced in the art, is the matter of
RF interference suppression. Fundamentally there are only a few basic
rules that must be observed, with a
considerable number of variations that
must be predicated upon the nature of
the particular application under consideration. In other words, methods
that would be ideal from the standpoint
of suppression may not be practical
from the standpoint of cost in lowpriced receivers, methods that may be
used on heavy current drain power
units may not be acceptable on light
power applications where efficiency is
important, and in general some compromise is usually necessary.
These basic fundamentals can be
listed as follows, although probably
none are more important than others:
First, proper and complete magnetic
and electrostatic shielding of the components of the power unit and of the
complete unit; second, proper selection of grounds in both the power-unit
and the receiver to reduce or eliminate
coupling and radiation; third, proper
VP-551
AL 0
VP-552
PT N MALLORV P
VP-G556
NO MAL
B-44617-1
RF-481
A-40980-2
TP-415
B-44617-2
RF·481
A-409BO-1
TP-435
RF-562
A-40919-1
Rf-563
A-40919-1
A-40389-3
725
A-40921-i
A-40922-1
B-111202-1
A-40389-6
725
A-4092H
A-40922-1
B-1I1202-1
A-40389-6
R'I'
N
B-44617-4
RF-481
A-40980-1
TP-435
A-42097-1
RF- 563
A-40919-1
A-403B9-3
G725
A-40921-1
A-4092Z-1
B-1 II 202-1
FIG. 28-SCHEMATIC WIRING DIAGRAM FOR VIBRAPACKS
Nos. VP-551, VP·552, VP-G556
83
THE
Section 4 •
MY E
TECHNICAL
MANUAl.
T RANSFORME;R_ _---:.RE~D_;:(:D~J_;:::::j._--,
and complete filtering in the leads to
and from the power-unit; and fourth,
proper orientation and shielding of the
receiver coils and transformers, etc., to
prevent coupling to the power-unit.
SECONDARY LEADS TO BE TWISTED
INTO 4 PAIRS LEADS OF SAME
LETTERS TO BE PAIRED.
Shielding of Components
sa
Shielq.ing methods have been dis·
cussed at a previous point, but to sum·
marize briefly, we find that the power
unit should be provided with some
method of securing a good magnetic
shield for all chokes and transformers,
including leads, and an electrostatic
shielding means that provides for a
short·circuited turn in the shield in
each plane or direction. This may take
the form of a separate chassis and cover
with all sides enclosed and electrically
V -
LEGEND
M l. OR
TRANSFORM.
C-I
C-2
C-3
C-4
C-5
CH-I
CH-2
RRECTIFIER
VI BRATOR
VI B. SOCKET
TUBE SOCKET
TERM STRIP
SWITCH
11-1
C·6
'A'GROUND
FIG. 29-SCHEMATIC WIRING DIAGRAM FOR VIBRAPACKS
V-54
3
PT.NQM
OR
-FS56
NO M
8-44617-1
RF·461
A-40960TP-415
TP-436
8-44617-2
RF·461
A-40960-1
TP-435
TP-436
R F·5 2
A-40 9-1
R F·563
-40919-1
A-40389-3
TVP oZ4
Y 625
A- 211-1
A-40978-1
A-40943-1
8-111202-1
A'40l89-6
TYPE e 5
T PE 825
A-I 211-1
A-40978-1
A-40943-1
8-111202-1
A-40l~'8
Nos.
0
8-44617-3
RF·461
A-42086-5
T P-435
T P- 438
A-42097-i
RF-562
A·409 9-1
A-40369-3
TYPE 024
TYPE F626
A-IS 11-1
A-40978-1
A-40943-1
B-II 1202-1
! ,~
Tp·410
VP-553, VP-554, VP-F558
1,1
LEGEND
"A
C-I
C-'
C-3
Co,
Co,
RF481
A-409SQ-6
A-4l0eO-2
A-42080-1
CH-3
J 01411
A-42204-1
A-4208]-!
A-40J89-3
A-1521i-l
A-40978-1
A-40922-S
A-40922-4
OZ4 A-40977-2
TYPE 825
A-40389-4
A-42092-1
fUSE
~AG 12~.t.4P
CH-I
,.,
CH-2
VIS SOCKET
TUBE SOCKET
TERM.STRIP·A"
TERM STRIP"B
RECTIFIERlU
VIBRATOR
R-3
I'~
OFl~5p;NOM vP~~NQ
V
TRANSfORM 8-44247-5
8-44247-6
RF 481
A-42G86-1
A-4Z080-Z
A_4l080- t
X-26080
A-42204-1
A-4208J-1
A-40389-]
A-15211-1
A-40978-1
A-40922-5
A-40922-4
6X5A-40977I
TYPE825
A-42092-1
3A_G 12 AMP I
FIG. 30-SCHEMATIC WIRING DIAGRAM FOR VIBRAPACKS
Nos.
VP-555 AND VP·557
A C / BATTERY-INPUT VI BRATOR POWER SUPPLY
connected, with radiating parts either
enclosed therein or mounted on same
with individual covers. Or, the power
unit may be mounted op. the main receiver chassis, as is more commonly tl;te
case in present stage of designing, with
partitions either welded, screwed, or
soldered in place to provide a cover for
components and leads. Or, again, the
power unit may be mounted upon the
receiver chassis, with few or no parti.
tions provided, and the outer case providing the additional shielding to a
more or less satisfaCtory degree, with
metal spring-wipers, bonds, screws and
studs, etc., completing the electrical cir-
A.C.SWITCH
~
A ..C.
PRIMARY
A: ~ :: ~'----'
/
'):'CHOKE
BOTTOM
VIEW OF
SOCKET
FIG. 31
84
SECONDARY
=-
VIBRATORS AND VIBRATOR POWER SUPPLIES
cuit to provide satisfactory suppression.
In general it can be stated that the' degree of difficulty in manufacturing a
receiver built in any of the above manners is directly proportional to the
elimination of shielding in the direction
of the steps outlined. Quite a few receivers of the last type mentioned have
been produced in large quantities, it is
true, but in order to secure satisfactory
uniformity after production started, experts devoted many hours of additional
labor to "remove the bugs" that could
not be foreseen, or if foreseen, the precautions necessary to prevent them arising were considered too much added
cost.
CIRCUIT FOR OPERATING VOLTAGE DOUBLER FROM VIBRATOR
HEATER
SECONDARY
#1
FIG. 32
CIRCUIT FOR UNIVERSAL INPUT POWER SUPPLY
USI NG SPECIAL SELF -RECTIFYI NG VI BRATOR
A
B
RI'
I
I
I
BATTERY
,
B BOTTOM
VIEW or
SOCKET
PILOT LAMP
OR
INDICATOR
-:-
I
I
~----------------
D.C.
OUTPUT
.----.
SMOOTHINC CHOKE
It is usually desirable to ground the
filament, or heater, "string" at one
point on the receiver, and to avoid
a loop effect formed by the "hot"
filament leads and this ground. Often,
dividing the flow of filament current
from a mid-point on the string will be
of assistance in preventing "hash" interference being carried into the highsensitivity end of the receiver. Selection of a ground on the antenna circuit
out of the region of any possible stray
field from the power unit is extremely
important.
A
I
• Section 4
FIG. 33
TYPICAL CIRCUIT FOR DCI AC INVERTER USING
TYPE 90 OR 627 SERIES VIBRATORS
Selection of Grounds
Universal rules for the placement of
grounds cannot be given as hard and
fast methods, because each design of
receiver must be considered as a separate problem. In general, it is wise
however, to have just one ground in the
power unit, if possible, at least for the
"A" or primary circuit components.
Another ground for the "B" circuit is
often permissible, as the magnitude of
the current in this circuit is such that
small radiation or ground currents can
be expected. If a separate power unit is
being used, this should be grounded to
the receiver chassis at one point only,
selected if possible to prevent a loop
being formed by the "hot" "A" lead
and the ground, or chassis, and to
ground as far from the RF end of the
receiver, or antenna coil, as is possible.
TRANSFORMER
A.C.
OUTPUT
(BOTTOM
VIEW OF
SOCKET)
Cz
r-I
C!.J...
,
<...,
::'
-r- <
<...(1
I
r
""'.
FIG. 34
DC
INPUT
85
Section 4
+fc
.
THE
BREAK
:
I
I
I
I
I
MA~E
TECHN"CAL
MANUAL
there is never an excuse for increasing
the number and cost of the filtering
components used over that required for
the purpose in question. Each case
must be considered again as an individual problem, yet there are certain
components that MUST be used as a
minimum for hash suppression. The design and quality of these components
are important factors, yet all types from
poor to excellent are often selected with
only the thought of cost, size, or availability as the determining factor. The
minimum amount of filtering· takes the
form shown in Illustration No. 37 in·
which an RF "A" choke is inserted in
I
I
I
I
I
I
I
0
MYE
WAVEFORM WHEN OPERATING INTO RESISTANCE LOAD-NO TANK CONOENSER
FIe. 35
Filtering of Leads
The term proper and complete filtering of the leads to the power unit may
be interpreted several ways. Naturally,
OCTO A C VI BRATOR POWERED INVERTER
USING TYPE 40 SERIES VIBRATOR
TAPPtD
AUTO-TRANSf'ORMtR
'-E---'\~~
BOTTOM Slot
Of SOCKtT
FIe. 36
r-~------~~B+
~----------------------~~B-
r----+x
HEATERS
~'AHOT
FIe. 37
86
senes with the center-tap lead of the
transformer, with a paper by-pass condenser connected from the center-tap to
ground, and a second by-pass condenser is connected from the "B" plus
high-voltage to ground. On receivers
with low sensitivity this may be sufficient, even with low grade components,
but as the sensitivity and compactness
of the receiver increases, the effectiveness decreases. The choke usually consists of a multi-layer coil of No. 16 or
smaller wire, with the "A" by-pass a
condenser of 0.5 mfd. The "B" con-.
denser is usually from .01 to .. 1 mfd.
Compare this circuit with the one
shown in Illustration No. 38, which
shows an improved form incorporating
the features found inJatest receiver designs, including improved chokes and
condensers. Choke No.1 is now a special bank-wound design instead of the
multi-layer type, and, while having approximately the same number of turns
and physical size, has much greater suppression power at radio frequencies
because of the elimination of high distributed capacitance between layers.
Choke No.3 is similar in construction
but may be of smaller wire size, since
voltage drop to the heater string is not
as important as to the vibrator. Choke
No.2 is usually a single-layer coil of
comparatively small number of turns
used primarily for ignition suppression.
However, in conjunction with its condenser it also aids in hash suppression.
Chokes Nos. 4 and 5 are small RF
chokes of small wire for hash suppres':
sion in the plate circuit leads, with
Choke No.5 used where B minus is not
at ground potential.
Condenser No.1 is the primary buffer condenser, required on 12-volt or
higher input voltages, but which may
take the form of an optional mica condenser on some 6 volt or lower applications for hash suppression. No.2 is
the timing capacity, in series with a
medium size resistance, as outlined previously, or in the optional arrangements
shown as dotted lines. No.3 is a patented type of hash-suppression RF·condenser (Mallory Types RF481, RF482),
which definitely eliminates the inductance loops formed by the leads on ordinary condensers. It will be noted that
the primary current to the transformer
and from the reed of the vibrator must
fl<~w directly across the plates of the
condenser, this being the best possibl ..
,~
!
• Section 4
VIBRATORS AND VIBRATOR POWER SUPPLIES
s+
COLD CATHODE
'-----_HEATERS
----- A HOT
CH.
FIG. sa
means of secui-ing a short-circuited path
for the RF currents. The vibrator reed
is grounded after the condenser in this
method, as shown. No.4 is a special
type of condenser developed recently,
and known in the trade as a "sparkplate," since its first application was
for the use of eliminatng ignition interference without reducing signal
strength, etc., in the antenna circuit.
Naturally its capacity is very low, but
the lack of inductance in its leads, and
close proximity to ground create an exceHent RF filtering device. Originally,
this condenser took the form of one or
more plates of metal separated by fishpaper insulation and riveted to the
chassis. The current was fed in one end
and out the opposite end of the plates,
in the same manner as No.3, thus eliminating the inductive effects. No.4 has
taken the form of a small mica insulated condenser which is soldered, rivetted, or screwed to the chassis, and has
been found to give excellent results in
difficult cases of hash elimination. No.
5 and No. 6 are ordinary RF by-pass
condensers, but may be of paper or
mica construction as the case demands.
OrdinariIy, little difficulty arises from
interference arising in the "B" circuit,
because subsequent filtering in various
parts of the receiver is usually sufficient
to minimize this source of difficulty. As
pointed out previously, where a coldcathode rectifier tube is used, No. 7
'condensers may be required if sufficient
filtering is not provided in the "B" circuit.
Two additional pointers are shown,
which may be of service in hash elimination. It is usually desirable to, connect the "hot" rectifier heater terminal
to the center-tap of the transformer
~"f
rather than to the heater string, unless
this involves carrying a long lead into
the receiver proper. The rectifier tube
is always "hot" with interference and
enough may be conducted through the
heater connection to nullify all of the
other filtering provided. The use of resistors Rl across the contact points of
the vibrators has great benefit in reducing, or eliminating, the type of interference known in the trade as "pop hash,"
that being the sharp intermittent variety, in contrast to the "tone hash" which
is the continuous, more or less regular,
type. The value of these resistors will
vary in different applications. Where
input current is not so important, as in
automobile receivers, or where chargers
are available for the battery, values
from 50 to 200 ohms have been used,
with probably 100 ohms being average.
This is for 6-volt applications; where
12-voIt applications would require resistors, approximately four times the
6-volt resistance is required to limit the
wattage to the same value, and for
higher voltages, the required size of the
resistance removes its effectiveness.
In general, where a design requires
intense hash elimination work, the best
rule is to provide every bit of suppression that is available and secure quiet
operation. Then, remove one component at a time until a change in interference level is noted, then replace that
particular part, and proceed. It is a
practical impossibility to judge the
value of a single component by inserting it alone when the interference may
be arising from a number of omissions,
or locations. Care should be taken that
the resistance of the vibrator "A" circuit be kept as low as possible, in order
to secure good starting, good efficiency,
and regulation. Added capacitors are
to be preferred rather than added
chokes.
Long-wavelength (low-frequency)
bands in communication or "all-wave"
receivers are usually the most troublesome to completely cure of hash interference. Here additional chokes and
high capacities are usually required
along with the other suggestions given
above.
r- -- - ------------ -----------------,
I
I
I
I
I
I
' - - : - '...+
L---L:;~~-=-~-:-_ _ -~+
I
L __ - - - - - -
.:r:
:::r::
:
----=--- - - - - --=---- --1
oV.
FIG. 39
87
Section 4 •
THE
MYE
TECHNICAL
MANUAL
portable receivers filament type tubes
are employed, one side of the filament
or cathode circuit automatically becomes connected to B-.
Very successful solutions have been
made to the problem, arid the discussion
following will make clear the principles
employed so that service procedure can
be confidently carried on in a logical
manner.
OSC.MOD.
608C
r - - - - - - - - - - - - - - - - - - - - - - - - ,I'
:
I
I
Types of Tubes
'--~---+_B+ TO "CT~R
L
T _____
_______
± _______
I
I
J
FIG. 40
Bias Supply Systems
Offhand it may seem a bit unusual
that a treatise on Vibrators and Vibrator
Power Supplies would treat grid biasing methods of radio receivers. However
the widespread usage of the deservedly
popular synchronous or self-rectifying
vibrators has led to the adoption of new
biasing methods, necessary in vibrator
power supplies employing synchronous
vibrators because' B- must be at
ground potential, and consequently bias
resistors cannot be inserted in the highvoltage negative lead of the power supply system. When heater type tubes are
employed, conventional cathode resistors will provide bias; but when for reasons of current economy in farm and
CONVERTER
6D8G
A-
A-
A-
c-
r----------- ---- -------- - - -
c--~
I
I
I
A-C
,
-
-
I:I
I
I
I
I
I
I
~-~--~----:-r---------------- _J
FIG. 41
88
-=--
B+
In using vibrator operated powersupplies to furnish plate voltage for
portable and battery-operated radio receivers for farm homes, or for places
where no AC power is available, current consumption must be held to a
minimum to secure g09~ life from the
batteries. Tube manufacturers have developed a considerable number of special types of tubes for this class of
service with the general characteristic
of low filament or heater P9wer, and
comparatively low plate and screen
power requirements. The cathodes of
these tubes are both indirectly and
directly heated in various tubes, being
either the common "heater" construction or filament types. Filament voltages are 1.4 and 2.0 volts, and heaters'
are 6.3 volt types. Quite often these
types of tubes are mixed in a receiver
for various reasons to obtain special
results.
Where the same cells of the battery
supply both the vibrator and the filaments of the tubes, it is usually necessary to isolate the filament "string," or
circuit, from the effects upon the battery of the hum "ripple" voltage impressed upon it by the vibrator pulsations, as illustrated at a later point.
This is usually done by placing an ironcore choke of low resistance (similar
to the voice-coil winding of an output
transformer), in the power lead to the
filament supply. This must not be in
the vibrator circuit. ,Quite often it is
also necessary to connect from the filament side of this ~hoke a high-capacity,
low-voltage, electrolytic condenser, of
elt least 1000 mfd., to ground or to the
other side of the filament circuit. This
filtering is usually not necessary if all
the tubes are of the heater-type unless
the system has unusually high gain, in
which case it may be that the first tubes
I"
I
!
• Section 4
VIBRATORS AND VIBRATOR POWER SUPPLIES
in the amplifier will require isolation.
Complements of tubes used in typical
radio receivers for this class of service
include types requiring: 6.3 volts for
the heater at currents of 0.40, 0.30, and
0.150 amperes; 2.0 volts for the filament at currents of 0.120 and 0.060
amperes, and 1.40 volts for the filament at currents of 0.100 and 0.050
amperes_ The maximum plate voltages
used are under 200 volts on the older
receiver designs, and as low as 60 volts
on recent portable units.
Circuit Diagrams
Shown in Illustrations Nos. 39-48,
are simplified circuit diagrams of the
tube complements, vibrator powerunits, filament or heater circuits, and
bias circuit connections for ten production models of battery-powered home
radio receivers that have been produced
in recent years. These diagrams offer <.
wide variety of combinations of tubes
and biasing methods that permit the
satisfactory operation of these receivers
with a "solid-reed," self-rectifying, vibrator power-supply in which the "B
minus" connection must be at supplybattery potential.
All Heater Type Tubes
The circuit shown under Fig. 39 illustrates a receiver equipped with all 6.3
volt, heater-type tubes of various
heater-current requirements. The Vibrator power-supply is conventionally
built into a separate unit consisting of
a sheet-metal box grounded to the radio
chassis at one point. A separate Type
6LSG. tube is used for Second-Detector
and A VC supply and a Type 6S7G tube
is used in addition for the lst-Audio
Amplifier tube. All of the heaters are
connected, of. course, directly across
the 6-volt battery. Bias voltages (negative) for the control grids are secured
for the converter, IF-amplifier, and
power-output tubes by self-biasing resistors in the cathode circuits. The first
audio tube is biased by means of a
Mallory Bias Cell, which is a primary
battery type of unit with extremely high
internal resistance, which generates approximately 1 volt on open circuit. It
is interesting to 'note here that a drain
FIG. 42
of only several micro-amperes will reduce the voltage read across the terminals of the cell, and thus a vacuum-tube
type of voltmeter is required to accurately measure the cell. However, in
the grid-circuits of radio receivers, no
current drain is required, and an AC
current passing through the' cell does
no damage to it, perhaps charging it
to a slightly higher voltage. A shortcircuit to the cell for a short period does
not damage it either, and the voltage
will rise to the original value as the cell
recovers. However, it is not recommended for u!le as bias for the output
",
6570
CQNVE:R'TE:R
6080
I.
eS7C
stage, inasmuch as continuous (DC)
grid-cl\rrent flow will change the cell's
characteristics to too great ~ degree for
satisfactory performance. To conclude,
the second -detector tube, being a
diode, -does not require grid bias. In
most respects, this design of receiver is
similar to most automobile receivers in
which vibrators have been used for
many years.
The circuit in Fig. 40 is quite similar
to that of Fig. 39, with two major
changes. The two. tubes used for
second-detector, A VC, and 1st-audio in
Fig. 39 are now combined into one tube,
OtT Ave
6LSCi
AUDIO
6S70
BIA$ CELL
+
'-r-+----+
B+
A+
FIG. 43
89
THE
Section 4 •
M Y E
TECH N , C A I.
MAN UA I.
Fig. 42 also shows a receiver with all
heater-type tubes, but with a zero-bias,
"Class-B" dual o,utput tube substituted
for the previously shown biased-type
tube. This tube requires a driver tube
preceding it to secure the maximum
power-output which it is capable of- delivering. The other tubes are biased as
in Fig. 40.
r-----------
-------~-----------1
I
I
I
I
I
I
I
I
I
I
I
I
,
,,
Heater and Filament Type
Tubes in Combination
B+
FILTER
rlLAM[NTS
,":""
,
I
L.. _ _ _ _ _ _ _ _ _ _ _ _
-::r; ___ -- =t='- _____
I
~
A-
FIc.44.
the Type 6T7G, and the negative gridbias supplied by the Mallory Bias Cell
for the 1st-audio tube is now omitted,
this circuit now being controlled by a '
10 megohm resistance.
The circuit shown in Fig. 41 is a
further variation of Fig. 40, in the manner of securing fixed bias for the tubes
other than the 1st-audio tube. The
cathodes of these tubes are now
grounded, as is the positive side of the
6-volt battery. The output-tube control grid connects to the negative of the
battery for a bias of minus 6 volts.
CONVERTER
1ST I.F.
le6
34
A+
2 NO I.F'.
34
The converter and IF -amplifier tubes
connect to the same point through a
voltage-divider to secure the desired
bias, and the diode of the AVC circuit
also receives a certain negative bias
from the same source. Iron-core "A"
circuit chokes are shown in the powerunit, but it should be pointed out that
these are of the high-frequency powdered-iron type, of comparatively low
inductance. The iron permits the use of
fewer turns of wire, making for a
smaller choke with lower primary-voltage drop.
I ST AUDIO
DIODE OET.
30
DRIVEft
30
30
A+ ,
I
MALLORY
BIAS CELL
~-~---------------------,
H
i
I
I
I
,
:
I
,
JI-+-=-+
B+
I
I
I
.i:ti~~~~~~~~~~~~;;~~
_______________________
FIG. 45
90
A+
OUTPUT
I.
In the circuits shown in Fig. 43 and
Fig. 44 it will be observed that a combination of heater-type amplifier tubes
and filament-type power:output tube
has been adopted, the latter being the
Type 19, a "Class B," dual output tube.
The Mallory Grid-Bias Cell is again
used for negative-bias on the 1st-audio
tube control-grid in each circuit. The
difference between the two circuits is
that in Fig. 43 the output tube operates at zero grid-bias (inasmuch as the
filament dropping resistor is on the
positive side of filament), while in Fig.
44 the output tube operates with 4 volts
negative bias (because the filament
dropping resistor is now in the negative side of the filament, raising the
filament 4 volts positive above ground
with the control-grids connected to
ground). The Type 19 is primarily intended for zero-bias operation; therefore, the use of the negative 4-volts bias
in Fig. 44 is for the purpose of further
reducing the "no signal" plate current.
In each circuit it is again necessary to
provide a: driver tube preceding thE
power-output tube to provide sufficien!
energy to attain full audio power.
Fig. 45 circuit diagram shows a combination of one 1.4-volt and six 2.0volt filament type tubes operated from
a 6-volt battery. This circuit shows the
simplest method of using this type of
tube, with each having its own filament
dropping resistor, but it should be
pointed out that the maximum conservation of battery current is not attained
to any degree with this system, in contrast to the possible series-parallel combinations which could be made. No
hum-filtering for the filaments has been
provided other than the dropping resistances. Inthe biasing of these tubes
I
}
• Section 4
VIBRATORS AND VIBRATOR POWER SUPPLIES
CONVE.RTER
I C70
OSCIL.LATOR
I H4G
OET 1ST A
r
IF7GH OR IF7GV
....---.,
r---------------------l
OUTPUT
6G6C
,..-----,
A-
I
I
I
I
B+
I
I
I
I____,iJ
I
t
• VOLTS
I::r:
::I::
1__
+~--:...-----------
FiG. 46
you will note a similarity to some of the
preceding diagrams. The power-output
tube is opera,ted at zero-bias, again being the type 19. The Mallory Bias
Cell is again used for negatively biasing
the 1st-audio tube control-grid, but in
addition adds one volt to the bias of the
driver tube control-grid, which receives
in addition 4 volts negative from the
fact that the filament dropping resistor
for this tube is on the negative side of
the filament.
The circuit shown in Fig. 46 is decidedly different from the others shown,
in that a combination of filament-type
amplifier tubes and a heater-type
power-output tube is used, and in that
a series-parallel filament circuit is used
to conserve battery current and secure
bias. The oscillator and second-detector
tubes are in parallel, as are the converter and IF-amplifier tubes, with the
two groups in series. An equalizing resistor is placed in parallel with the first
group to secure equal current and voltage distribution. The remaining 2 volts
of battery is dropped in the filament
iron-cored choke used for hum-elimination, as shown. The converter and
IF-amplifier tubes receive control-grid
negative bias by returning the grids to
the filament choke, thus securing negative 2 volts bias. A Mallory Bias Cell is
used for the 1st-audio control-grid,
while self-bias is used for the heatertype output-tube.
All Filament Type Tubes
The circuit of Fig. 47 shows a tube
complement of all 1.4 volt filament type
tubes, with push-pull triode poweroutput tubes. Here again the full con-
Ir
IOSC;
C-I ___________
servation of battery current is not attained, with all filaments in parallel, the
remaining .4.6 volts from the battery
being consumed in the series combination of resistor and iron-cored filter
choke. A high-capacity filter-condenser
has also been used in this receiver in
combination with the filament choke
for better hum-elimination. Two voltage dividers are placed across the 6-volt
battery to provide various bias voltages
for the control-grids of the tubes, with
the positive of the battery grounded.
The divider for the "RF" end of the
receiver is high in resistance, totaling
11 megohms, while for the audio end
of the receiver the divider is comparatively low in resistance, totaling 6000
ohms. This system provides a maximum
of 4.5 volts negative for biasing the
output tubes below the filaments. Again
a driver tube is required preceding the
output tubes.
The final circuit shown in Fig. 48 is
considerably different from the others,
and in many respects is the best from a
power-supply standpoint. One cell of
the 3-cell, 6-volt storage battery is used
exclusively for heating the filaments of
the tubes. The other two cells of the
battery are used exclusively for operating a 4-volt vibrator power-unit. This
isolates the filament circuits from the
pulsations impressed upon the battery
by the vibrator, and, by grounding the
negative side of the filament circuit,
permits the 4 volts of the battery used
2 NO Or.T
I H4C
~_=_
cc__________
:. _______________________
-IA-
I
t
I
t
I
I
I
I
I
t
t
I
6V
I
-,;-
IiI
-I
-=-
I
I
t
:=I=
L..::. _______~
-=- _______ ~
_______________________ :
~
.J
FIG. 47
91
a-
THE
Section' 4 •
for vibrator power to be used for biasing the control.grid of the output tube.
By filtering' this voltage through a
IC70
A+
TECHNICAL
M Y,E
MANUAL
single Mallory Bias Cell provides suffiCient negative bias for the tUbes requiring it.
resistor-capacitor netwo,rk, it could be
used as bias for the other tubes also.
However, in this receiver the use of a
IDeo
I"G
A+
A+
c:r-------------------------------------~----,
II
I
:'
I
I
I
I
I
I
I
1
I
1
I
1
:
'I
a+
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-
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L-'------~n -~~~:---~-c--------n m_'
FIG. 48
Features of vibrators illustrated and described in the preceding section are covered by U. S. Patents 2,187,950,
2,190,685, 2,197,607 et al. of P. R. Mallory & Co., Inc.
, 92
e
THE MYE
Section
5
TE~HNI~AL
MANUAL
Phono-Radio
,
Service Data
MALLORY
93
Section 5 •
r H,E
M'YE
r E C H N' CAL
MANUAL
I
"'\
PHONO·RADIO SERVICE DATA
Crystal Pickup Installation
A large portion of present day phono-radio
combinations (either built as a single unit
or radio receivers converted by the use of
record playing apparatus) employ crystal
pickups. Since the pickup medium is actually
the heart of the reproduction system, the
first logical step is to become familiar with
the characteristics, 'Operati'On, and care 'Of
these units. The foll'Owing discussi'On illustrates these points.
r:.
'
,If y'OU are called upon to select and install
a crystal pickup for record reproduction you
have available a c'Onsid~rable choice 'Of styles,
types and prices. The final quality of repr'O, duction, however, depends not 'Only on the
pickup itself but als'O on the meth'Od of installation. The response of the yery finest
crystal pickup can be ruined by failure t'O
observe a few basic, simple installation precautions. Actually, pr'Oper installation is a
simple matter, and by f'Ollowing the suggestions in this 'article, you sh'Ould obtain the
really fine reproducti'On for which quality
crystal pickups are noted.
Electrically the crystal is the equivalent
'Of a condenser with a capacity of ab'Out
1,500 mmfd. The impedance of the device,
therefore. is quite high (100,000 ohms at
1,000 cycles and 1 meg at 100 cycles) and
the lower the frequency, the higher the impedance. Instead 'Of a power generator, the
crystal pickup may be th'Ought 'Of as a
voltage generator which requires a very
high-impedance load so tha:t the greater part
'Of the generat'Or v'Oltage, at all frequencies
'Of interest, will appear across the load.
Terminal Impedance
Since the impedance of the pickup is highest at low frequencies, it is evident that the
ch'Oice of load resistance will directly g'Overn
the low frequency response. This effect of
terminal impedance 'On low frequency response holds regardless 'Of any other considerations. It is inherent in the use of the
crystal with its capacitive internal impedance. Crystal microph'Ones, of course, display
the same effect.
Fig. 1 sh'OWS how the terminal voltage is
affected by load resistance alone for a crystal
of 1,500-mmfd. capacity. A resistance 'Of
5 meg introduces practically n'O frequency
discrimination while lower values reduce the
l'Ow-frequency resP'Onse as sh'Own.
Fig. 2 illustrates the effect of load re-
Tran$i+ion LO$s ..
201og~
eo
0
Mmfd,
1500
e
o
---r
R
eL
~
1000
FIG. 1. Since the impedance of the crystal pickup is highest at the low frequencies, the choice of load resistance will directly govern the low frequency response.
94
sistance 'On the response curve of a representative high-quality pickup. Experience
has shown that for h'Ome reproduction 'On
sets with g'Ood speakers, most listeners prefer
the elevated bass' response obtained with
terminations of 0.5 meg 'Or more, and theref'Ore the service man sh'Ould make certain
that the point of c'Onnection to receiver or
amplifier presents a sufficiently high resistance to the crystal pickup. On the other
hand, if the speaker is very small, elevated
bass response in the pickup is likely to result
in bad distortion due to excessive speaker
stiffness and poor radiating ability at low
frequencies. In such cases, the practical solution is to reduce the bass response of the
pickup until the overall performance is suitable. Try 0.5, 0.25 and 0.1 meg terminations
until the best results are attained.
Since the,crystal is a capacitive generator,
the effect of shunt capacity is merely to reduce the voltage output of the pickup uniformly at all frequencies. No frequency dis>
crimination is introduced by capacity only.
Actually, however, the use of a resistance
potentiometer volume control, in the presence of various circuit capacities, may introduce some high frequency loss. This, how- ,
ever, also occurs with sources other than
crystal pickups. The effect can be minimized
by methods which will be discussed.
Many modern receivers have input termi·
nals which will accommodate a crystal pick.
up. The arrangement is frequently as shown
in Fig. 3 where the receiver volume control
is a potentiometer in the first a-f grid circuit.
The phono.radio switch simply shifts this
potentiometer from the phono input termi.
nals to the detector output and vice versa.
The receiver volume control also controls
the volume on phonograph. The potentiom.
eter should have a resist!lllce of 0.5 to 1.0
meg as explained previously for proper bass
response. Sometimes tone compensating cir·
cuits are tapped into the potentiometer. They
will not ordinarily affect the phono repro·
duction adversely, but if the quality of reo
production is poor, or if the frequency
response appears to vary considerably as
the volume control setting is varied, it is
advisable to test the effect of disconnecting
the tone compensating networks from the
potentiometer. If they prove to be the cau/je
of the trouble, they should be switched out
during phonograph operation. If the receiver
employs the volume control method shown
in Fig. 3 but has no provision for phono
I
PHONO.RADIO
SERVICE
ai
~
c
o
0..
'"
~
500
40
100
1000
er Second
Frequency- Cyc1eS P
FIG. 2. Experience has shown that most listeners prefer the elevated bass
response obtained with terminations of 0.5 meg or more across the pickup.
input, a single-pole double throw switch can
be mounted on the chassis and wired as
shown. The switch should be located near
the potentiometer so that leads will be short
and hum pickup possibilities minimized. It
is advisable to shield the lead from the
phono post to the switch. The switch should
make on the phono position before breaking
the radio circuit to avoid a t1J.ump due to
momentary removal of grid bias.
Occasionally the audio system will have
such high gain that the pickup will overload
the first stage at full volume and necessitate
working at such a low setting of the potentiometer that volume adjustments are critical
\ and quality of reproduction may be poor.
The remedy is a shunt condenser of 0.001
mfd or larger across the pickup at the input
terminals. Increase the condenser capacity
until there is no overloading apparent on
listening test with the receiver volume control wide open. Pay particular attention to
the bass reproduction during the listening
test, for the maximum peak levels occur at
FIG. 3. If the receiver employs the volume control metluxl shown, a single-pole double-throw
switch can be wired for phono operation.
the lower frequencies. Increase the size of
the shunt condenser until the bass is clean.
It is always good practice to attain normal
volume with the audio control of the receiver almost wide open. At medium and
low volume settings, the input capacity of
the tube plus stray circuit capacities form an
L network in conjunction with the resistance
in the upper section of the potentiometer
with a resulting Joss of the higher frequencies. This effect is largely avoided by
operating at near-maximum settings.
When a volume comro] is provided on a
simple crystal record player which is located
some distance from the receiver, there will
almost always be a Joss of highs due to the
effect of the connecting lead capacity in
conjunction with the potentiometer resistance whenever the volume control is turned
down below maximum. There is less loss of
highs with a relatively low resistance potentiometer (of the order of 0.25 meg) but this
may be offset by poor bass response, especially if the record player volume control
and the receiver volume control are in
parallel and combine to present a still lower
terminal resistance to the pickup. When the
feature of volume control at the record
player is not absolutely essential, t)te reproduction will usually be improved considerably by disconnecting the record player
control entirely, depending on the control at
the receiver. Of course these remarks do not
apply to record players of the wireless type
or to those which incorporate an audio amplifier tube following the pickup; in these
cases the tube associated with the pickup
may effectively isolate the pickup volume
control from the connecting line and subse-'
,quent equipment.
. Many receivers of early vintage haye no
provision for phonograph pickup connections; others have phono connections which
are only suitable for magnetic pickups. '1;'he
alert service man can build up his profits by
adding crystal record players to such receivers and by modernizing yesterday's phonograph combinations with improved pickups. Circuit changes to accommodate the
crystal pickup are not difficult if a few fun7
,DATA
• SectiC?n 5
dar6entais are kept in mind. In the first
place, transformers are not required. They
will not provide the proper terminal connections for high-quality crystal pickup performance. Connect the crystal pickup in the
grid circuit of an audio stage across a resistance of 0.5 meg or more (which may be
the radio volume control) and make certain
that no low-impedance circuits are across
the pickup.
A common receiver layout includes a
power detector feeding the output stage.
Radio volume control is probably effected
in a preceding r-f circuit. The best solution
is to switch the detector tube grid to a 0.5
meg pickup volume control mounted on the
chassis (or motorboard if a combination) at
the same time switching the bias to the
proper value for Class A audio amplification
instead of detection. Fig. 4 shows one possible arrangement.
As before, the switch blade connected to
the grid should make in the phono position
before breaking the radio circuit to avoid
switching thump. The shunt resistor R2
must have the proper value to make the
parallel combination of resistors afford correct amplifier bias. Measure the applied plate
voltage and then consult your tube manual
for the correct bias voltage and plate current
for amplifier operation.
Divide the required bias voltage by plate
current to find the resistance which the
parallel combination of' Rl and R2 must
provide. After installing the correct resistor
R 2, recheck bias voltage and plate voltage.
L.
L.~
~~
00..
Q.E
<
Rt
Original self-bios resistor (proper
value for detector operation.)
C t - Original bypass condenser
-
R t - Original self- bios resistor.
R2 - Resistor to lower effective bias
resistance in phono position to proper
value for amplifier operation.
C t - Original bypass condenser.
C 2 - Lorge bypass condenser (may be
high cap., low voltage electrolytic.)
FIG. 4. A common receiver layout includes a
power detector feeding the output stage. The
best solution is indicated.
95
THE
Section 5 •
MY E
TECHNICAL
MANUAL
trolytic or other suitable condenser at C 2•
Both the switch and volume control should
be located as close to the tube as possible.
After these parts are mounted and the set
operates properly on phonograph, it is wise
to realign the tuned circuit feeding the detector which will p.robably be a little high in
capacity due to that added to the circuit by
the switch.
POS'TION A
POSITION B
234
M]116UJ
I
. II
~
RE:VISE
THUS FOR
( FIXE:D BIAS)
\ .
Ftlter Condo
r----~
---------------,
CRYSTAL
PICKUP
~,:
\.
RADIO
J ••••,..
,k'
•0 5 t
:,
•
0
f.O MeS' I
Single·", PHONO.q
•.. ' ..
pole, I
..a.."*'"
.-:double- I
.,. Add .Of Mfd.
I
throw'
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Blocking condo
I
switch
PICKUP TERMINALS
I
Shield
.
--f--n-t\!
I
Chassis
I
~-------------------~
FIG. 5. In grid circuits employing fixed bias a
blocking condenser should be used to prevent
the application of the bias to the pickup.
Occasionally the applied plate voltage will
drop and necessitate a slight change in the
bias resistor.
The lowered bias resistance for amplifier
operation will require an increase in cathode
by-pass capacity. This can be provided by
installing a low-voltage high capacity elec-
.1
FIG. 7
Diode-triodes
TYPICAL
DUPLEX DIODE
TRIODE CIRCUIT
1234
Frequently the detector and first audio
element are combined in a single tube, the
familiar duplex-diode triode. Circuit variations are numerous and a careful study of
the individual circuit of the particular receiver is strongly indicated before the work
is started. The problem is to get at the grid
of the triode section, making use of the receiver volume control if possible. Particular
attention must be paid to the method by
which the cathode is biased.
A circuit in which fixed bias is employed
is shown in Fig. 5, together with the p~oper
switching circuit for crystal pickup. The
only modification is the provision of a singlepole double-throw switch to shift tbe highside of the volume control potentiometer
from the radio circuit to the phono input
with a blocking cpndenser in series to prevent the application of bias voltage to the
pickup.
FIG. 8A-Diode Load
I"
I
1,1
It should be remembered that even the
most complicated circuit can be licked .by
switching grid and cathode to a separate
phono volume control and self-hias resistor
and by-pass condenser, respectively. Keep
leads as short as possihle and shield wires if
hum is encountered.
FIG. 8B-First A-F
Typical Switching Circuits
Immediately following is a series of 23 circuits, Figs. 8 through 31, representing a
condensation of past and present methods
for wiring phonograph pickups, magnetic
and crystal, into radio rec.eivers.
These circuits have heen universalized to
the extent that sections of switch wafers or
gangs not directly concerned with the phonoradio transition are not included. This applies to such features as tone control position, wave band change, etc., where these
operations have been combined in a multipurpose switch.
FIG. 6.' Special needles provide some scratch
reduction because they cut-off earlier at the
'high frequency end.
96
A second treatment is the use of a standardized method of swit~h schematic drawing.
As far as we know this system has no name,
'hut we have referred to it as a "linear 'block"
switch illustration. We believe it represents
the most flexihle and at the same time, most
SCREEN
GRID
PHONO
OR'-'
PLATE
,-8+
~-
FIG. 9A-Diode Load
~ '"~O
~ORI.F.
B+~ SCREEN
~-
GRID
OR PLATE
FIG. 9B-First A-F
PHONO-IADIO
SIIVIC,
DATA
• Section 5
easily undwstood method of switch layout.
It is not original with U8; we first saw it em·
ployed in schematic diagrams of the Bel.
mont Radio Corporation and we are in·
debted to them for its use here.
Fig. 7 shows an e~ample of this system.
A88uming it is desired that a particular application have two leads connected in one
position, one of these leads to be unu8ed in
the second p08ition, and the second lead to
join two new leads not used in the first posi.
tion, the wiring in Fig. 7 would apply.
FIG. lOA-Diode Load
FIG. l2B-Fir.t A·F
In position A, leads 1 and 3 are connected,
leads 2 and 4 are out of the circuit. In position B leads 2, 3, and 4 are connected to·
gether with lead 1 open.
Figures 8 through 27 show circuits in
which the phono-radio switching operation
is incorporated either in the diode load circuit of the 2nd detector or the first a-f grid
circuit.
FIG. lOB-First A-F
FIG. 13
Figure 8 shows the most common switching circuit in use, namely that of circuit
transfer only. The switch is shown in radio
position and when pressed or turned it
transfers the a-f lead of the volume control
from the radio input to the phono input.
Fig. 8A is diode load, Fig. 8B fir8t a·f.
In Fig. 9 the second portion of the 8witch
serves to break the screen or plate supply to
an i.f or r-f stage to render the r-f portion
of the receiver inoperative, thus preventing
any radio signal from feeding through by
lead or part capacitance. Fig. 9A-diode
load; Fig. 9B-first a-f.
FIG. llA-Diode Load
FIG. llB"':"First A.F
Fig. 10 shows a further variation in that
the second portion of the switch breaks the
cathode circuit of an r-f or i.f stage to pro·
vide the result outlined above. The dotted
lines indicate the possibility of using the
same switch to provide a shorting action for
the unused input. Fig. lOA-diode load;
Fig. lOB-first a·f.
In Fig. 11 the second function of the
switch i8 also of a transfer nature. When the
switch is in the radio position the lower
section shorts out the phono mput and when
the switch is moved this shortout is transfemd to the radio input li3l1d. This circuit
is an even m!>re positive method of prevent.
ing any capllcitive tranllfer of the unuied
input lellds. It is ufiually incorporated in
receiver8 where the phono or diode leads
are by necessity rather long and possibly
parallel to Jellds in the a·f stage.
Fig. 12 illustrates an application combin·
ing circuit transfer and motor control. When
the a-f lead transfers to the phono input the
second switch sectian cuts in the motor
supply.
FIG. l2A-Diode Load
II ...
R.F..loIllC~R.
-=-
ORII: SCREEN
-
~
YlG.17
Fig. 13 is a combination circuit transfer,
cathode break, and m~tor control system.
97
1HE
Section 5 •
MY E
1ECHNICAL
MANUAL
When the first section transfers the a·f lead
to the phono input, the second seCtion trans·
fers the common or ground lead from the
cathode to the motor thus making the radio
section inoperative and turning on the motor.
Fig. 14 is similar to Fig. 13 except that a
three·section switch is used and the plate or
screen supply of an r·f or i·f stage is broken
instead of the cathode asin the case of Fig. 13.
FIG. 18
FIG. 19
FIG. 20
In Fig. 15 the functions of receiver on.off,
circuit transfer, B+ break, and motor con.
trol are combined in a three.section, four·
position switch. In the first position the
receiver power is off. In the sooond position
the radio section is used. In the third posi.
tion, the a·f lead transfers to the phono
input, the plate or screen supply of an r-f
or i·f stage is broken, and the motor is at
rest position for changing records. In the
fourth position the a·f lead.phono input
contact is maintained, the B supply still
broken, and the motor operates for playing.
Fig. 16 employs a three.section four.posi.
tion switch to provide receiver on-off, circuit
transfer, and motor control. Position 1 is
receiver -off, position 2, receiver on·radio
use, position 3 phono use.record change, and
position 4 phono use-record play (motor on).
Fig. 17 illustrates a system of circuit
transfer and removal of r·f, i·f or mixer
screen voltage. The second section of the
switch when in phono position grounds the
scret"n of the desired stage. In scts employing
this circuit, the screen voltage is low enough
or rather the screen dropping resistor suffi·
ciently high in value to prevent excessive
current flow through the resistor.
I
ANTENNA
FIG. 23A-Diode Load
9!--vvv'v'--,
AN~
-*
~
~~
~
FIG. 23B-First A·F
FADE~
.,-
CONTROL
FIG. 24
The system shown in Fig. 18 has the
following functions: circuit transfer, coil
change, radio shortout in phono position,
and motor control. Position 1 is radio receive
on a certain frequency;' position 2, radio
receive on a sccond frequency; and position
3, phono with motor cut in and diode return
lead shorted out.
98
FIG. 21
Fig. 19 combines the circuit transfer,
radio shortout and a·f load change opera.
tions in a three.section, two.position switch.
In radio position, sections 1 and 2 provide
an a.f load consisting of the volume control
"R." In the phono position, sections 1 and 3
provide a shunt circuit RI and R2 across the
control with the phono input entering at the
junction of Rio Rio limiting the voltage ap·
,plied to the a·f stage hecause of the series
connection of R2 and R," and further pro.
viding a load match for phono input, of RI
shunted hyR2 and R.
FIG. 22
Fig. 20 illustrates a circuit transfer type
with a second section transferring the ground
or common to the diode return lead. Thus in
phono position the cathode of an r·f stage is
broken and the diode return lead grounded
to provide positive radio cut out.
"HONO
FIG. 25
FIG. 26
PHONO-RADIO
SERVICE
DATA
• Section 5
CATHODE
FIG. 27
FIG. 32. Equalization for relatively flat response can be provided by means of a
fixed condenser and a resistor.
FIG. 28
FIG. 29
FIG. 30
~
j
PHOND
-
'\
"
FIG. 31
In Fig. 21 a three.section, two.position
switch provides for circuit transfer, diode
return lead shortout, and bias circuit change.
In radio position the high side of the volume
control connects to the diode return lead and
the low side of the control is connected to
the cathode. In phono position the high side
of the control connects to the phono input
and the low side of the control is grounded.
The diode return lead connects directly to
the cathode.
The circuit shown in Fig. 22 provides
circuit transfer, cathode break, and load
change for phono use. In radio position, the
a·f lead connects to the diode return and the
cathode circuit is complete. In phono posi.
tion, the a·f lead transfers to the phono
input which has a resistor shunted across it,
thereby lowering the grid resistance to a
value comparable to the specific pickup unit.
Also, the second section transfers the ground
or common to open the cathode circuit and
ground the low side phono input.
• Fig. 23 illustrates a different method of
silencing the radio section in that a second
pOFtion of the switch performs an antenna
shortout in the phono position. The first
section is the usual transfer on the a·f lead.
Fig. 24 can't logically be called a switching
circuit since no switch is employed, but it
does transfer from radio to phono by using
a center tapped control, tapered both ways
from the center. When the variable con·
tactor is on the lower half it controls the
phono input. As it passes the center ground
point the phono input gradually reduces to
zero and the radio input is controlled in the
upper haH.
A clever system for use in battery.pow.
ered receivers is illustrated in Fig. 25. In
this circuit the first section of the switch
transfers from diode to phono, while the
second section opens the filament leads of
the oscillator and i·f stages, rendering the
r·f section inoperative, and keeping the bat·
tery drain at a minimum.
Fig. 26 illustrates a system of circuit
transfer and grid load change. The second
switch section in phono position shunts reo
sistor R\ across the grid of tube, thus lower.
ing the input resistance of the stage.
In Fig. 27 the first section of the switch
performs the transfer operation while the
second section alters the cathode circuit.
Fig. 28 shows a transfer action employed
in a biased detector circuit, while Fig. 29
illustrates a combination shortout and motor
control system also employed in the biased
detector stage.
The system shown in Fig. 30 is another
which can't be termed 'a switching circuit.
The phono input is series inserted in the grid
return of the tuhe and the setting of the
control effects the trailSfer. This circuit is
also that of a biased detector.
Fig. 31 shows a simple transfer circuit for
use with a grid lead type detector, and com.
pletes the circuit examples for the phonoplaying switching opel'ations.
Equalizing
It has been intimated, elsewhere in this
article, that a large percentage of radio set'
buyers have been educated to prefer excessive
bass response. This fact probahly accounts
for the elevated bass response which il! char·
acteristic of most present.day commercial
crystal pickups.
Equalization for relatively flat rEll!ponse is
easily provided, should an occasional customer prefer high.quality music. As shown
in Fig. 32, all that is required is a fixed con·
denser and a fixed or preferably variahle
resistance, connected as indicated. If a vari·
able resistor is employed, any response curve
hetween the fully equalized and the normal
unequalized can be obtained at will. The
curves shown have been matched at the
high frequency end and therefore indicate
only the relative frequency response.
99
THE
Section 5 •
Scratch Noise
It has been a common notion that sharplytuned rejector circuits would eliminate needle scratch or surface noise in phonograph
reproduction. The reasoning seems to have
been that the disturbing noise was localized
in a naJ,"row band around 2500 or 3000 cycles
and that the removal of the audio components in suhstantially this band alone, would
considerably lessen the reproduced surface
noise with minimum effect on the general
quality of reproductiou.
Without going into detail regarding special cases that are of little practical interest,
it appears that there are no appreciable
benefits in narrow band-elimination from the
noise reduction standpoint. Surface noise
components are of random character and
are distributed throughout the entire audio
M YE
TECHNICAL
MANUAL
range. Effective noise reduction goes handin-hand with reduction in quality of reproduction. Special needles (such as halftone,
cactus, bamboo, etc.), provide some scrat~h
reduction because they cut-off earlier at the
high frequency end, with of course a corr~
sponding elimination of what may have been
recorded in the lost frequency interval. Ad·
justment of the ordinary tone control of the
receiver or amplifier, with its adjustable,
tapering high frequency loss, will probably
completely satisfy most listeners.
Additional Hints
Crystal pickups, crystal cutting heads,
and crystal microphones will not withstand
temperatures above 125 OF. for long periods
of time. Make sure that adequate cabinet
ventilation is provided. Deflect heat from
power and rectifier tubes if necessary with a
sheet of asbestos board or other heat insulating material. Such a baffle can be made
more efficient by cementing a piece of tin
foil to it on the side opposite the pickup
unit. Check-up with a thermometer placed
at the pickup position. Long experience has
proved that the temperature limitation is
easily satisfied if it is recognized and given
attention.
Should it be necessary to replace the
crystal cartridge or cordage, apply minimum
heat when un soldering and resoldering connections at the cartridge terminals. Cool the
lug with a cotton swab dipped in illcohol
immediately after removing the soldering
iron. Heavy-handed sweating-in of soldered
joints at the cartridge terminals is practically
certain to ruin the crystal. Quick soldering
with minimum heat, immediately cooling
the joint, is ahsolutely safe.
Wireless Record Players
Keeping in mind the infor~ation obtained
from the preceding discussion of crystal pickups- we can gp a step farther and see
how these units are employed in commercial
wireless players.
The popularity of wireless record players
is undoubtedly due to a numher of factor-so
In the first place, the mystery feature,
i.e., the fact that they play through the
radio without direct connection, is intriguing. In addition, the record player may be
placed at any convenient location, the location being limited only by the distance from
the receiver and the convenience of an AC
outlet. Further, these wireless players are
,
ffO-120V
It""...,
60-
'"
FIG. 33. WILCOX-GAY (A56, A57, A60).
100
relatively inexpensive and simple to operate.
When properly designed they are capahle of
good quality.
The principle of operation of these units
is quite simple. A~ pointed out previously,
these record players are nothing more than
a low-power broadcast transmitter. Referring to the typical circuit, such as Fig. 33, it
will be seen that the unit contains two tubes,
one operating as an oscillator-modulator and
the other as a rectifier. The oscillator-modulator. generally a 6A7 or similar tube, is
modulated with audio by means of the crystal pickup and the phonograph record being
played. The oscillator is tunable over a small
range in the broadcast band, this tuning being accomplished hy means of a trimmer.
Microphone connections are provided in
some of the units as an additional feature.
Crystal pickups are used in all cases. The
turntable speed is, of course, 78 rpm and all
units are designed to use either 10 or 12 inch
records. In most cases self-starting induction
motors are used to drive the turntable. although in some instances a manual-starting
synchronous motor is employed. As a result,
operation is from a 1l0-volt, 60-cycle po~er
supply. Detailed information as to trade
names, tubes used, turntables, pickups, etc.,
is given in the chart which accompanies
this article.
Various record players and their circuit
diagrams are shown in Figs. 33 through 44.
In referring to the schematic drawings a
number of rather unusual circuits will be
FIG. 34. G.E. (GMll).
noticed. One unit, for example, uses a 12A7
tube as a combined rectifier and oscillator.
(See Fig. 34.) Another unique feature of this
same unit is the method of obtaining heater
voltage. Instead of employing the more conventional method of obtaining heater volt-
FIG. 35. RCA (VA20, 21).
PHONO·RADIO
SERVICE
DATA
• Section 5
FIG. 39. SONORA.
FIG. 36. PHILCO (RPl).
age from the supply line through a ballast
resistor, it is tapped off the motor winding.
In this connection, it is interesting to note
that another unit employs a similar method
for obtaining voltage for its pilot lamp
(Fig. 35).
290w
line cord
A high·impedance magnetic or crystal pick·
up is recommended for use with this OSC.
FIG. 37. MEISSNER.
In Fig. 36 is shown a unique method for
automatically starting and stopping the
turntable by means of the lone arm. When
insulated from case
the pickup is placed on the record, it automatically closes the motor switch and starts
the turntable. Similarly, when the tone arm
is removed from the record, the motor switch
is automatically opened.
Also of interest is the phonograph oscillator shown in Fig. 37. This Iype of unit is
designed for operation through a direct connection to the receiver antenna circuit and
will not ordinarily supply sufficient radiated
signal to provide satisfactory wireless operation, even if the coil shield is removed. There
is no reason, however, why the same components and exactly the same circuit would
not prol'ide wireless operation if a simple
addition were made.
A radiator connected to the oscillator coil
(indicated as an antenna in the circuit of
Fig. 37) will provide satisfactory results,
especially if this radiator is included in the
power line cord. Four to six feet of wire
should provide ample radiation. Some difficulty may be experienced from broadcast
interference with the 8ign~18 from the record
play cr. In general tbe wireless units use a
radiation frequency which is more free from
such interference.
Particular attention is called to the Dewald Modcl 411, the schematic of which is
shown in Fig. 44.
[[ is a 2-tube wireless record player that
permits the owner to play recordings through
a remote radio receiver or directly through
an a-f amplifier and a small speaker incorporated in the playback unit. The device
employs two new multipurpose 0.3 amp
FIG. 41. ESPEY (922)
tubes, the 12B8GT r-f pent ode-triode and
the 32L7GT beam power amplifier-rectifier.
The high-mu triode section of the 12B8GT
amplifier tube serves as an audio amplifier
in both modes of operation. With the switch
.0001 Mfd.
MIca
FIG. 42. KNIGHT.
in the r-f playback position, the a-f amplifier is necessary to provide a high percentage
of modulation. In wireless playbacks where
the pickup operates directly into Jhe r-f
oscillator the percentage of modulation is
IOIHISV.
ISO-A.C.
On-Off Sw shown
counter~clockwjse
posrtion
Y
For 220V 50 cycle operatlon,break cIrcuit In
Place mark.ed PX· and use input resistance cord
A·f4962 shown dotted in place of A·j469S·/
FIG. 38. SPARTON (219P, 219PD).
FIG. 40. ADMIRAL (A Wll).
FIG. 43. LU"A YETTE.
101
FIG. 44. DEWALD 411.
often too low. This makes it necessary for
the listener to turn the receiver gain up
higher in order to obtain normal room volume even though a strong carrier is being
received from the oscillator. Excessive carrier hum results.
In addition. low percentage modulation
requires more radiation to produce a satisfactory signal at the receiver. Also. the interference range of the transmitter varies in-
-
TECHNICAL
M YE
THE
Section 5 •
MANUAL
volume control in the a-f position and the
modulation level control in the r-f position.
The high-mu triode feeds the beam-power
tube in the a-f position or the screen grid of
the pentode oscillator section in the r-f position. The plate of the power tube is returned
to the input of the filter while the screen is
connected to .the second filter section to reduce hum. In the a-f position, the oscillator
is cut off by opening the'screen grid lead.
In setting up a wireless record player, the
general procedure is as follows:
The radio receiver should be turned on
and tuned to it quiet spot in frequency range
covered by the oscillator. The oscillator
should then be tuned to the frequency of the
receiver. Adjust the volume controls on 1he
receiver and record player to the proper
levels. In very noisy locations, it may be
necessary to wrap several turns of the oscillator antenna around the antenna lead-in to
the receiver. In receivers having push-button
tuning, one of the buttons may be set up for
the oscillator frequency.
Figures 45 through 73 show schematic
diagrams of later types of wireless record
players. Most of these units have prototypes
already covered in this discussion, and no
commentary has been attempted. The general features of these players are listed in
the complete table following this record
player text. The chart also lists equipment
previously discussed.
versdy as the depth of DlOdulation. Too
high a modulation level. however, would
cause frequency modulation. and consequent
distortion. ··To prevcmt this a modulati~n
level control is incorporated. as an element
of the .pickup tone corrector.
With the switch in . the audio playback
position, a complete record player and amplifier is available with no additional equip-.
ment required. This' feature is. obtained !it
only a slight additional cost over an ordinary
wireless recorQ player, since the power supply, heater resistor and cabinet are required
even if this feature were omitted. A. power
output of 1.4 watts is available to the permanent magnet dynamic speaker.
Two controls are used, one for level with
the on-off switch incorporated and the a-f,
r-f switch. The carrier frequency is adjustable over a small range around 550 kc.
The padder is accessible through a hole in
the top of the panel.
A 4-wire line cord is used, 3 wires for the
power and filament resistor and the fourth
is the antenna. This arrangement with the
antenna coupled to the hot end of the oscillator tank through a 0.0001 mfd condenser,
allows satisfactory reception as a wireless
unit up to about 40 feet. A 0.1 mfd by-pass
condenser across the line keeps the r-f energy
from the lighting circuit.
A crystal pickup is employed with a tone
correcting load circuit. The resistor is the
Tvbe.
--
f-_...,..'_"_,"_"'_b"..-__+__....,._"_'_"-,-P--;==_I 01'..
f-_c._''';--'·_I'---;_·_'''_·"T''_I0_·~'-r__
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vm~ L---f--I---1--~:.=:
--:.
AJlId J,tacHa Corp.
N~~·~r
Knight
Contfrt._lbdkJ&
1'.~.~
Adflllral
hwold hdfo Mfg. COi1).
'
C,..,ttol
78
78
to'" or 12"
10" or 12"
Cry,hil
H.
78
10" Of 12"
Cty.tal
Ves
Cryd,!!
6A?
12A8GT
70L701
110·120
110·120
.0
""
1288Gr
32L70T
110·)20
60
S,lf Stort
25Z60T
110·120
60
S.lf Start
78
10" or 12'"
1I0·12D
60
78
10'" or 12'" Mognetic 3,000 @
110.120
110·120
60
60
78
78
10" or 12"
10'" or 12"
,No..
CW13
1.575
Dewald
411
550
.........
922
1475·1750
I1A
1200-1750
No
21,.,
22A
1300-1750
1250·175'0
No
No
GE
No. 47
.A7
2525
6A801
2SA7G
176
6K6GT
6SK7GT
OMII
1400·1600
No
HM21
11()()'1600
No
6A8G
.tN.23
1100·1600
No
6A8G
530·580
Ve.
Ve.
6A7
...
RPI {Cod., 111,
122,1231
-41·ap6
PlfotIin llectrk Corp.
Pilgrim
RCA
530·580
530·570
930
6JSGT
'0
v..
12A1
84
U
100,0000
~a9~etlc
400 Cy.
C:...,lfol
80,0000
1~
Crystol
C'1.tol
,~
"
,-+--f---f--INo
Ves
Yes
No
No
No
Ves
Ves
Ves
No
No
No
No
No
V..
Y.,
Nt»
No
No
V..
14
78
78
9
10"'Q112"
IO~Or 12"
CrySftll
S.1f S'ort
78
8
10":QI'1"2"
C')'sfell
10" or 12"
10" or 12"
10'" or 12"
"ymr
No
Crystal
No
Y..
Y..
Y.,
No
No
No
10'"
No
Ye.
No
60
60
60
No
. .7
76
110-120
60
530·625
No. 47
6A7
530·625
No
6S,4,7
25%6G
25!6G
110·120
110-120
60
60
$848
540·700
540·750
No. 51
No. T·46
35L6GT
3.,z6GT
2SZS
110·120
110·120
600
No
V..
SOL6GT
6 ...7
UZ5GT
2$Z$
110.120
110.120
60
1200·1700
Y.,
611.7
25t5
110·j20
540·750
No
3516GT
35Z.5GT
78
78
78
78
Cry.tal
12"
Cryttol
18
18
10'" er 12'"
10" Of 12'"
Crystcd
Crystol
60
78
10" or 12'"
60
1.
10'"
12'"
Crystctl
Cryltol
No
7.
78
10" or 12'"
10'" Of 12"
Cry.tol
Cr,.stal
JICo
Ve.
No
Combined
60
78
10'" or 12'"
Cryttal
Yel
V•• ~
1l0~120
60
78
10'" or 12"
\:rydal
Yu
60
78
10"
12"
Crystal
~:
:g: : :~:
~~~::
78
78
78
78
10'"
10'"
10'"
10'"
or 12"
or 12'"
or 12"
or
12"
Crystal
Cry.ral
Crystal
(r)'I'ol
78
78
10'" or 12'"
10" 0112'"
Crystal
Crystal
Manllal Start
Gr
Of
100,0000
1Yt
Ne
No
No
10
c.mb'-,.••-f--.--I-'-'!4--I--"-14+-,0-
S.rfSlori
hlfStart
110·120
110·120
110·120
'4
I--f--+--I--+--
60
84
16
Combined
60
s.
611.7
V..
Cryttol
60
0.7
U
Combined
110-120
110-120
. .7
·l-O
No
110·120
VA20, VA21
Ose.22
6226
r
LoCld
2SZ:;
Ves
______ f-:-_____ II-~:_3lC-'-.'_'_IIC_W_+'_'5_0_.'_"_O+_"".:...+6_'_K7_G_'___ "-6J_5_G_'_+'_'O_.'_'0+_.:.,:O_f-____ ~--78--.I_--410.. or 12"
CkMr.oI&ctricCo..
Imp.danc.@looon.e-OI\VoIH't.Wdth.Depth(w,.....,.J
Record
COflIblned
Combined
10*
14K
14~
6-h
3"
12Y2
8\4
.$
7Yt
4Y2
9
lTn
2~
71,4
Combined
Combined
~ko_"_'_h~.,-.~.__--r---------lr·-~-33-------~-5'-0-.'-25__ I--N_O'_'__
4 r'_'A_8_G_'__+_3'_U_G_'___f_'-'O-.'-20-r-6-0__ 'f_M_o-~-o-'~_o_rt.r-_78__.f--___ I-,o_·_o_'1_2_·f-C_'~r._~_' r'_·~O~_O_O_.+__'~__.r-N_0-t_C_~_b~"_'d__II__-1----I----r--T• ..,Jdon Corp.
Senelro
KVU-8S, KVU·97
P8W
60
S.lf Start
No
J.
114
13V.
10M
:-~~~~~~~______ I~W~I=~~W='=~_W_2_'_r~'~~~_I-__""___f-______32_r'_7-,-____ if_'-'.~"-20_f__.-O--I__--__-r--78__+----r'-0~·"--I2~·crO~'-~-'-~----_r---ll-y-e-.-~V-.--s ~I__--I____II__--I--__
$porb-Wlthlngton Co.
Spartan
219f,219PO
SflworI'.-.r0rntr
Stewott·Wcuner
11·211.1
Cqmblned
: W-:-' ' '~' '-:-' =I•.:--:c:-w-P.--I-:w:::-.'''';.,.~,---+::-::~=~------r:~~~:-:o~::"';~:-:g+--~-o-r:-:-:'-7~--f-~-~Z-4G-,-_~~~f-_:-:._.-:_:-~_g~rf-_~:~g~~rf-_~-_~-_~~+II-'~-~_:-_~·I:~~~~·:I:-g::_"'-o_,-:_~-~:-~~~~<'I~:_::~:-~~~~-_~~~I-_~~~~~I-_v-v_:-:~I:_~-:_-:_~!--_!--__II--_I___
Whotu.al\ Radio
Sarvlc. CO.
K2196S
Wlfeoll.OCIIY
:::
AU
8K2
8P2
540
Ne
6 ... 80T
76
110·f20
540·750
~
:~,~ 3516
~:~:
::g:!:~:~
No
540·730
V.,
1211.8
6A7
6A8GT
35Z4
2.5Z5
.5Z4GT
110_120
110-120
110-120
Yes
60
60
60
:-:::-::-::--::___I-:--:::-____1-:9:-:A2=:-:-____r--.::.54:.,:0_.7.:.50:..-f--.:.N::.O__ J-'::.'::.A8:..-__ j-:35::.Z::.4_·__+'~'O::..'::.20+ 60
ZenfHl
Redio Corp.
,'"I
I Z~nlfh
[,'::':"
1;lk.: ~
;" \,~!' }\;- r1.'
102
86622
$7000, S7001,
57002, S7003
S8500, S8501
1.540
{::·::o
Yel
6L7G
6X5G
110.12-0
No
No
12SA1GT
125A70T
35Z4GT
lSZ4GT
110.120
!to·120
hi' $tart
Self Start
Of
150,0000
3-"*
Ve.
No
1~
"""" V..
No
No
Y.I
No
Ve.
No
""
No
No
13
Contbtnecl
ColI'Ibined
V..
V.s
No-
-60--·f------11--7-8-11---+,O~.:-0<-,-,~. f-ery,-=--,o-' f----·f-----r-""-f-y.-.+-""-II----I---t---r-60
60
No
No
Y...
No
PHONO-RADIO
FIG. 45. CONTINENTAL CW13.
SERVICE
FIG. 50. PHILCO RP1 (122).
DATA
• Section 5
FIG. 55. RCA OI!lC.
~2.
FIG. 56. SEARS·RoEBUCK 5848.
FIG. 46. GALVIN llA.
FIG. 51. PHlLCO RP1 (123) .
....
......
FIG. 47. GALVIN 21A.
FIG. 52. PHILCO RP3.
FIG. 57. SEARS·RoEBUCK 6226.
mpmC. ,11~
FIG. 49. G. E. HM21, JM23.
FIG. 53. PHILCO 41·RP6.
FIG. 58. SEARS·RoEBUCK 6233.
FIG. 54. PILGRIM 930.
FIG. 59. SEARS.RoEBUCK 7061.
103
\,
rHI
Section ,5 •
MY I
rICH~'CAL
MANUAL
!--'
,,',
FIG. 60.
8BAltB.RoBBtICK
7063.
FIG. 65.
WARWICK
9·28.
"
"
FIG. 71. ZBNtTH 86622.
FtG. 62.
SoNOitA
FIG. 63.
SnWART,WARNBR
FIG. 64.
104
~.
'.
W17, W19, W24.
WARWICK
ll..2Al.
9·21.
FIG. 67. WILCOx~GAY 9A2.
FIG. 68. WILCOX·GAY
FIG. 69.
WILCOX.GAY
A·95.
A-63, A·64.
FIG. 72. ZENITH 87000, 87001,
81002, 87003.
PHONO-RADIO
SERVle.
DATA
• Section 5
It has often been noted that in the radio
industry and its allied fields, certain features
fan to become popular during the Beason of
their introduction. Then, after a number of
years of disuse, they are reintroduced with
improvements and experience immediate acceptance. Home recording, a feature introduced about eight years ago, has been dormant· until the recent introduction of lowpriced, improved recording systems. A typical example of this type of unit is the
Wilcox-Gay "Recordio."
.Home Recorders
EXTRA RECORD
HOLDeR
CUTTING
HEAD
This unit makes poeeible the recording of
{oice or music originating locally, as well as
providing a means of recOtding radio programs.
The appeal of this, and similar types of
equipment, ill further enhanced by the avail.
• ability of inell.pensive record blanks.
These recorders are extremely popular,
not only for their value as a home entertain.
ment device, but also because of their possi.
ble uses in the fields of public address, education, voice culture, .and personal correspondence.
The following discussion deals with the
components of the system, its operation, and
the procedure for servicing.
TURN TABLE
MICROPHONE
MOTOR SWITCH
There are numerous general types available such as the phono.player, recorder, and
P.A. system; another with these same fea·
tures plus radio·receive and radio.record;
completely portable types, etc. Since this
discussion is primarily concerned with reo
cording and reproduction the unit employed
for illustration is the Wilcox.Gay Portable
Recordio model A·72 pictured in Fig. 74
with schematic as in Fig. 75. The A-72 is of
the portahle type without radio-receive and
record, and was one of the first popular price
units to reach the market.
VOLUME CONTROL
AND ON-OFF SWITCH
FIG. 74
FIG. 75
Controls
Viewing the top of the A 72 Recordio there
will be found four controls, designated as
"Play," "Volume," "Tone," and "Motor."
The control labelled "Play" is a selector
switch that in its extreme right hand position
connects the equipment for public address,
in which position anything spoken into the
microphone will he heard to issue from the
loud speaker in an amplified state-degree
of amplification being controlled by the volume control. In the center, or play position
the equipment is connected for phonograph
reproduction, in which condition the recordings that have heen made cim he played
back, and, also any phonograph record may
be reproduced. Both the tone and amplitude
of sound will be controlled by the tone and
volume controls respectively. In its left hand
position or when the yellow dot is opposite
105
THE'MYE
Section 5 •
"cut," the equipment is connected for recording, at which time by .following the
directions below, a recording may he made.
The controlillbelled "Volume," is for the
purpose of controlling the volume of both
recording and playing back records as well
as when the unit is used for 'public address~
During the first portion of its clockwise tum
it operates the off-and-on switch connecting
the power supply to the equipment. Through
the remainder of its clockwise turu, the
volume is increased.
The control labelled "Tone" is for properly controlling the fidelity or tone of the
Recordio. Turned in a clockwise direction
the bass notes are emphasized. Turned in a
counter-clockwise direction the treble notes
are emphasized. THIS OONTROL SHOULD ALWAYS BE IN THE LEFT HAND OR HJGH POSITION WHEN RECORDING. Fai1ur~ to do this
result in a very poor recording.
The control labelled" Motor" is for starting and stopping the turntable. Turned to
the right it connects the power supply and
the table will rotate. Turned to the left the
supply is disconnected and the table will
stop.
TECHNICAL
MANUAL
FOLLOWER ARM STOP
LATERAL FEED SCREW
FOLLOWER ARM
l'i
I.
I'
will
MOTOR
BOARD
Figure 76 shows the Recordio with the escutcheon removed and the motorboard raised
to a vertical position. The components to he
later referred to under care of the instrument
are clearly identified in the illustration.
Recording
- - - 6Q7
---6J7
I
,~
MOTOR BOARD AND AMPLIFIeR, FIG. 76
To use this equipment as a recording
mechanism, whereby radio programs and
various other activities picked up on the
microphone can be preserved on a record,
first of all the "Play" control should be
turned to "Cut" and a blank record should
be placed on the turntable. A small pin is
located near the center of the turntable. It
will also he noticed that the record blank has
three holes in the center. The record should
be so placed on the table that the pin engages one of these holes. After this procedure,
the cutting arm, which is the arm on the
right of the equipment, should be raised up
to an angle of approximately 45 degrees and
the cutting head swung over 80 that the
cutting stylus will come in contact with the
'near outside of the record hlank when the
arm is lowered.
!
I,
Recording Microphone
To use this equipment for recording anything that is picked up by the microphone,
the controilahelled "PA," "Play," "Cut,"
106
eb
FIG. 77
PHONO·RADIO
mentioned above should be turned in its left
hand direction so that the dot is opposite
"Cut." If the microphone is going to be
spoken into, a few words should be spoken
into it while adjusting the volume. The
magic eye should be watched; and the volume should be adjusted so that the magic
eye just closes on the loudest words. The
turntable should now be started and whatever it is desired to record spoken into the
microphone in the same tone and level of
voice as used in initially setting the volume.
If it is found that during this process some
slight adjustment of volume is necessary,
this should be done, maintaining an adjustment so that the magic eye just closes. All
other efforts, such as speeches, recording of
orchestras, bands, etc., ..hould be accomplished by first of all noting and adjusting
the level and then turning on the motor and
making the record cut.
SERVICE
previously recorded material will be repeated. When it is desired to play ordinary
phonograph record!! on this equipment, all
that is done is to position the switch to
"Play" as above, place the record on the
turntable, at which time the pin on the turntable will disappear and allow the record to
lie flat on the table. A NEEDLE THAT HAS
BEEN USED TO PLAY A REGULAR RECORD
SHOULD NEVER BE USED TO PLAY A WILCOXGAY RECORD. Use a new needle.
To use this equipment for public address,
the selector switch should be turned to
"PA." The microphone should be used as far
to the side and rear of the equipment as
possible to prevent acoustical feed back between the loud speaker and microphone.
There are available 12}1 foot extension microphone cords for this equipment.
Cutting Arm and Head Adjustments
Recording Radio
Inserting Cutting Stylus
To record radio programs, the microphone
should be set up directly in front of the loud
speaker of the radio receiver supplying the
program and the radio receiver adjusted sO
that it is operating at normally low room
volume. The left hand control should be set
on "Cut," the tone control should be turned
to "high" and the volume adjusted so that
the magic eye just closes on the louder parts
of the -program. Any slight adjustment of
volume can be made, however, the individual expression of orchestras, as well as
of vocal selecti~ns, will be impaired if loud
and soft passages are compensated for by
either decreasing or increasing the volume.
Do not use any other make of cutting
stylus than Wilcox-Gay. This stylus is especially designed for this equipment.
After the cut has been made, there will be
seen to have bet\ll cut a small shaving out of
the record material. This will pile in the
center of the record. The machine is cutting
correctly if, after having completely cut a
6~" record, the wadded up shaving has a
total diameter of approximately % to ~
inch. THIS SHAVING IS NOT FLAMMABLE AND
THEREFORE THERE IS NO FlRE HAZARD IN
DISPOSING OF IT IN ANY MANNER.
Phonograph Play Back
The control marked "Play" should now
be turned to "Play," and the phonograph
arm, which is the arm at the left of the
equipment, should be equipped with a new
needle and placed in the outside groove of
the record. The motor should be turned on
and the volume and tone adjusted by' the
respective controls. After this procedure the
When this equipment leaves the factory,
the cutting stylus is packed in a small envelope to avoid its becoming lost. To prqperly install the cutting stylus, it should be'
pressed into the cutting arm in such a
manner that the flat side on the shank of the
cutting stylus is in front and is the surface
that the retaining screw tightens up on.
When the cutting stylus is correctly placed
in the cutting head and the cutting nead placed
on the record a small shaving will be seen to
be cut out of the record material. If the
needle is in backwards, it will not in any
crse operate correctly.
Extreme care should be exercised to see that
thJs cutting stylus is held in the cutting arm
tightly. Owing to the fact that the cutting stylus
is of very hard Norwegian ra1XJr steel and that
the retaining screw is hardened also, there is a
tendency for the cutting stylus to become
loosened in the head. It is suggested that the
retaining screw be given a little tightening turn
each time a recording is made.
Under no circumstances allow the cutting
stylus to rest on table top or any other metal
because its point is ra1XJr sharp and it will be
dulled if this precaution is not taken.
Effect of Dull Cutting Stylus
DATA
• Section 5
being dulled so that replacement is necessary.
Many times it may seem from casual observation that because an incorrect cut is
being made, an adjustment is in order to
bring about correct depth of cut. Actually
the trouble may be due to the cutting stylus
having become dulled, either accidentally o~
through natural wear.
It is well to FIRST TRY A NEW CUTTING
STYLUS before making any adjustments, to
preclude the necessity for a complete readjustment. Adjustments made with a dulled
cutting stylus being used will have very
little effect upon the depth of cut.
Depth of Cut
The depth of cut may be observed by
holding the record in such a position that a
light is reflected from the groove. If the
depth of cut is correct, the grooves will appear to be about as wide as the spaces between them.
The correct depth of cut will produce a
thread cut from the record surface that is
firm, although neither coarse and stiff, nor
light and "fluffy."
Provided a new cutting ,stylus, or one
known to be in perfect condition, is being
used, the correct depth of cut may be
gauged by permitting the cuttings to remain
upon the record until completed, then rolling
the cuttings into a hard ball. The size of the
ball thus obtained should be approximately
% inch in diameter for the 6~ inch record.
The depth of cut is regulated by an adjustment of the flat head screw on the top of
the recording arm, Figurt'l 77.
Turning the screw to the right (clockwise)
increases the depth of cut.
Turning the screw to the left (countercl~ckwise) decreases the depth of cut.
Important Notes
Leveling:
To derive the best operation from this
equipment, it should be very nearly level in
all directions. Because of the fact that many
floors are not level, it is suggested that
something round, like a round lead pencil, or
a marble, be placed on the top of the equipment to test which way it is low. The top
may be levelled by shimming the low side.
Both the operation of cutting the records
and reprod.ucing them will be improved if
this precaution is taken.
Groove JUInping with Offset Head:
With proper care the cutting stylus will
cut dozens of records satisfactorily before
Some phonograph instI'uments are
equipped with an offset, reproduction head.
107
;'
Section 5 •
TH.
By this is meant a head that is at an angle to
the pickup arm. If it is desired to play
records on this type of phonograph reproducing equipment, it is suggested that a
minimum internal diameter of 372 inches be
used. Otherwise the needle may have a
tendency to jump out of the record groove.
Groove Depth:
In some of the early Recordio models the
adjusting screw was threaded throughout
its full length, although only the lower portion of the screw over a span of approximately % inch contributes to the useful
range of adjustment. If the adjusting screw
is turned in a clockwise direction so a8 to
raise the spring holding lug to the upper
threaded portion of the screw, the adjustment will have passed through a "deadcenter" position, which will cause a bobbing
up-and-down movement of the cutting head.
If it is found that when using a new cutting stylus, the depth of cut is too shallow,
and the adjusting screw has been turned to
the fuIl clockwise position in the later models, or to the upper limit of the useful range
in the older modeJs, this is an indication that
the balance spring"is too strong. Its tension
may be decreased by spreading the coils of
the spring with II pair of diagonal cutting
pliers.
CAUTION: Care should be used in removing and replacing the cutting head, when
occasion arises, so that the balance spring is
not stretched to a length that will prevent
its returning to normal length and tension.
When the cutting head is in proper adjustment and the recording arm is raised to a
position approximately 25 to 30 degrees from
the vertical plane, the cutting head should
float freely in its mounting, with equ!l' up
and down movement. The balance spring
holding lug should be in a position on the
adjusting screw approximately U inch from
the shelf which holds the riveted end of the
screw. (Fig. 77)
Observe that the leads connecting to the
cutting head are shaped to form an "8,"
and that these wires are kept in the c1earnot touching the balance spring. Also, the
wire leads should not be permitted to droop
(arm horizontal) so t~at they will rub on the
turntable. Also observe that the holding
tongues of the finger grips on the nose of the
recording arm are bent back sufficiently 80
as not to interfere with free movement of
the cutting head.
108
MY.
T.CHNleAL
MANUAl.
Height of Recording Arm Adjustlllent
The components of the recording arm as·
sembly are positioned so that the cutting
head is parallel, and the stylus is perpendicular to the record surface (Fig. 77), which
condition obtains ONLY with the nose of the
recording arm adjusted to the correct height
of U int;h above the record surface.
An adjustable stop (arm height adjusting
screw, Fig. 77) is mounted on the arm platform to provide a means for adjusting the
height of the recording arm. With a blank
record on the turntable and a WILCOX·GAY
cutting stylus inserted in the cutting head,
the arm height adjustment should be made
so that the bottom of the recording arm is
U inch from the record surface as shown
in Fig. 77.
The connecting wires from the cutting
head should not be allowed to double up between the arm and arm platform, but should
feed freely through the hole in the platform
as the arm is lowered. Otherwise, the doubled
up wires may prevent the arm from com·
ing to rest on the head of the height adjusting screw.
There is little likelihood that the arm
height adjusting screw will get out of adjustment due to the lock nut becoming loosened.
However, there is the possibility that the
recording arm may be roughly handled by
the operator. II the arm were to be forced
backwards after having been raised to its
vertical position-or if, while being lowered
to its horizontal position to the right of the
turntable, the arm were dropped or forced
downward, the plate on which all of the recording mechanism is mounted may be bent
or sprung slightly. This would destroy the
U inch height adjustment, and readjustment of the arm height adjusting screw
would' be necessary to bring the nose of the
recording arm to exactly U inch above the
record surface.
Also, the straddle plate (Fig. 77) may be
bent down, which would effect the arm
height adjustment. In this event, the straddle
plate should be removed and straightened.
This is most easily accomplished with t,he recording arm in the lowered position. Grasp
the heel of the arm with the left hand and
raise the arni horizontally, at the same time
removing the arm lift lever from the slots in
the straddle plate. The straddle plate may
now be removed by sliding it towards the
rear.
The importance of the arm height adjustment may be 'judged by a study of Fig. 77.
Note that the halance spring serves to hold
the knife.edge pivot of the cutting head
mounting fuIly seated in the "V" shape
trunnion hearing of the cutting head mounting hracket. Also, that the "pull" of the
spring is slightly downward, as well as horizontal.
The initial tension and length of the balance spring must be such that when adjusted
to the proper tension to produce the correct
depth of cut, the spring holding lug will be
positioned on the adjusting screw as shown,
to create a slight downward "pull" on the
cutting head mounting.
As the stylus end of the cutting head is
raised and lowered slightly, when cutting
records which are not perfectly flat, the cutting stylus varies from its perpendicular
plane, and the angle of the cutting edges of
the stylus also vary. This tends to produce a
varying depth of cut which would place a
varying load on the motor, resulting in a
variation in the average pitch or tone of,the
recorded music or speech. This effect is commonly ()ailed "wow." However, the spring
tension, and consequently the stylus pressure, also, "Varies. This variation in stylus
pressure opposes the effect of the varying
stylus position, resulting in a substantially
uniform depth of cut.
It can be seen that if the balance spring
were adjusted to a horizontal position with
respect to the plane of the cutting head(a) The downward "pull" of the spring
would be lost, resulting in a pronounced variation in the depth of
cut when cutting a record having a
slightly warped surface.
(b) The cutting stylus would have a
tendency to chatter or dig into the
record, due to the "dead-center"
position of the spring.
It can also be seen that if the arm were
adjusted to an incorrect height above the
record surface, the cutting stylus would not
be perpendicular, and the tendency towards
a greater variation in the depth of cut,
which would be more pronounced, would not
be fully corripensated by the counteracting
effect of the varying tension of the balance
spring.
PHONO-RADIO
SIRVlel
DATA
• Section 5
Record.Changer Service Data
Supplement No.5 to the 3rd Edition Mallory
Radio Service Encyclopedia, published in
Fehruary of 1940, contained complete service
material on Capehart, Farnsworth, Garrard,
Magnavox, RCA, and ·Webster record
changer equipment current at that time. It
was the first step taken in the direction of
supplying data on all types of changers for
use by the radio servicemen in this somewhat puzzling, but rapidly expanding and
lucrative phase of radio receiver maintenance.
The field has grown tremendously, with
wider application of mechanisms then in use,
and the introduction of new or improved
changer systems. A really comprehensive
treatment of service operations on all models
now existent would entail a large volume on
the subject of changer systems. We are
happy to say that Mr. John F. Rider has
certainly fulfilled this requirement with his
excellent book "Automatic Record Changers and Recorders." For all those servicemen
actively engaged or desirous of entering the
record changer maintenance field Mr. Rider's book is a
{'e
must .'"'
The response to publication of the changer
section of Supplement No.5 was so enthusiastic, and the numher of requests for reprints so large that we are including this
material in this Technical Manual. Many
of the types are basic, so that the service
material can be used for later models. However, on mechanisms not covered, we respectfully refer you to Mr. Rider's book just
mentioned.
( ape ha r1- Model 16· E De Luxe Record
1. To Locate and Adjust the Record
Tray. (6687) (Fig. 83)_ In assembling the
record changer, the first tooth of the driver
quadrant (3551) (Fig. 82) should mesh with
the second tooth of the driven quadrant of
the tray as shown.
With the two gears properly meshed,
loosen the. Allen set screws which hold pins
No. 34133, Fig. 78, in place. This will allow
you to move the record tray sidewise, adjust
tray sidewise until the turntable spindle is
exactly in the center of the 10" record level
of the record tray. (The 10" record level is
that part of the tray where the felts No. 4913
are indicated in Fig. 83.)
With the control lever in the "one side"
posiJion, run the record changer through its
cycle until the large hole in the main cam is
exactly half way past the upper edge of the
record tray cam follower, as shown at No. 82,
Fig. 1. At this position, the points of the
ten-inch felts (4913) (Fig. 83) should be level
with the top of the turntable felt. If this tray
is too low or too high, it may be adjusted to
the proper level by loosening the eccentric
screw (3237) (Fig. 78) No.4 and turning this
Changer
screw until the proper level is obtained. Be
sure to tighten the lock nut after adjustment.
If the tray is too high, at this position, the
ten-inch records will not be centered over
the turntable spindle. If the record tray is
too low, the ten-inch records will slide out
over the ten-inch tray shoulder and hot
properly center.
2. The Adjustments of the Record Magazine. Before attempting to adjust the magazine, be sure that the center of the magazine pivot pins (34132) (Fig. 78) is 8%"
above the base plate. This height is very
important and we recommend checking the
height of the right hand pin, when looking at
the magazine, before any adjustments are
made.
The record magazine is positioned by
moving it sideways on its bearing. or pivot
pins. The two set screws underneath the
pivot pins lock the magazine in position.
Loosen these set screws, then see that the
left hand side of the record reverse assembly
fork (part of 6228, Fig. 83) is between ~"
and is" inside the left hand side of the Reverse crank, when looking at the magazine.
That is, the left hand edge of the record
reverse fork is about ~" or
to the right
of the left hand edge of the crank. After
moving the magazine, lightly set up the set
screws. Then with the selector arm in the
"Repea·t" position swing the record reverse
arm around in front of the magazine, to see
whether the record guide strikes either of
the record support pins (34138) (Fig. 83). If
the guide strikes either of the support pins it
will be necessary to bend the pin away from
the guide so they can not strike. If it is necessary to bend either pin, set the control lever
in the "Repeat" position, then raise the
record tray by hand, with a 10" record on it,
observing the way the record strikes the
support pins, the record should hit both
pins about
from the end of the pin; if it
does not it will again be necessary to adjust
the pin until the record hits both pins an
equal distance from the ends. If it is necessary to bend the pins, check the clearance
between the record guide arms and the pins
and between the arm carrying the record
guide and the right hand pin. Also if the
magazine has been shifted it is necessary to
see that the two points, which extend downward from the magazine, have ample clearance in the channels, in the record tray,
which are provided for their passage. If
there is possibility of the points striking it
probably means the magazine has been
shifted too much.
If the magazine has been adjusted, it is
also necessary to see that the record separator hook (6226) (Fig. 78) does not bind in
the slot in the end of the record separator
arm (6445) (Fig. 83). If it does the section
covering these parts gives the adjustment.
3. Magazine Stop Screw. The magazine
stop screw No.2, Fig. 82, should be adjusted
so that the crank pin (part of 6230, Fig. 78)
is approximately
from the edge of the
record reverse arm fork (part of6228, Fig. 83)
which is furthest from the magazine, when
the record reverse guide is in front of the
magazine, that is, in the reversing position.
4. Magazine Link Adjusting Screws (No.
2) (Fig. 78). The record magazine should always come back snugly against the magazine
stop screw, No.2, Fig. 82. If it does not, it is
. necessary to loosen the two set screws (No.
2, Fig. 78) to a sliding tension imd run the
record changer through a cycle of change.
When the magazine has reached the horizontal position, as shown in Fig. 78, press
down on the lower end of the magazine; this
will lengthen the link assembly. Then when
the magazine returns to its normal position,
the magazine link will adjust itself so that
the magazine is snugly against the stop
screw. Then tighten the magazine link screws.
ro"
ron
ro"
109
rHI
Section 5 •
MY I
r I eH
N" CAL
MANUAL
Fig. 78
2722 Switch AC Line
3059 Escutcheon Plate Off-On
3237 Shoulder Screw-Record Tray Slide
3982 Spring-Separator
4018 Main Shaft Bushing
4020 Record, Magazine Bushing
4719 Magazine Link Upper
4720 Magazine Link Lower
4925 Record Tray Shield Felt-Outer
5044 Stop Lever Roller Tubing
5658 Pickup Arm Lever Hook
5765 Pickup Cover
6178 Chassis Plug
6226 Separator Hook and Arm Assembly
6228 Record Reverse Arm and Fork Assembly
6230 Reverse Pinion and Crank Assembly
6693 Record Bumper Guide and Felt Assembly
34132 Pin-Magazine Pivot
34133 Pin-Record Tray Pivot
34147 Pin-Record Tray Slide
43159 U "-28 Hex. Cap Nut
43160 Lock Nut for Pivot Screw
64197 Pickup Arm Stop Lever Assembly
(Specify color).
662p4 Steering Arm Assembly.
I
6-32x %" Pickup Stop Lever Screw
NOTE: In ordering any part that is painted,
please specify color wanted .
•
5. Record Reverse Guide (6444) (Fig. 83).
With a 12" record in the magazine the record
reverse guide assembly (6444) (Fig. 83)
should be parallel with the record when in
the reversing position, in front of the magazine.
If the record reversing assembly is parallel
with a 12" record as above, it should come
around and lay against the reverse guide pin
tubing (34134) (Fig. 83), if the eccentric cl1m
(3825) (Fig. 85) is properly adjusted. This
cam can be adjusted, by loosening the screw
through the cam and turning it so that the
record reversing assembly returns to the reverse guide pin tubing. Care should be taken
when making this adjustment so that the
crank pin (part of 6230, Fig. 78) does not
hold the reverse guide away from the pin
tubing. This cam should be turned so that
the reverse guide assembly just touches the
pin tubing; if the cam is turned too far it will
allow the reverse guide assembly to hit the
pin tubing, but in the reversing position the
assembly will not be able to ass\lme a position parallel with a 12" record.
6. Reverse Assembly Link Rod. Loosen
lock nut No.9, Fig. 80, while the record
changer is in the reversing position, that is,
when the reversing assembly (6444) (Fig. 83)
is in front of the magazine. Remove the
screw (3241) (Fig. 85) holding the 'reverse
segment link (34141) (Fig. 85) to the reverse
segment (3550) (Fig. 85) and lengthen or
shorten the link, by the link thread until the
reversing crank (6230) (Fig. 78) stands with
the crank pin just barely touching, but not
hinding, against the front side of the fork
(6228) (Fig. 83). After the adjustment has
no
J~
been made, lock the link in place with the
lock nut No.9, Fig. 80.
7. Rccord Separator Adjustment. The
separator stop No.3, Fig. 78, should he adjusted so that a small 10" record will positively clear the knife portion of the separator
lever as shown in the following illustration.
A standard to use is to make certain that
there is approximately -h" clearance between the edge of the small record and the
point of the separator lever, as shown at
"A" in illustration below. However, it may
be necessary to vary one way or the other
from this measurement, depending on
whether or not the slotted end of the record
separator lever goes over the hook (6226)
(Fig. 78) without binding.
8. Record Separator Hook Adjustment.
After adjusting the record separator it will
be necessary to check the record separator
hook (6226) (Fig. 78) to see that it enters
the slot in the record separator without
binding. This hook is threaded and by loosening the locknut the hook can be turned in
either direction, to raise or lower it. After
the correct adjustment is obtained, tighten
the locknut.
It should never be necessary to change
these adjustments on record changers unless
they have been tampered with by an inexperienced person.
9. Separator Hook and Arm (6226) (Fig.
89). Be sure set screw No. 10 in Fig. 85 is
screwed all the way in.
10. Record Magazine Bushing (4020)
(Fig. 78). If a ringing noise is heard while the
instrument is changing records, i.e., such a
noise that might be made by a spring, it will
be found 'that the Durex bushing (4020)
(Fig. 78) is too tight, in which case it will be
necessary to loosen the lock nut of the holding bolt, and back the bolt out, from a
quarter to a half turn, then tighten the
lock nut.
n. To adjust the Tone Arm Height.
To adjust the tone arm height, first place a
12" record on the turntable and adjust the
tone arm stop lever (64197) (Fig. 78) so that
the record hits the rubher roller (5044) (Fig.
78) in the center. Start the record changer
through a cycle and stop it when the tone
arm lever hook (5658) (Fig. 78) just touches
the stop lever assembly. In this position adjust tbe tone arm height so that the top of
the stop lever is the same height as the
center of the hook. This adjustment is made
by loosening the two Allen set screws at the
rear of the tone arm. These Allen set screws
are accessible by raising the tone arm by
hand. After making the height adjustment it
is necessary to make certain that there is a
clearance of approximately %" between the
pickup head and the record tray. This distance may be checked between the bottom
of the record tray and the bottom of the
pickup when the record tray is approximately
parallel with the pickup.
12. To adjust the Pickup Elevation.
When the tone arm swings in towards the
record, the pickup arm lever hook (5658)
(Fig. 78) comes to rest against the pickup
arm stop lever (64197) (Fig. 78) and when
the tone arm lowers the pickup toward the
PHONO·IADIO
SEIVleE
DATA
• Section 5
Fig. 79
3243 Shoulder Screw-Repeat Lever
3244 Shoulder Screw Clutch Throwout Lever
3317 Screw-Clutch Throwout Cam
3319 Screw-Turntable Shaft Collar
3995 Spring-Reverse Arm
5333 Main Clutch Fork Lever
6326 Worm and Bushing Assembly
6450 Reverse Cam Arm and Roller Assembly
6460 Clutch Throwout Lever and Spring Assembly
6719 Turntable Drive Shaft Assembly
•
record it pauses momentarily before the
pickup arm lever hook goes through the stop
lever. H the record changer is stopped during
this pause, it will he found that the ball in
the end of the pickup arm lift shaft (6457)
(Fig. 86) is at the point marked "L" in
Fig. 86 on the lift cam (6449) (Fig. 86).
Now if the pickup, with a needle in the
proper position, is moved beyond the edge
of the record, the point of the needle will
extend below the top surface of the record a
distance equal to half the thickness of the
record. The correct elevation of the pickup
is made by the screw in the underside of the
tone arm fork against which the pickup
cover rests. Loosen the locknut, adjust the
screw to bring the needle to the position
mentioned above, then lock the locknut.
13. Pickup Feed in Adjustment. Tht;
collar of the pickup arm swing lever and
collar assembly (6232) (Fig. 86) should ride
on the leather facing of the friction cam
(6691) (Fig. 87) until the pickup arm lever
hook (5658) (Fig. 78) has engaged the stop
lever (64197) (Fig. 84). Then a slight amount
of friction should be maintained after the
ball at the end of the pickup lift arm (6457)
(Fig. 86) has engaged with tlfe lift cam
(6449) (Fig. 86). This friction should be
maintained until the needle has touched the
record, otherwise the pickup arm may move
away from the stop lever and the needle
miss the record. H the friction be maintained
too long the needle may be forced beyond
the first playing groove. To adjust this, the
pin locking the friction cam to the main cam
shaft should be driven out and the Allen
set screw loosened to a sliding tension. The
cam is rotated forward, in the direction of
rotation of the main cam shaft, to maintain
the friction a longer time and backward to
maintain it for a shorter time.
14. To Adjust the Pickup. After
removing the pickup cover, it should be
noted whether the stylus (5610) (Fig. 87) is
centrally located in respect to the pole pieces
(569) (Fig. 87). To center the stylus loosen
the locknuts (99·11.1) (Fig. 87), then loosen
the two headless set screws (99.28.3) (Fig.
87). These set screws hold the spool assemJt.ly
(6711) (Fig. 87). The spool assembly should
be shifted until the stylus is centralized with
the pole pieces, then tighten the 3et screws
carefully, so as not to crack the spool, then
tighten the lock nuts.
H for any reason it is necessary to shift
the pole pieces, which are held to the back
by two screws, the two set screws holding
the spool should be loosened before attempt.
ing to move the pole pieces. H any adjust.
ment of pole pieces is made, carefully check
the centering of the stylus before replacing
the cover by means of its three screws.
15. To Adjust the Stop Lever Hook
(5658) (Fig. 78). Always adjust the tone arm
position on a 12" record before adjusting for
a 10" record. Adjust the tone arm stop lever
hook (5658) (Fig. 78) by m~ving it in or out.
This hook is locked in place by a set screw
in the stud whose nut is shown in Fig. 78 as
No. 43159. This set screw is at the bottom
of this stud. Adjust the hook so that it will
pass through the notch in the pickup arm
lever (64197) (Fig. 78) without binding
against the top or bottom of the notch,
. when in the playing position. With a 12"
record on the turntable, the rubber roller
(5044) (Fig. 78) against the edge of the rec·
ord and the stop lever hook (5658) against
the blade of the stop lever (64l97) the
needle should stop on the record exactly h"
from the edge of the record.
With the record changer in exactly the
same position as described above, and with
a 10" record on the turntable and the hook
(5658) (Fig. 78) against the blade, the stsp
lever should allow the needle to stop on the
record :l{2" from the edge of the 10" record. A
6·32 screw shown in Fig. 78 is provided for
making this adjustment, simply by screwing
it in or out. A check should be made for
clearance between the roller and the tray,
this roller should never bind on the record
tray. This can he taken care of by slightly
bending the tone arm stop lever (64197)
(Fig. 78) up or down. If it is necessary to
bend the stop lever it will be necessary to
readjust for 12" records.
111
THI
Section 5 •
MY I
TECHNICAL
MANUAL
i
1\
Fig. 80
2764 Switch Assembly-Solenoid and Motor
3550 Record Reverse Pinion Segment
3977 Spring-Magazine Slide Arm
3986 Spring-Solenoid Lever Torsion
5326' Record Reverse Cam Shaft Lever
6178 Chassis Plug 5 Prong
I,
6713 Solenoid Assembly
34140 Pin-Long, Reverse Segment
•
!~
I
I,
16. To Adjust the Clutch Throwout
Lever and Cam. The clutch throwout lever
cam is shown at 15 in Fig. 79 and is adjusted
by loosening the shoulder screw (3317) (Fig.
79) to a sliding tension after the record
changer has been stopped in the playing
position. The clutch throwout lever cam
should just clear the point of the turntablc
throwout cam (6448) (Fig. 87) with the
clutch disengaged. Unless clearance between
the turntable throwout cam and the clutch
lever throwout cam is maintained the record
changer will jam. If too much clearance is
allowed the turntable throwout cam will not
disengage the clutch and the record changer
will continue to change records without
playing them.
17. To Adju~t Solenoid Wedge Spring.
This phosphor bronze spring is located on one
of the three spacers used to mount the solenoid plate bracket to the solenoid bracket.
It is used to prevent clutch ch,atter or bounce
when the clutch engages. The only adjust·
ment is to bend the spring to a snug fit with
a long screw driver 80 as to increase or de·
112
crease its pressure on the solenoid to clutch
lever (6455) (Fig. 88).
18. To Adjust the Reverse Cam Shift
Lever (5326) (Fig. 82). This lever is moved
by the record control shaft (3724) (Fig. 89)
and is held in position by an Allen set screw.
It should be positioned on its shaft 80 that
the record reverse cam (6325) (Fig. 81) is
firmly engaged with its pin (34144) (Fig. 85)
in the "Both Sides" position. In the "One
Side" and "Repeat" positions it should have
good clearance with the pin. If any adjustment of this lever is made be sure to check
the setting of the Reverse Cam Arm and
Roller Assembly (6450) (Fig. 85) as instructed in Section 7 of the instructions on
replacing a reverse cam.
19: To Adjust the Record Repeat Lock
Lever (5334) (Fig. 89). The purpose of this
lever is to prevent accidental shifting of the
Selector Arm while the instrument is not in
the playing position. In the "Repeat" position this lever is on the side of the Solenoid
to Clutch Lever (6455) (Fig. 88) away from
the main cam. In the "One Side" and "Both
Sides" positions it is on the main cam side
of the solenoid to clutch lever. With the tone
arm in the playing position (Main Clutch
Disengaged) this lock lever should clear the
solenoid to clutch lever by approximately
!oN when moved under it.
20. To Adjust the Reverse Cam Lock
Lever (5339) (Fig. 89). This lever should he
on the main cam side of the solenoid to
clutch lever when in the "Both Sides" posi.
tion. And on the opposite side when in the
"One Side" and "Repeat" positions. With
the main clutch disengaged the lock lever
should clear the solenoid to clutch lever by
approximately 'h" when moving under it.
21. To Adjust Reverse Cam Arm and
Roller Assembly (6450) (Fig. 81). See Section 7 under Instructions for Replacing a
Reverse Cam.
22. To Adjust Record Repeat Throwout
Lever (4663) (Fig. 89). No adjustment of
this part is necessary.
'
23. To Adjust Record Repeat Clutch
Lever (5332) (Fig. 89). The adjustment of
I"!
PHONO-RADIO
SERVICE
DATA
• Section 5
Fig. 81
1173 Condenser-O.1 Mfd. 400-Volt (in can)
3238 Shoulder Screw-Magazine Slide Arm
3243 Shoulder Screw-Repeat Lever
3550 Record Reverse Pinion Segment
3826 Record Repeat Sliding Clutch Cam
3976 Spring-Record Separator Hook Lever
3977 Spring-Magazine Slide Arm
3978 Spring-Record Repeat Clutch
3995 Spring-Reverse Arm
6450 Reverse Cam Arm and Roller Assembly
•
this lever is made by loosening the Allen set
screw to a sliding tension then moving the
part along the shaft. The sliding clutch
should engage in the "One Side" and "Both
Sides" positions, but should be disengaged
in the "Repeat" position. The fork of this
lever should not bind the sliding clutch in
either the "Repeat" or "Both Sides" position.
24. Lateral Location of the Main CaIn
Shaft. Both end bearings of the main eam
shaft are movable, and are used to locate the
cam shaft in its proper lateral position, as
well as adjust the amount of end play. The
main cam shaft is located laterally so that
the ball in the end of the tone arm lift rod
(6457) (Fig. 36) travels in the exact center
of the tone arm lift cam (6449) (Fig. 86). As
shown at H in Fig. 86.
25. To Adjust the Stop Trip Switch
(2792) (Fig. 84). This switeh is accessible by
removing the turntable, which will expose
the switch cover. To remove the switch
cover it is necessary to remove the trip arm,
which goes through the switch cover and the
two flat head screws which hold the cover in
place. The clearance between the contact
points on the fixed and movable arms of the
switch should be +S". After replacing the
trip arm (6510) (Fig. 84) in the switch, after
the switch cover has been removed, set the
turntable on the spindle, push stop trip arro
(4533) (Fig. 84) slowly about 74:" toward the
magazine and then turn the turntable
through one complete revolution. This will
insure the fibre cam, on the turntable, resetting the trip switch, the clearance between the trip arm and the movable arm of
the switch should be +S". The distance between the trip arm and the switch trip
guard finger should also be +S".
To adjust the clearance between the trip
arm hook (6510) (Fig. 34) and'the movable
switch arm, loosen the screw in the bakelite
switch base, at the end nearest the tone arm.
Move the switch until +S" clearance is secured between the trip arm hook and the
movable arm of the switch, then tighten the
screw holding the switch. In making this adjustment be sure that the stationary arm of
the switch is not bent when tightening this
screw.
On some models a headless set screw, near
the end of the coil spring, is used to lock the
switch in position; loosen this screw, adjust
the switch, then tighten the set screw.
26. To Adjustthe Solenoid Motor Switch
(2764) (Fig. 80). After the switch cover has
been removed the switch is exposed. The
upper switch points should make good electrical contact, while the main clutch is disengaged, in this position the clearance between the bottom points should be approximately j, ". While the clutch moves from the
disengaged to the engaged position the upper
switch points should remain closed until the
lower set of points are closed. When the
clutch is fully engaged the lower points
should make good contact and the clearance
between ihe upper points should be approximately j,1I.
To adjust the switch loosen the screw
through the bakelite switch base at the rear
of the switch assembly. After the position is
found where proper clearance is secured,
with the clutch engaged and disengaged, the
switch should be locked in position with
the screw.
In some machines a headless set screw is
used to lock the switch in position. This
screw is near the point of the tapered bakelite insulating block. Loosen this screw and
adjust switch to 'get proper clearance then
lock the switch in position by the set screw.
The two upper contacts are in series with
the auto trip switch and the two lower contacts are shunted across the motor switch.
When the clutch is engaged the auto trip
switch is out of circuit and the motor switch
is shunted by the lower contacts thus insuring the completion of the change cycle even
though the instrument is switched to radio
or turned off.
27. To Adjust the Friction Joint of
Automatic Trip Switch. The amount of
friction necessary in the friction joint hetween the auto stop trip lever-long (6510)
(Fig. 84) and the auto stop trip lever-short
(4533) (Fig. 84) should be just sufficient to
close the automatic stop'trip switch (2792)
(Fig. 84). The friction is regulated by adjusting the screw which tightens the flat
113
rN.
Section 5 •
M YI
r.CNNICAL
MANUAL
Fig. 82.
3240
3243
3319
3539
3550
3551
3826
3976
3977
3978
3981
5326
Shoulder Screw-Reverse Segment
Shoulder Screw-Repeat Lever
Screw-Turntable Sp,aft Collar
Worm Gear-Main Drive
Reoord Reverse Pinion Segment
Record Tray Gear-Driver
Record Repeat Sliding Clutch Cam
Spring-Reoord Separator Hook Lever
Spring-Magazine Slide Arm
Spring-Record Repeat Clutoh
Spring-Record Reverse Cam Control
Record Reverse Cam Shift Lever
I:
I
I'
i
I
~
•
spring (3998) (Fig. 84). If the tension is too
great the instrument may trip hefore finishing a record, if not enough tension is had the
instrument will not change records when the
needle hits the automatic change groove.
28. RecoJ,'d Size Limit. The 16-E Series
record changer will play any lOR or 12"
record of IItandard size. The minimum sbe
for 12" record. is 111-1/". The minimum size
for IOu recordil is 9ft". Records smaller than
theae limits are very apt to miss centering
over the tumtable spindle and in most cases
are broken.
Theile record changers will automlltically
trip on any record hllving an automatic stop
chllnge groove, either spiral or oscillating,
where the blank space in the center of the
reoord i8 not more than 631" in diameter.
29. Records. Always inspect the records to
lee that no rough edges are present., Occasionally you will find a record which has a
rongh out"ide edge. This rough edge will
greatly intedore with the satisfactory performance of the recqrd ohanger. A small
,piece of No. 00 sandpaper wiD assist you
greatly in romoving this rough edge.
114
30. To Adjust the Vertical Bumper
Guide (6693) (Fig. 83). This guide is located
hack of the magazine cro'ss har (6685) (Fig.
83). After the records are separated from the
magazine they are guided in dropping off
the separator so they hit the center of the
record humpers (5081) (Fig. 83). This vertical humper guide al80 guides the records
when the elevating hook, on the rear of the
record tray lifts the record. The vertical
humper should he set hack just far enough
to allow a 12" record, to drop onto the record
humpers freely. The lower part of the vertical bumper, which extends into the record
well, should extend toward the center of the
well ruhher humpers far enough to make
sure that the upper edges of the records fall
hehind the points of the upper record support (5517) (Fig. 83). This adjustment is not
-critical. In most cases it will he found that
the upper end of the vertical humper will
just clear the elevating hook on the rear of
the tray. In cases where it is found that 10"
records are chipping ahout the edges, due to
bounding against the points of the upper
record support (5517) (Fig. 83) it will he
necessary to hend the vertical humper (6693)
(Fig. 83) hack at the top to a point where it
just harely clears the elevating hook at the
rear of the tray. It should never he hent
hack far enough to raise the front of the tray.
31. Clutch Clearance. The clearance hetween the driven (6326) (Fig. 87) and driving (3630) (Fig. 87) members of the clutch
should he approximately ~020" (twenty
thousandths), and is adjusted hy loosening
screw No. 16 (Fig. 80) to a sliding tension
and adjusting the clutch fork (5333) (Fig.
79) and the solenoid to clutch lever and pin
assembly until the proper clearance is ohtained. After adjustment is made lock the
screw No. 16 (Fig. 80).
32. Motor Connections (21131). The '
21131 motor is a synchronous motor and
will run equally well in either direction,
when properly connected. For this reason,
all motors shipped from the factory are
equipped with a terminal strip and cable.
However, if it should ever he necessary to
disconnect the leads from the terminal strip
the leads should he replaced in the following
order: With the cable extending to the right
of the terminal strip and the mounting lugs
pointing down\\l'ard, and the soldering lugs
towards you, the leads go on from left to
right in the following order-emall hlack,
hlack with yellow tracer, hlue and large
PHONO·RADIO
4915
SERVICE
DATA
• Sec:tlon $
Fig. 83
7
Shoulder-Screw-Magazine Link
Shoulder Sorew-Separator
Pickup Needle Screw (Magnetic)
Turntable Drive Shaft Cap
Automatio Stop Trip Quadrant Bracket
Reoord Reversing Ann Lock
Reoord Reverse Arm Look Stop
Record Tray Felt-La~e
Record Tray Felt-Small
Reoord Magazine Felt
Lower RecoM Ejupport Felt
Reoord BUmper Guide Felt
Magazine Side Felt
Reoord Way Shield Felt Outer
Record Tray Bumper-Front
Record Tray Bumper-Rear
Reverse Ann BUmper
Reoord Bumper
~82 Pickup Arm Base
5517 Record Support-Upper
5615 Record Reverse Guide
5766 Pickup Arm
6228 Reoord Reverse Ann and Fork Assembly
(Specify color)
6444 Reoord Reverse Guide Assembly
6445 Record Separator and Hub Assembly
6510 Automatio Stop Trip Lever Asl!6mbly
6669 Pickup Ann Assembly oomplete
6685 Lower Record Support ASilembly
6686 Record Magazine Assembly
6687 Record Tray Assembly
6693 Record Bumper Guide and Felt Asaem.
34134 Pin-Reverse Guide Stop
34138 Pin-Record Support
34145 Pin-Record Control Rod
39130 Record Reverse Guide Spring'
64197 Pickup Arm Stop Lever Assembly
.
(Specify color)
3239
3242
3356
4320
4431
4659
4664
4912
4913
4915
4916
4917
4923
4925
5036
5037
5042
5081
•
black. In that order they are ground, one
side of nO.volt line, one side of the condenser, and the remaining nO-volt and condenser leads. The motor terminal strip should
be 'mounted to the cabinet torminal strip 80
that the cable extends to the right, with the
soldering lugs towards you.
33. Oiling Inlltructions. Due to its careful design and precise workmafillhip, the
Capehart 16-E record Changer requires a
minimum of oiling.
About once each year a light coat of
vaseline or petroleum jelly should be applied to all moving surfaces which were
coated with graphite at the factory.
A very light coat of vaseline should be applied to the surfaces of the magazine, indicated at "A" in Fig. 83. It is best to apply
this coating every six months. The vaseline
should be applied with, and removed by, the
fingers, on the magazine faces. Do NOT USE
EXCESSIVE AMOUNTS OF LUBRICANT ANY·
WHERE ON THE RECORD CHANGJl;R.
A good grade of machine oil, not too light,
should be used on the sliding clutches, reverse cam shaft and all eccentric and
shoulder screws.
N EVER OIL THE "DUREX" BUSHINGS, AS
THIS WILL CAUSE THEM TO DISINTEGRATE.
Once each year the motor oil cups should
be oiled with a good grade of motor oil. At
the same time the gear box should he inspected, and the grease replaced if it has
become hard. A good mixture to use ,here is
75% vaseline and 25% SAE 40 motor oil.
34. IuauuctiQns for Replacing the Record Reverse Cam and itll AdjUlitmentll.
1. Set' record changer in the playing position. Carefully mark the drive gear (3516)
(Fig. 87) on the main shaft and the driven
gear shown as part of 6623, Fig. 87, by prick
punch marks or scriber, so that the same
teeth can be engaged after reassembly, thus
insuring proper timing.
2. Remove the two bolts, one (3238)
(Fig. 81) securing the magazine slide aud
roller assembly to the magazine slide 8l'Ill
Jever, and one (3237) (Fig. 78) securing the
record slide arm and stud assemhly to the
record tray drive crank.
3. Looking in from the rear of tho iUlitrument, remove the Piu-ex bushing from the
end of the main cam shaft. nea\'est the
motor drin shaft. This iii accomplililhed by
loo.ening the bolt to the right of the main
shaft. Care sbould he taken when replacing
this bushing so all not to tighten the bel}t
enough to crush the hUilhing; I linug fit only
is roq"ifed.
.
4. Remove lowtlf balf
boann, and
Durex bushing frmn the other end ()f the
main cam shaft and work the cam shaft OUt
of the record changer. The 8ame precaution
agaiust crushiug this bushing should he
taken with this one as with the obe in the
preceding section.
5. Remove taper pin from gear and lool16n
set screw in the collllr. hoth shown as 6233
in Fig. 85, of the reverse cam shaft al8embly.
as well a8 the pin (34144) (Fig. 8'1) OVtll'
which the reverse cam forks, when in the
m
115
rHI
Section 5 •
MY I
rlCHNICAL
"'
MANUAL
I,
I'
Fig. 84
2792 Record Trip Switch Assembly-complete
3988 Spring--Automatic Trip Lever Pin
4320 Turntable Drive Shaft Cap
4533 Automatic Stop Trip Lever--Short
5044 Stop Lever Roller Tubing
6018 Selector Knob
6228 Record Reverse Arm and Fork Assembly
(Specify color)
6510 Automatic Stop Trip Lever Assembly
6723 Pickup Brush Assembly
34134 Pin-Reverse Guide Stop
34145 Pin-Record Control Rod
39130 Record Reverse Guide Spring
64197 Pickup Arm Stop Lever Assembly
(Specify color)
'.
,~
•
6&10
reversing position. After removing the coIlar
and sliding the gear to one side, file all burrs
from the edges of the holes in the reverse
catp shaft. Slide the shaft through its Durex
hushing toward the rear of the instrument
far enough to aIlow the removal and replacement of the reverse cam (6325) (Fig. 87).
6. Reassemble the reverse cam shaft assembly, making certain that the taper pin
holes in the shaft and gear are correctly
aligned to permit the taper pins being properly inserted. The set screw in the collar at
the end of the shaft shlilUld be properly
tightened.
7. Remove the reverse cam arm and roller
assembly (6450) (Fig. 79) and make sure
that the roller pin and arm are not bent, if
either of these items are found bent we suggest that you replace the reverse arm and
roller assembly.
8. In reassembling the reverse cam arm
and roller assembly (6450) (Fig. 79) in its
proper position for alignment with the reverse cam, be sure the roJler is about
inside the ridge on the reverse cam, when the
cam is in the ~eversing position.
+."
116
9. Remove the taper pin from the gear
(3516) (Fig. 87) on the main shaft, which
drives the gear on tbe reverse cam shaft
assembly (6233) (Fig. 87) and remount the
main shaft to the record changer chassis,
pushing the above gear, from which the pin
was removed, to one side so that it will not
mesh with its driven gear.
10. Locate the main shaft so that the
lower end of the pickup arm left shaft travels
in the center of the pickup arm lift cam, as
shown at "H" in Fig. 86. With the main
shaft in this position, adjust the main shaft
Durex bushings so that there is no end play
in the main cam shaft IIssembly.
11. Rotate the main cam shaft to the
playing position so that the pickup arm is
lowered over the turntable.
12. Set the reverse cam in its lowest position, with the control lever in the "Both
Sides" position, so that the fork of the reverse cam is meshed with the driving pin.
13. Mesh the reverse cam assembly driver
gear (3516) (Fig. 87) with the reverse cam
assembly driven gear so that the identifying
punch marks correspond to the original posi-
tion. The taper pin for the driver gear
should be inserted next. If the assembly has
been properly made there should be approximately:h" clearance between the roller
or the reverse cam arm and the reverse cam.
See "A," Fig. 86.
'
14. Throw the control lever to the "One
Side" position and rotate the reverse cam
with the fingers until it is in the reversing
position. Again throw the control lever to
the "Both Sides" position. Now there should
be approximately :h" clearance 'between the
reverse cam and the roller. See "B," Fig. 86.
If the clearan~e is not approximately -h" for
both positions of the reverse cam it indicates
either the gears are not properly meshed or
the reverse segment link rod may be bent. A
careful check of the latter while the main
shaft is out will save time and troub)e later.
35. Instructions for Rellloving the 16-E
Record Changer. There is a great possibility, when removing the chassis from the
cabinet, to mar or scratch the cabinet. If you
will place a piece of cardboard around the
record changer it will eliminate, to a great
extent, the possibility of marring the finish.
PHONO·RADIO
SERVICE
DATA
• Section 5
Fig_ 85
3241
3243
3244
3317
3550
3825
3826
3976
3977
3978
3981
3984
3995
5046
5331
5332
5334
6230
6233
6326
6450
6460
Shoulder Screw-Reverse Segment Link
Shoulder Screw-Repeat Lever
Shoulder Screw-Clutch Throwout Lever
Screw-Clutch Throwout Cam
Record Reverse Pinion Segment
Reverse Segment Stop Cam
Record Repeat Sliding Clutch Cam
Spring-Record Separator Hook Lever
Spring-Magazine Slide Arm
Spring-Record Repeat Clutch
Spring-Record Reverse Cam Control
Spring-Tone Arm Lever
Spring-Reverse Arm
Stop Lever Collar Pin Tubing
Record Repeat Throwout Hook Lever
Record Repeat Clutch Fork Lever
Record Repeat Lock Lever
Reverse Pinion and Crank Assembly
Record Reverse Cam Shaft Assembly
Worm and Bushing Assembly
Reverse Cam Arm and Roller Assembly
Clutch Throwout Lever and Spring Assembly
6719 Turntable Drive Shaft Assembly
34141 Pin-Short-Reverse Segment
34144 Pin-Reverse Cam Shaft
•
A rubber auto mat, with a hole for the record
changer, the same size as the one in the
cabinet, makes an excellent pad. This pad
can be split and is easily put in position and
removed.
Remove the backs from the record changer,
radio and amplifier compartments.
Release the play control cable and cable
housing from the bracket on the record
changer chassis, by loosening the two set
screws. Care should be taken to prevent
breaking the control cable when removing
it. The end which has been kinked by the set
screw should be straightened before attempting to reinstall it.
Remove the screws from the partition between the radio and record changer compartments, so it can be moved back out of
the way.
Loosen the two Allen ,set screws in the
flexible coupling and allow it to slide down
the motor shaft, so as to' clear the record
changer shaft.
Remove the wood screw, under the turntable, also the three bolts which hold the
record changer down.
Move the play control as far into the
radio compartment as possible.
Remove the two wood screws that mount
the play control.
Remove the screw marked "Boo in the
illustration on page 109. This is the middle
one of the screws holding the upper record
support.
Remove the female chassis plug, from the
male chassis plug (6178) (Fig. 78), the pickup lead, which runs from the radio chassis to
the terminal block, then dismount the terminal block by removing the wood screw in its
center, the straps holding the shielded lead,
which runs from the shorting switch, and the
nO-volt leads to the Play Control.
Remove the magazine link shoulder screw
(3239) (Fig. 83). This will allow the magazine to be swung out of the way. As soon as
the record reverse arm and fork assembly
have cleared the reverse crank and pin
(6230) (Fig. 78) it should be swung over the
magazine and locked with the record reverse
arm lock (4659) (Fig. 83), to keep it out of
the way.
Lift the record changer up, until the tone
arm just touches the top of the cabinet,
carry it forward through the doors, tilting it
to keep the main cam clear of the shelf.
All parts of the cabinet liable to damage
should be protected by soft cloths while
removing or installing the record changer.
It is not necessary that the above operations be carried out in the above sequence.
36. Alignment of True-Tangent Pickup.
When adjusting the TRUE-TANGENT pickup
the pickup head and tone arm should form a
straight line, when the needle is exactly one
and one-half inches from the point of the
turntable drive shaft cap (4320) (Fig. 83).
To adjust the pickup angle, loosen the nut
at the rear of the steering arm assembly
(66254) (Fig. 78), turn the steering arm
either right or left until the correct position
for the pickup is found, then set the locknut
up tight. Then see that there still is %"
clearance between the pickup and the record
tray per Section 11.
117
THE
Section 5 •
MY E
TECHNICAL
MANUAL
50(73
6.32;/' R.,.,N,P'
I:
504-ti
f)-3l X
I
1Y4
'I
FHMS
1,1
67
I.'
67/9
6449
-S03S
4320 ---_
A
I ~Jr
I
,">I I
'l{x 2.0
HEX NUT
Fig. 87
8
Fig. 86
6232
632$
6449
6457
Pickup Swing Lever and Collar :\s""mbly
Reverse Cam
Pickup Arm Lift Cum
Pickup Arm Lift Shaft
118
3319
3356
3516
3539
3626
·3627
36:30
3820
3822
3984
4210
4233
4243
4244
4:312
4320
46213
50:38
SOH
5046
50173
.51a9
569
Screw-Turntable Shaft Collar
Pickup Needle Screw
Gear-Reverse Cam Shaft Driver
Worm Gear
Ball Bearing
Bull Bearing
Turntable Shaft Clutch
Magazine Slide Arm Cam
Pickup Arm Swing Cam
Spring-Tone Arm Stop Lever
Thrust Washer-Worm Shaft
Main Cam Collar
Pickup Arm Stop Lever Collar
Turntable Shaft Collar
Pivot Bushing
Turntable Driveshaft Cap
Magnet Holder
Turntable Driveshaft Cap Tubing
Stop Leyer Roller Tubing
Stop Leyer Collar Pin Tubing
Tone Arm Insulating Bushing
Terminal Block
Pole Piece
5610
5765
5768
61212
6233
6a25
6326
6448
Stylus
PickUp Cover
Pickup Back
Pickup Magnet
Record Reverse Cam Shaft Assembly
Record Reverse Cam and Pin
Worm and Bushing Assembly
Turntable Throwout Cam and Hub Assembly
6449 Pickup Lift Cam and Hub Assembly
64197 Pickup Arm Stop Lever Assembly
6691 Pickup Arm Friction Cam Assembly
6711 Spool Assembly
6719 Turntable Shaft Assembly
6723 Brush Assembly
34144 Pin-Reverse Cam Shaft
34147 Pin-Record Tray Slide
99-11- 1 6-32 Hex. Nut
99-18-21 6-32x % H RHMS
99-28- 3 6-a2x J4 n Headless Set Screw
99-28-21 rr-a2x V. H Headless Set Screw
99-a8- 2 :S-o. 2 Woodruff Key
SER.VICE
PHONO-R.ADIO
DATA
• Section 5
bl7S
5323
S,1t..ENCER,
3977
Fig. 88
/6257
I
565
3241
3fl26
3H2.S
a077
3!l7H
3\)Hfl
--
3825
401~
IO-24XYz}
R HM S
4018
4022
4a:n
443:3
5040
5:32:3
5331
617H
G257
433!
G450
G455
---'"-1-.-.--____
t>713
3'241 -----.:.-tI---5331
34141-'
6455
3626
6460
6460
6713
34140
34141
Clutch Throwout Cam
Reverse Aegment Link Shoulder Screw
Ball Bearing
Reverse Aegment Stop Cam
Magazine Slide Arm Spring
Record Repeat Cluteh Spring
Solenoid Lever Torsion Hpring
Main Shaft Bushing
Record Tray Hhaft Bushing
Bearing Retainer Plug
Holenoid Plate Bra('ket
Pi('kup Arm Brake Facing
Magazine Hlicle Arm Lever
Record Repeat Throwout Hook Lever
Chassis Plug
Record Tray Gear and Sliding Cam
AHHembly
Reverse Cam Arm and Roller Assembly
Aolenoid to Clutch Lm'cr and Pin Assemhly
Clutch Throwout Lever and Spring Assembly
Aolenoid Assembly
Reyerse Segment Pin, Long
Reverse Segment Pin, Sh~rt
•
Fig. 89
2722
3240
3243
3550
3724
3977
3981
3983
3984
3995
4020
4238
42:39
4243
4663
5046
5326
5332
5333
5334
5339
6221
6223
6224
6226
6230
6231
6451
50117
OOx %
Ox U
AC Line Toggle Switch
Reverse Segment Shoulder Screw
Repeat Lever Shoulder Screw
Record Reverse Pinion Segment
Record Control Shaft
Magazine Slide Arm Spring
Record Reverse Cam Control Spring
Separator Hook Spring
Tone Arm Stop Lever Spring
Reverse Arm Spring
Record Magazine Bushing
r." Collar
fg" Collar
Pickup Arm Stop Lever Collar
Record Repeat Throwout Lever
Stop Lever Collar Pin Tubing
Record Reverse Cam Shaft Lever
Record Repeat Clutch Fork Lever
Main Clutch Fork Lever
Record Repeat Lock Lever
Reverse Cam Lock Lever
Record Tray Drive Shaft Assembly
Record Re,-erse Arm Shaft Assembly
Solenoid Lever Shaft Assembly
Separator Hook and Arm Assembly
Reverse Pinion and Crank Assembly
Record Control Lever and Stud Assembly
Separator Hook Lever and Roller Assembly
Main Frame Pad
Taper Pin
Taper Pin
NtH
cUo
/
401.0
/
50117
1\I&X14 -2
lUi. CAP S/;,
tlZt!
AS'I.
424'"
2121-
00 X 5/S
3qQS
0223
ASY,
119
Section 5 •
THE
MY E
TECHNICAL
MANUAL
Farnsworth - Model S 30
SERVICE
1. To Remove the Turntable (5i79) (Fig.
90). The turntahle unscrews from the record
spindle (37140) (Fig. 90) hy turning the
turntahle counter·c1ockwise. If the main cam
(3869) (Fig. 93) turns hackwards, damage to
the starting lever release assemhly spring
may result. Hold the main cam while un·
screwing the turntable.
2. To Adjust Drive Pulley (3672) (Fig.
91). In case "wows" are heard in the repro·
duction, additional tension should he placed
on the turntahle drive hracket spring hy
turning the spring clip, which is held hy one
of the motor mounting screws (99.19·19)
(Fig. 91) so as to increase the tension on the
spring. On earlier models, it may he neces·
sary to bend the hairpin spring.
3. To Replace Drive Pulley (3672) (Fig.
91). Remove the hairpin cotler key (99-34.
12) (Fig. 91r) and the drive disk thrust
washer (50209) (Fig. 91). This permits the
removal of the turntable drive pulley. In
replacing this pulley, the long shoulder goes
toward the hase plate.
4 .. To Replace Turntable Driv'; Bracket
and Stud Assembly (64216) (Fig. 91).
Remove turrttahle drive pulley (see 92)
and remove screw (99-19·2) (Fig. 91) and
nut, locknut and washer under drive pulley.
In replacing this part (64216) (Fig. 91) he
sure the nut and locknut under the drive
pulley are set up so there is very little play
between the hase and the bracket (64216)
but the hracket should move sidewise freely.
Replace the drive pulley (See 92).
5. If Records Feed Incorrectly. Record
shelves may he out of line. Run changer
through its change cycle until the back rec·
ord shelves are in their lowest position.
Roller (4057) (Fig. 93) is on point C of main
cam (3869) (Fig. 93). The front shelves. do
not move during the cycle. With the shelves
in place for a 12" record, 10" shelves raised,
a straight edge from shelf to shelf should
just clear the shoulder near the top of the
record spindle (37140) (Fig. 91). The shelf
may he adjusted while in the lower position
by adjusting the four nuts holding the lower
link (54107) (Fig. 92). Care should be taken
not to run one nut farther than another ahd
so get the link out of line wi th the suppor t
rods (37138) (Fig. 92). The screw (99·20.45)
(Fig. 92) is to prevent the upper nuts on the
lowering link from hitting the main cam.
Probahly it will not require any adjustment.
6. Adjustment of Reeord Centering Pin
(34&10) (I<'ig. 91 and Fig. 94). The record
120
centering pin should clear the record spindle
(37140) (Fig. 94) by approximately fi".
When the record spindle is rotated hy the
turntahle,it will be seen the tip descrihes a
circle. When the tip is at that point in its
rotation where it is nearest the hack of the
record changer, the rear face of the tip.
should he exactly ;(4~ ahead of the rear face
of the record centering pin. When rotated,
the tip should leave and go back under the
centering pin in the same relative positions.
If it does not, it is necessary to spring the
centering pin sidewise until it does. If this
adjustment is made, check the other two
adjustments in this section.
7. Setting Tone Arm Drop. The needle
should drop on the record ahout V8" from
the edge. To adjust, make sure the record
changer is in the playing position, that is
the tone arm has moved over so that the
needle is on the record.
Set the hutton (66364) (Fig. 91) for ten.
inch records. Loosen screw (99-20.5) (Fig.
92) in the tone arm crank (54108) (Fig. 92).
Place needle on record V8" from edge.
Press tone arm return lever (64212) (Fig.
93) firmly against the main cam, holding
tone arm crank against side of square hole
away from record, at the same time hold
tone arm crank firmly against the collar
ahove it. Tighten set screw (99-20-5) (Fig.
92) making sure the tone arm still has a
lillIe up and down motion of the lift rod
(43182) (Fig. 92). Check the adjustment by
letting the record changer go through a cycle.
Load 12" records and set button (66364)
for 12".
Adjust screw (99-18.19) (Fig. 93) until the
needle drops properly on 12" records, ap·
proximately V8" from edge.
Never set for 12" records first and then
for 10" records as the 10" adjustment affects
the 12" setting.
8. Adjustment of the Record Trip.
Changer Will Not Trip. If the leject hut·
ton has no effect and the record changer will
not trip when the needle enters the change
grooves, see that the reject lever (46304)
(Fig. 93) is not caught on or behind the
starting le'ver release trip (64215) (Fig. 94).
The reject lever should he free to move, have
very little motion up and down and should
hi t the cen ter of the trip finger (46287)
(Fig. 93). The up and down motion of the
reject lever may be corrected hy tightening
the nut that holds it against the hase. Do not
tighten it so as to cause the lever to hind;
it must move freely.
If the changer will not trip when needle
enters change groove hut will change when
reject hutton is pushed, hend starting lever
trip spring (39226) (Fig. 94) towards motor
spindle gear. On £ecords where the recording
occupies only Va to Yz the available space, if
instrument fails to trip in change grooves,
it may he necessary to loosen the Bristol set
screw in the trip friction collar (43185)
(Fig. 92) and move the collar slightly. Use
6-32 Bristol wrench (6075) for this adjust.
ment. Turn the collar a small amount clock·
wise, when viewed from the bottom of the
changer. Check the operation of the changer
on standard records as it is possible to move
the collar too far.
Changer Trips Too Soon. If instrument
trips when only half the record has been
played, check the position of the starting
lever release trip spring (39226) (Fig. 94).
The dog, on the motor spindle gear (35102)
(Fig. 94) should throw the spring hack so
the starting lever release trip (64215) (Fig.
94) overlaps the starting lever (46288) (Fig.
94) approximately h". In case the overlap
is less, bend spring slightly toward the motor
spindle gear until proper overlap is secured.
If instrument trips near end of record: Set
needle I%;" from record spindle, loosen set
screw in collar, pin and set screw assembly
(66355) (Fig. 92), turn collar slightly coun·
ter·clockwise (viewed from hottom of
changer). This will decrease the tension on
the friction trip lever spring (39228) (Fig.
92); tighten set screw and check tripping
action on records again.
Adjustment of Trip Finger (42687) (Fig.
93). The trip finger must not ruh on the
base plate when tone arm is raised. It may
be bent slightly to clear base plate if neces·
sary.
The trip finger must move freely. If it
moves stimy or binds, tone arm cam (66366)
(Fig. 93) may he dropped slightly.
The trip finger stop (46293) (Fig. 93)
sh~uld he set exactly 2Yz" from outside of
base plate.
9. Adjustment of Tone Arm Height.
With a 10" record on the turntable, a stand.
ard needle in pickUp and 10" records in the
magazine, there should be approximately
%" clearance between the top of the pickup
and the bollom of the hottom record in the
magazine during the change cycle. This
clearance is adjusted by the screw (99·26.15)
(Fig:93).
Still with a 10" record on the turntable,
pickup in playing position, lift pickup off
record so that both brush and needle clear
record. The point of the needle should drop
three·fourths of the thickness of the record
below the top surface of the record. This
height is adjusted by bending the tone arm
support (64219) (Fig. 91).
I,',
I~.(
Ii
\'I{
I
I
I:
I
I
PHONO-R.ADIO
To adjust needle preR"Ure: Move tone arm
"0 all the hrush is on t he record but the
needle clears the edge. Adjust the hrush
(6725) (Fig. 91) by the screw in the pickup
head 80 the needle is halfway between the
top and bollorn faces of the record.
Care should he taken to see that there is
some slack in the pickup lead he tween the
pickup arm and hase. If the lead is too tight,
the needle will skip over the record instead
of stopping in the first groove.
10. To Remove Tone Arm. Loosen tone
arm crank screw (99-20-5) (Fig. 93); loosen
set screw in collar, pin and set screw assemhly (66355) (Fig. 92); loosen screw holding cord clamp at rear of tone arm; lift tone
arm straight up
(Fig. 92).
SER.VICE
DATA
• Section 5
Recover lift rod (43182)
erly. It may he necessary to hend the lever
to secure proper mesh.
n. Replacement of Crystal Cartridge.
On Farnsworth 530 changer, the entire cartridge, cord and plug m;'st he replaced.
On Capehart Panamuse, only the cartridge need he replaced.
14. A Squeak during the change cycle is
usually caused by a lack of oil on roller
(4058) (Fig. 93). A drop of oil placed on it
will usually cure it.
12. Removal of Main Cam. Remove turntahle according to directions in Section 1.
Remove nut (99-]4-5) (Fig. 91) which holds
main cam spindle. Pull record shelves down
and main cam will slip out. Reassemble in
the reverse order.
13. If Gears Jam, and changer won't cycle,
see that starting lever (46288) (Fig. 94) is so
positioned that when it engages with pin
(34309) (Fig. 94) the first teeth mesh prop-
Any rumhle occurring during the change
cycle hetween the motor spindle gear and
the main earn gear, can he minimized by
loosening the three screws (99-19-17) (Fig.
91) and properly positioning the motor
spindle. Retighten the screws.
GARRARD .... See Magnavox Models
Re5, RC8, RCIO,
RCn, RC50, and RC51
-4-6186
---5780
781 Complete
3-4-313
6636-4
Fig. 90
3167 Tone Arm Support
46286 Record Support, 12" Rear
3360 Needle Screw
46295 Record Support, 10" Rear
4639 Wire Clip
46300 Record Support Bracket, Front
5568 Record Support and Lowering Bracket
Assembly
50206 Grommet, Rubber
,
5779 Turntable
66349 Record Support Bracket Assembly,
Front
5780 Tone Arm
5781 Tone Arm, Complete
6725 Brush
34310 Record Centering Pin
34313 Tone Arm Hinge Pin
37140 Motor
Spindl~
54110 Tone Arm Support Housing
(Part of 6287)
66350 Record Support Plate and Pin Assembly
(Farnsworth)
66391 Record Support Plate and Pin Assembly
(Capehart)
66364 10 or 12 Stop Cam Knob (Late Production: 6069)
Decalcomanias: 50226 and 50227 used on late
production with Knob No. 6069.
99-19-18 8-32x /0" RHM Screw
99-22-35 6-32x ~" Bind. HM Screw
99-22-37 4-36x J.B" Bind. HM Screw
99-23-13 8-32x Vs" Hinge Pin Screw
Where (Capehart) appears -behind a part,
this part is used on Capehart Panamuse Instruments exclusively.
46284 Record Support Plate (Farnsworth)
43180 Record Centering Pin Nut
46330 Record Support Plate (Capehart)
46285 Record Support, 10" Front
66363 Reject Knob (Late Production: 6(69)
Where (Farnsworth) appears behind a part
this part is used on Farnsworth combinations
exclusively.
121
THE
Section 5 •
MY E
TECHNICAL
MANUAL
Fig. 91
2328 Crystal Pickup Only (Capehart)
715-1 Crystal Pickup, Lead and Plug Assem.
(Farnsworth) AK-59 Only
716-1 Crystal Pickup, Lead and Plug Assem.
(Farnsworth-76, 95, and 96)
3671 Motor Drive Pulley
3672 Turntable Drive Pulley
6725 Brush
34310 Record Centering Pin
34315 Record Support Hinge Pin
37140 Motor Spindle (Part of 6287)
39225 Idler Spring (Changed to 39245 on Later
Models)
39235 Spring-Pickup Wire Clip, Long
39237 Spring-Pickup Wire Clip, Short
43180 Record Centering Nut
46285 Record Support Front, 10"
46286 Record Support Rear, 12" (Part of
64213)
46295 Record Support Rear, 10'
46297 Record Support Front, 12"
46306 Drive Disk Bracket
50173 Tone Arm Bushing
50206 Grommet Rubber
50209 Drive Disk Thrust Washer
64216 Turntable Bracket and Stud Assembly
64219 Tone Arm and Bracket Assembly
66363 Reject Knob (6069 Used on Later
Models)
66364 10-12 Stop Cam Knob (6069 Used on
Later Models)
Decalcomanias Nos. 50226 and 50227
Used on Later Models With Knob
No. 6069.
I'
I;,
I,
,.
99-13- 6
99-14- 5
99-19- 2
99-19- 6
99-19-17
99-19-18
99-19-19
Hex Nut.
Ux28 Hex Nut
8-32xU' RHM Screw
8-32x~" RHM Screw
8-32xh" RRM Screw
8-32xh" RHM Screw
8-32xn" RHM Screw
99-2()"18
99-20-29
99-20-54
99-34-11
99-34-12
99-36-21
99-42-11
1()"32xU" RHM Screw
10-32x /t" RRM Screw
10-32x1 ~. RHM Screw
Hairpin Cotter Key
Hairpin Cotter Key
Washer
Turntable Stop Washer
I,
Fig. 92
37138
39224
39227
39228
43182
43185
45165
46288
46292
47124
50203
54107
54108
64215
Record Support Rod (Part of 64213)
Spring-Record Lowering
Spring-1)'ip Friction, Flat
Spring-Trip Friotion, Coiled
Tone Arm Lift Rod
Trip Friotion Collar, Upper
Friction Trip Lever
Main Gear Starting Lever
Tone Arm Lift Bracket
Base Plate
Trip Friction Drive-Cork
Record Lowering Link (Part of 63119)
Tone Arm Crank
Start Lever Release Trip and Hub
Assembly
66355 Collar, Pin and Set Screw Assembly.
Lower
99-14- 3 ~x28 Hex Nut
99-20- 5 1O-24x ~" RHM Screw
99-20-45 1()"24x2" RHM Screw
99-42- 5 Washer
122
I,
I,,',
'J
i:t
!'
PHONO-R.ADIO
SIR.VICI
DATA
• Section 5
42162
46287
46293
46304
64212
Fig. 93
3162
3868
3869
4057
4058
21151
21153
Main Cam Stud
Tone Arm 10-12 Stop Cam
Main Cam
Roller-Record Lowering (Part of 63119)
Roller-Tone Arm Lift
Motor-60 Cy., AC
Motor-50 Cy., AC
34308
34309
34312
35102
39229
39234
39236
Pin-Record Lowering (Part of 63119)
Pin-Motor Spindle Gear
Pin-Tone Arm Lift Lever
Motor Spindle Gear (Part of 6287)
Spring-Tone Arm Lift Lever
Spring-Tone Arm Return Lever
Spring-Reject Lever
Fig. 94
'4111
3869,
6287
34309
34310
35102
37140
39226
Main Cam
Spindle and Gear Assembly
Main Cam Starting Pin
Record Centering Pin
Motor Spindle Gear
Motor Spindle
Starting Lever Release Spring
462~8 Starting Lever
64215 Starting Lever Release Trip and Hub
Assembly
66359 Spindle Gear and Bracket Assembly
Shoulder Spacer
Trip Finger
Trip Finger Stop
Reject Levllr
Tone Arm Return Lever and Hub Assembly
66347 Tone Arm Lift Lever Assembly
66366 Tone Arm Crank and Clamp Assemby
66359 Spindle Gear and Bracket Assembly.
99-12- 1 8-32 Hej[ Nut
99-13- 3 10-24 Hex Nut
9943- 5 10-32 Hex Nut
99-18-19 6-32x n," RHM Screw
99-19-13 8-32x~" RHM Screw
99-20- 5 10-24x ~. RHM Screw
99-20-45 10-24x2" RHM Screw
99-26-15 10-32x~' RHM Screw
99-34-11 Hair Pin Cotter Key
99-34-12 Washer-~' ODx-hxH TH
99-36-14 Washer-Ji' ODx",x-h
7344--1 Gauge for AdjUsting 8-30
63119 Record Lowering Link Assembly, ,Complete
64213 12' Record Support and Shaft Assembly, Complete
34311 Shelf Pin 10'-12' Front and Rear Record SUpport Assembly
66351 Friction Trip Assembly, Complete
4949 Felt Washer for Motor Spindle
54109 Spindle Support'Bracket
6287 Motor Spindle and Gear Assembly
.,J
;
111\
14110 _ _
11140 - -_ _,"
123
THE
Section 5 •
MY E
Magnavox -
TECHNICAL
MANUAL
Model G 1
SERVICE
Operating Instructions
This record changer ,Plays seven 12" or
eight 10" records automatically. The last
record remains on the turntable and repeats
as long as the record changer is in operation.
Records may be repeated as often as desired by raising the record removing arm at
"A" (Fig. 95) to the upright position.
To reject a record and play the nex t record
below it, pull the latch lever at "L" (Fig. 95)
forward.
'
To adjust the record moving arm to
handle 10" records set the record removing
arm change lever at "D" (Fig. 95) opposite
the numher 10 stamped on the base plate.
For 12" records set the lever opposite the
number 12.
To adjust the pickup to play 10" records,
push the pickup stop at "K" (Fig. 95) back.
(Away from the pickup needle.) For 12"
records pull the stop forward (toward Ihe
needle) as far as it will go.
Some unils are equipI)ed with two speed
motors, and others with 78 rpm motors.
"hen the two speed motor is used change
from one speed to the other by simply moving lever at "F" (Fig. 95) to position desired.
To start motor, throw switch (supplied on
same models) at "N" (Fig. 95) on the "on"
position.
(Fig. 95) as far as it will go in the direction
of swing indicated by the legends "33~"
and "78" on the base plate.
'
If adjustment of the speed change lever is
required for any reason, proceed as follows:
First loosen the screw which clamps the
I~ver to the motor shaft. This shaft is proVIded with a screw-driver slot in the -end.
Next, uSing a screw driver, tnrn this shaft
in a clockwise direction until you feel it
strike the stop. The motor is now in the
"33%" Rpm. position. Now set the levllr
against the lug provided in the base plate
and opposite the legend "33~" and tighten
the clamp screw. This places the lever in the
correct position on the motor shaft. The
final step is the adjustment of the eccentric
hushing at "G" (Fig. 95) which limits the
throw of the lever. First loosen the screw
which holds the eccentric bushing. Next,
throw the speed change lever to its farthest
"78" Rpm. position, (using care that the
lever does not slip on the motor shaft).
Then turn the eccentric bushing around
until it touches the side of the lever, and
tighten it in place with the screw provided.
Trip Mechanislll
The trip mechanism is the trigger that
sets the record changer in motion. This is
done by allowing, the latch bar at "0" (Fig.
95) to drop in front of, and be actuated by
the cam at "P" (Fig. 95). This cam is drive~
by, the motor and is in motion as long as the
motor is running. If this mechanism does
not operate smoothly, the precautions outlined in succeeding paragraphs should be
observed. '
First of all, make sure that the square pin
in the latch lever at ",U" (Fig. 95) latches
properly in the notch in the lift lever a t "I"
(Fig. 95). When latched, the notch should be
engaged approximately one-half of its depth.
The depth of engagement is adjusted by
means of the eccentric washer and locking
screw at "}" (Fig. 95). Now run the record
changer through its cycle. If the square pin
fails to engage the notch in the lift lever,
first check the tension of the latch spring at
"II" (Fig. 95) to insure that the notch can
engage the pin. Next check the tension of
the reset spring at "E" (Fig. 95). This reset
spring should not be under tension when the
latch bar is latched but should have enough
tension when the latch bar drops back off of
the cam to cause the square pin to over
travel the notch in the lift lever. IMPORTANT
-Before attempting to change the tension
of any spring, be sure that the parts involved
work freely without any tendency to bind,
as of course any binding condition would
preclude proper operation.
The record changer is adjusted at the factory to trip on a spiral trip groove record
when the phonograph needle is I%;" from
the edge of the hole in the center of the
record.
'
When eccentric or oscillating trip groove
records are used, tripping is effected by
I
I'
1
I
Motor Lubrication
. The motor installed in the record changer
IS governor controlled, with all gearing enclosed, and leaves the factory lubricated for
pro~er operation. For maximum satisfaction,
lubrIcate the motor at regular intervals with
SAE No. 10 oil. Do not use any other
grade of oil.
The governor disc engages with a ring of
hard felt, This felt is impregnated with a
lubricating solution sufficient for proper operation for approximately a year under
normal c~nditions. It may be necessary,
however, If the motor shows a tendency to
chatter or waver, to apply a drop or two of
oil to this felt ring.
~
I,
Motor Speed
The motor speed is adjusted by means of
,a lever at "C" (Fig. 95) which is mounted
under the turntable. The direction of swing
to fast or slow is indicated by the legends
"F" and "S" on the base plate.
o
33 1/3 RPM-78 RPM Shift
\
(Two-speed Illotors only)
Move the speed change lever at
124
"Jf"
FIG. 95
,I
PHONO-RADIO
means of the hardened steel pin in the end of
tone arm lift crank at "S" (Fig. 96) engaging
the serrated block on the trip lever at "T"
(Fig. 96). There must be a minimum of b"
play between the end of the pin and the
block, when, with a short needle, (%" minimum length) the pickup is resting on one
record on the turntable. If the pressure of
the pin on the block is not sufficient to insure
operation, then check the pressure spring
which is located up under the pickup.
The oval head pivot screw at "R" (Fig.
95) serves as a pivot for the lift lever at "I"
(Fig. 95). This screw should allow the lift
lever to be raised by the latch bar to its
FIG.
DAfA
SE,RVleE
from the top of this record down to the base
plate. This distance should be one inch. Now
by pulling the reject lever at "L" (Fig. 95)
first, it will be found possible to swing the
record removing finger at "Y" (Fig. 97) ov'er
to where it just touches the edge of the
record. If the adjustment is correct, the
record removing finger should just barely
rise over the edge of the first record. If adjustment is required it can be made by
means of the stop screw at "Q" (Fig. 97). In
the event the record removing arm raises the
record from the turntable and drops it back
in place without removing it, check the lift
adjustment at "V" (Fig. 95). This adjustment consists of an eccentric stud which is
provided with a locknut, and is made by
loosening the locknut and turning the eccentric stud. The lift adjustment should be
set so that the hole in the cellter of the record
just clears turntable spindle when the record
changer is in operation.
96
maximum height without binding but also
without any additional play.
If the record changer fails to trip, see if
the phonograph needle is jumping out of a
worn record trip groove. Next make certain
that all parts of the mechanism work freely
and smoothly. If it is found that the latch
bar at "0" (Fig. 95) is not dropping in far
enough to engage the cam at "P" (Fig. 95),
then check the tension of the trip spring at
"B" (Fig. 95).
FIG.
98
Pickup Lowering Mechanism
The pickup lowering mechanism has two
functions. First, it lowers the phonograph
• Section 5
needle gently to the surface of the record.
Second, it feeds the needle toward the center
of the record so that it will enter the playing
groove.
If the pickup descends too fast or too
slow, adjust the speed of descent by turning
the knurled thumb nut on the dashpot sleeve
at "w" (Fig. 96).
The unit is adjusted at the factory so that
the needle will be set down approximately
%" in from the edge of the record. An adjusting screw is provided on the side of the
pickup at "M" (Fig. 96). If the needle is
being lowered onto the playing surface of the
record, and the adjusting screw at "M"
(Fig. 96) fails to correct the condition proceed as follows: First stop the record changer,
with the pickup in the maximum raised position and check the clearance between the
underside of the pickup shelf at "Z" (Fig.
96) and the tip of the dashpot. This clearance should be very small as otherwise the
pickup will tend to hounce as it is lowered.
There must be sufficient clearance however
to prevent the pickup shelf from rubbing on
the tip of the dashpot, or the pickup will not
swing out far enough to allow the adjustable
stop at "K" (Fig. 96) to come to rest against
the dashpot. Check this clearance in both
10" and 12" record positions. If adjustment
is required, the height of the dashpot may be
regulated by loosening the nuts on the bottom of the lift lever stud at "X" (Fig. 98)
and changing their position on the stud. To
raise the dashpot turn the nuts clockwise, to
lower the dashpot turn the nuts counte~
clockwise. Be sure to lock the nuts tightly
together after the adjustment is made.
Models RC5, RC8, RClO, RCn, RC50, RC5l, (Garrard)
FIG. 97
Similarity of service and illustrative material for these models has made it
possible to combine certain portions of the text for more rapid reference. A
table has been prepared to indicate the correct portion of the text for each
model.
If, for instance, it is desired to study the service methods for adjusting speed
on the model RC8, simply look under "Speed Adjustment"-follow this column
until it intersects the column beaded RC5, R~8 and the reference is found to
be' paragraphs AlO, and All.
Record Removing Mechanism
The record changer is adjusted so that it
will always leave one record on the turntable. This is done to prevent the phonograph needle from damaging the covering
on the turntable.
In case the record removing mechanism
fails to operate smoothly, proceed as follows:
First make certain that all parts work freely
with no binding in pivots or bearings, and
that the record removing arm assembly rests
on the stop screw at "Q" (Fig. 97). Next
stop the motor in such a position that the
latch bar at "0" (Fig. 95) can swing by and
clear the cam at "P" (Fig. 95). Place just
one record on the turntable and measure
Operating Instructions . .................. .
AutoJDatic Trip ........................... .
Operation of AutolDatic Trip .............. .
Striker Adjustment ............. , ......... .
Friction AdjustD1ent ..................... .
Oversize Records . ......................... .
Pickup Arm Adjustment ....... ,., ........ ,
Pickup Arm Adjustment ....... , ..... , ... ,
Aut.omat.ic St.op . ......................... .
Speed Adjustm.ent ............. , .......... ,
Irregular Speed ....... , .............•......
Lubrication of AC Motor .................. .
Universal Mot.or . ......................... .
Aut.oDlatic Switch . ...................... .
Record Dropping ......................... .
Binding .. , ...... , ........ , ...... , ... , ..
Pickup, ...............................
ReDloving Changer . ......................
Replacing Tone Arm Baae ... ..............
.
,
.
.
Models
RC5, RCS
Models
RCIO, RCll
Models
RC50, RC5I
Al
A2
A3
A4
A5
A6
A7
A8
A9
AIO, All
Al2
Al3
AI4
AI5
A16, A19
Al
A2
A3,B3
A4
A5
Bl
A2
A3,C3
A4
A5
B6
A7
B8
A9
AIO, Bll
·A2i.~·A22·
A23
A24
····87····
CS
B9
AIO, BIl
Al2
Al3
Al4
·Bi.6~·Ai9·
. .. Ai:i ...
Al4
C3
A16, A17,
A18, Al9
A20
A21, B22
B23
125
THI
Section. 5 •
AI. This record changer plays eight 12"
records or eight 10" records (not intermixed)
automatically, and the changer stops oper.
ating after the playing of the last record. A
record may be rejected before playing the
entire selection by turning the right.hand
knob on the motorboard to the REJECT
position.
.
To operate the changer, first turn the left.
hand knob on the motorboard 80 that the
indicator is pointing to the 10" or the 12"
designation, depending on the sil'le of the
records to be played. With the record spindle
in position-angling section toward the rec·
FIG. 99
MY I
MANUAL
done by rotating the mQtorbollrd knob to
the STOP position.
A2. The automatic trip plays lin important
part in the operation of the reco~d changer,
and upon the certainty of the automatic trip
coming into action depends the whole opera·
tion of the record changer. The automatic
trip mechanism will operate on all makes of
records having a "run·off" groove, either
eccentric or spiral.
A3. The trip lever "A" (Fig. 99) is connected
to the pickup arm through a series of levers
and is moved forward towards the main
spindle a distance proportional to the ad·
vance made by the pickup. The striker arm
"B" (Fig. 99) is fiUed on the main spindle in
order to push back the trip lever, preventing
the automatic trip from functic;ming while
the record is being played. When the pickup
reaches the end of the playing grooves and is
carried into the "run·oW' grooves, the move·
ment transmitted to the trip lever is too
great to allow its being pushed back by the
striker arm. The striker arm then contacts
the metal trip lever which in turn operates
the changing mechanism.
B3. If the trip mechllnism does not operate
at the end of some records, projection "A"
should be bent towards point "c" on lever
"B" (Fig. 103) so that when the mechanism
is in the p,laying position (and the chan~er
stopped), the tone arm mlly be moved In.
wardly to a point where the needle is 1711"
from the edge of the motor spindle.
ca.
Old platform-place from one to eight rec·
ords of either the 10" or 12" type on the
record spindle. Rotate the right.hand knob
on the motorboard to the START position,
placing the changer in operation.
T.CHNICAL
If the automatic switch does not op·
erate at the end of the last record, make
certain that all of the levers are free and that
all the springs are in place. Also ;Qake certain
that the turntable 8pindle is frec in the mdin
spindle-it should move about Ya" when
depressed and should rise the same distance
when released. This" test should be made
while the changer is in the playing position.
Switch tripping adjustment can be obtained
by means of a small quadrant adjustment on
the top of the spindle operated by lever
"P" (Fig. 100).
A4. The correct functioning of the trip
mechanism depends on the rubber bushing
"H" (Fig. 99), on the tl'ip lever arm "G."
When the bushfng becomes badly worn, a
tapping sound will hecome apparent, and
the trip lever may operate before the end of
the record. This con!fition may be correeted
by turning the rubber bushing on the spindle
in order to present a new surface to the
striker arm "B."
A5. If the changer fails to operate at the
end of a record, the record apindle should be
removed and the turntable lifted from the
motor shalt so that the friction adjusting
screw "E" (Fig. 99) may be readjusted. Before adjusting this screw it is advisable to
make certain that the operating trip lever
"A" is not rubbing on the base plate, setting
up additional friction. To adjust the friction,
give the friction adjusting screw "E" a small
turn in a counter-clockwise direction to in.
crease the friction. If the changer 'trips be·
fore the pickup has reached the end of the
playing grooves, or if a humping noise is
heard in the speakers, the friction adjusting
screw should be turned in a clockwise direc·
Bl. Models RC.50 and RC-51 play eight
10" and 12" records, intermixed in any
order, automatically, and the changer stops
operating after the playing of the last record.
A record may be rejected hefore playing the
entire selection by turning the motorooard
knob to the REJECT position.
To operate the changer, raise the forked
arm and place IIny number of records-not
exceeding eight--on the record spindle and
lower the forked arm until it rests on the top
record. Turn the pickup head one·half turn
in a counter-clockwill6 direction lind in.ert a
phonograph needle, returning the pickup to
itll normal position. The needle IIhould be
inserted onl, when the IIrm is locllted on the
rest, a8 movement of the arm when it is in
IIny other position may affect the mechllrusm.
Tum the motorboard knob to the START
position, setting the changer in operlltion.
Be lIure to hold the knob in' this position
until the motor has started and becomes
engaged with the changer mechanism.
Should the changer be stopped for any
reason during, the record changing, it may
be necessary to give it help in restarting hy
turning the turntable by hand, due to the
excessive load imposed on the motor when
it is stopped in such a position. If it is desired
to stop the motor at any time, it may be
126
:\
PHONO·RADIO
tion to decrease the friction. This adjustment is very sensitive and the screw should
be turned not more than a quarter of a turn
at one time.
A6. The record platform, opposite the pickup arm on the motorboard, is normally adjusted to the correct position for all average
records, however if a very large or small
record is encountered, it may be necessary
to make a slight adjustment to the platform
position to accommodate these records. This
is accomplished by removing the nut, washer,
and screw "K" (Fig. lOlA) and turning the
bushing "L" clockwise to accommodate
larger records, and counter-clockwise for
smaller records. Replace the screw, washer,
and nut and check the .platform position by
placing a record on the spindle. If it is correct
the record edge should rest on the platform
just clear of the studs when the changer is in
the playing position.
B6. The record platform, opposite the pickup arm on the motor board is normally adjusted to the correct position for all average
records, however if a very large or small
record is encountered, it may be necessary
to make a slight adjustment to the platform
position to accommodate these records. This
is accomplished by removing the nut, washer,
and screw "Q" (Fig. 100), and turning bush.
ing "N" clockwise to accommodate larger
records and counter-clockwise for smaller
records. Replace the screw, washer, and nut,
and check platform position by placing a
record on the spindle. If it is correct the
record edge should rest on the platform just
clear of the pushing pawl, "12" (Fig 1(4),
SERVICE
when the changer is in the playing position.
A 7. Should the lowering position of the
needle require adjustment, the turntable
should first be turned by hand to bring the
pickup from the loading position to the
point where the needle has descended to
within
of the record. The screw "R"
(Fig. 102) which is accessible through a hole
in the motor board, should be turned either
to the right or to the left according to the
requirements-a quarter turn in either direction will give the maximum adjustment
obtainable. The adjustment should then be
checked by operating the changer and noting
the lowering position of the pickup.
ro"
B7. Should the lowering position of the
needle require adjustment, the turntable
should first be turned by hand, after the
STOP-START lever has been set to the START
position, to bring the pickup from the loading position to the point where the needle
has descended to within
of the record.
If it is seen that the lowering position must
be shifted either to the left or to the right,
the tone arm should be returned to the
"rest" p'osition by hand, at which time the
adjustable screw, whICh is accessible through
a hole in the motorboard near the tone arm
base, should be turned either to the right or
to the left according to the requirements-a
quarter turn in either direction will give the
maximum adjustment obtainable. The adjustment should then be checked by operating the changer and noting the lowering
position of the pickup.
ro"
A8. When making adjustments to the pickup arm, it should never be forced into posi-
DATA
• Section 5
tion, and when the turntable is turned by
hand it should never be turned other than in
a clockwise direction. If the pickup is lowered so that the needle contacts the smooth
surface of the record and does not run into
the playing grooves, check to make certain
that the motorboard is tilted slightly to the
left. Then check the lead to the pickup,
making certain that it is not twisted in any
way to prevent free movement of the tone
arm. Also check levers "S" and "Q" (Fig.
102) to see that they are free and that the pin
at the eRd of lever "Q" i~ not rubbing on the
bottom of the cam grooves. If required, the
pickup height can be adjusted by looseniug
the set screw in the counter-balance weight
"MOO (Fig. 100), and turning the weight while
holding the spindle. If this adjustment is
changed, see that the tone arm lifts high
enough to clear eight records on the turntable.
B8. If, after the playing of the last record
(when eight are played), the needle scrapes
across the surface of the top record as the
tone arm moves to its rest position, the
pickup height must be adjusted in the following manner. Loosen screw "8" (Fig. 102),
and rotate the counter-balance "7" a few
turns in a clockwise direction. The adjustment should be such that at the completion
of the last record, the pickup will move
across the top record with the needle at
least one-half inch above the surface of the'
top record. Tighten set screw "8", completing the adjustment.
CS. If the pickup is lowered so that needle
contacts the smooth surface of the record
and do~s not run into the playing grooves,
check to make certain that the motorboad
is level or tilted slightly to the left as ad·
justed at the factory. Then check the lead to
the pickup, making certain that it is not
twisted in any way to prevent free movement of the tone arm. If the needle scrapes
across the surface of the last record at the
completion of the playing of that record, the
pickup height requires adjustment. Loosen
the set screw in the collar at the bottom of
the pickup arm, lift the spindle and turn the
collar while holding the spindle. A few turns
in a counter·clockwise direction should be
sufficient. Tighten the collar set screw, completing the adjustment.
If the tone arm lowers to the record and
then immediately returns to the rest, it is
possibly due \0 the fact that the STOP-START
lever at the right side of the motorboard is
rubbing on the under side of the motorboard,
preventing the clutch from disengaging.
Bend the lever downward so that it operates
freely.
A9. The record changer automatically stops
after the last record has been played due to
the fact that there is no longer any weight
on the turntable spindle. The weight of a
127
Section 5 •
THE
MY E
TECHNICAL
MANUAL
the oil-retaining type, and with average use
will require lubrication about once every
three months. All oiling holes are accessible
when the turntable is lifted from the motor
spindle and are indicated on Fig. 99. A
few drops of fine oil may be helpful in the
tone arm pivot, if the tone arm shows signs
of sluggishness in moving into the playing
grooves after it has lowered to the record.
i' ,
I I..I' · , ;
I:
A14. The lubrication and speed adjustment
for the universal (AC-DC) motor is the same
as for the AC motor. If the brushes are allowed to become dirty and worn, brush
noise will develop. The brushes may be removed by unscrewing the bakelite caps on
the motor body and pulling out the brushes
by means of the springs. The brushes can be
cleaned by sanding them with a fine grade
of sandpaper or crocus cloth and cleaning
the dust from the surface before replacing
them. It is important that the brushes be
replaced in the same way in which they were
originally installed. The brushes when new
are -to" long under the springs-when they
have worn down to %", they shonld be
replaced.
record on this spindle moves lever "0"
(Fig. 100), which interrupts the movement of
the switch lever "P" (Fig. 100) from the cam,
so preventing the switch from operating.
When the record is removed from the center
spindle, the spindle raises and allows lever
"0" to move so that it does not interrupt the
switch lever "P," thereby allowing the
switch to operate.
B9. The record changer automatically stops
after the playing of the last record, due to
the fact that there is no longer any weight
on the turntable spindle. The weight of a
record on this spindle moves lever "J" (Fig.
101), which interrupts the movement of the
switch lever "K" (Fig. 101) from the cam, so
preventing the switch from operating. When
the record is removed from the center
spindle, the spindle raises and allows lever
"J" to move so' that it does not interrupt the
switch lever "K," thereby allowing the
switch to operate.
A10. Due to the differences of line voltages
in various localities, a slight adjustment of
the speed indicator lever (that projects from
the edge of the turntable) may be necessary.
To make this adjustment, first set the motor
speed to 78 Rpm., using the stroboscope
disc (on AC models) furnished with the unit.
To set the speed on the AC-DC unit. operating on direct current, place a piece of
paper under a record on the turntable and
count the revolutions in a period of 30
seconds. If there are more or less than 39
128
revolutions the speed adjustment lever
should be moved a slight amount in the required direction, and the process repeated.
All. After the motor has been set at 78
Rpm. the turntable should be removed and
the quadrant screw (near the spindle on the
speed-control lever) should be loosened very
carefully and the lever moved until the
pointer is in position on "78" on the indicator plate, holding the quadrant stationary while making this adjustment. Now
tighten the quadrant screw and replace the
turntable.
BU. After the motor speed has been set at
78 Rpm., the turntable should be removed
and the set screw in the collar of the speed
control lever should be loosened very carefully. The speed control lever should be
moved until the knob is in position on the
center mark of the escutcheon. Now tighten
the set screw. Be sure that the screw stud
does not move during this adjustment.
A15. If the automatic switch does not operate at the end of the last record, make
certain that all of the levers are free and that
all the springs are in place. Also make certain
that the turntable spindle is free in the main
spindle--it should move about Ys" when
depressed and should rise the same distance
when released. This test should be made
while the changer is in the playing position.
Switch tripping adjustment can be obtained
by means of a small quadrant adjustment on
the top of the spindle operated by the switch
lever "P" (Fig. 100).
A16. If the first record does not drop when
the changer is switched ON, this is due to the
leather brake pad becoming worn and not
braking the turntable sufficiently when the
previous record was completed. To adjust
this pad, loo,sen the two screws "F" (Fig. 99)
and turn the brake lever slightly to bring the
leather pad nearer to the turntable rim.
Tighten the screws and check to see that the
switch breaks contact before the leather
brake pad touches the turntable rim.
e
A12. If an occasional "slowing up" is noticed
in the reproduction, the trouble is most
likely due to the record slipping, due to its
being warped. If a record slips while it is
being played, examine the center hole for
burrs. These burrs should be carefully removed with a penknife. Warped records
may be flattened by subjecting them to a
warm temperature and pressing them.
A13. The motor should always be "elilubricated, as noise will develop if the bearings
are allowed to run dry. All bearings are of
FIG. 102
I~
P H 0 N 0 - I A D I. 0
SEIVleE
DATA
• Section 5
one record to feed to the turntable at one
time, depending on the direction of the bend.
Extreme care should be tlSed in bending the
sl?indle back into position, should this be·
come necessary, as it may be broken very
easily.
-
=--
A20. If the mechanism should bind during
operation, it may he possible to free it by
depressing the pushing pawl "12" (Fig. 105)
FIGURE 103
BEND LEVER"A" SIDEWAYS TOWARD"B"APPROXJMATELYII16'
AT THE SAME: TIME BEND IT OUT SO THAT IT CONTACTS
"B"NEAR THE CORNER"C~
B16. If the first record does not drop when
the changer is switched QN, this is due to the
leather brake pad becoming worn and not
braking the turntable sufficiently when the
previous record was completed. To adjust
this pad, loosen the screw "F" (Fig. 99) and
turn the brake pad slightly to present a new
surface to the turntable rim. Now tighten
the screw "Ji''' and L-heck the adjustment.
A17. If the records do not drop properly, it
is possible that the forked arm is sprung to
the right, preventing the pushing pawl "12"
(Fig. 105) from pushing the records from the
platform. To correct this condition, spring
the foeked arm to the left a slight degree and
check to make certain that the bottom rec.
ord contacts the smooth surface of the
record platform. The vertical motion of the
record platform may he controlled by adjust.
ating the mechanism. If the motion of the
platform is still not sufficient to push the
records to the turntable; the bushing should
be turned a few revolntions to further
lengthen the lever arm, however, it is not
probable that a second adjustment will he
required.
A19. Occasionally a record may stick to the
spindle and not drop to the turntable as it
should. The record may be excessively thick
and must be removed from the stack. The
reason for the "thick" record sticking is that
the slot at the angle in the spindle is not
sufficiently wide to let the record slide into
place. Never attempt to file this groove as it
will then be possible for two "thin" records
to drop to the turntable at one time.
If the spindle should be hent, it will
either cause records to stick, or more than
and allowing the pickup to come to the rest
position. Tum off the motor and slide the
nameplate that covers the mechanism in the
record platform from its holder, exposing a
small set screw in a stop lever. Loosen the
set screw and move the stop forward a slight
amount. Tighten the set screw and check
the adjustment. If the mechanism still binds,
the stop lever should be advanced a little
more. This position is quite critical and the
lever should not he moved more than -I."
during each adjustment. If the mechanism
should bind as a result of the turntable being
rotated manually, it is probably caused by
the fact that the motor end.hearing has been
forced from its correct position in the end of
the motor frame, allowing the motor gov.
ernor set screws to strike the main gear of
the motor. To correct this conditiOll, loosen
the small set screw that holds the motor e&d.
bearing in place---located adjacent to the
nameplate on the motor frame-press the
bearing in as far as it will go. and tighten
the set screw. This adjustment should per.
mit the motor to operate properly, however,
if it still binds it may be necessary to loosen
this set screw again, rotate the end.hearing
a fraction of a turn and tighten the set screw.
This adjustment may be necessary to keep
the spacing around the armature equal at
all points.
A21. If the quality of reproduction is di&torted, or if the volume of the signal is unusually low, it may be due to a defective
ing the bushing "V' (Fig. 100), after the
nut, screw, and washer at ••K." have been
removed.
A18. If the records do not feed properly
from the spindle, it is possible that the hori·
zontal motion of the record platform is not
llufficient to push the lower record from the
stack on the spindle to the turntable. To
increase the distance of motion, the lever
arm with bushing "N" must be lengthened
by removing the nut and screw "Q," sliding
the bushing "N" from the lever and rotating
the bushing a few turns in a counter-clock.
wise direction. Slide the bushing back to the
lever and install the nut and screw "Q" in
place. Now check the adjustment by oper.
'3
~-~~~~"~ ~ ;(
... ..
lFiG.10~
129
Section 5 •
THI
MY I
TICHNf'CAL
'M A N U A L
crystal pickup. If no signal is heard when the
pickup is used and the radio is operating
,properly, it is probable that the pickup lead
is broken or shorted on the pickup arm. ,
II
A22. To remo'\>e the pickup cartridge assembly. remove screw "I" (Fig. 104) and
pull the cartridge from the arm, examining
the connections to the bakelite terminal
block. To remove the cartridge from the
assembly, remove the two retainer plates
"2" and "3" (Fig. 1(4), and Unsolder the pigtail connections from the bakelite block.
:/
I,',',
I
I'
I,
II,!,
I~
!,
i
B22. To remove the pickup cartridge as·
sembly, remove screw "I" (Fig. 105), and
pull the cartridge from the arm, examining
the connections to the bakelite terminal
block. To remove the cartridge from the
assembly, remove the two retairler plates
"2" and "3" (Fig. 105), and slide the cart·
ridge from the housing.
C22. To remove the pickup cartridge as·
sembly, remove the four screws securing the
cartridge rj'ltainer plate and pull the cartridge
from the arm, examining the connections to
the bakelite terminal block. Pull the plugs
from the bakelite block to free the cartridge
from the arm.
A23. When removing the record changer
unit from the cabinet, first remove the two
connecting co.zds from the radio chassis by
withdrawing their plugs from the sockets.
Disconnect the ground, lead from the radio
chassis by sliding the spade lug from the
securing screw that has been loosened a few
turns. Remove the nuts and springs from the
four mounting screws and lift the unit from
the cabinet. When replacing the mechanism,
be sure that the heavier springs are used on
ibe top of the mounting cleats and the
lighter springs on the' bottom. The changer
should be tilted slightly to -the left, 80 that
the needle will slide into the first grooves of
the record easily.
When replacing the pickup lead plug in the
chassis (on Windsor style numbers CPAR.
320, and CPAR-352 and on Regent style
numbers CPAR-319, CPAR-329 and CPAR356), be sure that the felt ~asher is used
to prevent the metal cap of the male plug
from contacting the radio chassis. If this
rule is not observed, a distinct hum will be
heard in the speakers when the phonograph
is used.
B~.
When removing the record changer
unit from the cabinet, first remove the two
connecting cords from the radio chassis by
withdrawing their plugs from the sockets.
130
I':
FlO) 105
Remove the nuts and springs from the four
mounting screws and lift the unit fr<;lm the
cabinet. When replacing the mechanism, be
sure that the heavier springs are used on the
top of the mounting cleats and the lighter
springs on the bottom, being careful to
mount the unit so that the turntable is
perfectly level.
after the plug has been unsoldered from the
lead.
C23. When removing the record changer
unit from the cabinet, first remove the two
connecting cords from the radio chassis by
withdrawing their plugs from the sockets. If
the metal motorboard of the changer is secured to a wooden sub-base and the entire
assembly "floated," remove the nuts and
springs from the four mounting screws in
the wood sub-base and lift the unit from the
cabinet. If the metal motorboard has beenI
"floated" in the cabinet, remove the nuts
and springs from the mounting screws and
remove the changer in the same manner as
described above. When replacing the mech·
anism, be sure that the heavier springs are
used on the top of the mounting cleats and
the ~ighter springs on 'the bottom. The
changer should be tilted s~ightly to the left
SO that the needle will slide into the first
groove of the record easily.
4. Remove the screw from the casting and
rotate the base 180 degrees exposing another
screw which should be removed from the
casting.
A24. If the bakelite tone arm base should
need replacement, it can be removed by
following the instructions outlined below:
1. Loosen the small set screw "4" (Fig.
104), and punch the pivot pin "5" from the
tone arm using a small punch and ha~er.
2. Lift the tone arm from the base "6"
and pun the pickup lead up from the bottom,
3. Remave the two mounting screws that
secure the tone arm base to the motorboard,
and rotate the base until the large hole in
the rear of the base is directly over a screw
in the casting beneath the motorhoard.
5. Slide the assembly to the rear of the
hoard, removing the lever pins from their
guide slots.
6. Remove the counter-balance weight
"7" by firs t removing the s~t screw "8" and
then turning the weight in a counter-clock.
wise direction until it drops from the shaft.
7. Now loosen the set screws in the bushing "s" and remove the lever arm from the
shaft, holding the assembly over a small box
so that the ban bearings will not be lost.
S. Slip the casting from beneath the base,
off the shaft and replace the bakelite base.
There are fifteen bearings above and fifteen
bearings below the base, that should be replacell before the assembly is reassembled.
9. Reassembly of the unit is not difficult,
however the counter-balance "7" will reo
quire adjustment to allow proper lowering
of the tpne arm to the record. Instructions
for this adjustment are given in paragraph
AS.
PHONO-RADIO
R ( A-
SERVICE
DATA
top of record shelf, the vertical spacing between the knife, in its lowest rotational
position, and the shelf, is .072-.078 inch.
Models RP139A and RP14S
SERVICE
A. Main Lever. This lever is basically im·
portant in that it interlinks the various
individual mechanisms which control needle
landing, tripping, record separation, etc. Ro.
tate the turntable until the changer is outof-cycle; and check rubber bumper bracket
(A). The roller should clear the nose of the
cam plate by approximately -h inch.
B. Friction Clutch. The motion of the
tone arm toward the center of the record is
transmitted to the trip pawl "22" by the trip
lever "7" through a friction clutch "5." If
the motion of the pickup is abruptly accelerated or becomes irregular due to swinging
in the eccentric groove, the trip finger "7"
moves the trip pawl "22" into engagement
with the pawl on the main gear, and the
change cycle is started. Proper adjustment
of the friction clutch "5" occurs when movement of the tone arm causes positive movement of the trip pawl "22" without tendency
of the clutch to slip. The friction should be
just euough to prevent slippage, and is adjustable by means of screw "B." If adjustment is too tight, the needle will repeat
grooves; if too loose, tripping will not occur
at the end of the record.
C. Pickup Lift Cable Screw. During the
record chauge cycle, lever "16" is actuated
by the main lever "IS" so as to raise the
tone arm clear of the record by means of the
pickup lift cable. To adjust pickup for proper
elevation, stop the changer "in-cycle" at the
point where pickup is raised to the maximum
height above turntable plate, and has not
moved outward; at this point adjust locknuts "c" to obtain 1 inch spacing between
needle point and turntable top surface.
D. & E. Needle Landing on Record. The
relation of coupling between the tone arm
vertical shaft and lever "20" determines the
landing position of the needle on a 10 inch
record. Position of eccentric stud "E" governs the landing of the needle on a 12 inch
record; this, however, is dependent on the
proper 10 inch adjustment.
To adjust for needle landing, place 10 inch
record on turntable; push index lever to
reject position and return to the 10 inch
position; see that pickup locating lever "17"
is tilted fully toward turntable; rotate mechanism through cycle until needle is just ready
to land on the record; then see that pin "V"
on lever "14" is in contact with "Step T" on
lever "17." The correct point of landing is
4% inches from the nearest side of the turntable spindle; loosen the two screws "D" and
adjust horizontal position of tone arm to
proper dimension, being careful not to disturb levers "14" and "17." Leave approximately -i> inch end play between hub of
lever "20" and pickup base bearing, and
tighten the blunt nose screw "D"; run mechanism through several cycles as a check, then
• Section 5
tighten cone pointed screw "D."
After adjusting for needle landing on a
10 inch record, place 12 inch record on turntable; push index lever to reject and return
to 12 inch position; rotate mechanism
through cycle until needle is just ready to
land on the record; the correct point of
landing is 5% inches from nearest side of
spindle. If the landing is incorrect, turn
stud HE" until the eccentric end adjusts lever
"14" to give correct needle landing. The
eccentric end of the stud must always be
toward the rear of the motor board, otherwise incorrect landing may occur with 10
inch record!!.
F. & G. Record Separating Knife. The
uppeJ plate (knife) "25" on each of the
record posts serves to separa!e the lower
record from the stack and to support the
remaining records during the change cycle.
It is essential that the spacing between the
knife and the rotating record shelf "27" be
accurately maintained. The spacing for the
10 inch record is nominally .055 inch, and
for the 12 inch record is .075 inch.
To adjust, rotate the knife to the point of
minimum vertical separation from the record
shelf and turn screw and locknut "F" to give
.052-.058 inch separation. Screw "G" must
not be depressed during this adjustment.
After setting screw "F," adjust screw "G"
so that when its tip is depressed flush with
H. Record Support Shelf. The record
shelf revolves during the change cycle to
allow the lower record to drop onto the turntable. Both posts are rotated simultaneously
by a gear and rack coupled to the main lever
"IS," and it is necessary that adjustment be
such that the record is released from both
shelves at the same instant. To adjust, place
a 12 inch record on the turntable, rotate
mechanism into cycle to the point where
both separating knives have turned clockwise as far as the mechanism will turn them;
lift record upward until it is in contact with
both separating knives. Then loosen screws
"H" and shift record shelves "27" so that
the curved inner edges of the shelves are
uniformly spaced approximately -h inch
from the record edge. Some backlash will be
present in the rotation of these shelves. They
should be adjusted so that the backlash
permits them to move away from the record
but not closer than the approximate -h inch
specified above. Tighten the blunt nose
screw HR," run mechanism through cycle
several times to check action, then tighten
cone pointed screw "H."
If record shelves or knives are bent, or not
perfectly horizontal, improper operation and
jamming of mechanism will occur.
J.
Tone Arlll Rest Support (not shown).
When the changer is out-of-cycle, the front
lower edge of the pickup head should be fo
inch above surface of motorboard. This may
be adjusted by bending the tone arm support
bracket, which is associated with the tone
arm mounting base, in the required direction.
FIG. 106
131
THI
SectIon 5 •
K. Trip Pawl Shop Pin. The position of
the trip pawl stop pin "K" in relation to the
main lever "15" governs the point at which
the roller enters the ~am. By bending the pin
support either toward or away from trip
pawl bearing stud, the roller can be JIlade to
enter the cam later or earlier, re~pectively.
This adjustment should be made so that the
roller definitely clears the cam outer guide as
well as the nose of the cam plate.
Lubrication. Fetrolatum or petroleum jelly
should be applied to cam, main gear, spindle
pinicm gear, and gearR of record posts.
Light machine,oil should be used in the
tone arm vertical bearing, record post bear.
ings, and all other bearings of various levers
and pulleys on underside of motor board. The
turntable spindle bearing of RP·145 must be
lubricated from the top of the motol'lboard.
Using an oil can with a long spout, reach in
between the turntable and motorboard and
apply oil directly to the spindle.
On Model Rp·139·A apply a few drops of
light machine oil (SAE·IO) to the motor oil
hole adjacent to the spindle bearing after
each 1,000 hours' of operation. Tbe oil hole
has a screw plug.
Do not allow oil or grease to come in con·
tact with rubber mounting of tone arm base,
rubber bumper, rubber spindle cap, or rub·
ber parts of friction drive mechanism of
Model RP·145.
MY I
TECHNICAL
MANUAL
E. Adjust at "EO. to provide approximately
-h of an inch between outer end of "Liuk
Slot" and screw when rubber "Bumper" is
ir. contact with stop bracket.
F. and G. Remove rubber silencer at "F"
and adjust "F" and "G" so ejector tip "F"
is in line with "Spindle." Longitudinal move·
ment, with respect to "Ejector Arm," may
be effected by loosening hex. head at "F."
Lateral movement of "Ejector Arm" may
be effected by adjustment "G."
H. Adjust "H" so under side of pickup head
can be raised 2Yz inches above motorboard.
J. Adjust screw "J" until friction will just
force "Trip Finger" to mov;e "Trip Pawl"
when "Index Lever" is in "12" inch position.
N. Adjust needle pressure by turning screw
under center of "Pickup Arm" so that a
force of 72 grams (2.5 ounces) is reqnired to
lift needle from the record. Hook scale under
needle screw to measure force.
I
Mount motorboard on a level support.
Remove turntable and cover at rigbt of
turntable. Adjustment locations are desig.
nated on Fig. 108 as "A," "B," etc. The ad·
justments are explained under corresponding
symbols below. Perform adjustments in the
following order:
A. Trip rod "A" should be engaged in
"Switch Lever" slot. Adjust trip rod "A" to
obtain about U of an inch clearance from
motorboard.
B. Adjust "B" to the position shown.
C. With "Index Lever" in "Manual" posi.
tion. "Pickup Arm" rotated to extreme left,
and switch tripped to open contacts "C,"
adjust contact points "C" by bending the
stiff contact arm until points are opened 10
to 30 thousandths of an inch.
D. With "Index Lever" in "Manual" posi.
tion. release set IIcreW "P" lind force "Man.
ual Index Finger" as far as it will go towards
"Trip Pawl Stop Pin." Tighten set screw.
27
FIG. 107
132
\
I,
I.,I
RECORD CHANGER ADJUSTMENTS
III
I
K. Adjustment "N" must be performed
prior to this adjustment. With a 12" record
on turntable, turn on "Motor Switch," place
"Index Lever" to "12" position and adjust
Model UI09
COliER
I
FIG. 108.
AUTOMATlC RECORD CHANGER ADJUSTMENTS.
(Top and bouom views.)
PHONO·RADIO
"K" so that "Cable" tension will allow
needle to lower slowly on start of record at
completion of eject cycle. Turn "Motor
Switch" oft" aher eject cycle i8 completed and
check to see that "Cable" is slightly loose
when "Pickup Arm" is moved against
"Spindle." Replace turntable and put a
needle in "Pickup."
L. Adjust "L" so needle will drop into
center of smooth portion at the start of a 12"
record when "Index Lever" is in "12" inch
position and "Pickup Arm" is to extreme
right.
M. Loosen three screws "M" and rotate
"Spacer" untll pointer on "Spacer" is in line
with ICrew to right of "Pickup Arm."
P. Adjust turntable height by insertion or
removal of thrust washers at "P" 80 ejector
wlll not eject bottom 12" record but will
eject second from bottom record.
Q. Adjust position of shorting switch at
"Q" so switch closes wh~ needle is just
outside a 12" record.
R. Adjust screw "R" upward just enough
80 that with one record on 'turntable and
ejector tip "F" resting on record surface,
there is if of an inch clearance between
screw "R" and "Ejector Arm."
RECORD CHANGER SERVICE HINTS
1. "Ejector Arm" goes through normal
cycle but does not eject records. Adjust "F"
and "G." See that "Spindle" slides freely.
S.RVIe.
2. Ejects bottom record. Lower turntable
by removing thrust washers at "P."
3. Ejects records properly down to second
from bottom of pUe. Raise turntable by
placing thrust washers at "P."
4. Eject cycle does not start aher needle
reaches eccentric groove. Adjust "1" (turn
screw clockwise).
5. Eject cycle starts before eccentric record groove is reached. Adjust "1" (turn
screw count~r-clockwise). Set "Index Lever"
to "12" inch or "10" inch position after
starting to play record. Do not jar motorboard during automatic operation.
6. Lateral movement of "Pickup Arm"
has no control over starting and stopping.
Adjust clearance of rod "A." See that rod
"A" engages in Illot of "Switch Lever."
7. Fails to eject top record of a pile because "Ejector Arm" strikes record in returning to center at end of eject cycle. Ad.
just screw uR" upward to provide greater
incline so that roller in "Ejector Arm" will
roll back 'during cycle.
8, Pickup strikes record during eject cycle.
Adjust "K" and "H."
9. Starts playing record several grooves
in from beginning or needle millses record
entirely. Adjust "L."
10. Needle falls on smooth portion at start
of record but does not move into playing
groove. Adjust "M." Check to see that
motorboard is level.
DA1A
• Section 5
11. Automatic stop does not operate after
needle reaches eccentrc groove. Adjust "B"
and "C."
12. Motor does not restart when "Pickup"
is returned to rest position. Adjust "C." See
that switch mechanism parts move freely
and springs are functioning.
IS. Starts eject cycle although set for
"Manual" operation. Adjust "D."
14. Noise in loudspeaker while changing
needles. Clean "Shorting Contact" and adjust "Q."
IS. "Wow" in record reproduction-In.
strument should be warmed to about 65 0 F.
Ejector tip should be centered and free to
rotate (adjustments "F" and "G"). There
should be no solid particles on gear teeth or
in grease; no tendency to bind. Turntable
plate should be in dynamic balance and
"Spindle" should be straight. Proper lubrication is important.
Lubrication. Clean motor gear-box thoroughly before regreasing. Apply less than a
tablespoonful of a grease, sucb as "Cities
Service No. 70SS.Al" or "Koolmotor Uni·
versal Trojan .No. 1," directly on gears
taking care to get none in rotor bearings.
Put medium motor oil (S.A-E. No. SO) in
the oil holes. Cover main gear and cam of
automatic mechanism with a light grease
such as "Sooony.Vacuum No.2." Any good
household oll, Lluch as "S·IN -ONE" is sultable lor the ejector,-tip "F" bearing.
MALLORY TECHNICAL INFORMATION SERVICE
• Throughout its long association with the radio
and electronic industry the Mallory organization has
consistently given its services or advice on technical
problems submitted by those who have seen or heard
of our ofters to help to the best of our ability. That
we have made good on 'our ofter is evidenced by the
many letters of appreciation we'have in our files for
services large or small.
There is no charge or obligation for this servic~,
and many have asked how we can justify the cost of
such a service without direct monetary return. Our
answer has been essentially as follows:
1. Any help which we render to the field, the
serviceman, or the ultimate consumer reflects as a
general credit to the industry of which you and we
are a part.
2. In many past cases, our work and study on
problems submitted has been of real value to ourselves in obtaining a dearer picture of maintenance
operations, in finding new applications, or substantially iqtproving product features for existing ones.
In view of the present restrictio,!s on the design
and manufacture of electronic parts, we realize that
the field will be faced with an increasing number of
problems relating to changeover, adaptation, etc.,
with the limited types available. We reaffirm our
desire to help, and ofter the benefit of the experience
and knowledge of our technical personnel, to all
who request it.
Add,.",
TECMNICAL INFORMATION IIRVICt
Who,••a'. DIv,.'on
P.
R.
MAL LOR Y
&
CO.,
INC.
3029 I. W..hlnato.. • Indlonopoll.
133
THE
Section 5 •
MY E
. Webster-Chicago SERVICE
The changer plays twelve lO-inch or ten
12-inch records. To reload, revolve the two
posts sJightly, 'grasping them underneath the
shelf plates. Turn them back after the played
records are removed; they will fall and lock
when they are in the proper position. Place
the new records on the shelf plates and push
hutton "R" to put changer in operatiou. To
play the other size records, turn the knob at
the top of each post until the proper figure is
opposite the pointer. Press the "10" or "]2"
button, to agree with the pointer setting. To
reject a record (or to start a change cycle as
for testing purposes) simply press the "R"
(release or reject) button, at any time while
the needle is upon a record. To play manually, turn plates out of the way as for reloading, and press button "M."
The photos illustrate all the vital parts of
the changer. Letters are used alphabetically,
to refer to points on the photos; thus, motor
oiling holes "AK" are found by glancing
down column "A" (left side of Fig. 109) to
leiters "AK."
TECHNICAL
MANUAL
Models 11 and W1270
, the proper points; through the hole marked
"AM," see felt wick and drpp the oil directly
upon it; through the hole marked "AN," see
felt wick and drop the oil directly upon it.
l { squeaks are heard compare the squeak
with and without a load of records; any
stack of wax records in motion is likely to
squeak a little against a pin through their
'Center. ,See that all five wicks are in position,
including three %-inch round wicks in frame
of motor, one washer-shaped wick on lift
"CV," and one on cam lever "CS." See that
each wick is thoroughly saturated (as it may
not be if insufficient oil or too heavy oil has
been used). Lift out all three motor wicks,
with tweezers; see if old oil has become
gummy (commonly due to use of low-grade
oil or low-viscosity oil). If necessary, clean
gummed-up wicks with Kerosene. See that
each is saturated with good oil; then, before
replacing them, drop a little good oil into the
holes. The gearbox of the motor is packed
with a semi-fluid grease at the factory, and
it should not be necessary to take it apart
for lubrication purposes.
Change Cycle
Oilin~
The changer should be lubricated once a
year with about a dozen drops of good light
machine oil at each of the following 6 points:
(All points can be reached from above,
through holes in the mounting plate.) Three
oil holes ou motor gear housing; reach all
three through two holes "AK;" through hole
marked "AL," drop the oil upon the flat
surface of the cam, it will distribute itself to
PI./SH BUTTON ASSEMBLY hR"
, II
,,'
1\
, II "
I!" " ,
II
'II.
\I
"M"
"t2~
"10"
An automatic record player for records of
two sizes has three principal duties to perform. These duties are here performed by
three mechanisms, interconnected and built
together but largely separate in their operation.
(I) The record-changing mechanismbrought into operation originally by the
contact oflifter cam "DG" with pawl "DH"
-is the simplest of the three. It is driven by
the cam groove (not visible) on u,mler side
(in Fig. 110) of cam gear "DF." As cam lever
"CS" is forced, by the pawl, out underneath
lift "CV" (which is shown revolved to the
right for visibility) the lift rises and forces
roller "DJ" into the under groove in cam
gear. The motion is transferred to rear
changer shaft (at "ED") through cam connecting rod "DE" ("EC"), thence through
changer connecting rod "FD" to front
changer shaft "BB."
(2) The pickup-operating mechanismlikewise brought into operation originally
by the cam-and-pawl action upon cam lever
"CS" is driven in part by the groove in upper
(visible) side of cam gear "DF." As cam
lever is forced out, at the beginning of the
change cycle, against link "CG," it causes
the link to push upward upon pickup plunger
"DA," thus lifting needle from rec~rd. The
same pressure upon link "CG" works,
through guide arm "CD," to force stud
"DD" down into the groove on the cam
gear. This rotates the pickup arm, while
pickup plunger "DA" holds it up off of
record. It is rotated first out beyond the
turntable until selector plates "BL" have
dropped the next record, then rotated back
to proper position to start playing.
(3) The mechanism for bringing needle
into correct starting position must operate
accurately for both lO-inch and 12-inch records. Partly due to this requirement, the
starting position is not determined by the cam
action. The upper groove on cam gear is designed so that it, acting alone, would carry
the needle farther back toward record pin
than would ever be desirable as a starting
adjustment. Travel of pickup arm toward
record pin is then stopped, at proper point
for lowering onto the record, hy action of
lever hub "CL." The stopping takes place as
lug "EW" (upon the lever hub) strikes the
shoulder on rod "EX." This enables the entire mechanism rotated by cam action on
guide arm "CD" to travel on past the proper
point of rotation for record-starting, while
the pickup arm itself, which is held rigid to
BA CHANGItR
8a·
\I"
. SI'~.A11II'"'I"\ ..
Be
CHANGER POST'
,PICt
. ' ...'
~~ ~~f~G~R CONNl!C'tING !roo.
EA
EB
EC
ED
E'e'
e'F
EG
~~ rlL~~~tl:RSI;:EEVI!:
(a R!U'D)
FH MANUAL KEY ROO '
F'I REuECTJON ROO
F.) MANUAL
FUt..!. ROO SPRINt).
FK EXTENSIQN. ROo .
FL KEY CONT. BRACKET.
a
~r
1M) SUe-pL.ATE AND GEAR ASSM .. E.!
AD", ROO ASSM.
EK
CONNl!:CT1NG ROO LIFT (CY) El.
CONNECTING ROD L.iFT SPRING EM
CHANGER MODEL NUMBER EN
n
SERIAL
U
EO
RE.JECTlON 1>,00 SUPPORT
Ep
AD". ROO LEVE:R SPRING
EQ
PICKUP LEADER SPRING (CO) ER
PICKUP CORD ES
POST NUT ET
SHAXEPROOF WASHltR EU
MALE PLUG
EV
LUG ON LEVER-Hue ASSM. EW
AD..). ROD EX.
FIG.
UNIT
FN AD.). ROO sPRING
FO CONT. UNIT TRUSS SAl"!
FP NEEOLE LANDING AOu'lNG CAM
FQ AO,JUSTING ROD SRACKtt
FR PICKUP CARTRIDGE
FS CARTRIDGE CLAMP
f'T TONE ARM LIFT PLATE
FIJ HINGE PIN SPRING
f'V TONE ARM HINGE PIN
IlL The correct adjustment for the starting position of the pickup arm requires only the correct adjustment of rods EX and FK.
not have been properly done; old oil may
have become gummy.
(b) Changer may have been in a very cold
place, and may not yet have reached room
temperature. Give it a fair chance to get
warmed up before concluding that motor is
defective.
(4) Squeaks or other noises, during playing
of records.
(a) Check oiling.
(b) See that all setscrews are tight.
(5) Motion of pickup toward recoril pin
will not trip clwnger mechanism.
(a) (Only on models not having trip adjustment hole "AR:') It may be found that,
instead of trigger being actuated, there is
stretching of swivel spring "CK," allowing
the spreaders to open. Increase tension of
the spring, by bending the lug on either
spreader slightly. If this increased tension
causes needle to jump across the record,
needle may he a little out of vertical, radially-it may lean toward center of record.
To remedy this, grasp pickup arm and twist
it, very slightly, in a clockwise direction
(looking from needle end) so that it stands
vertical, or even leans a little in outward
direction.
(b) ] f trigger is being properly actuated,
prohahly cam lever "CS" is hinding against
suhplate "CU." Look for dirt or ohstruc, tions; see that pawl "DH" and trigger "CP"
are working freely on their rivets. If the
lever engages the pawl so that lift "CV"
forces roller "DJ" up into the under groove
on cam gear, and, if setscrews are tight, the
change cycle must operate, as cam gear
turns.
(6) Pressing button" R" doesn'ttrip changer
mechanism'.
(a) Check key control unit "FM": see
whether there is an obstruction or a bent
part which prevents operation of button
"R" clear down to the end of its travel.
(b) Examine reject. rod "FI." If it does
not trip, even when properly revolved by
complete depressing of button "R," the rod
has probably been bent, and must be restored in same way. Grasp the two ends and
twist it slightly.
(c) If trigger "CP" is being properly actu-
136
fM
ated but without starting a change cycle,
see directions above.
(7) Pressing button "M" jails to put
changer mechanism out of action so as to
enable manual operation. First see that button goes clear down; then follow its action
through manual rod "FH."
(8) Motor stops immediatply when changer
switch is turned off during a change cycle
(instead of continuing to run, as it should,
until needle is again upon a record, and
then stopping). Or(9) Turning on-off switch jails to stop
changer at all. Either of these two conditions
would indicate flliture of cycling switch
"EH." Cycling switch operates normally
to short-circuit the manual on-off switch
(which may be located in position shown
at "FA" or elsewhere) during change cycle
only. Such damage to cycling switch (not
likely to occur) would necessitate returning
either the subplate assembly or the entire
changer to factory.
(10) Needle lands properly on record but
fails to move over into record groove. Pickup
arm is normally impelled toward center of
records by lead spring "ER." Should a
slight increase in its tension be found necessary, this can be easily obtained by bending
the lug, to which it is attached, down against
main plate. If tendency then appears for
needle to jump acrOS8 record, check angle
of needle.
(11) Records jatl unevenly upon turntable.
Seldom objectionable (some unevenness may
even be advantageous); this is due to record
pin not hei~g correctly centered between
changer posts. If necessary, it can be corrected as described above.
(12) Last record drops on one side only.
This suggests a changer post bent out of
perpendicular to main plate. Test as directed above. If post must be straightened,
be careful not to bend other parts.
(13) Changer continues cycling. Probably
due to failure of lift "CV" to be drawn back
out of engagement with c.am gear. Check
the various rivets at which motion occurs,
to find the point where friction or binding
is interfering with freedom of motion.
(14) Record is driven, but not heard, or
not heard with proper volume. See that pickup
cord is plugged in. Check amplifier· and
speaker and connections to them, thoroughly. If then trouble is still suspected in
pickup, test its output with a vacuum-tube
voltmeter. Playing an average record, output
should test 1 to 2.5 volts if pickup cartridge
is of crystal type, or 0.5 volt if of magnetic
type. If pickup cartridge is found not to
deliver proper output, remove it and install
another.
•
(15) Selector plate jails to separate bottom
record from stack. This is due either to a
badly warped condition of the record, or
to its being of a thickness very considerably
different from those now in standard use.
The design of both selector and shelf plates
is such as to accommodate a maximum
variation in thickness and flatness of records,
but certain records may be found which are
so far out as to be impracticable for use in
automatic changers.
If Necessary to Disassentble the
Changer
First detach the entire changer mechanism
(except changer connecting rod assembly.
"FD" and cam connecting rod assembly
"DE," also seen at "EC") from main plate
"ED." To do this, first take out shoulder
screw "CT," to free the rest of the mechanism from assembly "DE." Then remove the
three screws "AO," which hold subplate assembly "DJ" to main plate "EB." Also remove screw "BN," which holds cam gear
"DF." Pull off the four key control buttons.
Remove the two screws that hold key control and "FM". to main plate. Now remove
control unit truss bar "FO," rejection rod
support "EP," and extension rod bracket
"FQ"-this means taking, out five screws.
Remove flat spring "FJ," by taking out one
screw. Rods "FH" and "FI" can then, with
due care, be extracted without bending.
Free the cam connecting rod assembly" D E,"
by loosening setscrew holding spreader hub
"EE" to rear changer shaft. In reassembling,
reverse the prO'cedure, taking care to ge t all
springs properly connected as shown in the
photos, without stretching any of them.
I.
1
I
I:
e Section 6
THE MYE TECHNICAL MANUAL
Automatic Tuning
MALLORY
137
Section 6 •
THE
MYE
TECHNICAL
AUTOMATIC
The past four years have witnessed the widespread
adoption of automatic tuning systems by practically
every radio receiver man,ufacturer. The appeal of this
feature to the public has been fostered by intensive
sales promotion and advertising campaigns which have
established it as a necessary adjunct to a modern receiver. It presents to the radio service engineer a
unique opportunity for the establishment of closer
customer contact since the original setup of selected
stations as well as the maintenance of continued satisfactory automatic operation is a function which he
alone is technically capable of rendering.
As everyone acquainted with radio receiver details
will realize, automatic station selection is not a new
development but rather a refinement and perfection
of principles which have been in use for several years
past. It is interesting to note that the continued progress
towards the ideal of simplification of the tuning requirements of radio receivers has been the result of a
series of cycles in which improvements in mechanical
design have in every case followed and been initiated
by the introduction of new radio circuits. In the present
case the development of automatic frequency control
of superheterodyne oscillator~, stabilization of drifts
due to temperature and humidity and the expansion of
IF amplifier circuits have simplified the design of automatic tuning devices by allowing considerable latitude
in the mechanical and electrical precision of selectors.
The present article is a combinat,ion of the texts appearing in the 2nd Edition Radio Service Encyclopedia
(pages 249-274), and the Automatie Tuning Supplement Number 8 to the 3rd Edition Radio Service Encyclopedia. In each of these articles a system of listing
all models in table form with reference to specific portions of the text applying to the particular model was
used, and the present article continues this method.
The present article has a greater utility not only because of integrated form but also because it combines
the basic theory of operation as covered in the 2nd
Edition with the specific set-up and service information appearing in the Supplement.
In setting up this reference system it has been nec138
MANUAL
TUNING
essary to classify the material under nine headings as
follows:
Section 1
Section 2
Section 3
Section 4
Section 5
Section 6
Section 7
Section 8
Section 9
Mechanically Operated Manual Types
Tuned Circuit Substitution Types
Motor Operated Types
Electric Tuning Motors
Station Selector Switches
Transfer Devices
Silencing Equipment and Operation
Station Selector Commutator Devices
Special Mechanisms
Some of the sections have subdivisions to cover the
many variations of a basic operation and references in
the table are made directly to the subdivision in such
cases. Two subdivision references are frequently given,
one for theory of operation, and the second for specific set-up data.
The column headed "Type" in the reference table
actually names variations of the three main types, that
is, manually operated, circuit substitution, or motor
operated. For instance, it is more informative to refer
to a particular system as dual mica, or mica and permeability type rather than to the general classification
of tuned circuit substitution.
The column headed, "Number of Buttons,." refers to
the number of sele~tors actually used for station reception. Transfer buttons, tone control buttons, etc.,
are not included in the number shown.
The "Special Descriptions" column refers to portions of the text devoted to transfer devices, audio
silencing systems, etc., applicable to models carrying
the reference. Altogether there are seven subheadings
under the Special Description classification as follows:
Button Indexing Adjustment, Tuning Motor, Push-Button Station Selector Switch, Transfer Device-Manual
to Automatic, Audio Silencing Circuit and AFC
Release During Tune, Station Selecting Commutator
Device, and Stop or Lock-In Mechanism.
It should be noted that the method of referring receivers of one manufacturer to those of another manufacturer for illustrative purposes does not indicate that
the receivers are identical or even similar; only that
the automatic tuning device operation is basically the
same.
AUTOMATIC
TUNING
REFERENCE
MANUFACTURER
AND MODEL
AIR KING
910,911 ............... .
ALLIED
A9757, A9758 .............. .
B10525, BI0526 ... '" ..... .
BI0537, BI0538, BI0539 .... .
BI0540, BI0541, BI0542 ... .
BI0580, BI0581, BI0582 ... .
BI0799 .................... .
EI0704 .................... .
EI0705, EI0706 ........... .
EI0707, E10708 ........... .
EI0709, EI0710 ......... '"
EI0711, EI0712 ........... .
EI0718, EI0720 ........... ..
EI0721, EI0722, EI0723 .. .
EI0726 .................... .
EI0727 .................. .
EI0728 ................... .
EI0740 ................... .
£10741, EI0742, EI0743 ... .
EI0744, EI0745 ........... .
EI0751 ................... .
EI0773, EI0774 .......... .
EI0786, EI0788 .......... .
EI0790, EI0794 .......... .
EI0795 .................... .
EI0797, EI0798, E10799 .... .
EI0800 .................... .
EI0806 .................... .
EI0807, EI0808, EI0809 .... .
E10810, EI08H, EI0812 .... .
E10813, EI0814, EI0815 .... .
E10825, EI0826, El0827 .... .
EI0828, E10829, EI0830 .... .
EI0840, EI0841, E10842 .... .
EI0850, EI0851. ......... .
EH)870, EI0872, EI0874 .... .
E10875, EI0876, EI0877 .... .
E10880, EI0881 ............ .
EI0882A to EI0887 A ....... .
EI0890 .................... .
EI0893, EI0894, EI0895 .... .
EI0897, EI0898, EI0899 .... .
EI0900, EI0901, EI0902,
EI0903 ................ '"
EI0905 ................... .
EI0906, EI0907 ............ .
E10920 ................ .
AUTOMATIC
855,892 .................. .
No.
of
But·
Sec-
tons
tion
SubDivision
Dual Mica ......... .
5
2
2A,2B
Telephone Dial. .... .
Motor Operated .... .
Motor Operated .... .
Telephone Dial ..... .
Telephone Dial ..... .
Rocker Bar ........ .
Cam and Lever . ... .
Rocker Bar ........ .
Rocker Bar ........ .
Dual Permeability .. .
Dual Permeability .. .
Rocker Bar ....... "
Rocker Bar ........ .
Dual Permeability .. .
Rocker Bar ........ .
Dual Permeability .. .
Rocker Arm ....... .
Dual Permeability .. .
12
8
8
10
12
6
4
6
6
7
7
6
6
7
Type
1
3
3
1
1
1
IE
"aD' .....
1
1
2
1
2
1
Cam and Lever ... .
Rocker Bar ........ .
Rocker Bar ........ .
4
6
7
6
7
6
6
4
8
6
6
8
4
5
4
6
1
lC
IE
IB, IBI
lA,1Al
IB,1B1
IB, IBI
2B
2B
IB, IBI
IB, IBI
2B
IB, IBI
2B
IB, lBl
2B
3B
1A2
2B
1B
IB
IB
2B
1A1
IBI
2B
IBI
2B
IBI
lBl
lAI
3B
2B
2B
3£1
1B
lA2
IBI
IBI
Dual Permeability .. .
Dual Permeability . . .
Rocker Bar ..
Rocker Bar ..
9
4
6
4
2
2
2B
Permeability & Mica.
6
2
~a~O!2rL~~t::
. . :::
Dual Permeability .. .
Rocker Bar ........ .
Rocker Bar ........ .
Rocker Bar ........ .
Dual Permeability ..
Cam and Lever . ... .
Rocker Bar ........ .
Dual Petmeability .. .
Rocker Bar ........ .
Dual Permeability .. .
Rocker Bar ........ .
Rocker Bar ........ .
Cam and Lever . ... .
Motor Operated .... .
Dual Permeability .. .
Dual Permeability .. .
:t::k!r~::.a.t~~:::: :
6
7
4
6
8
5
5
4
4
5
9
1
1
1
2
2
1
1
2
1
2
1
2
3
1
2
1
1
1
2
1
1
3
2
2
3
1
1
1
1
1
• Section 6
SPECIAL DESCRIPTION
Button
Indexing
Adj.
Tuning
Motor
PushButton
Station
Selector
Switcb
5B
1C4
.. 'ic~i'"
.. ·4B· ...... ·SB· ....
4B
5B
Transfer
Device
Manual to
Automatic
Station
Selecting
Commutator
Device
t,::r-'i~
Mechanism
60
6B
60
60
... 6B.. · ..
lC4
Audio Silencing
Circuit and
AFC Release
During Tune
7D,7K2
7H,7K4
7H,7K4
7A
7D,7K2
8C
8C
... 4B" ... . .. SB" ... . .. 6D .... . .. 'iii,' 7K4 .. . ..
8C
.. ,4B" ...... i;iJ ....... iiD .. .. .. 'iii,' 7K4 . .. ..
8e
2B
IB
IB
5B
6B
................
1-------1----------1-----
BELMONT
408A ....................... Cam and Lever.
5
1
IA1
418A ....................... Cam and Lever.
6
1
1Al
501A ....................... Cam and Lever.
5
1
1Al
5HA ....................... Cam and Lever.
6
1
1A3
517A, 519A, S20A, 52lA ...... Cam and Lever.
6
2
2B
524A ....................... Cam and Lever. . . ..
6
1
lA3
526, 527, 529, 531B. . . . . . . . .. Cam and Lever. . . . .
5
1
lAl
553A ....................... Cam and Lever.....
6
1
lAl
577A, 577C, 579 ............. Cam and Lever. ....
5
1
IA4
582, 583A, 6lIA, 612A. . . . . .. Cam and Lever. . . . .
6
1
IAI
632A, 633A, 634A, 63SA, 636. Cam and Lever. . . . .
5
I
IAI
637 A, 638.. .. .. .. .. .. .. .... Cam and Lever.. .. .
6
1
1Al
665A ...................... Cam and Lever. .. ..
6
I
lA3
676A ....................... Cam and Lever. .. ..
6
I
lAS
677. . . . . . . . . . . . . . . . . . . . . . .. Cam and Lever. . . . .
6
I
lA4
678. . . . . . . . . . . . . . . . . . . .. .. Cam and Lever. . . . .
6
I
IA5
751A ....................... Cam and Lever.....
6
I
lA6
761A, 765A ............. , . .. Cam and Lever. , . . .
6
1
lA3
767A ....................... Cam and Lever. ....
6
1
lA6
791A ....................... Cam and Lever.. ...
6
1
IA3
792, 793. . . . . . . . . . . . . . . . . . .
Cam and Lever. . . .
6
1
lA7
6
1
lA8
794 ......... '............... Cam and Lever.....
796,797 .................... Cam and Lever....
6
1
lA3
·'iB.. · ........
860 ........... , ..... , ...... Cam and Lever. . ...
8
1
lA3
7B
860A ....................... Cam and Lever.. ..
8
1
lA3
867A........ ............... Cam and Lever ....
6
I
lA6
1075A, 1075B. . . . . . . . • . . . . .. Dual Permeability. . .
6
2
2B
.. ·'iB···········
1175... ............ ........ Cam and Lever. . . ..
8
1
lA3
7B
1175A ...................... Cam and Lever.....
8
1
1Al
....................................... .
BUICK
1---------------1--------1-------1--------1-------1-------1-------1------------1-----980598, 980620 ......... , ... . Rack and Pinion . ...
5
9
90
CADILLAC
1433970 ................... . Permeability Tuners.
S
2
2B
CHEVROLET
985283 ................ , ... .
985425, 985426 ........ , ... .
8
5
8
1
8D
IB2
5
4
5
2
2
2A
2A
2A
CLARION
55A, 57A, 58B. .............
70X. . . . . . . . . . . . . . . . . . . . . ..
93,1105....................
---------------1---Dual Mica ......... .
Dual Mica ......... .
Dual Mica ......... .
2
........................................................................
139
THEM Y E
Section 6 •
TECH N I CAL
MANUAL
REFERENCE
MANUFACTURER
AND MODEL
Type
No.
oE
But·
Sec~
Sub.
tons
don
Division
Button
COLONIAL (Sea.... -Roebuck) .
4610,4666,4686 ............ .
46111 ...................... .
4786 ...................... .
4787 ...................... .
4791,4792 ............... .
Telephone
Telephone
Telephone
Telephone
Telephone
Dial .....
Dial. ....
Dial. ....
Dial. ....
Dial .....
.
.
.
.
.
11
11
11
11
11
CONTINENTAL
SA ........................ .
5B ........................ .
6B,6C .................... .
6G ....................... .
6K ...................... ..
7G, 8A, 8AU .............. .
9G, 11A, 118, 16R, 16S.
55 ..................... .
Cam and Lever ....
Rocker Bar ........
Motor Operated ....
Dual Permeability ..
Rocker Arm .......
Dual Permeability ..
Motor Operated .. .
Cam and Lever.
.
.
.
.
.
.
4
4
6
6
4
6
8
5
I
I
3
2
I
2
3
I
IA1
lBI
3B
2B
IB1
2B
3B
lA2
Rocker Bar ........ .
Rocker Bar ........ .
5
5
4
5
1
1
1
1
1
1
1
IB3
IB3
IB3
1B3
IB3
IB3
IB3
CROSLEY
A158, A168, A169, A258 ..... .
A268, A3S8 .......... .
418,428 ................•....
438M, 448 ................. .
458 ....................... .
548 ................. ..
588,598 ................. ..
617 ....................... .
628,638 ................... .
648 ....................... .
718,758,818 ............ .
828 ....................... .
1018 ...................... .
1118 .................... .
1127 ...................... .
1137, 1227, 1237 ....... .
5628 ................. .
Rocker Bar ...... , .
Rocker
Rocker
Rocker
Rocker
Bar ........ .
Bar ........ .
Bar ..... .
Bar ....... .
4
5
4
Motor Opera ted .... .
Rocker
Rocker
Rocker
Rocker
Rocker
Bar ........ .
Bar ........ .
Bar ........ .
Bar ..... .
Bar ........ .
'Motor Operated .... .
Motor Operated .... .
tt:ctk':r ~ae:~.t~~.' . : ..
SPECIAL DESCRIPTION
Push·
IC
lC
lC
lC
lC
3
1
5
4
5
8
5
8
1
3
8
5
3
1
1
1
I
3
Button
Indexing
Tuning
Station
Selector
Adj.
Motor
Switcb
ICI
ICI
ICI
lCI
lCI
Transfer
Device
Manual to
Automatic
6A
6A
.. ·4il....
·sii ....
Audio Silencing
Circuit and
AFC Release
During Tune
Station
Set".:'.!!~g t:tI~
mUtator
Device
7A
7A,7Kl
7A
7A,7Kl
7A
Mech ..
ani8m
lC8
IC8
lCS
Ica
lC8
6D
... 4il ... . .. S»" ... . .. 60
3A
4C
IB3
IB2
IB3
IBa
IB3
3B
3A
3B
IB3
.. '4C"
4C
4C
5D
·7G· ...... · .. "80'
7G ...... · .. · . '80"
"SA"
50
5A
----------1------1----1---1------------------1·-DELCO
R667, R669 .......... .
R675, R677, R678 ...... .
Rll~.. ............. .
RU34, R1135, RU39 ....... .
R1140 ................ ..
R1141, R1l42, R1143, R1144.
Delco-Matic
Rocker Bar ..
6
5
8
Delco-Malic.
Cam and Lever..
..
Dual Permeability ..
Dual Permeability ..
5
5
6
9
1
9
1
2
2
9B
IB4
9B
lAI
2B
2B
-----------1----·--- ---------1--- - - - - - - - -----1------1--DETROLA
175, 183, 185 ............... .
191, 192, 193, 195(C4), 204.
209, 210 ................ .
220, 221, 222 ....... .
223,225 ........... .
226, 227 .................. .
228 ..................... .
231 ....................... .
Motor Opera ted ... .
8
Motor Operated ... .
Dual Permeability ..
10
3
6
4
6
4
6
8
6
2
I
1
1
1
3
1
6
2
Rocket Bar .... , .. .
Rocker Bar ....... .
Rocker Bar ....... .
Rocker Bar ....... .
Motor Operated .. .
233 ....................... . Rocker Bar.
258, 259, 270 ....... .
Dual Mic•...
3
3B
3B
2B
4B
4B
5A
5A
7G
7G
.4»'
SA
7G
8C
8C
IBI
IBl
IBI
IBI
3B
IBI
2A
--·--·---------1-------·-- - - - - -------1·----1----- - - - ---·--1-------1---ERLA
11 Tube 3 Band ........... .
11 Tube 3 Band ........ .
76A ...................... .
78B, 78BE, 82A, 82AE, 86AE.
91B, 95B .............. .
Flasb Tuning .
Telephone Di.1.
Flash 1'uning .... .
Telephone Dial ..... .
Telepbone Dial .... .
12
10
12
10
10
Automatic Dial. ... .
Automatic Dial .... .
Automatic Dial .... .
Single Adjust. Mica ..
Single Adjust. Mica ..
Rocker Bar ........ ,
Single Adj ust. Mica ..
Instamatic ......... .
Instamatic ......... .
Instamatic ......... .
Rocker Bar .... .
FADA
A66PC, A66T, A76PC ...... . Dual Mica ......... .
A76T,6A39 .............. . Dual Mica ........ .
358, 366, 366PT, 368 ........ . Ftashomatic.
FAIRBANKS-MORSE
9AC4, 9AC5 ............... .
12AC6 .................... .
10
10
10
1
1
1
6
6
2
2
6
6
2
9
6
6
4
9
9
1
6
6
6
2
2
2
4
--------------1---·-
IC4
ICa
lC4
IC3
lC3
IC
lC
IC
2C
2C
IBI
2C
9E .
9E
9E
IBI
lCI
lCI
lCl
6B
6B
6B
6B
6B
7D,7K2
7D,7K2
7D,7K2
7D,7K2
1D,7K2
-----1-----1------1----1----1------- - - - - -
-----1---------1---
EMERSON
ARI7I, AR173, ARI74 ...... .
AR176, AR180, AIU85 ...... .
AT170, ATI7:!, AT181. ..... .
AV193, AY194, AY195 ...... .
AZ196 .... ~ ............... .
BB208, BB209 ............. .
BDl97, BDl98 ............ .
B0223, B0225, BQ228. . ... .
B tt224, B tt226, B U229 ...... .
BU230, BW231. ........... .
CA208, CA209, CA234 ..... .
IE
lC
IE
IC
lC
1
15
15
2A
2A
IC
lC
lCll
lCll
lCll
.....
lCI
,
....
7A,7Kl
7A
I,
lC8
-------------1--------1--- ---1----1----1----1-----1----1----- - - - ---FIRESTONE
S7407·5 ... : ............... .
1175 ...................... .
01009,01010 ............... .
01029 ..................... .
01030 ..................... .
015040, 015050, 015060, ...... .
015070 .................... .
015080,015090 ............. .
015100, 015110, 015120 ...... .
015130 .................... .
100502 ....... ,' ............ .
FORD
FI740, 6MF490 .............
140
Ratchet Switcb ....
Cam and Lever ....
Cam and Lever ....
Cam and Lever ....
Cam Ilnd Lever ....
Rocker Bar ........
.
.
.
.
.
.
6
8
5
8
6
4
Cam and Lever .... .
Cam and Lever .... .
Rocker Bar ........ .
Rocker Bar ........ .
Cam and Lever .... .
4
4
6
Ratchet Switch .... ,
5
2
1
1
1
1
1
1
1
1
I
I;
20
lA3
lAI
lAl
IAI
I,i,
~~
i
IBI
......... .
IBI
......... .
lA3, lA8 ......... .
1A9
......... .
IBI
......... .
1
1M
2
20
......... .
AUTOMATIC
TUNING
REFERENCE
MANUFACTURER
AND MODEL
No.
of
But·
Type
tODS
GALVIN
1938 Auto Models .......... .
8.60.8.80 ............... .
IOn. 12Y. 12Yl. .......... .
9·49. 9·69. 15F ............. .
16C ...................... .
170. 17DA. 180. 19B ....... .
20P. 21L, 22S. 24K. 25N ... .
89K1. 89K2. 89K3, I09Kl ... .
109K2 ................. .
Spot Tuning .......
Motor Operated ....
Motor Operated ....
Motor Operated ....
Rooker Bar ........
Rooker Bar .......
Motor Operated ....
Motor Operated ....
.
.
.
.
.
.
.
.
Motor' Operated .... .
GAMBLE-SKOGMO
AI. A2. A3. A6 ............. . Motor Operated ....
Cam and Lever ....
527A, 527C ............... .
CMO ...................... . Cam and Lever ....
645 .....•.................. Dual Mica .........
648 ...................... . Rooker Har ........
677 ...................... . Cam and Lever ....
678 ...................... . Cam aad Lever ....
735 ....................... . Dual Mica .........
761 A. 796. 797 ............ . Cam and Lever ....
867A ...................... . Cam and Lever
Any
No.
6
19
6
5
6
6
6
6
.
.
.
.
.
.
.
.
.
8
5
6
GAROD
782.782.1 ................. .
Prestomatic ........ .
GENERAL ELECTRIC
F96 ..................... .
FI07. FI09. FI37 ........... .
G50 ...................... .
G53 ...................... .
G55 . . . . . . . . . . . . . . . . . . . .
G56. G6l. GM. G66, G68 ... .
G69. G75. G76. G78 ........ .
G85 ...................... .
G86 ...................... .
G95 ...................... .
G97 ...................... .
G99 ...................... .
mos. GI06 ................ .
G655 ..................... .
GA62 .................... .
GD51. .................. .
GD52. GD52A. GD60. GD63.
GD610 .................. .
H73, H77. H78. H79. H87 ... .
H116. H118..... . ....... .
H634. H638. HMO ..... I • • • • .
HJ905. HJ908 ............ .
HJlOO5 ................... .
HJl205 ................... .
Touch Tuning .... .
Motor Operated ... .
Telephone Dial. .... .
Dual Mica ......... .
Telerhone Dial. ... .
Dua Mica., ...... .
Dual Mica ........ .
Dual Mica ........ .
Dual Mica ......... .
Motor Operated .... .
Dual Mica ......... .
Dual Mica.... . ..
Motor Operated .... .
Dual Mica ........ .
Rocker Bar ....... .
Cam and Lever .... .
Dual Mica ......... .
Cam and Lever ... .
Permeability & Mica.
Permeability & Mica.
Permeability & Mica.
Permeability & Mica.
Permeability & Mica.
Permeability & Mica.
GENERAL HOUSEHOLD
UTILITIES (Grunow)
585 ..................... .
588., .................. .
Teledial. .. . .... .
Teledial ......... .
Teledial. ......... .
622 ..................... . Teledial. .......... .
623 ...................... . Teledial. .......... .
624.632 ................... . Teledial. .......... .
63S. 1067... .......... . .. Teledial. . . . . . . .
1081. 1091. 1181. 1183. 1185
Teledial ....... .
1291.1293 ............ .
Teledial .......... .
589 ...•...•...............
13CS-E .................. .
HERBERT H. HORN
I1A ...................... .
Motor Operated.. .
9
9
9
6
6
I
2
I
I
6
2
2A
2
2A
9A
IB2
2A
IB2
2A
2A
2A
2A
3B
2A
6
8
6
8
6
6
8
6
I3
9
1
1
1
I
9
1
2
I
2
2
2
2
3
6
8
2
2
I3
3
2
1
1
6
5
5
5
5
6
8
5
5
6
8
2
1
2
2
2
2
2
2
10
8
10
8
10
8
10
16
15
.
Indexing
Adj.
IC6
.. ·iC2····
Tuning
Motor
Button
Station
Selector
Switch
5C
2A
3B
3
3B
2
2
2
2A
2A
2A
2A.2B
3B
2A.2B
9
9F
... 6C·····
f.:tI~
MechaniSM
. 'iC'lS"
lel3
~.
4C
7G.7K2
... 5ii ....... i;ri ... .
···4A.... ·
5B
6B
5B
5B
60
60
... 7E,"7K.S······
8B
···i;B·· .. ·
.. ·i;ii· .. ·
6B
6B
6B
. ··6B·····
6B
3B
2A
lBl
IA1
2A
IAI
2A.2B
2A.2B
2A.2B
2A.2B
2A.2B
2A.2B
2
3
Station
Audio Silencing Selecting
Circuit aod
Com·
AFC Releaoe
mutator
During Tune
Device
.......... .......... . ......... ',E'··········
4B
5A
2~
lC
IC
IC
IC
IC
IC
IC
IC
IC
Transfer
Device
Manual to
Automatic
"'6B" ...
···5B.... · ..........
60
1C3
ICl
7A.7KI
7A.7KI
7A,7K1
7A.7KI
7A.7KI
7A.7Kl
7A.7Kl
7A.7KI
7A.7K1
Ica
ICl
IC3
IC3
IC3
ICI
IC1
.. 4B.. ···
5B
5B
60
6A
5B
60
. .. iii······ .. ·
1C8
ICS
ICS
1CB
1CB
IC8
lC8
ICS
ICS
..............
BC
I---------------~---
HUDSON
SA40 ....•................. Solenoid ........... .
MAJESTIC
62A ....................... .
639. 639B ................. .
6S1-EB ................... .
739 ....................... .
1056X. 1058X ............ .
1356X. 1656X ............. .
11056 ..............•........
11058 ..................... .
11356 .................... .
11656 ........... .
3
9
1
1
6
5
Motor Operated ....
8
1---------------1---HOWARD
210 Adapter. 211 Converter•.. Dual Mica ........ .
8
8
240.240.2 ............... . Dual Mica ......... .
318, 3180. 3250. 368A .... .
8
Dual Mica . . . . . . . .
375 ...................... . Permeability & Mica.
6
4OOA.425A ............... . Motor Operated .....
8
6
418. 468. 525. . .. . ......... . Permeability & Mica.
MAGNAVOX
CR10IM. CRI08M ......... .
CR121 .................... .
CRl22 .................... .
CRl2s .................... .
CR124 .................... .
CRl28 .................... .
10
3B
3C
9G
IB
1B
9G
9G
9G
1
3
2
6
8
Dual Mica ........ .
Sub.
DivisioD
5
6
6
GILFILLAN
5TH ...................... .
Button
9C
IAI
1AI
2A
1BI
1M
IA5
2A'
lA3
lA6
13
SPECIAL DESCRIPTION
Push·
Sec.
tion
• Section 6
Motor Operated ....
Dual Mica .........
Motor Operated .. .
Rocker Bar ........
Dual Mica .........
Rocker Bar . . . . . .
6
.
.
8
.
.
6
6
Rocker Bar ........ .
Rocker Bar . . . . . . . .
Dual Mica ........ .
Rooker Bar . . . . . . .
Dual Permeability .. .
Dual Permeability .. .
Motor Operated .... .
Motor Operated .... .
Motor Operated .... .
Motor Operated ... .
6
8
6
4
6
4
4
5
7
6
8
10
12
2
2
3
S'
2
3
1
2
I
I
1
2
I
2
2
3
3
3
3
4B
4B
5B
5B
5B
5B
7H.7K4
8C
60
.. ·60 .. ··
... 60·· .... ·iH··· .. ·· .. ·
"'SC'"
3B
· .. 6:8·· ..
2A
3B
IB
.. ·6B·····
2A
IB
1----1-------1------·1------11-----1·---------- - - - - - IBI
IBI
2A
IBI
2B
2B
3B
3B
3B
3B
..........
6B
141
'Section 6 •
THE
MY E
TECHNICAL
SPECIAL DESCRIPTION
REFERENCE
MANUFACTURER
AND MODEL
MIDWEST
VTl6, VTI8, VT20.
No.
of
But·
tons
Type
Motor Operated .....
18
Cam and Lever .... .
Cam and Lever .... .
Motor Operated .... .
Dual Permeability ..
Cam and Lever. , .. .
Cam and Lever, ... .
Cam and Lever .... .
Cam and Lever.
Dual Permeability, , .
Dual Permeability" .
Motor Operated .... .
Cam and Lever .... .
Motor Operated .... .
Cam and Lever .... .
Cam and Lever .... .
Dual Permeability .. .
Dual Permeability .. .
Cam and Lever .... .
Cam and Lever .... .
Cam and Lever .... .
Cam and Lever .... .
Cam and Lever .... .
Dual Permeability .. .
Cam and Lever .... .
6
6
8
----------1---------------1----
MONTGOMERY-WARD
62·274,62-280,62.282"", ...
62-284, 62-288,62·290"" .
62.303, 62-321 " .... ,.,.
62·322 . . . . . . .
62.323, 62-324. , ..... , ' . ,
62.350 .. , .... , ... ,., ..
62·361 ... , , . , ...... ' . , .
62·362 ........ ' . . . . . ,
62.363, 62·370, 62·390 ... , .. , .
62·401, 62·403, 62.422 ... , . , ..
62·433. , ... , , . , ' .. , ..
62.434,62·435.,.,.,., .... ,
62·451, , . , . , , . , ... , . , .. , .. .
62·453 .... , . . .. ." .. ,.,.,.
62·459 ......... .
62·463,62·470,62·479", .....
62·490 ............. ..
62·501, 62·502, 62.504A
62·505A, 62.552, 62·553.
62·554 ", .. ,'
62·558. , , ..... , , , ' , ... , .
62·601. , ...... , .. , .. .
62·650
62.651, 62·652 .......... ,
62.653 ."
....... .' __ ..
62.654, 62.655, 62.656. , . , .. .
62·700 .. ,'., ... , .. '...... .
62·713 ....... ,..... ., .. .
62·750, 62·751 ..... .
62.900, 62.1100 ... .
62·1558 .. ,., .... .
04BR.609A."., .... .
04BR678C .... " ..... , ... , ..
93BR462A ... , ...... " .... .
93BR508, 93BR509 .. , ...... .
93BR560A ........ , .. ,.,
93BR561A, 93BR563A .. ,.
93BR564A ..... , ..... ,.,.
93BR657A ............. , ... .
93BR658A, 93BR659A .. , .. .
93BR660A .. , .. , ........... .
93BR713A.. . . .. . _...... .
93BR714A, 93BR714B .. , .,
93BR715A, 93BR717A ... , ..
93BRI20IA, ....
Cam and Lever.
Cam and Lever.
Dual Permeability ..
Cam and Lever ....
Cam and Lever
Dual Permeability ...
Cam and Lever.
Cam and Lever.
Cam and Lever.
Cam and Lever.
Cam and Lever
Cam and Lever.
Cam and Lever .....
Cam and Lever .. , .
Cam and Lever
Cam and Lever.
Cam and Lever.
Cam and Lever.
Cam and Lever
Cam and Lever
Cam and Lever
6
6
4
6
6
6
6
8
6
8
6
5
6
6
6
6
5
6
6
6
6
5
6
6
6
6
6
6
6
6
6
4
6
6
6
6
6
6
6
'6
6
6
Sec~
tion
Sub.
Division
3
3B
I
I
IAI
IAI
9C
2B
IA3
lAI
IAI
IA3
2B
2B
9C
IA3
9C
IAI
9
2
I
I
I
I
2
2
9
I
9
I
I
2
2
I
I
I
I
I
2
MANUAL
Button
Indexing
Adj,
Tuning
Motor
4B
Puoh·
Button
Station
Selector
Switch
5A
Transfer
Device
Manual to
Automatic
6F
Audio Sil~ncing
Circuit and
AFC Releaoe
During Tune
7C
Station
Se~:c.!!~g f~~tI~
mutator
Device
Mech·
anism
SC
tAl
I
I
I
2
I
I
2
I
I
I
I
I
I
I
I
I
I
I
I
1
I
I
2B
2B
IAI
IAI
IAlO
IA3
IAI
2B
IA6
IAIO
IA6
2B
IAll
IA6
2B
IA3
lAI
IA5
IA3
IAI
IAll
IAI4
IAI
IAll
IAI4
IA14
IAll
IAI4
lA14
IAI4
2
2
1
2
2
2A
2A
IE
2A
2A
I
1
---------1-------------- - - - - - - - - - - - - - - --------1-------1-----1-----------1----NOBLITT-SPARKS
6,68" ......... , .. , ..
92 . . . . . .
818AT, 828AT. 838AT ..
1237,1247, 1247A ....
1427 .....
Dual Mica ....... .
Dual Mica .. ,.
Phantom Tuning ..
Phantom Tuning
Phantom Tuning
OLDSMOBILE
982126,982127.
Rocker Bar.
6
IB2
PACKARD BELL
160.
Motor Operated ....
8
3B
PACIFIC (Chicago)
Converter Unit .......... .
SeJectro~Matic
6
PACIFIC (Loa Angele.)
37, 37A ..
Dual Mica .....
6
PACIFIC
8AC. .. ..................
501, 601, 602 ....
Rocker Bar, ...... ..
Rocker Bar, .... , ..
6
4
6
6
10
6
10
.. 6iJ
5B
5B
6A
-'AO'_" tIP-3S
LEFT END VIEW OF MECHANISM
FIG. 87
tuning shaft causes the star wheel to
force down the kickout arm. This releases the depressed button and slides
back the friction roller into engagement
with the friction wheel for manual
tuning.
The flywheel on the back end of the
tuning shaft provides a "spinner" action while tuning manually.
The station selector cams are prevented from turning on their shaft by
an expansion and contraction type
locking mechanism. The assembly is
locked when the device is expanded or
unmeshed as shown in Fig. 90B. Unlocking is accomplished by pulling out
the set-up knob and turning it clockwise
until a click is heard. This contracts the
MOTOR MOUNTING
SCREWS
BRACKET MTG,
SCREWS
15
_==#;==;==FRICTION
~~~~~~ WHEEL
/ AI1II,,-1"tII.!!'<:t--. AND - 18
MOTOR
PINION
28-PAWL
FRICTION_ 16
ROLLER
12-COLLAR
CLUTCH-II
ESCUTCHEON SUPPORT
6-
BRACKET
FRICTION SPACER
WASHER-17
J.
10
~
KEY
TOP VIEW OF MECHANISM
FIC.88
185
- Section 6 •
THE
MY,E
TECHNICAL
MANUAL
b. Allow the set to warm up for twenty minutes before settIng it up.
c. Set up the buttons from left to
right, that is, the' right hand buttons
should be the last to be set up.
d. Avoid setting buttons on weak or
fading signals.
e. Tune cart;.fully when setting up.
f. After a button is set up, do not
push that button again until the mechanism is locked. To do so will spoil the
setting of that button.
g. Lock up tight. Continue to force
the set-up knob in a' counter-clockwise
direction even after it seems to reach a
definite stop. If you do not use force,
the settings of the buttons may change.
en
Z
o
t=
fd
z
z
o
o
0::
LLI
:r:
.....
o
II:
0
0::
Q
f2
~~
..:
u
U)
-...
~
~CD
CD
is
AUTOMATIC
5 t-~~~~__-+-+_P~I~lO~T_l~I~GH~T~~~~~~~--~
en::(3
'-SMAll ~LUE
SCHEMATIC WIRING DIAGRAM
OF TUNER WITH MECHANISM
IN MANUAL POSITION
~
INSULA TION---
II:
o
~ (EARLY TYPE BACK & SIDE SWITCHES)
L------------'3I:%
Fie. 89
locki:t;lg mechanism and allow~ the selector cams to turn on the shaft for setting up.
Pawls
If a Pawl does not fall completely into
the notch on the station selector cam,
check the setting of the back switch. It
is probable that the Power contacts are
opening too soon. Notice that in order
to fall into the notch, the pawl must
work against the bar carrying the bakelite cam. Anything that makes this bar
operate hard should be corrected. See
that the end of the pawl and notch on
the station selector cam are smooth and
~ree from burrs. Then try closing up the
Power contacts on the back switch a
little more, but only after checking the
above points. This may be done by
bending the Power blade so the Power
contacts are closer together. Do not
change the outline of the pawl or cam
notch.
186
I,
I,
Setting Up Procedure
z
II:
....
I
Setting Up
The following points must be ob,served during the setting up and use
of the automatic mechanism if best
results are to be obtained.
On some models the tone control
broadens the tuning when in the treble
position, maximum clockwise, therefore
, this position positively must not be used
during set-up.
a. Use a good antenna.
, In brief, the setting up procedure is
as follows:
a. PuII off the tuning knob. This reveals the set-up knob (Fig. 87). Pull
the set-up knob out. Unlock the mechanism by turning the set-up knob clockwise until a slight click is heard.
b. Push in a button. After the pointer
has stopped moving, grasp the set-litknob and tune in the station to which
the button is to be set.
c. Push in another button. After the
pointer has stopped moving, again
grasp the set-up knob and tune in the
station to which this button is to be set.
d. Continue to push in buttons and
tune in the stations until as many are set
up as desired. Then release the last button set up, by pushing the set-up knob
part way in.
e. Pull the set-up knob back out.
Lock up the cam assembly by turning
the set-up knob counter-clockwise as far
as it will go. Continue to force the setup knob in a counter-clockwise direction even after it seems to reach a definite stop. If you do not use force, the
settings of the buttons may change.
LATCH ARM
LATCH SPRING
SPRING
RETAINING
WASHER
CAM ASSEMBLY LOCK
FIC.90A
FIG. 9GB
I
i f~
I,
I
AUTOMATIC
f .. Push in the set-up knob and reo
place the tuning knob.
In case of complaint that a button set
for some frequency, does not tune to that
point within 10 K.C., or more, after locking up, it usually develops that the station selector cam has inadvertently been
moved before it was locked. This may
come about by turning the set-up knob
slightly when releasing the button, preparatory to lockin~ the mechanism. Another possibility, if the back switch is
not adjusted properly, is that by pushing a second button the motor will start
before the pawl falls clear of the first
cam, thus causing this cam to be shifted
slightly before it is locked in place.
A short may occur in the unit due to
the tuning shaft bearing stop (Fig. 87)
getting out of place. It then catches
on the set-up gear. When the gear is
turned counter-clockwise it forces the
bearing stop against the hot blade of the
side switch. Solder the bearing stop in
place.
• Section 6
TUNING
rotation. Fig. 91B shows the tuning
button depressed with the stop lever
bearing agaihst the outer periphery of
the brake shoe. The ball on the end of
the switch lever is depressing the switch
plunger causing the motor to run. The
motor will run the system until the stop
lever drops into the notch and allows
the switch lever ball to leave the switch,
thus stopping the motor with the setting
disc firmly locked in place, as shown in
Fig.91C.
Fig. 91D shows the manner in which
the setting disc is released from the
brake drum to allow it to be set at the
correct point for station tune. The station is tuned in manually with the system as shown in Fig. 91D. The brake
drum turns freely within the setting disc
until it is clamped in place by the cams
on the drum release and auxiliary lever,
as the setting button is withdrawn.
Study of the position of the various
parts as shown in Fig. 91 will disclose
the sequence of operation.
Audio silencing is obtained by a
switch operated by axial movement of
the motor shaft.
.
SECTION 9D
Buick Sonomatic
The push-button tuning mechanism
of the Buick Sonomatic Model 980620
is illustrated in Fig. 92. One button
is removed to show the lock screw.
SECTION 9C
Wells-Gardner
"Electric Drive"
The Wells-Gardner "Electric Drive"
is a combination of mechanical and
electrical interlocks which allows station "set-up" from the front of the receiver. The station stop mechanism consists of a series of discs which are geared
to the condenser drive system and are
encircled by brake shoes having notches
which co-operate with stop. levers as
shown in the sequence of drawings of
Fig. 91.
Above each station tuning button IS
a setting button used. only when it is
desired to change the pre-set tuning
choice. The station tuning buttons are
interlocked by means of a side-acting
latch in such a manner that the act of
depressing a station button will move
the latch and release any previously held
button. This side-acting latch or locking
plate is also actuated by the manualelectric transfer control.
Fig. 9lA shows the system of rocker
arms and stops in position corresponding to a released plunger. It will be seen
that all parts of the stop system are clear
Qf the brake shoe and will allow its free
(Al
I
ELECTRIC MANUAL LEVER IN L
L&E\..~~
ELECTRIC POSITlON--BOTH
BUTTONS OUT--SWITCH IN
TUNING
S.PRING
","UTTON
LOWER-OFF' POSITlON-- STOP
LEVER AND ROCKER ARM STOP
FREE DF SETTING DISC.
-Setting Disc-Off Position
-Setting Disc-On Positfon, Stop Lever on Edge of Di.c
SET1'ING
OISC
(e)
(0)
TUNING BUTTON DEPRESSED
PAWL PUSHED BACK
STOP LEVER IN NOTCH OF SE TTING DISC
ROCKER ARM STOP RIDING ON SETTING
OISC"SWITCH IN UPPER OFF POSITION
BOTH BUTTONS OEPRESSED--SETTING
BUTTON ENGAGING ROCKER ARM-ROCKER ARM ENGAGING DRUM RELEASE
LEVER--STOP LEVER IN NOTCH OF SETTING
DISC--SWITCH IN UPPER OFF POSITION
~Settjng
Disc-Stop Lever in Notch
~Setting
Disc-Setting Button Depressed
Fie. 91-Wells-Gardner "Electric Drive" Details
187
Section 6 •
THE
MYE
It is important that this set be connected to a six-volt battery before any
attempt is made to operate the tuner.
Magnetic clutch "E" (Fig. 92) must
operate to remove the load of the
manual tuning system before the push.
buttons will operate.
In set-up anll operation this tuner is
very similar to the rocker bar types._
Pushing pawl "F" pushes against the
.. "C"
pair 0 f racks "D" to turn pInIOn
to the desired position.' Pinion "C" is
connected directly to the dial mechanism and geared to the condenser side of
the magnetic clutch "E." The switch
contacts which operate the clutch are
closed by the very slightest touch of a
button.
To set up stations on this receiver
proceed as follows:
First remove the push-button by
pulling the button spring to the right
and pulling straight out on the button,
Then loosen lock screw "A" wit4 a
coin or screwdriver. Carefully tune in
the desired station ~y ~eans of the
manual control, then push the loosened
screw in as far as possible and retighten.
TECHNICAL
MANUAL
SECTION 9E
Emerson Instamatic
PUSH IN THE BUTTON
WITtt A flRIIt·RAPO
MOTION. AS FAR IT
WILL GO, SO THAT IT
REMAINS OEPRESSED.
'The six push-buttons provide a choice
of six favorite broadcast stations for
Miracle Instamatic Tuning. Adjustments for any particular station must
be made by means of the small crossslotted button immediately below the
chosen push-button. The following procedure must be carefully observed in
making these adjustments:
Insert the line plug in the- electrical
outlet. Turn the receiver on by rotating the tone control knob clockwise
until the switch is heard to click and
then rotate this knob to the extreme
clockwise position. Wait about a minute for the tubes to warm up. Turn the
wave-band switch to the broadcast position, clockwise. Turn the volume control clockwise to about half of its full
rotation.
I~
I
11
II,:"
~~:,v~~~~~foaid
Ii
by meons ot c..:IJusting
, button.
I
when tuning station
,:
"
'~~~~jib
U
TURN THE SLOTTED
ADJUSTING SUTTON
JiITH A COIN ANO
OBSERVE DIAL FACE.
TUNE IN STATION IT
MEANS Oil' THIS
AOJUSTING BUTTON
I'
I'
II
i~
I
I
FIG.~3
FiG. 92
188
Push in the manual selector knob
(second from right). When pushing in
the selector knob or one of the pushbuttons best results are obtained by using a firm rapid action.
With the selector knob depressed
tune in the desired station. Rotate the
selector knob until the mark on the dial
face corresponding approximately to
the frequency of the station appears at
the black indicator line on the conical
escutcheon window. Identify the station and note the approximate position
of the dial face,
Push in the button to be adjusted for
this station. (See Fig. 93.)
Insert a small thin coin in one of the
slots of the adjusting button immediately below the push-button. Turn the
adjusting button until the mark on the
dial face corresponding approximately
to the frequency of. the station again
appears at the black indicator line on
the conical- escutcheon window. Once
the station is heard, tune it in carefulJy
I,
I'
AUTOMATIC
UP
DOWN
FIG. 94
TO UNLOCK: Turn Manual Tuning
Control down about 70 to 100 strokes
after word UNLOCK appears. Turn until control turns hard after turning
easily. Never force control after this
point is reached.
by turning the adjusting button back
and forth slowly. From the standpoint
of performance it is of paramount im·
portance to tune in the station accu·
rately. (See Fig. 93.)
.
It is very important, when tuning in
a station by means of the adjusting but·
ton, that the last turning motion of the
adjusting button be in the counterclockwise direction, as indicated in
Fig. 93.
Check the results by moving the dial
face, using the selector knob, to a dif·
ferent position and then pushing in the
·button. The station should be received
clearly and with maximum volume.
Adjust the remaining buttons, one at
a time, following the procedure out·
lined above.
SECTION 9F
TO LOCK: Turn Manual Tuning Control up about 711 to 100 strokes after
word LOCK appears. Turn until control
turns hard after turning easily. Never
force control after this point is reached.
(c)
(d)
(e)
(f)
Hudson Feathertouch Tuner
IMPORTANT PRECAUTION: In order to
assure perfect results you must observe
all instructions. One very important
precaution during set· up is to never
touch a button already set while control unit is unlocked. For example, if
some buttons are set and while work·
ing on the remainder you accidentally
touch one already set, the setting on
this button will change. This will ne·
cessitate resetting of the button acci·
dentally touched.
How to Set Up Push·Buttons
(a) Operate set for about ten minutes
before setting up buttons.
(b) To Unlock Tuning Mechanism:
Rotate right (tuning) control downwards until word Unlock shows at
(g)
• Section 6
TUNING
the left side of diaL Continue to
'turn until wheel tightens. (70 to
100 strokes will be required.) A
more complete description of this
procedure is given below under
the heading "Unlocking Tuning
Mechanism. "
Tune in desired station with (tun·
ing) control.
Hold down the button selected and
move tuning control up and down,
leaving it in position where tone
is deepest. Release button.
Follow same procedure for other
buttons. IMPORTANT: After setting
any button, it must not be touched
until after mechanism has been
locked as in (f). Otherwise it is
necessary to reset it as in (c) and
(d) .
To Lock Tuning Mechanism: Ro·
tate tuning control upwards until
word LOCK appears at right side
of dial. Continue to turn until
wheel tightens (70 to 100 strokes
will be required). A complete de·
scription of the locking operation
is also given below.
Insert station call letter tab in
front of each button. The tabs are
inserted by flexing them and al·
lowing them to snap into place in
the buttons.
2. Now hold the manual tuning can·
trol and push the button to be set
up several times.
•
3. After pushing and releasing button
several times, hold button down
and again tune station carefully by
turning manual tuning control back
and forth slightly.
4. Repeat for other buttons.
The essential difference between this
procedure and the one given above is
that the button is pushed and released
several times in quick succession after
desired station is tuned in but before
final tuning adjustment is made.
Unlocking Tuning Mechanism
In setting up this mechamsm, you
must understand the action of the con·
trol during locking and unlocking.
The l)-nlocking operation begins after
the tuning control is turned to the point
where the word unlock appears. To
complete the unlocking operation, the
tuning control must be turned quite a
bit after this point is reached. When
unlocking begins, the tuning control
may turn quite hard, but then it begins
to turn quite easily. You must continue
to turn it downwards until it again
turns hard. Because of the high gear
ratio, it may require 18 to 24 complete
turns of the tuning control to reach this
point. Since you can turn this control
only a quarter of a turn at a time, it
may require 70 to 100 strokes of the·
finger on the control to completely unlock the mechanism. The tuning control
will not reach a definite stop when the
mechanism is unlocked. However, when
the control turns easily for quite a
while, then turns harder, the unlocked
position is reached. In this position the
tuning control wiH spring back when
you take your finger off after turning
it. At this point, the tuning indicator
will function if you turn the tuning con·
trol back (up). Important: When this
position is reache.d, do not force the
tuning control further down.
Setting Up Early Radios
Locking Tuning Mechanism
Some of the earliest radios produced
require a slightly different set·up pro·
cedure than given above. This same
procedure can be used on later sets
though it is not necessary.
After unlocking the tuning mechan·
ism, proceed as follows for each button:
1. Tune station in manually.
The locking action begins when you
continue to turn the tuning control up·
wards after the word lock appears.
The action is much the same as de·
scribed 'under unlocking and it will reo
quire as many turns of the tuning con·
trol to lock the mechanism as were
needed to unlock it.
189
Section 6 •
THE
M YET E C H N " CAL
MAN U A L
PUSHBUTTON
FI.,. 95-Magnet Plunger in "OUT" Position
Fu;. 9O--Magnet Plunger in "IN" Position
Refer to Fig. 95 and Fig.' 96. When a
push-button is depressed, it makes mechanical contact with the cam operating
bar located under it, and depresses the
bar so that the gathering bar can make
contact with it. At the same time, the
key forces the contact plate downward,
making electrical contact through the
contact screw. When the contact screw
makes contact, it energizes the winding
of the magnet assembly causing the
plunger to be drawn completely into
the magnet as shown in Fig. 96. The
plunger is mechanically coupled to the
gathering bar and gathering bar shaft,
'so that when the plunger is drawn into
the magnet, it causes the gathering bar
to be forced ahead. The gathering bar
engages the cam operating bar which
is depressed by the push-button key and
drives it forward as shown in Fig. 96.
This position of the cam operating bar
is indicated by the ends of. the cam
operating bar extending from the mechanism frame (see Fig. 98). When the
cam operating bar moves forward, the
cam stops attached to the bar engage
the cam, rotating it until it is in the position indicated in Fig. 96. The rotation
'of the cam causes the cam shaft and
gear segment to rotate likewise, rotating
the gang condenser to a position corresponding to the station to which this
particular key is set..
threaded collar is turned upon the
threaded section of this cam shaft, exerting pressure upon the cams and friction collars, thus locking them securely
in position. When the cams are unlocked, this threaded collar is turned
so as to unscrew it and exert a minimum of pressure on the cams and friction collars. The only pressure then exerted upon the cams to hold them in
position is that exerted by a spring
washer near the threaded end of the
shaft. Thus the cams are. held so they
cannot move of their own accord, but
are still loose enough to permit them to
be set to correspond to the desired station.
The threaded collar is connected
through the clutch to the manual tuning control, permitting adjustment of
the cams from outside the tuning unit.
How the "Locking-Up"
nlechands~ ~orks
The cam shaft assembly consists primarily of a shaft on which five cams
are alternately spaced between friction
collars. On the clutch end of this bar is
a short threaded section upon which
screws the collar which is part of the
clutch and clutch spring assembly.
When the cams are locked, this
190
Operation of Clutch and De-Clutch Arin
The clutch mechanism of this tuner
(see Fig. 98) functions every time a
push-button is depressed. Its purpose
is to de-couple the manual tuning control and its associated gears from the
automatic portion of the tuner when
tuning electrically. The clutch is a dual
unit, providing positive mechanical
coupling between the manual tuning
gears and the cam shaft, and it also has
CAM ON
GATHERING BAR
SHAFT
DE~g~~C~~-G--":-'::::-.='-'T-_--r'_...J
ARM
FiG.97A
Correct Position of
Cam on Riser
a leather friction disc which operates
in conjunction with the positive coupling element to remove ex~essive backlash when tuning mechanically.
When the plunger is drawn into the
magnet, turning the gathering bar
',shaft, the cam attached to the shaft
(Fig. 98) moves downward on the riser
of the de-clutch arm, releasing the pressure on the de-clutch arm, which bears
against the inside section of the clutch.
When this pressure is released, the
clutch return spring contracts, separating the two halves of the clutch, thus
disengaging the manual tuning gears.
When the push-button is again released, allowing the plunger to be withdrawn from the magnet, the cam on the
gathering bar shaft moves upward on
the de-clutch arm riser, again exerting
pressure on the de-clutch arm, and in
turn on the clutch, thus engaging the
two clutch sections, and making manual tuning possible.
Set Tunes
I:
I'
I
I~properly
If the set fails to tune in stations
properly, first check the set-up of the
various buttons. If the set-up is incorrect, the set will tune consistently to
the same point, and thIs condition can
. be remedied by res~tting the buttons.
If the set will not tune in stations,
although the plunger tends to move,
make sure the Bristo headed set screws
in the retaining collar are tight. This is
the collar which is almost touched by
the condenser drive gear sector when
the condenser plates are unmeshed. A
loose set screw may strike the unit
frame, causing the plunger to stick in
either the IN or OUT position.
If the set fails to tune properly, and
the djal stops at different points when
approaching the station from opposite
ends of the dial the mechanism may
not be properly locked up (see "Locking Tuning Mechanisms"). The. next .
step is to check for binding of the
~-~~
.~ ~R ~
FIG.97B
Position of Cam
Too Low
I'
FIG.97c
Position of Cam
Too High
..
FIG.97D
Correct Position of
Cam on Alternate
Type Riser
I
I
I
AUT 0 MAT' C
• Section 6
TUN ,'N G
mechanisms. Below are enumerated
some of the reasons for binding:
SET
GANG
CQUNTER-
Rubbing Light Diffusion Plate: Two
types of light diH usion plates were
used, the new tyPt' being riveted to the
cover, while the old type is mounted
on the unit itself (see Fig. 99). If the
new type light diffusion plate, which is
mounted in the cover of the control
head, rubs against the dial scale due to
warping of the celluloid, cut this plate
as shown by the shading in Fig. 99. This
can be done without removing the
shield from the cover. In' some early
units, this diffusion plate was mounted
on the unit itself. In this case, enlarge
the notch fitting over the dial lamp
wire as shown in Fig. 99. Exercise care
when enlarging the notch, as the celluloid is quite brittle and may break.
Then cement the diffusion plate to the
front of the contact plate assembly so
that the shield rests flat against this
metal plate.
SPRING
FIe. 98
mechanism (see section on "Binding").
This trouble also may occur if the pulling force of the magnet is not great
enough. This may occur when the battery voltage is low (below 5 volts).
It may also be due to too large a gap
between the plunger and the pole piece
of the magnet assembly. On later sets
the gap can be adjusted as described in
paragraphs 5 and 6 of "Replacing
Magnet Coil Assembly." The adjqstable magnet assemblies are identified
by the Gap Adjusting Screw and Locking Nut shown in Fig. 98.
In the early type of magnet assemblies the gap is not adjustable. If one
of these magnets is found to have insufficient pull, the remedy is installation
of the new type magnet assembly.
. However, before replacing a magnet
assembly, make sure that improper
tuning is not due to low battery voltage
or the other causes mentioned above.
Mechanism Where Tuning Control Fails
to Reach Stop Dudng Unlocking
This is probably due to the shearing
off of the "C" washer on the clutch end
of the cam shaft (see Fig. 98). On the
earlier mechanisms, this "C" washer
holding the clutch and gear assembly
to the shaft was made of a fairly soft
steel. Occasionally these washers may
shear off if the customer continues
turning the tuning wheel after the
mechanism has become completely unlocked. This continued turning forces
the gear and clutch assembly against
the "C" washer, shearing it off completely. Replace this washer with the
new hardened washer. This can be done
without removing the tuning unit from
the case. First lock the mechanism,
then remove the nuts holding the triangular plate on the clutch end of the
tuner. Unhook the plunger return
spring so that no pressure will be exerted by the clutch. The washer can
now be removed and a new washer installed.
On all early sets, replace this "c"
washer even if the old one is still all
right.
Shearing or partial shearing of this
washer may cause slipping of the
clutch or sticking of the plunger in the
OUT position.
.
If a bronze washer is present between the "c" washer and the gear, nimove it and discard it. If a steel
washer is present, it must be left in
place. On early mechanisms, a nil
steel washer was used in this position
and it must be left in place.
Binding
If the radio tunes improperly, check
for binding in the dial and tuning
~I
OLD TYPE
I~
PORTIONS SHOWN SHADED TO BE CUT AWAY
FIG.
99'--Illustration Showing Method of
Cutting Light Diffusion Plate
Ends of Drum Rubbing Brackets:
The dial drum should have a slight
amount of end play. If it doesn't, it
may be binding. This may be due to
improper placement of the volume control mounting bracket. To correct this
difficulty loosen the two screws holding
this bracket and move it slightly farther
away from the drum.
.
Similar binding may also be due to
a loose end cap on the dial drum. In
this Gase, force the cap back on the
drum and punch-mark the cap to hold
it in place on the dial drum.
In a few cases it may be found that
dial end bearing is out of line or
slightly off center. The bearing can
generally be benr slightly to restore it
to its proper position. If this cannot
be done, replace the dial scale assembly.
Binding of the drum on the mount·
ing brackets may be due to the fact
that the control units fitted too tightly
191
Section 6 •
THE
in early cars. This causes the escutcheon to be forced sideways, thus pressing on the tuning controls, which may
move the dial drum brackets. This
binding can generally be eliminated by
bending the brackets slightly outward.
Similar difficulties will be encountered if the control head is not properly installed. / When mounting the
head, tighten the wing nuts evenly, so
the control head will not have a tendency to hind against the dash opening,
which would push the escutcheon
,against the controls.
Drive Pulley Striking Antenna Coil
Shield: Check to see that the dial drive
pulley is properly located on condenser shaft. Its bushing should touch the
condenser pinion gear.
Also, the antenna coil shield can
may be moved slightly away from the
drum by loosening the two nuts holding down the can.
It may also be possible to move the
entire tuning unit slightly away from
the shield can. Loosen the four screws
holding down the unit and shift it. '
Chassis Wiring Improperly Placed:
, If the leads from the on-off switch and
other leads in the vicinity of the "A"
filter assembly are not properly located,
they may interfere with free motion of
the dial cord or the condenser drive
gear sector. Dress these leads so that
they cannot touch these moving parts.
, Binding Between Sector and Pinion
Gears: Excessive friction between these
gears can be reduced by changing the
position of the pinion gear so that the
set screw indicated in Fig. 10 points upward when the gang is completely
closed. This draws the pinion gear
slightly farther away from the gear sec- .
tor, reducing the pressure between
them.
Counter-Weight Strikes Case: Should
the gang counter-weight strike the wraparound case, loosen the four screws
holding the tuning mechanism to the
chassis and shift the tuning mechanism slightly so counter-weight clears
case. Keep in mind that !;he case side
may be pulled in slightly when the
cover is put on. If the case is warped'
inward, bend it slightly outward till
counter-weight does not strike it.
Slipping Clutch (Backlash)
A slipping clutch is indicated by ex, cessive backlash during manual tuning.
192
MYE
TECHNICAL
MANUAL
First check to see that the correct
plunger return spring is used_
The correct type of spring may be
determined from the following table
giving the dimensions of the three types
of springs which have been used.
No. Length
Outof
of Overall side
Turns Body Length Diam.
Correct Spring... 36
%"
,Light Spring.34 or more %"
Heavy Spring.
24
H"
1%"
1JA,"
1%"
is"
*"
If"
If the unit has the light or heavy
spring, replace it with ,correct one.
When changing springs, it is also desirable to replace the magnet assembly
if it does not have the Locking Nut and
Gap Adjusting Screw shown in Fig. 10.
Ho}Vever, this is only necessary when
there is insufficient pull of the solenoid
to operate the mechanism.
Next check the position of the cam
on the end of the gathering bar shaft
(copper plated shaft) with relation to
the riser of the de-clutch arm while the
plunger is out. See Fig. 98 and Fig. 97A.
The cam should be halfway up the
curved portion of the riser as shown in
Fig. 97A.
If the cam is not halfway up the
riser while plunger is out, as shown in
Fig. 97A loosen the two Bristo set
screws in the retaining collar on the
other end of the gathering bar shaft and
move the retaining collar on the shaft
until the cam is properly positioned on
the riser. A special set screw wrench is
needed to fit the Bristo set screws.
In all cases wher,e slipping clutches
are reported, check to see that there is
no excessive friction in the gang condenser, dial or gang condenser drive
gea~s. See section on "Binding."
plunger and the pole piece is 'adjustable. Adjustable magnets are identifi,ed
by the gap adjusting screw and locking
nut on the end of the magnet assembly
(see Fig. 98). In these sets, loosen the
locking nut on the rear of the magnet
and turn the gap adjusting screw,
outward {counter-clockwise) one-half
turn, and re-tighten the locking nut. If
this sticking occurs in early units, replace the magnet with the newer type
assembly. Read the paragraph "Replacing Magnet Coil Assembly" for instructions for replacing and adjusting
the magnet assembly.
The plunger may stick in the OUT
position, if the "C" washer on the
clutch end of the cam shaft (Fig. 98) is
totally or partially sheared off. Check
this washer, and if found defective, replace with the hardened type of washer. A faulty "C" washer allows the
plunger to come out too far, ~d also
allows the cam to reach a position too
high on the de-clutch arm riser (see
Fig. 97C).
After checking the "C" washer, check
the adjustment of the cam on the riser,
as explained under "Slipping Clutch."
If the cam is too far up on the riser
(see Fig. 97C) it lets the plunger come
out of the magnet too far and this may
cause sticking. If the cam is not far
enough up on the riser (see Fig. 97B) the clutch may slip.
If the position of the cam is correct
as shown in Fig. 97A, but the plunger
still sticks, loosen the two screws holding
down the magnet and shift it slightly
until the plunger moves freely, then retighten the screws. If this does not
clear up the difficulty, replace the entire
magnet assembly.
Sticking Magnet Plungers
Replacing Magnet Coil Assembly
If the automatic tuning mechanism
does not operate, but manual tuning is
possible, the plunger may be stuck in
the OUT position (see Fig. 95). If manual tuning control turns easily but does
not tune stations, the plunger may be
.stuck in the IN position (see Fig. 96).
A loose set screw on the retaining collar on the gathering bar shaft may
strike the frame and cause the plunger
to stick, so check the set screws first.
If the plunger sticks when the plunger is all ,the way in, it is sticking against
the conical pole piece of the magnet assembly.
On the later sets, the gap between the
To replace a magnet coil assembly,
proceed as follows:
1. Remove top and bottom' covers of
tuning unit. Unsolder red and
black magnet wires froni points to
which they connect.
2. Take out two round headed screws
holding magnet to mounting plate.
3. Lift off old magnet assembly and
install new assembly.
4. When replacing this magnet assembly, before tightening the screws
holding down the unit, check to see
that thll plunger moves freely inside the magnet coiL If it has a
I',
I
I~
AUTOMATIC
tendency to bind, shift the position
of the magnet slightly until the
plunger moves freely, then tighten
down the holding screws.
5. It is now necessary to set the large
adjusting screw on the top of the
new magnet. Loosen the nut and
turn the screw out several turns.
Now push down one of the push.
button shafts next to the drum dial.
Then with a screwdriver, push the
plunger into the magnet as far as it
will go.
6. While holding the plunger in very
tightly, you can now release the
push-button shaft and turn the magnet adjusting screw in, until you
feel the screw striking the plunger.
When this happens, back the screw
out one complete turn and retighten
the locking nut. This adjustment
must be made very carefully, since
if the threads are tight it is difficult
to notice the exact point where the
screw strikes the plunger.
Important: To get proper adjustment, a push-button shaft must be depressed before pushing in the plunger
so that the plunger operates the tuning
mechanism as indicated by one of the
cam operating bars extending from the
frame (Fig. 98). If the above adjust~
ment is done while the power is on the
unit, the plunger will pull in by itself
as soon as you depress one of the pushbutt~n shafts. It is then merely necessary to hold the plunger in tightly with
a screwdriver and release the push-button shaft. The adjustment can then be
made.
• Section 6
TUNING
bly. When the gang condenser or any
of its associated parts are replaced or
otherwise . adjusted, before tightening
the set screws holding the condenser
drive pinion gear to the shaft, set the
rotor plates so that their upper edges
are flush with the top edges of the stator
plates. Then turn the condenser drive
gear segment until the stop arm on the
cam shaft strikes the fixed stop on the
frame, then tighten the set screws.
When this adjustment is properly
made, and when the stop arm adjusting
screw is correctly set, no strain is put
on the rotor plates of the condenser in
either the open or closed position of
the gang condenser.
tion is to counter balance the weight of
the gang condenser. When the weight
is in correct position the edge of the
weight nearest the set screw is approximately straight up and down with the
gang condenser fully meshed. When replacing the dial drive drum, always
check to see that this weight is in the
position described above, or the tuning unit may not operate satisfactorily.
SECTION 9G
Motorola Electric
Automatic Tuner
Adjustment of Contact Screw
NOTE
Th~
contact screw, once properly set,
seldom requires readjustment. Improper adjustment may be identified by the
following symptoms:
Contact Scr.ew Too Far In: When a
push-button key is depressed, the magnet will operate, but the cam operating
bar may not be pushed through as
shown in Fig. 98.
Contact Screw Too Far Out: This
may permit the push-button key to exert too much pressure on the cam operating bar and cause it to stick.
Chattering of the mechanism may be
caused when the screw is either too far
in or too far out. Adjust the screw un. til the unit operates properly when any
one of the push-buttons is depressed.
All seven tuners are identical in construction, except for the condenser
gang.
E5T has a 3-gang condenser and is used
in Models 9-49 and 9-69.
E6T has a 2-gang condenser and is used
in Models 15-F, 20-P, 21-L, 22-S,
24-K, 'and 25-N.
E7T has a special high frequency condenser gang and is used in Police
Cruiser Model P-69-14.
Ell T has a 3-gang condenser and
used in Model 500.
IS
E12T has a 3-gang condenser and
used in Model 700.
IS
Position of Gang Condenser
Counter-Weight
E13T has a 2.gang condenser and is
used in Models 34K6 and 34K7.
Refer to Fig 98. The purpose of the
counter-weight shown in this illustra-
E14T has a 3-gang condenser and is
used in Model 550.
Stop Arm Adjusting Screw
The function of this screw (Fig. 98)
is to prevent damage to the gang condenser plates when the rotor plates are
fully opened. This screw is adjusted so
that the stop arm on the cam shaft will
strike it just before the gang condenser
plates open so far as to strike the sta·
tionary plates. Set this screw so the
stop arm will strike it when the rotor
plates are approximately Y8" from the
stator plates. Then tighten the locking
nut so as to hold the screw in this position.
There is also a fixed stop whose purpose it is to stop the condenser plates
just before they strike the fixed plates
when the plates are fully meshed. This
fixed stop is part of the frame assem-
FIG-IOO
193
Section 6 •
THE
M Y ErE C HI N I CAL
MAN U A 1
Motor Does Not Run
Mot~r Fails to Reverse
4. Die Cast Hub Expanded. This usual-
1. Motor Contacts in Control Head Not
Closing. Open the control head and in·
spect the motor contacts. If the gap is
too great, contact will not be made when
the button is pressed. Adjust by bending carefully.
1. Reversing Switch Not Properly Adjusted. See instructions on page 195.
ly causes the two outside rings to bind.
Can be corrected by filing hub.
2. Open Circuit in Motor. If one side
oLmotor circuit is open, motor will run
in one direction only.
Fails to Stop at Station
2. Poor Contact at Push-Button Plug.
Inspect the contacts between the plug
and the receptacle on the chassis.
3. Open Circuit in Motor. Check all
connections to motor and check motor
winding for continuity.
4. Motor Brushes Not Making Contact.
Check contact between brushes and
commutator. Clean dirty commutator
with carbon tetrachloride.
5. Low Battery Voltage. A weak or defective battery in the car would not deliver sufficient voltage to run the motor.
6. Flexible Tuning Shaft Binds. Binding in the flexible tuning shaft places
an additional load on the motor. If this
load is too great, it will prevent the
motor from turning the mechanism.
7. Magnet Fails to Release. If the magnet which. has previously been energized, fails to release the latch bar for
any reason, the motor cannot turn the
mechanism.
Mechanism Runs Sluggishly
1. Low Battery Voltage. A weak or defective.battery will not deliver sufficient
voltage to turn the motor at normal
speed.
2. High Resistance C~ntact in Control
Head. High resistance at the push-button contacts will cause a voltage drop
which will prevent the motor from turning at normal speed. _
3. Poor Contact Between Push-Button
Plug and Receptacle. This will also result in voltage drop, and lessened motor
power.
4. Binding in Tuning Shaft. Binding in
the flexible tuning shaft will place an
additional load on the motor which can
slow it down considerably. Install tuning shaft with minimum amount of
bending and check alignment where the
tuning shaft enters the receiver housing.
5. Gears Not Properly Meshed. Check
all gears in assembly for binding due
to improper meshing.
6. Defective Motor.-Replace.
194
3. Open Magnet Winding. An open
magnet will not pull latch down; consequently will not cause motor switch
to reverse.
4. Latch Bar Spring Too Tight. If the
latch bars operate under too much tension the magnet may not be able to pull
the latch down.
Fails to Retain Original Setting
1. Latch Rings Not Locked Securely.
The locking screw must be pulled down
securely, otherwise, the shock of the
sudden stopping will tend to slide the
rings away from the original setting.
2. Original Setting Not Accurate. Resetting of magnets may be necessary
after several days' use, during which
time the mechanism goes through a
"shaking down" process.
3. Electrical Drift. This is usually the
result of a great change in temperature.
Automatic compensation is provided in
the circuit to take care of the normal
operating temperature range. Before
making original setting, turn the set on
and permit it to play long enough to
arrive at a constant operating tempera'
ture. In zero weather do not expect the
set to tun~ "on the nose" until after a
constant temperature has been reached.
In severe cases of electrical drift occurring at normal operating temperature,
change the compensating condenser.
Impossible to Set Up Stations
. 1. Too Much Tension on Locking Levers. When the automatic locking screw
is loose, the station rings should move
freely. If the levers still hold the station rings partially locked, the screws
which hold the levers in position should
be loosened one-quarter to one-half
turn.
2. Latch Rings "Out of Range." If the
1. Open Magnet Winding. Check for
continuity and replace if necessary.
2. Magnet Contact in Control Head Not
Closing. Inspect contacts. Adjust or
clean if necessary.
3. Latch Bar Defective. Inspect latch
bar to make sure that it has not been
damaged. Replace latch bar, if required.
4. Poor Contact at Push-Button Plug.
A poor contact here means a voltage
drop which reduc~s the pulling power
of the magnet.
5. Improper Spacing of Magnet. Check
the spacing between the latch bar arma·
ture and the magnet pole. When the tip
of the latch bar is seated all the way
down in the notch in the latch ring, the
armature should not quite touch the
magnet pole. A hair line of light should
be visible between them.
6. Latch Rings Not Locked Securely.
If the latch rings are very loose the
motor will continue to turn the gang until the plates are completely meshed.
Latch Bar Sticks in Notch
1. Manual Tuning Shaft Binds. Bindin the tuning control shaft causes
the latch bar to press hard against one
side of the notch and may prevent it
from releasing as the magnet is deenergized.
~ng
2. Latch Bar Spring Weak. Check latch
bar tension spring to make sure it is
pulling away from the magnet with
sufficient force. Spring tension is adjustable.
3. Magnet Contact in Control Head
Stuck. Check the magnet switch in the
control head to make sure it breaks
contact when pressure is released on the
button. Check for frozen contact points,
or for sticking button.
4. Armature Rivet Wom. There is a
loosened latch rings slip ort the drum
until the notch falls out of reach of the
latch bar, they can be brought back to
position by following exactly the "setting procedure" outlined on page 195.
brass rivet at the tip of the armature, to
prevent the armature freezing to the
magnet. If this rivet is worn down, permitting the steel armature to actually
touch the magnet pole, it may freeze in
that position.
3. Die Cast Rings "Out of Round." In-
5. Burr on Tip of Latch. Lat~h tip
stall new rings.
should be smooth and shiny.
i
AUTOMATIC
6. Binding in Latch Bearings. Latch
must move freely but not sloppily.
. 7. Latch Tips Not Centered on Latch
Rings. Latl?h tips must not rub bake·
lite guide rings. The latch bar bearing
shaft is adjustable.
8. Friction Clutch Too Tight. A tension
washer between the motor pinion and
the brass pinion collar acts as a friction
clutch to absorb the shock of stopping
the motor quickly when a station is
tuned. If the tension is too tight, thl'!
torque of the stopped motor will hold
the latch bar tip in the notch.
9. Motor Brushes Too Tight. Too much
friction between the motor brushes and
the commutator will cause the same
thing.
TUNING
down. A faint "click" should be heard,
indicating that the tuning magnet has
attracted the latch bar.
5. Holding the magnet energized,
turn the dial manually all the way to
the high frequency end (1550 K.C.)
and then all the way back to the low
frequency end (535 K.C.)
6. Still pressing on the button, tune
in the station to be set on that button.
7. Proceed to set the remaining five
stations. For each station follow steps
3, 4, 5, and 6, as outlined above. At no
time in the setting up procedure should
the Tuning Motor be permitted to run.
8. Tighten the automatic locking
screw very securely. Do not hold the
tuning knob while locking the auto-
Setting StatioDs
NOTE: Before setting any station, let
the set warm up for not less than ten
minutes. If you wish you can "set" the
automatic tuner on the service bench
before installing the radio in the car.
Use a short aerial and peak the antenna
trimmer to it: Then readjust the antenna
trimmer after the installation in the car.
IMPORTANT-You will note that the
9·contact plug on the end of the control
head cable has one pin that is shorter
than the others. For the "setting up"
procedure, this plug should be inserted
in its receptacle on the receiver only
half way. This will cause all of the mag·
net terminals to De connected, but will
not permit the tuning motor to run duro
ing the adjustment, since the'short pin
will not make contact, thereby holding
the motor circuit open. The motor
should not run at any time during the
"setting up" procedure.
1. From the set of call letter tabs
provided, detach the proper ones for
the six stations. The station tabs should
then be inserted in the space provided
in the face of station tuning buttons.
Cover the tab with a small rectangular
piece of celluloid. Both tabs and celluloids snap into position.
2. Loosen the Automatic Locking
Screw. This screw should be turned
counter-clockwise four or five revolu. tions-far enough to assure plenty of
looseness.
• Section 6
matic, but allow the mechanism to turn
to its natural stop.
9. Push the plug all the way into the
receptacle on the receiver housing so
the short motor pin will also make contact.
Reversing Switch
NOTE: Four adjusting screws extend
upward through the switch mounting
plate, three of them in line, and one set
off by itself. (See Fig. 101.)
1. Turn the rotor assembly until the
High sides of all latch rings rest opposite the latch tips.
2. Turn screw "A" in until all latch
bar tips touch High side of ring and
then turn the screw back one-half turn.
(Spacing between latch tip and high
side of ring at point "X" should be 8
to 12 thousandths of an inch.)
3. Hold any latch bar tip down on
High side of ring and adjust screw "c"
(center screw) until the bakelite insulator on the center switch leaf just
Q:
UTING. MAGNET
MUTING ARMATURE
~
,
BOTTOM VIEW
'8"
.RONT
CENTEit
RCAR
3. Turn the dial all the way to the
low frequency end (535 K.C.)
4. Press the fint button and hold it
FIG. 101
195
Section. 6 •
THE
barely misses touching the heel of the
latch bar at point "Y." (Check adjustment by pressing other latch bars. The
depressed latch bar must not lift the
center contact even slightly.)
4_ With latch bar at rest position adjust screw "B" (front screw) until top
motor contact is lifted from center
contact by 12 to 15 thousandths of an
inch at point "Z." (15 thousandths =
1/64".)
5. Turn rotor until Low side of ring
rests under latch tip. Press any latch
bar down and make sure switch actually reverses. (Bottom contact must break
and top contact make sufficiently to lift
the top switch leaf slightly from the
bakelite spacer.)
6. Turn screw "D" (rear screw) until muting relay armature rests 15 to 20 .
thousandths of an inch from the mag-·
net pole. (Too close spacing will cause
intermittent muting due to vibration.)
(15 thousandths = 1/64".)
To Remove Latch Bar Assembly
1. Back up on front switch adjustment screw (A) until latch tips rest
outside the diameter of the bakelite ring
separators.
2. Remove comb shaped latch tension
spring. (E) Fig. 102.
3. Remove the hex-head machine
screw' which extends through the small
angle bracket into the brass latch bar
bearing shaft underneath the tuner.
4. Pull out latch and shaft assembly.
(F)
NOTE: To re-assemble, reverse the
above procedure, and take particular
care that:
1. Latch bar tips center on latch
rings. They should not rub bakelite
ring separators. (Spacing is adjustable
through elongated hole in small bracket under tuner.)
2. When readjusting screw (A),
turn it all the way in until latch tips
touch high side of rings; then back
screw up one-half turn. (See reversing
switch adjustment on page 195 ..
MYE
TECHNICAL
MANUAL
4. Lift the locking nut off the end
of the rot~r shaft.
5. Carefully loosen the three screws
(J) which hold the ring assembly to
the rotor hub, and remove all rings
and separators as a unit, being careful
to keep the three screws in position
through the assembly.
NOTE: To reassemble, reverse the
above procedure. Work carefully-do
not let the rings and separators get off
the screws.
To Replace Defective Latch Ring
1. Remove the entire latch ring assembly from the rotor hub. (See instructions above.)
. 2. Lay assembly on flat surface with
screw heads down.
3. Remove rings; separators, and
brass spacing collars, one at a time, until the defective ring is exposed.
NOTE: Reassemble parts one at a
time, being careful that rings, separators, and spacers are in the correct position.
CAUTION: Be careful to replace rings
in original position. Turning the ring
over will reverse the position of the
notch and will result in faulty tuning.
To Remove Defective Bub and Gear
A.
B.
C.
D.
E.
F.
G.
H.
J.
K.
L.
M.
N.
P.
R.
S.
T.
Fig. 102
Switch Adjustment Screw
Switch Adjustment Screw
Switch Adjustment Screw
Switch Adjustment Screw
Latch Spring (6 finger)
Latch Assembly Complete
Automatic Locking Screw
Clamping Lever
Ring Assembly Screw
Idler Gear Assembly
Motor Pinion
Pinion Collar
Tuning Motor
Relay Magnet Assembly
Reversing Switch
Manual Drive Shaft
Tuning Magnet
2. Loosen the four Bri!1to set screws
in the rotor hub ..
3. Loosen the one Bristo set screw
in the bakelite flexible shaft coupling.
. 4. Pull the rotor hub off the gang
shaft. The manual tuning gear and
coupling will have to be removed at
the same time. The brass collar on the
motor shaft may also need to be removed.
NOTE: When installing a new hub,
turn the gang to full mesh and the hub
gear against its stop before tightening
set screws.
SECTION 9H
Flash Tuning
1. Remove the entire latch ring assembly from the rotor hub. (See instructions above.)
I,
I
!
I
. The Flash Tuning mechanism consists essentially of the toothed disc at
-':0...
To Remove Latch Ring Assembly
I
1. Back up on switch adjustment
screw (A) until latch tips rest outside
the diameter of the bakelite ring separators.
2. Remove locking screw. (G) .
. 3. Remove the three locking levers.
(H)
196
I.'
I.
F'Ic.102
AUTOMATIC
the rear of the variable condenser
and the relay. The function of the
toothed disc is to operate the relay
when the variable condenser is turned
to the various pre-selected stations. The
relay contacts close the Flash Tuning
light circuit, illuminating the station's
call letters. At the same time they remove the high negative bias which
blocks off the audio, keeping the receiver silent until the pre-selected station is tuned in.
The relay coil normally is energized.
It is short circuited by the bent up tooth
of the disc contacting the movable arm.
This is why the Flash Tuning light
flashes for a second or so when the receiver . is first turned on-the rectifier
has not heated sufficiently to furnish
current to energize the relay.
Turn the Flash Tuning and Selectivity Switch knob to the "SHARP" position. Then tune in the first station on
your list of selected stations.
Leaving your station tuned in, go to
the rear of the radio. You will see a
semi-circular toothed disc, as illustrated
in Fig. 103. There is also a flat spring
arm, with a small rounded projection
near its end, that moves over the teeth
of this semi-circular disc as the Station
Selector knob is turned. Still leaving
your station tuned in, carefully not~
which tooth on the semi-circular disc is
directly under the rounded projection
of the spring afI~. Mark this tooth with
a pencil. Note that there is a double
row of teeth and either the tooth that
faces you or the tooth that faces the
front of the radio may be bent up, depending upon which one is nearer the
rounded projection of the spring arm.
After you have marked the tooth, turn
off the radio. Then tune away from the
station (with the Station Selector knob,
not the movable arm) and bend this
marked tooth straight up, using the
slotted end of the tool provided. See
Fig. 103. It is important that the slot
of the tool fit as far down as possible
on the tooth before bending. This is
necessary so that the complete tooth
will be bent up instead of just part of
the tooth. When this is properly done,
the projection of the spring arm will
touch the bent up tooth when the
toothed disc is rotated by turning the
Station Selector knob.
Turn the radio on again and tune in
• Section 6
TUNING
the next station on your list of selected
stations. Mark the tooth that now is
under the projection of the spring arm
when this station is tuned in. Turn off
the radio, tune away from the station
so that the spring arm will not be in
the way and bend up this marked tooth,
using the tool provided. Proceed in the
same manner for each of the other stations on your selected list. Turn off the
radio each time before hending up the
tooth. Otherwise a slight spark may
occur, although there is no danger of
shock. When properly done, the spring
arm will touch each of the teeth that
has been bent up but will not touch any
of the other teeth, as the Station Se,
lector knob is turned. Since the mechanism will already be set up on teeth
close to the ones· you will want to use,
these old teeth must be bent back down.
Turn the Flash Tuning and Selectivity Switch knob to the "FLASH" position. Now again tune in the first station
on your selected list. As its position is
reached, the bent up tooth will'touch
the spring arm and a light will flash on
the' dial at a position opposite the end
of the dial pointer.
SECTION 9J
Packard 333915
First turn the receiver on and allow
it to operate for twenty minutes before
making these adjustments.
POSITION OF TOOL
AFTER SLOTTED END
HAS BEEN USED TO
BEND UP TOOTH
Press in the "DIAL" button and hold
it in until the tuning motor stops, indicating that your receiver is now connected for manual tuning.
Using the tuning knob, tune in the
station whose call letters appear on the
extreme left hand button (Button No.
1, Fig. 104). This is done so you can
identify the station by its program.
Remove the front cover on the receiver case. Two slots are provided at
each side of the case so that the cover
can be pried off easily. CAUTION: If
cover is pried off with a screwdriver,
do not push screwdriver too far into
case. After the cover has been removed,
you will note two rows of adjusting
screws in the receiver (See Fig. 104).
Press in the button bearing the call
letters of the station you have just
tuned in manually (Button No.1 on extreme left). Hold this button in until
the tuning motor stops running. Then,
using a screwdriver, adjust the screw
marked lA (in the receiver case) until
the station you were just listening to is
heard again.
Adjust the screw marked IB for
maximum volume. Repeat adjustment
of lA, making sure you set it to the
point where the tone is the deepest, also
where hiss and noise are at a minimum.
These adjustments must be made very
carefully to assure good reception.
The set-up for this station is complete and you can proceed to set up the
next station which you have labelled on
the push-buttons. Proceed as follows:
(a) Press in "DIAL" button, and hold
it in until tuninl? motor stops.
SCREW
IMPORTANT
TOOL MUST BE
PUSHED AS FAR
POSSIBLE ON
TOOTH BEfORE
BENDING
POSITION OF TOOL
PRIOR TO BENDING
U~ TOOTH
REAR OF RADIO
FIG.
103
\
'197
Section 6 •
THE
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FIG.
Receivers
FIG. 6
transmitting antennas are usually located on tall buildings, mountains or
other high elevations. Special antenna
arrays are also employed with the intention of concentrating the signal in
the horizontal plane. Such an array is
the "turnstile" antenna, illustrated in
Fig. 6. The height of the receiving antenna is of equal importance with that
of the transmitter, as, in general, trans'mission is essentially limited to "line of
sight" distances. Fig. 7 is a chart for
obtaining this distance, knowing the
heights of the receiving and transmitting antennas. By laying a ruler between the proper points on the outside
scales, the line of sight distance will
be given by the interception on the
middle sc'ale.
204
The design of a receiver for F.M. is
similar in many respects to that employed in A.M. practice, but is somewhat more complicated. The superheterodyne circuit is used universally, but
the different fr~quency coverage brings
in many variations from usual A.M.
practice and, in addition, there is included such features as limiters, discriminators, etc. Let us start at the antenna ,end of an F.M. receiver and discuss the salient design points of the
various major component divisions.
In standard broadcast reception a
makeshift antenna is frequently adequate; in F.M. reception this is not so.
While it is true that good F.M. reception is often obtainable using the least
possible bit of antenna in the immediate locality of the transmitter, out in
the more remote sections field strengths
are of the order of a few hundred
microvolts per meter or less. In an
F.M. rer:eiver there is a definite advantage in getting all possible pick-up, as
the noise-reducing ability of the set is
a direct function of this factor. All
modern F.M. receivers give acceptable
noise reduction on signals of only a
few microvolts, but at these low signal
levels ,the noise reduction is not absolute. Thus any improvement in the sig-
100
50
7
nal delivered by the antenna to the receiver proper means just that much
more increase in the signal to' noise ra·
tio, until ultimately we reach the level
at which reception is practically noise
free. For this reason most up.to.date
F.M. installations utilize dipole antenna
installations. This consists of a hori·
zontal rod assembly, cut in the middle,
one-half wave length long (about 11112
feet), and connected to the receiver by
a twisted pair transmission line. Such
an antenna is most receptive to signals
coming from a direction at right angles
to its plane, a fact which is of great
value in those areas where two stations
of the same frequency and essentially
equal strength are received, as previ.
ously described. By orienting the an·
tenna to favor pick-up from one station
over another the favored station alone
will be received devoid of interference.
In cases where most of the desired stations are in one general direction and
more pick-up is desired, a reflector may
be added. This consists of another halfwave rod located a quarter wave length
behind the other, in a direction away
from the ,desired stations. This is frequently done, in television reception,
but is usually not advisable in F.M. installations, as it reduces the reception
in the other direction. Many of the
~odern F.M. receivers incorporate
built-in folded dipoles in the cabinets.
I.'
II
~
I,
fREQUENCY
MODULATION
FIG. 8
These antennas, or other similar pickups, will be found generally acceptable
in the strong field strength localities,
as, for example, in Metropolitan New
York City. For more remote installations more elaborate dipoles may be
added. Fig. 8 illustrates the construction of dipoles and reflectors as described above.
The R.F. end of an F .M. receiver
has somewhat the. same functions to
perform as in an A.M. receiver, but the
relative importance of the various factors is different. For example, I.F. rejection is of lesser importance, mainly
because of the usual choice of an I.F.
which is generally interference free.
Image rejection in itse)f is not so important, as the current choices of I.F.
place images' of F.M. stations outside
the band; however, the R.F. selectivity,
which would determine the image rejection, is of importance in reducing other
spurious response points. The major
function of the R.F. end of the receiver
is to add as much as possible to .t;lte
stable gain of the set, so that sensitivity
shall be high, with attendant good signal-to-noise ratio. There is a definite
limit to the amount of stable gain
which can be incorporated in an I.F.
amplifier without excessively elaborate
shielding and filtering, consequently
the more gain which can be obtained
from the R.F. amplifier and the converter the better.
The R.F. end of the set has generally
fallen into two categories in current receivers. Most manufacturers use a
more or less conventional type of R.F.
amplifier, wherein the R.F. tube is usually one of the high mutual conductance
types, the amplification is done at the
input frequency (42-50 mc.) ana the
amplified signal is then reduced to the
l.F. in the converter. Converters may
be of types similar to those used in
broadcast practice, with one tube performing the dual function of oscillator
and modulator, or separate tubes may
be used for these functions. In the latter case a high Gm tube is usually used
for the modulator, or "mixer," tube,
and a separate triode for the oscillator.
This has several advantages. For one
thing the resultant sensitivity is excellent, as such a combination has probably the highest transconductance. In
addition good frequency stability is
possible, as the best tube for the oscillator from this standpoint may be
chosen, properly located and properly
compensated.
Where even higher sensitivity is desired a dual superheterodyne is used.
In this system the incoming signal at
42-50 mc. is first heterodyned down to
• Section 7
a moderately high I.F., amplified at
this frequency, then heterodyned again
to the lower or usuall.F. This permits' ,
of higher Qverall gain because relatively few tubes are working at the same
frequency, consequently the problems
of regeneration are not so severe. Receivers of this type have been coqstructed which will give acceptable
noise reduction on inputs of the order
of a tenth of a microvolt.
General Electric has developed a
modification of the dual superheterodyne which employs the same number
of tubes as a conventional R.F. amplifier-single converter combination, yet
permits considerably higher gain. The
basic portion of this circuit is illustrated in Fig. 9. In this arrangement a
variable first, or higher frequency, I.F.
is used, the same oscillator being used
to beat the incoming signal to this frequency and thl(n to beat it down again
to the final I.F. The operation of this
circuit may be understood from the following, together with the equations and
references on Fig. 9:
Let us assume an incoming signal of
46 mc. The input circuit, Ll and Cl, is
tuned to this frequency, and the signal
is then applied to the grid of the first
converter Vl. Tube V3 is a conventional triode oscillator, utilizing the
Hartley circuit, and is tuned to a frequency of 20.85 mc. by L3, C3. L3 is
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205
THE
Section 7 •
magnetically coupled to Ll, consequently tube VI has impressed on its
grid, oscillator voltage of frequency
20.85 mc., in addition to the 46 mc.
signal. These two frequencies are
mixed in this tube and the difference,
25.15 mc., is produced. Tuned circuit
L2, C2 is resonant to this frequency,
and also passes along the oscillator
voltage, supplying tube V2, the second
converter, two signals of frequency
25.15 mc. and 20.85. These are mixed
in this tube, and the difference, 4.3 me.,
is produced and passed along to the
I.F. amplifier by the first I.F. transformer T. Thus as long as the oscillator
is of frequency equal to one-half the
difference of the incoming signal and
the final I.F., and the intermediate
tuned circuit L2, C2, is resonant to onehalf the sum of these frequencies, this
system will function properly.
This system is capable of greater
gain than a conventional RF. stage for
several reasons. First, the RF. stage
(considering the plate circuit of VI,
the coupling transformer and the grid
circuit of V2 to be an RF. stage) is
working at about half the frequency of
a conventional R.F. amplifier and, since
the maximum theoretical gain with
stability of an RF. stage is proportional to the square root of the reciprocal of frequency this means a very considerable increase in gain. Secondly,
the input impedance of a converter or
RF. tube varies with 'frequency, as
does also the tuned circuit impedance
of the transformer secondary, both im·
pedances in parallel being about twice
as high at the lower operating fre-
I
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JFM90
FIG. 10
206
12o
MY E
TECHNICAL
MANUAL
quency, than they would be at the input
frequency. This permits considerably
greater gain from the coupling transformer. Another factor is overall regeneration. If the R.F. amplifier is operating at the same frequency as input
signal there is considerable coupling in
the supply circuits, in the tuning condensers, between other associated parts,
which further reduces the possible stable gain. All these factors taken together result in a gain of about four to
one due to the use of a dual super in
this circuit over a conventional R.F.
amplifier.
The converters used in these modern
F.M. sets differ from conventional A.M.
practice mainly, as pointed out above,
in the usual use of separate oscillators
and of compensation to reduce frequency drift. This compensation takes
the form of small ceramic capacitors
connected across a portion or all of the
oscillator tank circuit. When properly
located so that they will heat up at
about the same rate as the principal
components of the oscillator tank (coil,
gang, trimmers, etc.), they will cause a
reduction in tank capacity sufficient to
balance the increase in the capacity of
the above-mentioned components, with
the result that the frequency stays very
uniform, and it is not necessary to re·_
tune the set after it heats up. Inciden·
tally, it should be pointt)dout that best
practice dictates that every precaution
be first taken to reduce drift to a minimum without compensation, by proper
choice of insulating materials, location
of parts, coil construction, etc., then
compensation may be added to remove
the remaining drift. In this manner the
departure from fin~l frequency at any
time during the warm-up period will be
held down. Fig. 10 shows how well this
factor may be held down by modern
design.
The design of the I.F. amplifier of a
modern F.M. receiver is one of the
most complicated jobs in it. This is
largely due to the inclusion of the A.M.
band in these receivers. Of course it
would be relatively simple to have two
entirely different receivers for each operation, but today's sets are designed
for economy and maximum result per
dollar, consequently considerable consolidation is required. This makes itself particularly felt in the I.F. design,
as here we must pass both the A.M.
1
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I F SELECTIVITY CURVE
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JFM 90
FIG. 11
LF., usually 455 kc., and also the F.M.
I.F., ordinarily 4.3 mc. or higher. The
choice of the F.M. LF. involves many
factors, such as spurious responses,
image responses, sensitivity, stability,
cost, etc. In general the majority of
sets at present use an I.F. of 4.3 mc.,
but there is some tendency to go to considerably higher frequencies than this
on the more elaborate sets.
In practically all ,sets the I.F. transformers comprise units for both I.F.s
connected together, usually with the
various windings in series. This means
that the I.F. system will respond to
either frequency, although in the broadcast band it is customary to short out
the F.M. winding on at least one transformer to prevent the second harmonic
of the oscillator ,from blocking the LF.
tube. High Gm tubes are usually used
in modern sets, permitting a very high
amplification to be obtained. Originally it was thought that the I.F. system
for an F.M. set needed to be flat topped.
Present-day practice relies on the limiters to smooth out any amplitude modulation introduced by the LF. system,
and uses LF. transformers set at about
optimum coupling, with the overall selectivity ddwn 2·1 at about ±75 kc.
This is illustrated in Fig. 11, which
shows the selectivity of the G.E. trans·
'lator, model JFM 90. This receiver ac·
tually has selectivity in excess of current needs, as it was introduced at the
time when local stations were still on
I
I
fREQUENCY
adjacent channels, and current conditions do not require quite as good skirt
selectivity_
Limiters
The limiter is one part of an F .M.
receiver design not found in conventional broadcast receivers, although
noise limiters have been used in deluxe sets and communication receivers.
The limiter forms one of the most important factors in obtaining the great
improvement in performance of F.M.
over A.M. Limiters are largely responsible for the outstanding ability of an
F.M. set to reduce the noise background to practically the vanishing
point, for, though noise reduction is
also contributed by the discriminator
at balance, as will be described later,
when the frequency swings away from
the mid-frequency, any amplitude noise
present can then come through, and
consequently will make itself apparent
as noise distortion on modulation.
Limiters are the reason an F.M. set can
discriminate between two stations on
the same frequency as long as they differ in strength by about 2-1. They
contribute tremendously to the ability
of an F.M. set to reject static, both
natural and man-made. Actually, two
factors which Major Armstrong originally established as essential to proper
operation of an F.M. receiver were
the wide frequency swing and the use
of a limiter_
A limiter is essentially an amplifier
stage which saturates at a certain level.
It may be likened to a dam, which al-
MODUI.ATION
lows the level of the water in a reservoir to rise to the overflow level, then
maintains a constant level regardless of
how much water is poured in. Limiters
in general work on two principles, grid
rectification and current limitation. In
the former type a fairly high resistance
is incorporated in the grid circuit,
shunted by a small capacitor. No fixed
bias is supplied this grid, consequently
it will draw grid current upon the application of a signal. This current
flows through the grid resistor and the
resultant bias reduces the gain of the
tube and maintains a fairly constant
output. This sounds much simpler than
the actual operation of this device really is. To elaborate on the operation of
this apparently simple device let us
consider the circuit of Fig. 12, which
shows two limiters in cascade. Consider, for the time, only one of these
limiters. Let us assume an LF. signal
of several volts is impressed on the
grid of this tube. This strong signal
will charge up the condenser Cl, in the
low side of the grid return, to approximately the peak amplitude of the signal. Condenser 'Cl will in turn discharge through its shunt resistor Rl,
but, since this resistor is usually fairly
high, the discharge rate is slower than
the charge rate through the tube, con:
sequently a steady bias will build up
on the grid. With this bias on the tube
n~arly equal to the peak of t1;te impressed signal, the grid will swing positive only on the peaks, for relatively
short durations. The length of these
durations will depend upon the rate of
discharge of the grid condenser Cl by
the grid leak R1. Thus in the plate circuit there will be a succession of cur-
CASCADE:
LIMITER
SG+
~I
B-tFIG. 12
• Section 7
rent pulses, the height and width of
which depend upon the applied input
signal and the grid circuit time constant (product of Rl and Cl). If this
time constant is properly chosen it will
be found that, over a considerable range
of input signals, the width of these plate
pulses will vary inversely as their
height, i.e., an increase in input signal
causes the plate pulses to become higher but slimmer. The average value of
these pulses remains practically constant over this range, with the result
that any amplitude variation present
on the grid will not appear in the plate
circuit.
This phenomenon may be demonstrated in a very interesting manner by
reconnecting the discriminator circuit
of the F.M. receiver as a conventional
amplitude detector and impressing an
amplitude modulated signal on the grid
of the limiter. For low inputs it will be
noted that the output increases linearly
as the input level is raised, indicating
no limiting. Then the output will start
to level off, then drop, and finally it
will be noted that for certain conditions of grid circuit time constant,
screen and plate potentials and regulation, etc., the amplitude modulation
will practically vanish. Above this input it will usually increase again somewhat, and then once again reduce to a
very low value. Thus when using a tube
such as the 6SH7 in a single limiter
with values for Cl and Rl of about 30
mmf. and 150,000 ohms, respectively,
it will be noted that these points of best
limiting will fall at about 1 volt and 7
volts, respectively, on the grid of the
6SH7. With a single limiter it is possible to get very good reduction in amplitude modulation as indicated by this
test, but not really outstanding reduction except at the above noted points.
Another factor which has an extremely
important effect on the choice of grid
circuit time constant is the susceptibility to impulse noise, such as ignition. If
the time constant is too high, i.e., condenser or resistor too great, the impulse noises will not be sufficiently restricted. This requirement usually dictates that the condenser Cl be of the
order of 20-40 micro-microfarads and
the resistor Rl of about 50,000-150,000
ohms.
This brings us to the use of dual or
cascade limiters_ As was pointed out
207
j
t.
Section 7 •
THE
a .single limiter usually has one or
more input levels at which it is really
effective, one volt or seven volts in
the case given. If two limiters are
used in tandem, and the first adjusted
to limit in such a manner as to put this
critical input, say seven volts, on the
grid of the second limiter for most
values 'of input signal above the limit- .
ing level, it is obvious that well-nigh
perfect limiting is possible, and this is
the case. The value of inductance, of
coil L in the plate circuit of the first
limiter is such as to resonate with the
tube plate capacity and associated
shunt capacities to the LF. frequency,
and its Q is made of such a value (as,
for example, by shunting it with a resistor) as to make the gain from the
grid of the first tube to that of the'second just the correct amount to place
an input of about 7 volts on this second tube over that range of input signals on the first tube for which it is
effectively limiting. The first tube is
therefore working at a range of inputs
over which it has acceptable limiting,
and is holding the second limiter on
that point for which it has very good
limiting. Thus the use of two limiters
doesn't merely double the signal to
noise ratio; it increases it manyfold.
Returning to our original simile a cas·
cade limiter is like the water from our
c9nstant level reservoir supplied
through a small pipe in such manner
that the flow must always be constant.
In the cascade limiter there is more
latitude of time constant, and one limiter may be made to be especially effective to impulse noise, or both may
be, depending, upon how perfect limiting on regular steady noise is desired.
On G.E. model JFM 90, for example,
Cl is 47 mmf., Rl 47,000 ohms, C2 is
22 mmf., R2- 180,000 ohms. Referring
~gain to Fig. 12 it will be noted that
there is considerable gain in the first
limiter, particularly at levels below its
limiting threshold. The RC circuit of
the first limiter may be broken up, with
th·e condenser CIon the high side of
the transformer and the leak Rl between grid and ground .. Occasionally it
is better this way, as it reduces the capacity across the leak by the amount of
strays in the transformer.
In the otherI basic type of limiter,
screens and plates are operated at very
much reduced potentials, so that a
208
MY E
TECHNICAL
small signal will produce current saturation. In general operation it is quite
similar to the grid bias type of limiter,
and the same advantages accrue here
due to the use of two limiters in cascade. In general it will be found that
more sensitivity may be obtained with
the grid bias type of limiter, particularly at low input levels where limiting is
just beginning to take hold, as at thest<
levels the two limiters are acting similar to regular I.F. stages, and while
the reception of signals in this "twilight" zone does not represent good
F.M. operation, it still often gives usable intelligence, particularly in contrast
to A.M. reception.
Incidentally it should be mentioned
that in general, best results in limiters
are obtained with sharp cut-off tubes,
and that high Gm is desirable here, too.
Recently such tubes as the 6SH7 and
the 7T7 have become available, and the
use of these tubes has correspondingly
lowered the requisite input level at
which limiting now takes place.
Discriminators
It will be recalled that the older
A.F.e. systems employed a device
'which translated the variations in frequency into D.C. potentials, which. in
turn were applied back to the reactance
control tube to restore the oscillator to
its proper frequency. This device was
termed a discriminator, in that it discriminated between signals of different
frequency. This same device is now
used in similar manner in F.M. receivers, to transform the F.M. signal which
is being wobbled in frequency, into an
audio variation corresponding to this
wobble.
In general there are three different
types of discriminator circuits. The
simplest works on the principle of resonance, and is illustrated by the circuits
of Figs. 13 and 14. In these circuits we
have a series circuit consisting of inductance, capacity and resistance, with
a rectifier (a triode, in these illustrations, although diodes can also be
used) connected across one of the reactive elements. The mean operating frequency is slightly off the resonant frequimcy of these reactances, consequently the portion of the, applied voltage appearing across the rectifier will be de-
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FIC. 13
pendent upon the frequency. The circuit of Fig. 13 is not balanced, i.e., only
one rectifier is used, consequently the
output will be dependent upon signal
level as well as upon frequency. As a
result such a. circuit is susceptible to
noise modulation of the carrier which
may succeed in getting through the limiters. The circuit of Fig. 14 is balanced so that at the center frequency
no voltage appears across the output
terminals, and hence noise is balanced
out during quiet passages. Another type
of tuned circuit discriminator uses two
diodes, one across the inductance, the
other across the capacitor, with the two
load resistors in series. This is also
bala:nced to noise. In general it may.
be noted that any type of dual discriminator wherein equal voltages are
impressed on the two rectifiers at the
operating center frequency, will be
noise balanced. These tuned circuit
types of discriminators, while interesting, are comparatively low in audio
sensitivity, and are consequently not
used in current designs.
The next type of discriminator circuit to consider is illustrated in Fig.
15. Here an I.F. transformer is used"
with the secondary split, one side of the
secondary being tuned to resonance
slightly above the center frequency, the
other side slightly below. It is obvious
. that as the frequency is varied either
side of resonance one diode or the
other will get a greater applied signal,
and will create a greater D.e. voltage
than the other. If both signals are
equal, as is the case at the center frequency, the D.C. output is zero, as the
!'
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FREQUENCY
• Section 7
MODULA7'ON
grees out of phase with the secondary
current, which is in phase with the induced voltage. The resultant of these
four relationships is a total shift of 90
degrees between primary and second·
ary voltage at resonance.
Since the top of the primary con·
nects to the center of the secondary,
the primary voltage acts in series with
FIG. 15
FIG. 14
two series voltages are then equal and
opposite. If the upper diode gets the
greater voltage the output will be negative, or positive if the lower diode gets
the higher signal voltage. Thus the
voltage appearing across the series load
resistances will be an audio voltage corresponding to the F.M. signal modulation, and may be applied to an audio
amplifier. This type of discriminator
was extensively used in the earlier days
of A.F.e., but has the disadvantage of
being more difficult to align, and has
been displaced by the phase shift type
to be described next.
In the third basic type of discriminator, and the ~me used almost entirely to. day, the phase shift between primary
and secondary of an I.F. transformer is
utilized. Fig. 16 shows a typical phase
shift discriminator. It will be noted
, that a more or less conventional I.F.
transformer is used, provid,ed with a
center tap, which is connected through
a blocking condenser to the plate of the
preceding tube, and also through an
R.F. impedance (a choke in this illustration) to the center tap of the two
resistors in series. The audio output
is ohtained across these two resistors.
The manner in which this circuit works.
is very interesting and will be described
in detail.
With the applied frequency of a value to which both primary and secondary are resonant, the voltage appearing across the secondary (E1 plus E2)
will be 90 rlegrees out of phase with
the primary voltage Ep. This follows
from the fact that the secondary at resonance reflects only a resistance to the
primary, consequently the current
through the primary inductance will be
90 degrees out of phase with thtt applied voltage. The induced voltage in
the secondary circuit is again 90 degrees out of phase with the primary current, and finally the voltage across the
secondary tuning capacity is 90 de-
one-half of the secondary voltage on one
diode, and in series with the other half
on the other diode. Thus the resultant
voltage on each diode is the vector sum
of two voltages in phase quadrature at
resonance. On one diode the secondary
voltage leads the primary voltage by
90 degrees as viewed from the diode,
on the other it lags. If we assume, for
the purposes of illustration, that the
primary voltage equals the total secondary voltage, the voltage on each
diode at resonance would then be approximately 1.12 times the primary
voltage (square root of the sum of the
squares of Vp and Vp/2).
FIG. 16
209
SectJon 7 •
rH,E
,As the frequency 4eparts from resonance the secondary voltllge also departs from, this 9O-degree ,phase relationship .witit the primary, approach~g '~ither zero or 180-degree phase
shift with the primary applied voltage,
depending upon which way the frequency shifts .. In this event the voltage
in one-half of the secondary will approach nearer to being in phase with
the primary voltage, while the voltage
of the other half approaches nearer to
phase opposition. If carried far enough
one-half of the secondary would ultimately be directly additive to the primary, whereupon the voltage applied
to that diode would be 1.50 Vp, while
the other diode would have .50 Vp applied to it. Another factor enters here,
however, in that the primary voltage is
falling off' as the frequency is varied
from the resonant point. As a result
the voltage applied to the diode will
increase at first as the frequency is
changed due to the phases of the
two component voltages approaching
equality, then will reach a peak value,
and finally decrease as the frequency
is further changed, due to resonance.
Simultaneously the voltage across the
other diode will be decreasing, consequently the D.C. voltage across the
two diode loads connected in series
will vary through zero to plus or
minus as the frequency is varied, thus
developing an audio voltage corresponding to the modulation, which is
passed on to the subsequent amplifier.
This type of discriminator has the highest degree of sensitivity, as the output
is obtained as the difference between
two equal and quite large voltages, so
that relatively small variations in these
voltages result in really considerable
outputs. Also, since the output at bal. ance is zero this system is not responsive to amplitude modulated noise
when no modulation is present. Bear
in mind, however, that when modulation occurs the frequency swings away
from the b~lance point, and then the
output depends upon the amplitude as
well as the frequency of the applied signal. Unless a limiter system is used,
amplitude noise modulation will then
make its presence known in the form of
hash on the program modulation. Thus,
it should be emphasized that complete
noise reduction depends upon a great
many things, signal strength, R.F. sensi-
210
MYE
.
TECHNICAl.
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Dlse~IMINATOR
CURVE
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-1 50
MANUAL
+50
FREQUENCY
DEVIATION
+100
+150
-10
-15
JFM90
-20
I
FIG.
sion for better high frequency response
on F.M., where the full audio range
up to 15,000 cycles may be utilized.
This usually takes the form of better
audio amplifiers, more power output,
considerably better acoustic systems,
including many cabinet refinements designed to improve the overall response.
Also, in F.M. the high frequencies are
pre-emphasized at the transmitter in
order to improve the signal-to-noise ratio, consequently the receivers are
equipped with de-emphasis networks
when in the F.M. position, to restore
the fidelity to normal. Some of the
current receivers employ audio degeneration to further smooth out the
overall response curve and reduce harmonics.
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17
Alignment
tivity, conversion and I.F. gain, design
of the limiters and the type of discriminator used.
Most of the discriminators used today are of the type described above. In
the General Electric Model LF-1l5,
shown in Fig. 19, a modification of
this circuit is employed which permits
the use of a grounded single cathode in
the associated dual diode. In this arrangement the secondary is opened at
the center, one side going to ground,
the other being effectively bypassed to
ground by a capacitor. The two diode
loads are connected between this point
and ground, and thus are less "hot"
than in the usual arrangement. By tracing the circuit out it will be seen that
it is essentially the same fundamentally,
with the, primary being in series with
one half of the secondary to each diode.
Fig. 17 shows the discriminator
characteristic of a typical modern receiver. It will be noted that this curve
is linear over a plus or minus 100-kc.
region, thus adequately caring for the
maximum permissible swing, together
with a reasonable safety factor for detuning and drift.
Audio Amplifiers
The audio systems of modern F.M.
receivers differ from corresponding
A.M. practice primarily, in the provi-
The alignment of frequency modulated receivers includes several operations similar to those employed in regular A.M. practice, and several peculiar
to F.M. In conventional A.M. alignment the simplest method involves the
use of a signal generator, which is a
source of amplitude modulated waves,
and which may be anything from an
elaborate piece of equipment, complete
with accurate coritrols of output, modulation, etc., to a simple modulated oscillator. Output is usually indicated by
a simple output meter, although the
more elaborate service installations also
have cathode ray oscilloscopes for I.F.
alignment. These oscilloscopes are extremely valuable in A.M. alignment,
but by no means indispensable. In
F.M. alignment a cathode ray oscilloscope is an even more valuable tool, as
it makes the visual effect of the I.F.
and discriminator transformer tuning
adjustments very noticeable. The signal generator employed for F.M. alignment differs from that used on A.M. in
that it must supply a more widely differing range of frequencies than usually
employed on A.M., namely, I.F. frequencies varying from about 2 mc. up to 8
mc., or even higher, plus the signal frequencies of 42-50 megacycles. Also
these signals must be frequency modulated. A conventional A.M. signal generator or test oscillator that covers the
required range of frequ~ncies may be
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FR.EQUENCY
used in aligning F.M. receivers by
using an unmodulated signal and a meter to indicate resonance, as will be described later_ There are not very many
F.M. generators on the market yetBoonton Radio Corporation makes a
very good F.M. signal generator, their
model 150A. In addition Hickok has a
model 188X generator, and General
Electric their type TMV-97-C Test
Oscillator and TMV-128A Frequency
Modulator. Any good oscilloscope may
be used in conjunction with these generators to give visual indication Of
alignment.
To illustrate the usual alignment
process for an F.M. receiver, let us consider G.E. model LF-115 receiver. On
the schematic, Fig. 19, will be noted
two points, "A" where the audio output from the discriminator is connected
to the volume control, and "B," on the
grid of the first limiter. These two
points are the usual alignment points
for connecting meters or oscilloscope in
practically all F.M. sets. Point A is
used for discriminator alignment, B for
I.F. and R.F. alignment.
In aligning this set with one of the
above-mentioned signal generators the
oscilloscope is connected first to point
B through a half-megohm resistor.
6SK7
ell
I" J.F.AMPL.
6SK7
Z"' I.F.AMPL.
• Section 7
With the signal generator set to the LF.
frequency, 4.3 me. in this particular
set, and applied to the grid of the 6SG7
converter tube through a small mica
condenser, the oscilloscope should show
a curve like that of Fig. 22, when the
circuits are properly aligned. In aligning such a set it is customary to align
the last LF. trimmers first, and then
proceed forward.
After the LF. has been properly
aligned the oscilloscope is shifted to
point A, still through the resistor, and a
curve as in Fig. 23 will be obtained
when properly aligned. The effect of
the secondary trimmer of the discriminator transformer is to shift the crossover point of the two straight lines up
and down, while the adjustment of the
primary trimmer affects the straightn~ss of these lines. The proper adjust-
FIG. 22
6AB7
I" CONY.
MODULATION
6SJ7
I" LI MITER
6H6
6SJ7
Z"'LlMITER
C33
T4
DISCRIMINATOR
OUTPUT
C5
PARTS DESCRIPTION LIST-MODEL JFM-90
Symbol
CIa
C1b
C1c
C2
C3
C4
C5
C6
C7
C8
C9
C10
Cll
C12
C23
C24
C25
C26
C27
C28
C29
C30
C3l
C32
Description
Oscillator section of tuning condenser
1st converter section of tuning condenser
2nd converter section of tuning condenser
5-24 mmf. oscillator air trimmer
2-20 mmf. 1st converter trimmer
2-20 mmf. 2nd converter trimmer
40 mmf. t~perature compensating capacitor
470 mmf. mica capacitor
50 mmf. temperature compensating capacitor
470 mmf. mica capacitor
470 mmf. mica capacitor
470 mmf. mica capacitor
470 mmf. miea capacitor
.01 mfd. paper capacitor
.01 mfd. paper capacitor
.01 mfd. paper capacitor
47 mmf. mica capacitor
.01 mfd. paper capacitor
.01 mfd. paper capacitor
47 mmf. mica capacitor
47 mmf. mica capacitor
22 mmf. mica capacitor
47 mmf. mica capacitor
47 mmf. mica capacitor
Symbol
C33
C34
C3S
C36a
C36b
C36c
C37
C38
C39
C40
Ll
L2
L3
PI
R1
R2
R3
R4
R5
R6
R7
R8
R9
RIO
Description
50 mmf. temperature compensating capacitor
47 mmf. mica capacitor
220 mmf. mica capacitor
15 mfd. dry electrolytic
30 mfd. dry electrolytic
1() mfd. dry electrolytic
0.1 mfd. paper capacitor
.02 mfd. paper capacitor
8 mmf. temperature compensating capacitor
.01 mfd. paper capacitor
Antenna coil
Interconverter coil
Oscillator coil
Dial lamp, Mazda No. 44
33,000 ohms carbon resistor
3.3 megohms carbon resistor
6800 ohms carbon resistor
2200 ohms carbon resistor
1000 ohms carbon resistor
3.3 megohms carbon resistor
12,000 ohms carbon resistor
1000 ohms carbon resistor
1000 ohms carbon resistor
47,000 ohms carbon resistor
Symbol
Rll
R12
RI3
R14
R15
RI6
R17
R18
R19
R20
R21
R22
R23
R24
R25
R26
R27
R28
Sla
SIb
T1
T2
T3
T4
T5
T6
Description
15,000 ohms carbon resistor
47,000 ohms carbon resistor
2200 ohms carbon reaistor
2.2 megohms carbon resistor
47,000 ohms carbon resistor
10,000 ohms carbon resistor
180.000 ohms carbon resistor
68,000 ohms carbon resistor
22,000 ohms carbon resistor
100,000 ohms carbon resistor
100,000 ohms carbon resistor
100,000 ohms carbon resistor
1200 ohms 7.4 W, wire wound resistor
3300 ohms 1 W. carbon resistor
47,000 ohms carbon resistor
470,000 ohms carbon resistor
47,000 ohms carbon resistor
47,000 ohms carbon resistor
Power switch
F,M.-Phono switch
1st LF. transformer
2nd LF. transformer
3rd I.F. transformer
Discriminator I.F. transformer
Power transformer for 50-60 cycles
Power transformer for 25 cycles
FIG. IS-Schematic Diagram Model ]FM·90
211
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Section, 7 •
H I
MY I
.
T'CHNleAL
I
MANUAL
ment is obtained when the two lines are
straight and cross in the middle.
When an oscilloscope is not available,
a high resistance, voltmeter may be
used, preferably one with at least 20,000 ohms per volt. This meter is first
connected to point B through the halfmegohm resistor, and .the signal generatol-" is now unmodulated. All, the trimmers are adjusted for maxinium voltage as indicated by this meter. The
meter and resistor are now shifted to A,
and with the secondary purposely detuned, the primary is tuned for maximum voltage. Then the secondary is
tuned until this voltage drops to zero.
This adjustment is faidy critical, and
the voltage changes polarity as it is
passed through.
..
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23
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The R.F. end is best aligned by the
meter method, and adjustment is made
for maximum output, using as low a
level of signal inpu~ as possible. The
conventional procedure is usually followed, with the signal being nrst
brought in /;\t the correct calibration
point by the oscillator adjustment, then
the ·antenna and R.F. trimmers are adjusted for maximum output voltage at
point B.
When an F.M. receiver hall a built·in
dipole, it is best to couple the signal
generator to it by capacitive pick-up,
using a radiating rod or loop on the
generator. Where external antenna is
required the usual dummy antenna may
be about 50 ohms.
'
Schematics of several samples of current production are shown in Figs. 18
to 21, inclusive. Fig. 18 shows the
G.E. model JFM-90 translator, intended
to be used with any regular A.M. audio
system, Fig. 19 illustrates G.E. model
LF·l J5 and associated models, Fig. 20
illustrates Stromberg-Carlson models
925 and 1025, and Fig. 21 shows Zenith
14Bl chassis.
212
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THE MYE
Section
8
TE£HNI£AL MANUAL
Fundamentals of
Television Engineering
215
Section 8 •
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E C H N I CAL
MAN U A L
I
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Editor's Note
Commercial television, whose prospects were so brilliant a year or so
ago, has been temporari!y stalemated by the present emergency.
While there is no doubt that advancements comparable to the rapid
strides previously made in the technique of visual transmission and
reception are still being made every day, these developments have
been limited, rightly, to the armed services.
To those interested in this field, we scarcely need to point out
that communications, warning services, etc. of the Army and Navy
have placed great emphasis on high frequency operation. Both Army
and Navy are training large forces for the design, operation, and maintenance of high frequency equipment. With the end of the war the
return of this personnel to civilian life will provide an adequate supply
for the rapid expansion of all the broadcast services employing high
frequency operation. We believe it possible to predict without undue
risk that television will have the nationwide adoption it deserves, as
soon as peacetime and a normal material supply make such an undertaking practicable.
The following article by Mr. Everest gives an excellent portrayal
of the fundamentals of commercial television. The wartime interim
from the publication of this text until the readvent of commercial services, may produce changes or improvements in systems, but the basic
theory of this article provides a sound groundwork for· the future.
216
I.
FUND~"NrALS
OF fELEVISION ENGINEERING
• Section 8
THE FUNDAMENTALS OF TELEVISION ENGINEERING
Reprinted from the Television Engineering Section. COMMUNICATIONS
Part I: 'lte EssentIal Elements of a '.I.vl.lon System
T
HOSE in the communication field
today are witnesses to the addition
of a new phase to this already manifold
field, namely, instantaneous sight at a
distance. Communication over great
distances has been developed through
the perfection of the arbitrary signalsymbol stage, through sound broadcasting, and now the addition of sight to
sour,d promises to open up a multitude
of new opportunities for exploitation
and development. It should be pointed
out here that to the careful student of
these matters, there appears to be no
factual basis for expecting the combined sight and sound type of broadcast
to supplant the common aural broadcast
as an entertainment and educational
medium for many years to come. Even
though the present-day television equipment is in an apparently advanced stage
as compared to the broadcast equipment
at the inception of that service, there are
many problems, both technical and commercial which seem almost insurmountable at this time. Based upon past attainments in technological fields, however, there is no reason to doubt the
ultimate solution of these difficulties.
In the translation of a picture from
light values to electrical currents, some
manner of photo-electric device is
needed. The accidental discovery of the
photo-conductive properties of selenium
by May in 1873 appears to be one of
the important stimuli to the development
By
F. ALTON EVEREST
Au/.tant Profellor of Electrical EngineerillQ,
Oregon State College
of means to transmit sight. At about
the turn of the century, results from
Hertz's discovery in 1887 of the photoemission phenomenon began to appear.
This finally bore fruit in the photoelectric cell which was so prominent in
the early development of television and
which has such widespread application
in other fields today.
There is something else essentially
necessary, however, beside the translation of light to electric current. For
instance, if a photo-sensitive device were
held up before an image to be transmitted, it is obvious that the transmission of the image as such would be
unsuccesSful. A signal would be transmitted which would be proportional to
the average illumination of the subject
only. A comparable occurrence in photography would be snapping a picture
with the lens removed from the camera. True, the film would be exposed,
but absolutely no information would
be revealed because the film would be
uniformly exposed over all of its surface
to a degree depending upon the illumination of the subject and the length
of exposure.
From this fact that any photo-electric
element delivers an electric current proportional to the a'lJerage illumination,
falling upon it, it is evident that to
convey visual information it is nefessary that the photo-electric device does
not look at the whole subject to be transmitted, but rather at one elemental area
of it at a time. In this way, the signal
corresponding to the average light intensity of each elemental area can be
The problem then retransmitted.
solve5 itself into a problem of analyzing
the picture into many of these elemental
areas, allowing the photo-electric device to look at each area in turn transmitting a signal corresponding to the
average light intensity of each small
area, converting this signal back to
light of the correct intensity at the. receiver, and the re-assembling of the picture. While this method is rather complex and unwieldy, at the present stage
of the art it is the only practical one
available"! If, as in the eye, the image
would be thrown upon a mosaic of
photo-electric elenlents each of which
was connected to a similarly located reproducihg element on the receiving
screen, we would have a simple system
in its action but quite impractical. One
reason for this impracticability can be
seen in the fact that the eye has about
A 441·lIne televiflon
Image of L. E. Gulala.
President. Phllco
Radio & Television
Corp. Picture tranl·
mltted over port.
able system ullng
RMA standards.
441 .11 n e tel evil ion
picture tranlmltted
by Philco system
uling RMA stand·
ardl. Jean Muir.
Warner Bros. Star.
217
Section 8 •
THE
MYE
TECHNICAL
MANUAL
TRANSMISSION
SYSTEM
F"i . i a
five million of these discrete elements
(the so-called rods and cones) and a
separate cOllnection between each and
the receiver (the brain). The interconnection of just a few conductors between the ~levision transmitter and
each receiver would be hardly feasible,
to say nothing of five million of them.
The image, then, must be broken
down into many tiny elemental areas,
each of which will be transmitted independently. There have been innumerable systems of scanning proposed such
as, for instance, spiral "canning. radial
scanning, and sine-wave scanning. Most
of these suffer from the effects of a
change in scanning rate on different
parts of the image or some form of nonuniform resolution of detail over the
image surface. The method which has
withstood the test of years of experimentation is a simulation of the form
disc patented by Nipkow in Germany in '
1884. By means of a relatively large
disc with a spiral of small holes arranged near its periphery, the image
was scanned along a narrow line by
one hole and along another line just
below or above the first line by the
next hole in the spiral and so on across
the image in a regular sequence.
Showing scanning strip and
slgnall.
A simple analogy of the form of scanning usually used today is that of reading a page of a book. The eye starts
in the upper left-hand corner of the page
and progresses at a uniform rate along
the first line. At the end of the line,
the eye snaps back to the beginning of
the second line at a much faster rate
and then along the second line at the
original uniform rate. This continues
to the bottom of the page and then is
repeated in an identical manner on following pages. This could be classed as
"uniform speed sequential scanning." If
the book were especially prepared in
(a)
(b)
I
Fig.3
~
Distortions. Scanning spot width
comparable to scanned detail.
such a code that the story was continuous by reading the odd lines first and
then going over it again on the even
lines, the same information could be
imparted with only a little additional
trouble, and it could be classed as an
"interlaced scanning" process.
In
either case, -the image is scanned in a
definite, pre-arranged order, and the
size of each elemental area would be determined mainly by the width of each
~trip. The greater the number of strips
per picture, the smaller each elemental
area and the smaller the picture detailthat can be resolved. We shall discuss
the~e essential qualities of a tele'vision
image in more detail later.
218
ANALYSIS OF TELEVISION SYSTEMS
AI! television systems can be broken
down into a very few essential functions as shown in block diagram form
in Fig. 1. Here we are dealing with
the sight transmission and receiving system alone, because broadcasting the
sound accompanying the image has already reached a high state of perfection and its working is more or less
common knowledge. The scanning dcvice by which the image is to be tom
into the elemental areas can take am'
numher of different forms. Represent;;tive of the mechanical methods arc: (1)
Apall/red disc, sillgle or ml/ltiple
spiml; (2) apertllrcd drllm; (3) apcrIlIrcd clldless balld; (4) mirror drum;
(5) vibratillg mirrors; (6) prismatic
disc: (7) 11Iirror screw.
The optico-electrical device could be
the ordinary photo-electric cell arranged
singly or in banks, possibly even
equipped with electron-multipliers to increase the sensitivity. The radio transmitter section will not be discussed, because no new theories or modes of
operation arc introduced for television
work. The suitable transmission of the
wide frequency bands required, however, and the transmission at the ultrahigh frequencies introduce many new
problems, but they have all been met
by extensiolls of fundamental electrical
theory.
It will be noticed that the scanning
device aud the optico-electrical device
are also connected with broken lines
which indicate that these two functions
can take place within one instrument.
In this series, which will deal mainly
with electronic methods, this is particularly the case. For instance, the
Tmage Dissector and the Iconoscope
which will be taken up in great deta,il
later, utilize electronic methods of scanning in such a way that the photoelectric emission and the scanning take
place within the same evacuated glass
envelope.
Basically, however, these
highly developed devices take their place
in the ,block diagram of Fig. 1 along
I~
!,
fUNDAMENTALS Of TELEVISION ENGINEERING
• Section 8
RECEIVING
SYSTEM
Fi .~ b
with the humble scanning disc and
photo-electric cell.
For these two
devices, we must add electrostatic and
electromagnetic deflection of electron
beams as two other systems of scanning
to follow the list given above.
At the receiver the signals are demodulated and amplified by the customary methods (except for extension
of the pass bands) and the varying
voltage is used to actuate the electrooptical device. In the mechanical svstems this device may take one of the
following forms: (1) flat plate 1leOI1
lamp; (2) Kerr cell; (3) supersonic
light valve. The re-arranging device on
the receiving end of mechanical systems can be anyone of the devices
listed as scanning- (kvices at the transmitter.
For electronic television, in
which \ve are particularly interested, the
electro-optical device and the rearranging device are found in the same
instrument as at the transmitting end.
The cathode-ray tube ordinarily used
contains an electro-optical device in the
variation of fluorescent screen excitation
;ind the resulting emission of light by
the variation of the electron density of
the beam. Hel'e again the re-arranging
,ystem may be electrostatic or the electromagnetic deflection of this electron
beam. This, too, is a special study and
will be dealt with in detail later.
REPETITION RATE
As far as the units in the block diagram of Fig. 1 are concerned, there is
no difference between facsimile and television transmission.
Both demand a
tearing down of the image to be tt'ansmitted into strips and the opticoelectrical analysis of the light and shade
intensities along that strip at' the transmitting end, and the reconstitution of
the image at the receiver by the t\'anslatioll of the ekctrical signab hack to
their corresponding light intensities, and
the arrangement of these picture elements into their proper order. However, the speed with which the process
takes place and whether or not a record
is to be made of the received image determines whether we shall call ours a
television or a facsimile system. A
typical facsimile system might logically
require fifteen minutes to transmit a
photograph eight by ten inches. At the
receiver, at the end of this time, a
permanent record of the image will have
been produced. For television, a C0111plete picture of the subj~ct would be
transmitted and completely reproduced
in, possibly, 1/30 second. Each picture
will differ slightly from the preceding
one due to any motion that has taken
e - About j
]h'
h
~
Min,ute of Arc
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fk'.
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about 1/10th second after the stimulus
has been removed. By impressing about
fifteen separate pictures per second
upon the retina, the eye will be unable
to follow the dark spaces between pictures. However, at repetition rates as
low as fifteen per second, the flicker
may be objectionable, and it is standard
motion picture practice to project
twenty-four "frames" per second. Interlaced scanning giving thirty complete
pictures per second, but scanned in such
a way that each picture is traversed
twice with scanning lines which do not
coincide, actually shows sixty pictures
per second, and hence the flicker effect
is practically eliminated.
APERTURE DISTORTION
The number of lines with which a
subject is scanned determines the fineness of the detail which can be resolved.
It is obvious that we cannot expect to
reproduce clearly details that have dimensions comparable to the scanning
spot, or in other words the width of the
scanning strip. An effect which is impOl·tant in this regard is a distortion due
to the finite size of the "aperture" or
scanning spot which is called "aperture
distortion." Fig. 2-a shows in greatly
magnified form a scanning strip having a light detail on it which changes
abruptly fr0111 dark to light at its edges.
As we have seen, the reason we are
iO.021!1~ /
.:,
Ij/
o O":_-'-""fO'--'--:-20'--'-..J30'----'-4..J0-.l.-S..lo---l
/
Viewing Distance
Left: Showing minimum detail eye
can resolve.
Feet
Fig.4
place in that time. Because of a char:lcteristic of the eye which is called
"persistence of vision," it will not be
able to distinguish between the sC{larate
pictures, but will see what appears a
continuous, uninterrupted flow of motion
of the subject. Once the retina of the eye
is stimulated with a single picture focused upon it, the impression remains for
219
Section 8 •
THE
scanning the picture 'at all is because
our photo-electric devices can respond
only to the average illumination and,
therefore, we get the average illumination of the area covered by the spot in
this case. When the spot is in position
(a), the photo-electric current will be
zero because of the black surface. At
(b), half the circl~ is on white and half
on black, and the resulting photo-electric
current would correspond to gray. At
( c), maximum signal corresponding to
white will result. At the right edge
of the white detail, sil!Jilar signals would
be produced in reverse. While the signal for ideal reproduction is that shown
in Fig. 2-c, the actual signal resulting
is shown in Fig. 2-b both for circular
and square scanning spot. Therefore,
when the scanning strip width is com·
parable in size to the detail being
scanned, we must exp~ct distortions
such as shown in Fjg. 3. In (a) is
shown the case of a horizontal detail
unfortunate enough to lie between two
strips, and in (b) is shown the stairstep effect produced in diagonal elements.
It is evident froJ11 this that in order
to analyze the details of, say, the face of
R subject, there mUst be a relatively
great number of lines scanning it. If
the eyes of the subject are about the
MYE
TECHNICAl.
<.
MANUAl.
saJ11e width as the scanning strip, all
one could expect is a blur. If in the
scene peing televised a man is in the
far distance, perhaps a blur is enough,
for the observer's eye has very definite
limits in analyzing fine detail. The
acuity of vision of the normal eye is
between 0,5 alld 2 minutes of arc.
This means that if two details are
separated by an angle greater than this,
the eye can distinguish them as separate
details, but if their angular separation
is less than this amount, the two details
will merge into a blur. This results
from the fact that the rods and cones
on the retina of the eye are spaced a
finite distance apart, and each is capable of responding only to the average
illumination falling upon it. Fig. 4
shows the relation of the minimum size
of the detail that the eye can appreciate
in relation to the viewing distance.
SUMMARY OF PICTURE QUALITIES
The excellence of the television image
is a function of many things, all intimately connected together. The con'rast range, or the relative difference in
.ntensity between "black" and "white" on
the reproduced image is very important.
The brightness of the image is another
factor, and its overall value may be
quite low because the screen is illuminated on only one< elemental area at
a time. For a modern television picture,
the spot brightness may have to be sev:eral hundred thousand times the required overall picture brightness because of this fact. The definition of the
picture, of course, is a function of the
nUl1,lber of scanning strips per picture
which goes hand in hand with the spot
size. With cathode-ray reconstitution,
a doubling of the numbel' of lines in
a picture will increase the definition and
require a spot size of half the .former
value. As the tight flux is proportional
to the square of the spot diameter, the
received picture brightneS5 will be reduced to about one-fourth its original
value.
Picture size, the number of strips per
picture, and the viewing distance are
also closely tied together. For a given
picture size and number of lines, there
is a proper viewing distance at which
the acuity of the eye as expressed in
Fig. 4 and the smallest detail that can
be resolved in the picture are at such
a balance that the eye does not notice
deficiencies in the picture. At a closer
viewing distance, the picture will appear coarse, and at greater distances
some of the definition will be going to
waste.
I
I
I
I
Ii
i
I '~
Part II: The Necessity for Wide Frequency Bands
TRANSMISSION OF INFORMATION
I
T is a well-known fact that the frequency band available and. the time
available for the transmission are two
very important factors which govern
the amount of information that can be
transmitted' . This holds true in a general way for all types of signals such
as telegraphic, voice, music, facsimile,
or television and for all media of transmission, such as air for sound waves,
wires, or the medium in which radio
waves are propagated. The amount of
information that can be transmitted can
be arbitrarily specified in a rather vague
term which we will call "information
units." The frequency band available
extends from some lower frequency, f"
to some higher frequency, f2' and covers
a frequency range of (f2 - f, ) cycles.
The time t available for the transmission
let us' express in seconds. These factors
can be expressed as
Information units
220
= (£2 -
f,) t
'" (1)
Equation (1) can best be explained
by a practical illustration. It has been
found that a certain photograph can be
sent via a facsimile system in 300 secunds and that the band required had a
maximum width of 2000 cycles. By
multiplying 300 by 2000, we get 600,000
information units contained in this picture of practically perfect quality. To
obtain the same quality with a television
image containing 600,000 information
units in a time of 1/30 second to come
within the eye retentive period for
avoiding flicker would require a wider
frequency band< The width of this band
would be found by dividing the number
of information units by the time avail-
able, or 1/30 second. This gives a frequency band width of lR,OOO,OOO cycles
necessary to transmit this nearly perfect
picture in 1/30 second. Actually, however, it has been shown that an information content of about 1/6 of this, or
100,000 information units is ample for
television. This brings the necessary
frequency range down to a m11ch lower
value.
Often it is found that the transmission
of a certain amount of information takes
up a much wider frequency range than
indicated by equation (1). It must be
pointed out that equation (1) is only a
qualitative statement. One of the reasons for this lies in the fact that "information" is such an intangible quan"
tity. It is evident that more actual
information exists in a television image
than in the click of a telegraph sounder,
but how much more? How call one
measure it? A Chinese proverb tells us
that "a picture is worth ten thousand
words", but yet one is forced to question
I
i
.~"
I"
I
FUNDAMENTAlS OF TELEVISION ENGINEERING
• Section 8
the absolute accuracy of the proverb
it probably errs on the conservative
side.
Equation (1) also says nothing about
how efficiently the (f,-f, ) frequency
band is used.' With the ordinary television signal, the energy distribution
throughout this band is simpar to that
shown in Fig. 1. It is seen that there
are: energy concentrations in the region
of the line-scan frequency!HI. ' This fref!ue~cy may be found from
f ..
(f) (n)
.................. (2)
a~
=
(b)
Where
f"
linc scan frequency, cycles per
second
frame repetition rate, or the
number ,of complete pictures
per second
11
total numher of scanning lines
per frame.
=
=
=
For the present standards (see Table I)
f = 30 and n = 441, making f" = 13,230
cycles per second. Concentrations of
energy will then be found in the regions surrounding 13.2 kc, 26.4 kc, 52.8
kc, etc., the amount of energy decreasing greatly as the frequency increases.
Even though the actual shape of these
concentrations change with picture content, it is obvious that the (f, - f,) frequency band is not being used to the
fullest extent. The use of double-sideband transmission is also representative
of inefficient use of the (f, - f,) band".
So even though equation (1) is highly vulnerable from the quantitativc
standpoint, it does rest upon a basic law
TABLE I
SHOW1NG A SUMMARY OF SOME OF TIlE
MAJOR
STANDARDS
PROPOSED
BY
RMA TELEVISION COMMITTEE
Channel Characteristics
Television channel width... 6
me
Separation between sound,
and picture carriers ...... 4.5 mc
(Sound carrier higher frequency than picture carrier)
Guard band between sound
carrier and high-frequency
edge of. channel. . . . . . . .. 0.25 m(;
Pictllre Characteristics
frame frequency.............. 30
Field frequency for interlacing.. 60
. Number of lines per fra~e ...... 441
width .
4
Aspect ratio - - -........... .
height
3
Fig.2
which demapds a payment in the form
of an increased frequency band required
tn exchange for an increase in picture
quality.
FREQUENCY BAND WIDTH
DETERMINATION
A common method of determining
the frequency band required for the
transmission of television images will
be described which, although criticized
by many for its crudeness, does give a
physical picture of the process. This
atlalysis is based upon the scanning of
a checkerboard pattern with squares the
size of the elemental areas. That is,
the squares are the same width as the
scanning spot. The theoretical signal
resulting from scanning across one line
of the pattern of Fig. 2-A" is shown as
the rectangular wave of Fig. 2-B.
Neglecting such things as aperture distortion, etc., the rectangular wave can
he simulated by the sine wave of Fig.
2-C, and its frequency can be determined .fr0111 the speed of the scanning
spot. This, the frequency band representing the scanning of these alternate
black and white squares, which represents the worst possible conditions of
picture resolution, is given by
Approx. frequency band required
1
-n'Rf ............ (3)
2
where
number of lines per frame
n
f
number of frames per second
=
=
=
width
R
= aspect ratio = --- of picture
height
Practical experience has indicated that
the value calculated from equation (3)
is a pessimistic figure and that only
about 70% of this band is actually
needed. Adopting the standard motionpicture aspect ratio of 4/3 and lumping
1/2, the 0.7 factor and the 4/3 aspect
ratio into one constant, equation (3)
becomes
Actual Frequcncy
J>and required
0.47 n' f .............. ; ( 4)
Let us calculate an example using the
present standards of f::= 30 frames per
second and n = 441 lines per frame.
This results in a calculated necessary
frequency range of 2.75 mc, which, with
double-.side-band transmission, ca1Js for
a frequency band of 5.5 me plus enough
for the accompanying sound and the
necessary guard bands. The frequency
band required is directly proportional
to the frame repetition frequency and
proportional to the square of the number
of lines. Doubling the number of lines
gives rise to fJuadrupling' the frequency
band required.
RESULTS OF DeMANDING WIDE
FREQUENCY BAND
Here we see the penalties we must
pay for transmitting lots of information
at a rapid rate as, for instance, a television picture which has high quaiity
221
r
Section 8 •
HEM Y E r E C H N I C'A L
MAN U A L
Televisionl=:lr:;=r=:==i=:'~~F=~=~=;.=!.=JL
Channel'
Number _
._
---..IL..--J
;.
-.
1111
••
...
..
.
.
-----~--
.
Overall Sand
Width __ _
SMe.
- - - -__
-------_ 4
0.25 Me.---_•
•5 Me. ---------~t
_.~
~
°-ry~~~~EJ
Pie"'''r'e
F:requ
eney arr','
esacyc/es
rig. 4
Sound ,/
I
C
uer
M
44
STANDARDS OF TELEVISION
TRANSMISSION
\
I
4'"
y / :
Carrier~
and which shows motion. The penalty,
of course, is the wide frequency band,
and the use of these wide frequency
bands makes the case for television quite
difficult.
First, it is evident that a series of
6-mc transmission channels is not available in the common radio spectrum as
usually used today. The entire broadcast band is only about I-mc wide and
even if this region were unused, it
would not be satisfactory because the
side-bands generated would be such a
large percentage of the carrier. A ratio
of about ten-to-one between the carrier
frequency and the highest modulating
frequency is highly desirable from the
circuit design standpoint. The spectrum
from a few hundred kilocycles to several megacycles is already allotted to a
multitude of different services. The
prior rights of these services on these .
frequencies must be respected. All of
these factors point toward the utilization of the ultra-high-frequency regions,
the propagation characteristics of which
relatively little is known. But considerations taking into account the lack
of sky-wave, the video-frequency band
width, the urban propagation characteristics, and apparatus limitations, have
led to the adoption of the region around
40 t(') 100 mc for television transmission.
One characteristic of these waves 4• 5• 6
from 3 to 6 meters is that they behave
very much like light in that they tend
i:t~:;;!o',cast shadows behind mountains, etc.
".
b,<:y also are not ordinarily reflected
"". ""~22
interconnecting television transmitters
lies in the ~tilizationof highly airec-·
tional beam radio transmitters. Fre-.
quencies of the order of hundreds of
megacycles are ideally suited for the design of highly directional radiating systems. It seems entirely feasible to operate these receiving-transmitting relay
links unattended. The cost of such systems, whether special land lines or radio
links, is very high at the present state
of development.
from the ionized layers except at acute
angles', and thereby do not follow
around the curvature of the earth. This,
of course, limits the service area materially, 30 to 50 miles· being the general
order of maximum distance to which
satisfactory signals can be transmitted.
The absolute distance, however, depends
upon many factors such as height of
transmitting antenna, height of receiving antenna, intervening structures or
hills, and the base noise level of the locality. Interference from automobile
ignition systems is particularly troublesome at tn,ese frequencies causing a
speckled picture (g.iving the appearance
of a snowstorm) and often the tempor.ary loss of synchronization. The signal
strength must be high enough to override such interference of local origin.
In general, a single transmitter of moderate power can cover a metropolitan
area very well at these frequencies.
Television will not have reached the
acme of development until it too has an
interconnected network of stations from
coast to coast. The short transmission
range complicates this problem greatly
for the type of interconnecting links
that can transmit the necessary wide
frequency bands are very expensive.
Coaxial cables have been developed to
the point where they can be used for
such purposes, and the recent progress
in the development of wave-guides,
which are metallic tubes filled with some
dielectric, appears to have merit for this
purpose. Another possible means of
For a successful service, it is necessary ,that any television receiver
manufactured any place in the United
States operates satisfactorily on transmissions from any television broadcast
station in the United States. In order
to accomplish this with such a complex
system, the necessity for some close cooperation between manufacturers and
television broadcasters is obvious. This
cooperation has been realized in this
country through the efforts of the Television Committee of the Radio Manufacturers Association ' •. This committee
to formulate standards was composed of
men representing practically all of the
major television organizations. It is
evident that if this committee mutually
agrees upon television standards, the
television industry which they represent will abide by them for the benefit
of all, including the consumer.
This committee has been working
since 1935, and it was not until the
first of 1939 that the final decisions
were completed. The Federal Communications Commission has made ex·
perimental allocations upon the basis of
these standards. It is fortunate that
such thorough investigation has preceded the formulation of these standards, for once adopted, they will tend
to solidify techniques. The further the
advance before solidification, the greater
the net progress.
THE PROPOSED STANDARDS
Table I gives a sUn1maryof the
standards proposed by the RMA Television Committee which are of the most
interest at the receiving end. Fig. 3
shows graphically the location of the
seven television channel assignments,
each of 6-mc width. In addition to
these ,seven channels between 44 and
108 mc, there are twelve additional 6-mc
channels tentatively set aside for television between 156 and 294 mc. These
are considered more important for relay
and research purposes than for regular
fUNDAMENTALS Of TELEVISION ENGINEERING
television broadcasting at the present
time. To allow room for the increase
in definition and the resulting increase
in frequency bands, vestigial side-band
transmission is contemplated. A typical
channel (Channel I) is portrayed in
Fig. 4 using vestigial transmission. One
side-band (the upper one) is transmitted completely and 0.75 mc of the
Beginning at this
lower side band.
point, the lower side band is attenuated
as rapidly as possible with circuits available for operation at these frequencies.
The overall band width is 6 mc. A
0.25-mc guard band is allowed between
the upper edge of the channel and the
sound carrier. The picture carrier is
placed 4.5 mcbelow the sound carrier.
Because of the relative crowding of
the region within the channel as shown
by Fig. 4, and because television channels are adjacent to each other and to
other services, it will be imperative that
the lower side band transmitted vestigially be cut off entirely within the
channel limit. The need for highly
selective receiver circuits is also evident.
BIBLIOGRAPHY
(1) Hartley, "Transmission of Information," Bell System Technical Journal, Vol.
VII, No.3, July 1928, p. 535.
(2) Mertz and Gray, "A Theory of
Scanning," Bell System Technical Jo_l,
Vol. XIII, No.3, July 1934.
(3) Wilson, "Television Engineering"
(Sir Isaac Pitman and Sons Ltd.), Chapter
I V, "Analysis of Finite Aperture Scanning Methods"; Chapter XII, "Physical
Limitations." (An excellent list of references is included at the end of each
chapter.)
• Section 8
(4) Jones, "Propagation of Wavelengths Between Three and Eight Meters,'·
Proc. Institu,te of Radio EngilU!ers, Vol.
21, No.3, March 1933, .p. 349.
( 5) Trevor and Carter, "N otes on
Propagation of Waves Below Ten Meters
if( Length," Proc. l.R.E., Vol. 21, No.3,
March 1933, p. 387.
(6) Beverage, "Some Notes on UltraHigh-Frequency Propagation," RCA Review, January 1937. (Also giving extensive bibliography.)
(7) Pock and Epstein, "Partial Suppression of One Side Band in Television
Reception," RCA Review, January 1937.
(8) Everest, "Amplification Problems of
Televison," COMMUNICATIONS, January
1938, p. 15.
(9) Goldsmith, "Television Economics,"
COMMUNICATIONS, Feb. 1939, Section A-I,
p. 18.
(10) Murray, "Television Standards,"
COMMUNICATIONS, Dec. 1938, p. 14.
Part III: Television Cameras
I
T makes little difference where one
might go throughout the world examlnmg electronically-operated television pick-up devices, he will probably
find only variations from the two fundamental patents issued originally in
this country, one to V. K. Zworykin
about 19281 and the other to P. T.
Farnsworth about 19312. These two devices pretty much dominate the international television picture at the present
time. In foreign countries, the television cameras may appear under unfamiliar names, but a closer scrutiny will
probably reveal the basic principles of
operation of one of the two cameras to
be described in this installment. For
instance, in England the Emitron camera of the Marconi-E. M. 1. Company
resembles Zworykin's I COlloscope, and
the Baird Electron Camera is similar
to Farnsworth's Image Dissector. Because of this fact, a study of the two
pick-up systems used so extensively in
the United States today will give us an
up-to-date working knowledge of the
television pick-up systems of the world.
In Part I of this series, the necessity
for s~anning and for the translation of
the average light level of each incremental area of the picture into an electric current of corresponding intensity
was pointed out. In both types of television camera tubes widely used today
both of these processes, i.e., the scanning and the optico-electro translation,
occur within the same device. In addi-
tion to this, several models also include
means for amplification of the feeble
signals so that they have a fighting
chance against the circuit noises.
The operation of the I mage Dissector
is made clear by Fig. 1. The image to
be scanned is focused by a conventional
system of lenses onto the cathode surface which has been treated uniformly
for photo-electric emission. It is evident that the bright areas will cause
many electrons to be emitted and that
the darker regions of the image will
cause fewer electrons to be emitted
from this photo-cathode surface. The
anode in the opposite end of the tube is
held at a positive potential with respect
to the cathode so that all of the photoelectrons emitted will be accelerated
toward the anode. Leaving the photoelectric cathode, then, is a beam of electrons about the size of the image whose
electronic density along its cross-section
will vary in a manner similar to the
light variations over the image as it
falls upon the cathode. In other words,
if one could take an imaginary slice
fro111 this electron bundle leaving the
photo-cathode he would find that in the
regions of the slice corresponding to
the light parts of the image, there would
be found many electrons and the areas
corresponding to the dark parts would
be represented by only a relatively few
Sc:hematic:
diagram of
Image
Dinedor
tube.
223
Section 8 •
THE
MYE
TECHN.ICAL
MANUAL
will cO):lfirm this. Let us assume the
electrons. This arises from the fact that
usc of RMA standards of 441 lines per
the photo-electric emission from the
image, 30 complete frames per second,
cathode is a function of the intensity
4
of the impinging light.
and aSpect t:atio of - . The number
Becaus!": aU· of the electrons in a beam
3
possess a negative charge, there will
be mutual repulsion between the various
electrons comprising the electronic
image. This effect is further augmented
by slight initial variations in velocity
and direction as the photo-electrons are
emitted. These effects tend to make the
electronic image bundle to spread apart,
but this spreading is minimized by"
focusing coils A, A' mounted coaxially
with the tube. Its magnetic field is
parallel to the direction of travel of the
Fig. 2. The bosic Iconosc:ope.
electrons, and any electron attempting
Photo courtesy RCA Review.
to travel diagonally to this magnetic
field has a force acting upon it tending
4
to bring it back into line.
of elements per frame is (441)"Above and below the evacuated
3'
cylinder is a pair of coils (B and B')
=
259,000.
As
there
are
30
of
these
connected in series, so situated that their
frames
per
second,
the
time
that
one
axis is perpendicular to that of the tube.
single elemental area will be in front of
The magnetic field resulting from cur1
rent flowing in these two coils will
. the aperture will be - - - , - - - - result in the electronic image bundle
(259,000) (30)
being deflected upward or downward in
seconds
=
0.129
microsecond.
I Now,
the plane of the paper in Fig. 1. Anlet us assume the use of an F-4.5 lens
other pair of coils is arranged one on
in front of our Image Dissector throwthe side of the observer and one on the
ing a brightly illuminated outdoor
back side so that its magnetic field is
scene
upon the photo-electric cathode.
perpendicular both to the axis of the
Under these conditions, the total light
tube and the plane of the paper. By
falling upon the cathode will be In the
means of a current in these coils, the
order of 0.1 lumen. Let us also assume
electronic image bundle may be deflected
that the photo-electr;c surface has a sentoward or away from the observer.
sitivity of 75 microamperes pCI' lumen,
These two sets of coils make it possihle
an extremely sensitive surface which
to deflect the electronic image at will
within the tube by the simple expedient
of sending currents of suitable wave
Schematic drawing of an RCA
Ic:onosc:ope.
form through the coils outside the tube.
As the electronic image approaches
the anode pillar, a few electroris will go
through. the aperture, hit the tiny target
inside the anode pillar structure, and this
constitutes the signal current. The two
sets of deflecting coils are so energized
that each picture element is scanned in
the proper sequence. For RMA standards of operation, the image beam
would be deflected horizontally 441
times per second and vertically 60 times
pe. second to give a 441-line, 30 frames
per second, interlaced image. ~he entire electronic image is moved across
the aperture to accomplish the scanning
process in this Farnsworth Image Dissector, while the scanning point is movable over a stationary image in most
other systems.
The photo-electric current representirig the light intensity of one elemental
area is very feeble. A brief calculation
224
has been obtained by much research
work. The photoelectric current representing a single elemental picture area
(75 x 10-") (0.1)
IS
28.9 X 10-12 am259,000
peres or 28.9 micromicroamperes per
element. This current flowing for the
0.129 microsecond is equivalent to
3.74 x 10-18 coulombs which is equal
to 23.5 electrons. In an extremely generous mood, we will call it an even 24
electrons, which, one must still admit,
is not much of an electric current. This
signal current would undoubtedly be lost
in the noise associated with ordinary
thermionic amplifiers and because of
this inherently feeble signal from the
Farnsworth Dissector, electron multipliers are used. In one of the later models,
this multiplier is built into the anode
pedestal.
An early type of RCA Iconoscope
(Greek: "image observer") television
camera tube is shown in the photograph
of Fig. 2. A schematic drawing of a
commercial model (Type 1849 and
1850) recently put upon the market is
. shown in Fig. 3. The type 1849 Iconoscope is designed for motion-picture
pick-up, while the type 1850 is much
more sensitive and is intended for direct
pick-up at low levels of scene illumina-,
tion.
The heart of the Iconoscope is the
mosaic electrode which has been
especially treated for high photo-electric
emission. The mosaic may be formed
by the deposit of a multitude of tiny
silver globules upon an insulating sheet
such as a thin sheet of mica. These
globules are then photo-sensitized by
caesium and each globule, which is in-
=
fUNDAMENTALS Of TELEVISION ENGINEERING
sulated from all its neighbors, becomes
a minute photo-electric cell. These globules are so small that there may be
dozens of them in one elemental area
of the mosaic or the area of the scanning spot. In general, about 30% to
40% of the area of the mosaic is covered by the globules.
An electron gun and associated beam
deflecting system are mounted in the
neck of the Iconoscope. This gun is
very similar to that found in the usual
cathode-ray tube and consists of a
thd'mionic cathode for emission of the
electrons, means for accelerating the
electrons, and means for focusing them
into a very fine beam. By means of an
electromagnetic or electrostatic system
(the lconoscope uses the former), the
beam may be deflected to any spot on
the mosaic electrode. To meet the RMA
Standards, this beam would be swept
horizontally across the mosaic 441
times per frame, and the beam would
also be deflected slowly in a vertical direction so that each line would fall adjacent to the preceding one, the 441
lines scanning all parts of the mosaic
1
surface every -th second.
30
Let us examine the mechanism by
which the signal currents are generated.
The image is focused upon the mosaic
by means of a suitable external lens
system. The light falling upon the
mosaic $:auses photo-electrons to be
emitted from each element of the mosaic.
The sensitized silver globules lying in
a part of the image which is light will
give off mor~ electrons than the dark
portions. The electrons given off from
each mosaic element photo-electrically
are attracted to the silver coating on the
inner side of the tube which constitutes
the anode and which is held at a positive potential with respect to the mosaic.
It is obvious that the leaving of the
electrons from the mosaic element' will
Filii. 5.
The new Image Ic:ono·
5c:ope. RCA Photo.
leave a deficiency of charges upon it
and, by virtue of the capacitance existing to the metallic backing plate on the
opposite side of the mica sheet, this will
actually result in a charging of this
tiny condenser. The magnitude of the
charge will depend upon the intensity of
the light falling upon it for a given
length of time. Because each of these
mosaic elements is highly insulated
from every other element, it is seen that
a scene focused upon the mosaic will
immediately give rise to a potential distribution over the face of the mosaic
which varies electrically as the light and
shade of the scene itself varies optically.
The function of the electron beam is
to discharge these tiny charged condensers in a certain order. The sweeping of the electron beam across a
Sc:hematlc: drawing of tube shown
in Fig. 5.
• Section 8
charged element will mean the equalization of the charge, or the discharge, of
that condenser element. The charging
current which flowed t6 perform this
equalization is proportional to the
amount of charge on the element, which
is in turn porportional to the intensity
of the light falling upon that element.
The current which flows through resistor R of Fig. 3 produces a voltage
which varies as the light variations
along that particular scanning line, and
this constitutes a feeble· signal voltage
which can be amplified and utilized.
As mentioned before, the area covered by the scanning beam contains
many of the~ mosaic elements. Becaut\e
of this, the signal output of one elemental area of the mosaic will be proportional to the average charge attained
by all the globules in that elemental
area.
The sensitivity of the Iconoscope is
much greater than the fundamental Dissector. This results from the storage
effect that takes 'place by the more or
less continuous process of charging the
minute condensers. While the signal
from a single elementary area of the
Farnsworth Dissector tube might be in
the order of 24 electrons, the signal
from a single elemental area of the storage type would be much greater because
its charging process has been progressing while all the rest of the approximately 259,000 elemental areas were being scanned in turn. In other words, the
Dissector tube has only the time required to scan a single element for the
photo-electric emission of its signal
current (about 0.13 microsecond (while
the Iconoscope merely releases during
this same time a charge that has been
1
accumulated for about - second. The
30
theoretical gain of the Iconoscope over
the Dissector would be about 259,000,
but an advantage of only a few thousand
has actually been realized.
The Improved Fernsworth PiClk·up Tub.
An interesting thing about the improved types of Farnsworth and RCA
tubes is that the new Farnsworth tube
utilizes a photo-mosaic and the new
RCA tube uses electronic images.
The improved Farnsworth· tube is
shown schematically in Fig. 4. The image is focused upon the special "photoisland" grid after passing through the
transparent anode on the end of the
tube. This grid has about 160,000 holes
punched per square inch in a thin nickel
plate. One side is coated with a dielectric material which has deposited upon
225
Section 8 •
THE
MYf
TECHNICAL
MANUAL
Illustrating
the
improved
Farnsworth
tube.
it many photo-sensitive "islands" which
ate so-called because they are insulated
from each other as are the globules on
the Iconoscope mosaic. The image
focused upon this "island" surface
causes an electrical potential image to
be set up over its face. The beam of
electrons from the gun hit the special
surface on the nickel plate liberating
copious quantities of secondary electrons. This cloud of secondary electrons acts as a rapidly moving virtual
cl1-thode source, and these electrons are
drawn through the tiny holes of the
mesh to a degree depending upon the
amount of positive charge built up on
the "photo-islands" on the other side.
In other words, the "photo-islands" act
as the control grid of a triode in that
they control the number of electrons
which shall go to the electron multiplier
to represent that particular area. The
intensity of illumination determines the
amount of positive charge on the islands, and this positive charge determines the number of electrons allowed
to go to the electron multiplier which
constitutes the signa! curnmt.
The main advantage of this tube is
that its sensitivity is increased to about
ten times that of the conventional Iconoscope. Another advantage is that a
peculiar shading signal common to the
Iconoscope and evidently a result of
roving areas of spurious charges over
the mosaic does not appear. A difficulty
at the present time is constructing the
photo-island mosaic so that its charge
.
.
1
leaks off in about - second so that no
30
residual charge remains when the next
frame starts,
Improvlld RCA Icono$coplI
The Image Icot;loscope recently
described has resulted in greatly superi-
226
or performance. A photograph of this
tube is shown in Fig. 5, and a sectioned
schematicdiag-ram is shown in Fig. 6.
Fig. 8. A new RCA Iconoscope
tele"isicllt .camera.
'Referring to Fig. 6, the image to be
televised is focused upon the plane
photo-electric cathode near the end of
e
Fig. 7. Two wen·
known television
res e a, r c h engi.
neers. Dr. Y. K.
Zworykin ('eftl and
E. W. Engstrom.
examine a special
e'ectronh: tub e .
Dr. Zworykln is the
Inventor 0 f th e
Ico!lOlcop.. RCA
photo.
the tube. By virtue of the potential
existing between the anode and this
cathode, an electronic image is released
from the opposite side of the cathode.
With the aid of special focusing arrangements, the electronic image impinges upon the mosaic at the opposite
end of the tube. The only major difference between this mosaic and the one
in the basic Iconoscope is that this one
is not treated for photo-electric emission. The electronic image hitting the
mosaic knocks off secondary electrons
from the globules. In this manner, the
potential distrihution corresponding to
the image di~tributi()n of light and shade
is set up over the face of the mosaic.
The secondary electrons are carried off
by the anode and leave a deficiency of
electrons or a positive charge on each
tiny condenser which each globule
forms with the metallic backing plate.
The value of these charges depend upon
the number of secondary electrons
given off, and this in turn depends upon
the number of photo-electrons representing that particular part of the electronic
image. The electron gun and deflecting
.system scans the mosaic in the usual
way, and the signal is taken off as in
the ordinary Iconoscope.
The advantages of this pick-up tube
lie mainly in the fact that the sensitivity
is increased to about ten times that of
the old Iconoscope due to the fact that
secondary emission is more effective
than photo-emission in building up the
charges on the mosaic. Another advantage is that the photo-cathode is so
close to the end of the tube. This 'allows
the use of short focal length lenses, and,
consequently, a large aperture optical
system can be used. The spurious shading signal generation effect is still present in this tube, though in at least some
cases is slightly less severe.
e
FUNDAMENTALS OF TELEVISION ENGINEERING
BIBLIOGRAPHY
(1) U. S. Pat. No. 1,691,324 (1928).
(2) U. S. Pat. No. 1,773,980 (1931)
(3) "Television by Electron Image Scanning," Farnsworth, Journal of Franklin Institute; Vol. 218, Oct., 1934.
( 4) "Television by Electron Image Scanning," Farnsworth, Electronics, Aug.,
1934.
(5) "Farnsworth's New Tube," Electronics, Dec., 1938, pages 8, 9.
(6) "Theory and Performance of the
Iconoscope," Zworykin, Morton, and
Flory, Proc. IRE, Aug., 1937.
(7) "lconoscopes and Kinescopes in TeleviSIOn," Zworykin, RCA Review,
July, 1936.
(8) "The Iconoscope-A Modern Version of the Electric Eye," Zworykin,
Proc. IRE, Ji.nnuary, 1934.
(9) "Tubes for Television Show Technical Advances," Electronics, July,
1938, p. 12, 13.
(10) "Television Economics," Goldsmith,
Part II, Section E-l (Video Pickup Equipment), COMMUNICATIONS,
March, 1939, page 19.
(11) RCA Rating Pamphlet on 18;9, 1850
lconoscopes.
• Section 8
•
Fig. 9. A typical
scene during the
broadcasting of a
television p la y .
Note the trucks
upon which the
cameras are
mounted and the
powerful lights required. RCA photo.
•
(12) "The Latest Emitron Camera," Television and Short-Wave World, July,
1938, p. 397 (London).
(13) "A New
Farnsworth 'Pick-up'
Tube," Telev. & Short-Wave World,
May, 1938, p. 260.
(14) "A New Emitron Camera," Telev.
& Short-Wave World, January, 1938,
p. 11.
(15) "A New Electron Camera," Tele'll.
& Short-Wave World, August, 1937,
p. 467.
(16) "The Television Camera," Telev.
& Short-Wave World, June, 1937, p.
329.
'
(17) "The Baird Electron Camera," Jones,
Telev. & Short-Wave World, Sept.,
1936, p. 487.
Part IV: The Cathode-Ray Tube as a Television Reproducer
T
HIS installment will deal only with
the cathode-ray tube as a television
reproducer, although there are many
mechanical systems by which the separate picture elements can be reassembled
at the receiving end. This does not
mean that the mechanical systems hold
no promise for the future, but rather
that in the United States at the present
time practically all of the activity is
confined to cathode-ray reproducers.
The major limitation of the cathode-ray
tube, as will be pointed out later, is the
lack of light, and the mechanical systems have advantages in this regard due
to the fact that they control a powerful
local light source such as an intense incandescent lamp, an are, or the recently
introduced high-pressure vapor tube.
The cathode-ray tube is particularly
adapted to the demands of high-definition television, and this fact is largely
responsible for its more or less universal adoption throughout the world at
this stage of television development.
Faraday, observed the effect of application of a high potential between two
electrodes within a crudely evacuated
glass envelope. The Giessler tube giving interesting color effects within its
fancy glass-work was a novel result.
Better exhaust techniques, however,
gave rise to tile discovery of new effects, one of which was the cathode-ray
phenomenon, so named by Plucker
about 1879. The Crookes tube showed
that the "rays" were more properly
discrete particles leaving the cathode at
-right angles to its surface. These particles were later (1890) identified as
electrons suggesting that a better name
for cathode-rays would be electron
beam, and this flas been generally
adopted while speaking of the beam,
but not the tube itself. Many improvements have been introduced, among
them magnetic focussing (1898), the
hot .cathode 'for electron emission by
Wehnelt (1905), and various arrange-
.
Fig, 5·a. Resolution test pattern,
Grid modulated at about 2 me/s_.
Spread vertically to show individual Iconnlng tine.. Photo
court •• y IRE Proc.
HISTORY OF THE CATHODE-RAY TUBE
Many people who have only recently
become acquainted with the cathoderay tube may be somewhat startled to
learn that tubes bearing that very name
have been in existence since 1876. Even
earlier than this, Coulomb, and later
227
Section 8 •
THE
MYE
TEe H N I CAL
'M A N U A L
Fig. 4. An RCA projection type
~athode.ray television tube. Small
Image can be projected on 3 x 4
ft. screen. Photo I:ourtesy IRE
Proc.
become indispensable to the communication engineer.
DESCRIPTION OF THE CATHODE-RAY TUBE
Above: Fig. 6. A 12" tube being
tested with a special test pattern. RCA Photo.
Below: Fig. 8. Removing fluorescent material from a furnace.
RCA photo.
The cathode-ray tube as used today
in television receivers is shown in Fig.
1. This is one of the largest tubes extensively made and has a screen diameter of 12 inches and employs el~ctro
magnetic deflection. In the neck of the
tube the electron emitting and focussing
eleme~ts a:e assembled constituting
what IS qUIte appropriately called the
electr~n gun. The beam originating
~ere IS attracted by the higher potential on the various anodes and then impinges upon the fluorescent screen. The
energy which the electrons have by virture of their mass and velocity is given
up at the screen and some of it is translated to visible light producing a luminous spot.
Fig. 2 shows a partial section view
showing the construction of a typical
electron gun. At the extreme left the
cathode, or the electron emitting device
is shown. The filament within the ca~
thode sleeve is heated by an electric
current which in tllrn heats the cathode
sleeve. The end of this cathode tube
toward the fluorescent screen is coated
with a material which has a high electron emission efficiency when heated.
The first anode, which is held at a very
high potential with respect to the cathode, attracts the emitted electrons
and they are pulled through the hole i~
the cylinder which is usually called the
grid. It is so called, not because of its
structure, but because it performs a
function comparable to the grid in the
ordiriary triode. The intensity of the
luminous spot on the fluorescent sCt:een
is a function of the speed with which
the electrons arrive and the number of
electrons. With fixed electrode voltages,
the speed remains constant, and the light
intensity of the luminous spot is controlled by the variation of the number
of electrons in the beam. This is accomplished by the grid. Because it is
so much closer to the electron source'
a certain low voltage applied to it ha~
the same effect on the electron density
of the beam as a very much greater
voltage on the first anode. Therefore a
relatively small video signaL volt;ge
(say 20 volts) applied between the cathode and grid is sufficient to vary the
beam from full brilliancy to cut-off.
The beam next passes through two
holes in discs within the cylinder which
comprises the first anode. The beam
then passes through the second anode
which may be either a hollow cylinder
with a partially closed end as shown
!n ~ig. 2 or a conducting coating on the
Illslde of the funnel-shaped portion of
the glass envelope. In either case, the
electrostatic equipotential surfaces are
so arranged and adjusted that the electrons in the beam may be brought to a
very fine focus at the fluorescent screen.
The large end of the glass envelope
UP0t; w~ich the fluorescent coating is
appJted IS curved an amount that will
retain the spot focus even though the
beam is bent in any dil'ection by the deflection system.
Because tlie beam is composed of
many individual electrons travelling in
the same direction within a well-defined
space, they should react in the same
Showing approximate spectral
energy distribution compared to
eye sensitivity.
i
\
Re lotive 4-4--I--+--I--+-iH
60 f--- rad iant e n e r g y '
distribution
/
IIJ
40
228
\
I-I--':~ 1~~Ui~~r--t-t/t-t--t-t--1lr-t--f\~+--+-\--L-.l--+~\"+--I
screen
~Relative
\
/
Fig. S·b. Area within white circle
of Fig. S·a enlarged four times to
show detail. Photo from IRE Proc.
ments for focussing the beam electrostatically. Intensive research work during the last few years has resulted in
bringing the cathode-ray tube from a
laboratory curiosity to a tqol which has
\
\
nen~fivity - ' \
\
(
Near
Ultra_ Violet
Violet
Blue
Green
Yellow
Orange
Red
I
I
I,
!
fUNDAMENTALS Of TELEVISION ENGINEERING
manner as· electrons flowing in a conductor occupying the same space. We
know that a c~nductor which has electrons flowing in it is surrounded by a
magnetic field and that it will have a
mechanical force exerted upon it if another magnetic field approaches it. This
is the well-known motor principle uflon
which so many electrical, devices depend.
This electron beam can thus be de
flected to any point on the screen by
suitable currents flowing in suitably arranged coils around the neck of the
tube. Two pairs of coils whose axes
are oriented 90 degrees from each other
are used, the whole assembly being enclosed and mounted around tube's neck.
We also know that each electron has
a small but definite negative electric
charge. Because like charges repel and
unlike charges attract, the electrostatic
deflection system of plates shown on the
right in Fig. 2 will bend the beam. If
the top horizontal plate is made positive
with respect to the lower one, the beam
will be deflected upward an amount
which depends linearly upon the magnitude of the difference of potential applied. If the plate nearer the reader of
the other pair is made positive with respect to the far plate, the beam would
be deflected toward the reader By
means of these two pairs of plates, the
beam may be moved to any part of the
screen. The actual refjuirements and
relative advantages of the tW!) types of
deflection systems will be covered in
some detail in the next installment.
The focussing system is quite effective as demonstrated by the photograph.
of Fig. 5 (a) and (b) which has been
t;tken from Burnett's paper. 4 Regular
scanning methQds were em!Jloyed, and
the grid was modulated at about two
million cycles per second. Each of these
dots is of approximately the same order
of magnitude as an elemental picture
Show in,:! a partial sec:tlon view of
a typic:al elec:+ron ,:!un.
• Section 8
Fig. 1. Comparing 12" television
tube with a small metal tube.
Both tubes are used in same rec:elver. RCA photo.
area, although the lines have been separated for ease in observation. This enlarged area.of Fig. 5 (b) has been taken
from the center of the screen and has
been enlarged four times. A certain
amount of de-focussing, blurring, and
change in spot shape occurs near the
edges of the iluorescent screen, although
this effect is not serious. Fortunately,
also, the center of interest usually lies
in the center of the picture.
LUMINESCENCE
The law of conservation of energy
states that energy may be transformed
from one form to another, but can be
. neither created nor destroyed. Energy
can exist in many invisible forms. For
instance, a small amount of current can
be passed through the filament of an
incandescent lamp causing a radiation
of energy, but the effects of the energy
cannot be seen until enough current is
passed to make the filament become
white-hot and radiate energy within the
visible spectrum.
In nature, there are many substances
which have the power to change invisible ultra-violet radiation energy or cathode-ray ~nergy into visible light. The
study of this phenomenon is in general
known as luminescence. This may be
broken down into two parts, fluorescence and phosphorescence. Flu01'escence is an emission of luminous radiation which stops as soon as ·the exciting
stimulus is removed. Phosphorescence
is that luminous radiation which persists after the excitation has been removed. For example, if a sheet of paper were coated with a certain luminous
coating, it would appear white in daylight and be invisible in the dark. However, let some ultra-violet light fall upon
Above: Fig. 7. A 12" cathode.ray
tube being subiected to factory
t.sts. RCA photo.
B.low: Fig. t. Ma.ufacturlng
pro .... of loiftl09 shaak and tub•.
RCA photo.
Electrostatic
Deflection System
FI':!. 10. A television type c:a·
thode-1liiy tube under,:!oin,:! life
test. RCA photo.
1+----='-- 2000 Volts -.!.-----loi
Approx.
Vertical
Deflection
Voltage
Fig.2
229
Section 8 •
THE
it and it fluoresces with some characteristic color. When the ultra-violet
light is removed, the color continues,
dying away slowly. This latter 'is called
phosphorescence or aiter-glow. Phosphorescence continues for days or even
weeks with certain substances. It is believed that fluorescence is associated
with a change withitjthe molecule itself while phosphoresce1lce is associated
with th~ transit of electrons from one
molecule to another.
The coatings used on television ca·
thode-ray tltbes rely principally upon
the fluorescent effect and, hence, are
usually called fluorescent coatings. The
after-glClw or time lag caused by the
phosphorescent effect is, in fact, usually
very detrimental in television pictures.
For instance, a moving part of the image would leave an eerie trail behind it.
A ball thrown would appear to have' a
tail like a comet. Suitable screen materials should have what is termed short
persistence or medium persistence characteristics. Phosphorescent characteristics of several substances as given by
Levy and West1 are:
Duration of
Material
Phosphorescence
Calcium Tungstate
8 microseconds
Willemite
2-8 milliseconds
Zinc phosphate
About 0.25 second
Zinc sulphide with Fraction of 1 microsecond,
nickel
A scre~n whose relative brightness de~ays to within 10% of "black" in about
15 milliseconds is deemed satisfactory
for television reception, and it would
fall under the medium persistence classification.
COLOR OF EMITTED LIGHT OF
FLUORESCENT COATINGS
The screen that has been used very
extensively for general steady-state oscillographic work is the Willemite
screen. This substance is found in mi.ture ;lnd can also be made synthetically.
This material has been so popular because practically all .of its energy is
developed in a region in which the eye
is very sensitive. Fig. 3 shows the relative eye sensitivity plotted against the
wavelength of light in Angstrom units.
It will be seen that the eye is most
sensitive to yellow-green light. The
spectral energy curve of Willemite is
shown, and it will be seen that almost
all of its energy is concentrated in the
green, where the eye is very sensitive.
230
MY f
TECHNICAL
MANUAL
Although cathode-ray tubes giving
green light were and are used in many
experimental television receivers, the
fact remains that a more sui table and
pleasing color would be white. The approximate spectral energy distribution
of one mixture is shown as a broken
line in Fig. 3. This is an inefficient arrangement because, although the white
screen may have the same efficiency
from the energy standpoint, much of
this energy is expended at wavelengths
at which the eye is relatively insensitive
and, therefore, wasted as far as apparent light intensity is concerned. Even
though the white screen is inefficient,
the public will insist upon something
very close to white because of the comparison to motion pictures which television is always subjected to.
Other difficulties· confront the white
television screen. For instance, the predominating hue shifts to a longer wavelength with higher intensities. The
bright parts of the image may have a
cast that is somewhat different from
the less bright portions. In general,
however, this effect is more pronounced
at the lower intensities as almost any
fluorescent coating tends to appear
white at extremely high intensities.
The extraneous illumination falling
on the screen also influences the apparent color. A screen that appears white
in a totally dark room may appear tinted
if an incandescent lamp is burning in the
room. Added to all this, there appears
to be a wide variety of individual ideas
as to what a "white" screen really is.
In spite ot these difficulties, several
fluorescent coatings have been developed
which give essentially black and white
pictures.u One method of attack is to
mix two or more highly colored substances in such a way that their composite effect is essentially a white. For
instance, substances exhibiting blue and
red-orange fluorescence will produce
white .. Progress is being made in this
direction, and increasing the luminous
efficiency seems to hold real promise.
Because the maximum visible light energy emitted is only in the region of
4% or 5% of the electron energy input,
there is ample room for improvement.
PROJECTION CATHODE-RAY TUBES
Fig. 4, which is taken from Law's
paper,2 shows a cathode-ray tube which
gives a small, intense image so bright
that it can· be projected onto a screen
giving a 3 x 4 foot projected image.
Light may be compared to butter, the
greater the area over which it is spread,
the thinner it lies. This answers the
question often asked as to why a lens
system is not used on an ordinary cathode-ray television image tube. It can
be done, but the picture gets dimmer
the greater the area it is made to cover.
This projection cathode-ray tube is designed for high-voltage operation (10,000 volts), high-electron gun current,
and a small fluorescent screen image
(2.4 x 1.8 inches) which is projected
onto a screen for enlargement. With
such terrific electron bombardment, the
fluorescent screen has a much shorter
life than that of an ordinary directviewing tube. The progress of the projection tube now seems to be bound up
in the development of more durable
fluorescent materials.
BIBLIOGRAPHY
(1) Levy and West, "Fluorescent Screens
for Cathode-Ray Tubes," Journal
lEE, Vol. 79, 1936, pp. 11-19.
(2) Law, "High Current Electron GUll
for Projection Kinescopes," Proc.
IRE, Vol. 25, No.8, August, 1937,
pp. 954-976.
(3) Zworykin and Painter,· "Development
of the Projection Kinescope," Proc.
IRE, Vol. 25, No.8, AugUst, 1937,
pp. 937-953.
(4) Burnett, "A Circuit for Studying
Kinescope Resolution," Proc. IRE,
Vol. 25, No.8, August, 1937, pp.
992-1011.
(5) Zworykin, "Iconoscopes and Kinescopes in Television," RCA Review,
Vol. I, No.1, July, 1936, pp. 60-84.
(6) Maloff, "Direct-Viewing Type Cathode-Ray Tube for Large Television Images," RCA Review, Vol.
II, No.3, January, 1938, pp. 289
(7) Laverenz, "Problems Concerning the
Production of Cathode-Ray Tube
Screens," Journal of the Optical Society of America, January, 1937.
Reprinted in T clevisioll, Vol. II,
RCA Institutes' Teclmical Press.
(8) Wilson, "Television Engineering"
(Pitman), Chapter VIII, Cathode
Rays and Fluorescence.
(9) Randall, "The Theory of Luminescence," Television (London), July,
1937, p. 408. Abstract of paper
appearing in Royal Society oj Art!
Journal, March, 1937, p. 146.
(10) Parr, "The History of the CathodeRay Tube," Television (London),
February, 1937, p. 85.
(11) Schmidling, "Fluorescent Materials
for Television Tubes," COMMUNICATIONS, April, 1939, p. 30.
I
I
jl
<
,
I'
I.
"
fUNDAMENTALS Of TlUVISION INGINffRING
• Section, 8
, Part V: Electron 8eam Deflection Methods
I
N an electronic television system which
uses a'cathode-ray tube as the reproducing element, we have seen that the electronic density of the electron beam is
made to vary with the signal corresponding
to the variations of light and shade of the
image being transmitted. In order that
the visual intelligence be successfully received, it is necessary that the electron
beam of the reproducing tube be made
to traverse the area of the screen which
corresponds exactly to the area being
scanned at that instant at the transmitter.
Exact synchronism must be maintained
between the two extremities of the system,
a subject which will be covered later in
this discussion. In addition to this, means
must be provided whereby the electron
beam can be deflected to any part of the
fluorescen~ screen. As mentioned in Part
IV, the two possible methods of obtaining a deflection of the electron beam are
the electrostatic and the electromagnetic
methods.
tween the deflecting plates, E. is the
accelerating anode potential, and the
other symbols are a's explained in Fig.
1. Equation (1) is derived from the
equation of motion of an electron trayeIling in the y direction, considering
the charge on the electron and the mass
Screen-1+----
Y ---~
ll~
Fig.i
Electron-,'
Beam
lIIustratlllg the prillciple of
electrostatic deftectloll.
Showillg how electromagnetic
deftectloll il accompllslled.
r---+
y
-----.I
x=-
...................... (1)
lEad
where Ed is the potential applied be-
Electromagnetic Deflection
The electron beam can be compared
to a current flow in an extremely flexible conductor. If this beam traverses
a magnetic field, a force will act upon
the beam tending to move it. This
phenomenon is exactly the same one
which causes electric motors to turn,
the well-known "motor action" based
upon Ampere'.s law. Consider an electron beam entering a perfectly uniform
magnetic field whose direction is from
the observer into the paper in Fig. 2.
By means of 'the old familiar left-hand
rule (remembering that electron flow is
opposite to the conventional current
flow) , the direction of the deflection
can be determined. The amount the
beam is deflected is given approximately by:
0.3 Hly
x = - - - . .................. (2)
ylE.""
Electrostlltic Deflection
In the case of electrostatic deflection,
the beam of electrons leaves the gun
and passes between two parallel (at
least considered parallel for this analysis) deflecting plates arranged horizontally. The electric field set up between these two plates causes the beam
to be bent upward and downward in a
vertical plane. The beam next passes
between another similar pair of plates
arranged at right angles to the first
pair. An electric field set up between
these two plates causes the beam to be
deflected in a horizontal direction and
by means of the composite forces acting
upon the beam by the two pairs of
plates, it may be deflected to any part of
the fluorescent screen. These forces
acting upon the beam arise, as pointed
out before, from the fundamental action
of charged bodies: like charges repel,
and unlike charges attract. The beam,
being composed of negative electrons,
will be deflected toward the plate which
is positive at that instant.
The amount of the deflection is gi\ien
by
great anode voltage) requires a relatively large deflecting voltage for a
given deflection.
Electron Beam .;
Fig.2
of it due to its velocity. The trajectory
of the electron is rectilinear before entering the electrostatic field between the
deflection plates and after emerging
from it, but while it is travelling between the plates, its path is cur~ed.
From the mathematical statement of
equation (1) we can see that the deflection x is directly proportional to the
deflecting voltage Ed, the length l of
the electrotatic field traversed by the
electron, and the distance from the
plates to the screen. It is inversely
proportional both to the deflecting plate
separation and the accelerating anode
potential. Of these parameters, all are
fixed quantities for a given cathode-ray
tube except Ed and Ea. The greater
~., the greater the velocity of the electron 'travel and the less time the electrostatic field between the plates has to
act on it. For this reason a "stiff"
beam (one accelerated by a relatively
where H is the field strength in gauss
and the other symbols as explained in
Fig. 2.
It should be emphasized that equations (1) and (2) are only approximate due largely to the fringing effect
and the resulting non-uniformity of
the electric and magnetic fields.
Sawtooth Generating Systems
In order to obtain uniform spot
travel along a line and equally spaced
lines over the whole raster or scanning
pattern, the potentials that must be applied to the deflecting plates -must be of
saw-tooth waveshape.
This shaped
wave can most easily be produced by
a circuit such as that shown in Fig. 3
in simplified form. The condenser C is
charged from th~ d-c source at a rate
determined by the resistor R. When
the voltage across the condenser terminals, and thus across the gas triode
VT" has attained a certain value which
is determined by the grid voltage E c ,
VT, will become conducting and discharge the condenser C very rapidly.
Thus, we have a voltage which increases at an essentially constant rate
up to the firing point of VT, and then
rapidly decreases to zero and again begins a new cycle of ascent producing a
231
Section 8 •
THE
)"
_' .. ,lit
\ ,'{f~.
e2
it
A popular type of .aw-tooth
t •••rator u.ed by RCA.
saw-tooth shaped wave. The frequency
may be varied by varying R or changing the value of C, and the amplitude
may be adjusted by varying E.. To
obtain an essentially linear ascent, the
crest saw-tooth voltage must be only a
relatively small percentage of the applied doc voltage, because the voltage
built up across C is an exponential
function of time. The resistor R may
be replaced by a pentode tube whose
pllite current is essentially independent
of its plate voltage. In this way, the
tube acts as a constant-current device
making the saw-tooth ascent linear over
a greater proportion of the applied voltage. The limitation of this saw-tooth
oscillator utilizing a gas triode is that
the firing point of the tube varies
slightly with aging, temperature, etc.,
causing somewhat erratic operation,
and that there' is a very definite upper
frequency limit due to the finite deionization time. Newer gas triodes
using gases other than' mercury vapor
have overcome. many of these disadvantages; and it is PQssible to use this
type of saw-tooth generator for the line
scan for modern high-definition pictures which is 13,230 cycles per second.
While the mercury-vapor type of'gas
triode only was available, its limitations caused much work to be done
along the line of high-vacuum sawtooth generators. Fig. 4 shows a circuit" '. 8 which, has proved to be very
satisfactory as to stability and highfrequency operation. In fact, highvacuum generators have been made to
operate at frequencies as high as one
megacycle, which gives them a distinct
advantage over the gaseous type even
for oscillographic uses.
In Fig 4, VT. is the high-vacuum
232
MYE
TECHNICAL
MANUAL
triode which acts as the discharger of
the condenser C and VT. has the duty
of aiding this discharge operation. The
acfual discharge and charge circuit is
shown with heavy lines to facilitate an
understanding of the- circuit. U~t us
follow a cycle' of operation through,
starting with the condenser C discharged. At the moment the 300-400
volts ?-c are.. switched on, the full voltage appears across R causing the
cathode of VT. to be highly positive
with respect to ground. The grid of
VT, assumes the potential of the lower
end of R. which depends entirely upon
the plate current flowing through VT.
which in turn is determined by the
screen voltage setting on R.. The grid
of VTl can thus easily be made highly
negative with respect to its cathode.
This results in VT. being non-conducting while C is being charged. As the
F"ig.3
A simplified circuit for producing
saw-tooth voltago.
voltage across the terminals of C increases, the plate voltage of VT. ultimately attains a value which causes
VT. to become conducting in spite of
its high negative bias. As the plate
current of VT1 flows through R" voltage drop appears which is coupled to
the grid of VT. through the C.-R. circuit driving it in a negative direction
which in turn decreases the voltage
drop on R.. The grid of VT. thus becomes less negativ~ allowing more and
more plate current to pass. The grid
of VT. goes positive, and the condenser
C is discharged very quickly through
VT.. When the voltage across C decreases, enough, the VT. grid again
gains control and the' cycle repeats.
The resistor Rl controls the discharge
time Which is aided by the gain of VT,.
Resistor R. controls the amplitude of
the sweep. A pentode can be used as a
constant-current device in place" of R
if the refinement is justified. Synchronization can be obtained by injecting the
pulse on the suppressor grid of VT.
or repla.cing R. by a triode with adjustable cathode resistor and injecting the
pulse on the grid of this tube. The
values of components for 1O,OOO-cycle
operation as suggested by Parr" .are included in Fig. 4.
A simpler single-tube circuit of the
blocking oscillator type is shown in
Fig. 58. The condenser C is charged
in the usual way from a ld-c source
either through a resistor R or a pentode
tube. The discharge tube is connected
across C, the primary of a transformer
being in the plate circuit and the secondary in the grid circuit and the two
windings closely coupled. The tube
is biased beyond cutoff by R. which is
by-passed by C, to provide a smooth
bias voltage for the tube. The method
of action is as follows: the grid is
biased beyond cutoff and the condenser
charges until the plate voltage is great
enough to allow current to pass through
the tube even with the high bias. The
plate current flowing through the
primary of the transformer induces a
voltage on the grid which bucks the
bias from R.. This process rapidly
continues, until the condenser is discharged and the cycle repeats. The
resistor R. is connected across one of
the windings of the transformer and
adjusted so that the tube will not oscillate continuously but will produce es~ential1y a single pulse of current. Synchronization may be realized by inserting the pulses into a third winding.
The resistor R. controls the amplitude,
and R the frequency of the saw-tooth.
Typical values of constants suggested
by Parr" are included in Fig. 5.
There are several other types of sawtooth generators but none as much in
use in this country as that used by
RCA as illustrated in Fig. 6.•.•. 1 Here
Circuit for obtaining balanced sawtooth for el.drostatic d.fI.dlon.
---r--------------~~~-oDf
C2
B+
Fig.S
I.
!
I '~
• Section 8
FUNDAMENTALS OF TELEVISION ENGINEERING
again the ascent of the saw-tooth wave
is obtained by charging the condenser
C. through the resistor R. from a d-c
source. The tube VT. is normally biased beyond cutoff so that it does not
influence the charging cycle. However,
at certain intervals determined by the
selection of constants and the synchronizing signal, the blocking oscillator incorporating VT, delivers a large
positive pulse to the grid of VT., causing it to have a very low impedance
and discharging the condenser C. after
which a new cycle begins. The waveshape of e, is shown in Fig. 6, the
broken portion in the negative region
serving only to drive VT. farther beyond cutoff. The solid positive pulses,
however, are the ones causing VT. to
discharge C.. The phase relationships
between the discharge pulses of e, and
the output saw-tooth wave e. is as
shown in Fig. 6.
contacts for all deflecting plates. The
two types of distortion arising when the
deflection voltages are asymmetric are:
(I) a variation of sensitivity produced
by the deflection voltage which adds or
subtracts from the accelerating anode
voltage, and (2) an inter-modulation of
the two pairs of plates. Both forms of
distortion are avoided if balanced deflecting voltages are used. The effect
of these distortions is the degeneration
of the normal rectangular raster to one
of trapezoidal shape. To avoid this, a
push-pull amplifier stage should be used
to apply the deflecting voltage to the
plates.
Figs. 7, 8, and 9 show three means
of attaining a balanced saw-tooth for
electrostatic deflection. Fig. 7 is a 'conventional circuit, VT, being a straight
amplifier of the unbalanced input, and
VT. is the phase-inverter stage by ob-
A saw-tooth circuit for electrostatic dettec:tlon.
c
'f
Fig.9
B+
orz'." , -
'11("\1
'"
/"?
'.'
,
' I
·~e:l~t~>:)
,.
..
~
Fig.tO
An assembly of horizontal and vertical deftec:ting coils are used in RCA receivers.
voltage appearing across C, divided by
the actual gain of VT,.
Fig. 9" shows a circuit which is inherently balanced to ground. This is
accomplished by dividing the charging
resistor into two equal parts, Rl and
R 2, and placing one on either side of the
S'1.w-tooth genllFating condenser:. To
vary the charging rate (and thus the
frequency) either R, or R2 may be
made adjustable within small limits
without seriously disturbing the balanced conditions.
Electrostatic Deflection
It has been pointed out that in charging a condenser through a resistor (the
case in many of the saw-tooth generators described), the condenser can be
charged only to a small percentage of
the + B voltage if linearity is to be
obtained. There are two ways to get
around this limitation, one to use a
pentode in place or the charging resistor and the other is to amplify the
relatively low saw~tooth generated with
the charging resistor. In either case,
more component parts are required.
One thing that must be met in electrostatic deflection is the distortion
arising when the saw-tooth voltage is
applied to the plates asymmetrically, or
unbalanced to ground. Many of the
small oscillograph cathode-ray tubes
have one horizontal and one vertical
plate bonded within the tube, but the
larger tubes, especially those in television service, always have separate
DIAGRAM
ASSE:M6LE:D YOKE: . /,:>
Electromagnetic Deflection
Fig.7
Circuit fot attaining balanced
saw-tooth for electrostatic deftec:tion.
taining its driving voltage from the
plate circuit of VT 2 • 1~
JllJllfTIlfl
output~
R
Fig .4
Showillg the actloa of the basic
horizontal pulse seleethlCJ circuit.
is actually a simplified version of three
filter sections in cascade as shown in
the plate circuit of the vertical ampli"
fier of Fig. 3.
Pulse Generation
A glance at the complex waveform
of Fig. 1 impresse5 one with the close
tolerances which must be observed for
,.;atisfactory television operation. It is
both interesting and instructive to
understand a method of keeping the
proper relationship between line and
field-pulses. It is also highly desirable
that the 60-cycle output of the vertical
sweep generator be locked into step
with the 60-cycle power frequency.
This results from the disturbing effects
of a-c hum in the vertical or horizontal
deflection circuits or both. The disturbance created is much more discon-
certing to the eye if it is in motion as
would be the case if a slight difference
existed between the field and power
frequencies. Wiggling and creeping
edges and vertically moving horizontal
bands due to uneven line spacing result at the difference frequency. To
avoid this, relatively complex systems
are used. Fig. 6 shows one such possible system. A master oscillator of
some type controllable over a narrow
range operates at 13,230 cycles per second which is the line frequency (441 X
30 = 13,230). This frequency may be
used to control the frequency of the
horizontal synchronizing pulses. This is
fed into a multivibrator circuit which
doubles the frequency and into four successive multi vibrator stages which act
as frequency dividers of 117, 1/7, 1/3,
and 1/3, respectively. The output frequency is 60 cycles. To keep this output frequency the same as the powerline frequency, it can be compared to
the power frequency by means of a suit-
ShowlnCJ action of' the basic: ver·
tic:al pulse seleetlnCJ c:ircuit.
able electrical circuit, and the frequency
of the master ()~cillator ad jllsted to COlllpensate for any differenc~ b~tweell the
two frequencies.
Bibliography
(1) Murray, "Television Standards," COMMUNICATIONS, December, 1938, p. 14.
(2) Murray, "RMA Completes Television
Standards," Electronics, July, 1938,
p. 28.
(3) Goldsmith, "Television Economics,"
Part III, Section E-3, "Synchronizing
and Video Controls," COMMUNICATIONS, April, 1938. p. 26.
( 4) Engstrom and Holmes, "Television
Synchronization," Electronics, November, 1938, p. 18.
(,5) Zaharis, "Synch Impulse Generator
for Television Deflection Circuits,"
Electronics. June, 1939, p. 48.
<.6) "Practical Television by RCA," Service Division, RCA Manufacturing
Company, Inc.
Part VII: Television Receivers
As
far as the basic principles of
operation are concerned, the television receiver does not differ from the
usual broadcast sound receiver. The
television receiver does differ greatly
in several details, however. The carrier
frequencies al'e much higher for the
television receiver (44 to 108 megacycles for seven channels) which alone
demands many refinements for satisfac-
tory operation. The television receiver
must receive and care for two carriers
simultaneously, one for sight and one
for sound. The sound channel must be
very wide (about 2 to 4 megacycles)
SYNCH.
SEPARATOR
FiCJ. 1.
Bloc:k diaCJram of typic:al receiver
58.00 me
FICJ. 6. Rear view of larCJe RCA rec:elver.
237
Section 8 •
THE
inUiiJV\
(a)
a:
F"req.----+
ai~
(b)
TECHNICAL
MANUAl.
TABLE I
P:obable frequency relationships when
:ecelver tuned to television channel I (44,,0 mc)
.
~icture carrier fre.quency ..... . 45.25 mc*
Sou!ld carrier frequency ..... . 49.75 mc*
O~cdlator frequency ........ . 58.00 mc
Picture I F frequency ....... . 12.75 111C*
Sound IF frequency ......... . 8.25 mc*
'Plus sidebands.
F"req. _ _
D~ilo
(c).
MYE
F"req. _ _
Fig. 2. Va rlous response
charaderlstlcs.
to pass the high-frequency components
of the normal video signal. The ex~
istence of this wide pass band introduces problems concerning noise. Although this ultra-high-frequency region is practically immune from natural
static, it is particularly vulnerable from
man-made interference such as that generated by automobile ignition systems,
street cars, diathermy machines, various domestic appliances, etc. The interference generated by many of these
devices is of a random character having its energy distributed more or less
evenly throughout the spectrum. The
Below: Fig. i. Checking frequency
response In RCA plant..
gain of the video channel is thereby
somewhat limited due to the wide pas's
band and the resulting greater noise
level. This means that the sensitivit,·
of the television receiver is less tha;l
the ordinary broadcast receiver. The
necessity for wide video pass bands results in the realizing of only a relatively low gain per stage, more or" less
offsetting the lower sensitivity advantage economically.
The superheterodyne receiver has
been almost universally adopted for
television receivers. The tuned-radiofrequency receiver can be used, but
eco~omi~ cons!derations rule largely
agamst It. Serious variations of sensitivity and pass-band width throughout
the tuning range are also detrimental.
Fig. 1 shows a highly simplified block
diagram of a typical television receiver
for both sight and sound. The degree
of simplification of Fig. 1 can be
realized by counting the number of
tubes in the television receivers now
on the market in this country. The
number varies from 16 tubes for a 5inch receiver designed to use the audio
F19. 3. Front view of
Philco receiver.
power amplifier of a usual broadcast
receiver to 32 tubes· in a receiver having a 12-inch cathode-ray tube which
is complete plus an all-wave receiver.
The usual sight and sound receiver
complete utilizes about 25 vacuum tubes.
Future development and research will
undoubtedly lead to simplification.
The radio-frequencv amplifier if one
is included, amplifie~ both th~ video
carrier and its side-bands and the audio
carrier and its side-bands at the same
I
Fig. 5. Front view of RCA
receiver with 12" tube.
I
,
238
'UNDAMENTALS 0' TELEVISION ENGINEERING
FiC). 4. Rear
view of Phil co reo
ceiver.
time. This is accomplished by designing the tuned circuits to give essentially uniform response over a wide band
and yet provide ample discrimination
against unwanted signals. This usually
entails the use of a coupled circuit
rather than a heavily loaded singletuned circuit, because the selectivity for
a given band width is better for the
former. The new high transconductance
type 1853 tube is almost universally·
used in this position, because it will
give a satisfactory stage gain with relatively low plate load impedance.
As shown in Figs. 3 and 4 of Part
II , there is a constant spacing of 4.5
megacycles between audio and video
carriers in each of the television channels when arranged for single-side-band
transmissions. This paves the way for
simplification of tuning controls, as both
the sound and sight signals may be
tuned by the same operation. This
spacing of 4.5 megacycles has superseded the 3.25-mc spacing which is discussed in the first twelve references in
the bibliography. The process of readjusting a receiver to accommodate the
new sound-sight carrier spacing of 4.5
mc is a minpr one, however.
The output of the radio-frequency
amplifier is fed to the first detector or
converter stage. Here the local oscillator signal is heterodyned with the incoming signal resulting in sum and
difference frequencies as in the conventional superheterodyne receiver. The
oscillator may be adjusted to operate
at a frequency above that of the incoming signal. The sound carrier is always at a higher frequency than the
video carrier by 4.5 mc. This would
cause the video intermediate-frequency
(i-f) channel to lie at a higher frequency than the sound i-f channel,
which is helpful in designing the video
i-f channel circuits to pass the necessary band width. The various frequency relationships when the receiver
is tuned to accept the lowest frequency
television channel (44-50 mc) are
shown in Table 1.
It will be noted that the intermediate
frequencies are selected in the order. of
10 mc. This choice is determined by
the necessity of avoiding strong signals
from local transmitters at the intermediate frequencies. As amateur transmitters are probably the most likely
sources of interference, the 7 and 14-mc
amateur bands must be avoided. A
lower picture i-f is not practical since
with even 12.75 mc, a video-frequency
band of 4 mc represents about 30%
• Section 8
of the intermediate frequency. This
complicates circuit design to achieve
the necessary pass band.
The television receiver is actually
two separate receivers beyond the converter stage. The sound only is accepted in the sound i-f channel for it
is tuned sharply to that frequency. The
picture signals are passed through the
picture i-f channel, as the sound channel is not sensitive to frequencies lying
within this range. It is interesting to
point out that a short-wave broadcast
type receiver tuned to 8.25 mc for channel I could replace the entire sound
channel of the television receiver including i-f amplifier, se.cond detector,
audio amplifier, and loudspeaker. The
broadcast receivers now appearing with
claims that they t
economical and satisfactory combination
at the present time.
D·C Component
In voice transmission the wave "!Jape
is essentially symmetrical with the axis
242
Distortion Requirements
at all times, the axis being defined as the
line which equally divides the area under
the wave. In television transmission this
is usually not the case. The degree of
bymmetry is determined largely hy the
image being scanned at that instant l .
This continuous axis shift may be considered as a varying d-c component. To
improve the transmi tter efficiency hy
reducing the dynamic modulation rallge,
this d-c component may be used to shift
the average carrier to follow the average
illumination of the picture. At the j'eceiver this d-c component is re-inserted
at the cathode-ray tube grid so that a
faithful video reproduction results. The
d-c insertion at the transmitter is only
for more efficient operation of the transmitter, however.
Fig. 3. Diagram of RCA l-kw
television transmitter.
The hum-level requirements of a television transmitter are essentially the
same as those of a high-quality broadcast transmitter. The harmonic distortion requirel!lents for visual broadcasting are much less severe than for ~ound
broadcasting. This arises from the fact
that the detail of the picture wiII not
suffer particularly from a non-linearity
of the system, but only one degree of
l1alftone reproduction at the reproducing
tube. That is, details of the image transmitted through a non-linear system, although appearing in their proper position and size, Illay not have the proper
degree of light and shade as compare.d
to the other parts of the image. ThIS
relative insensiti\'ity to a modest degree
of nonlinearity als~ makes grid modulation more attractive.
Fig. 1 is a photogTaph of a I-hv television transmitter recently placed on the
market bv RCA, Fig. 2 is a rear view
of one un'it of this same transmitter. Fig.
3 is a highly simplified hlock diagram
\7
CRYSTAL
05C.
BUFFER
~ Do8~LER
i·807
I-
t-814
TRIPLER
~
2·808'5
POWER
POWER
AMP.
AMP.
~
2-834'5
2-833's
I-
FINAL
POWER
~
AMP.
2-899'5
SIDEBAND
FILTE:R
t-
~\
"
Vide~~
Input
VIDEO
AMP.
2-S07'5
~
VIDEO
AMP.
4-807's
-{
MODULAT'
ING
AMPLIFIER
m-St3's
Grid
"Modulation
t-
D.C.
INSERTION
i·tV
~ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ---
-
- --- - - - - - - - - - - -
I:
!'
FUNDAMENTALS OF TELEVISION ENGINEERING
of the radio-frequency and video-frequency sections showing the tube complement utilized.
Fig. 4 shows video control position in
the National Broadcasting Company's
television studio 5. The operator has
command of the studio floor t~ough
windows before him which are tinted to
minimize glare from the highly lighted
studio. The three knobs at the operator's
left control the electrical focusing of the
iconoscopes in the studio cameras. The
operator is adjusting the brightness and
video gain controls for best contrast and
brightness in the image. The group of
knobs to the right of the operator insert
voltages of various shape and phase into
the video signal to counteract the effect
of spurious "shading" signals generated
in the iconoscope. These spurious signals apparently are due to the fact that
more secondary electrons are generateu
at the iconoscope mosaic than are supplied by the beam and a shower of electrons falls back on the mosaic. These
electrons cause a random charge distribution over the mosaic which has no
relationship to the video signal, but
causes the "dark-spots." These dark
spots are neutralized as well as possible
by the adjustment of the knobs shown
in Fig. 4. These spurious signals cannot be entirely eliminated as shown by
the image of Fig. 5, which is the image
appearing on the monitor tube above the_
operator of Fig. 3. The dark areas and
the white borders on the picture are a
result of these effects and the attempt
to neutralize them. The waveform of the
video signal is constantly monitored by:
means of the oscillograph beside the image tube.
Fi,. 8 (Below). Experimental steps
in determining optimum proportions of antenna in Fig. 7.
l~Ilfft11
°6 4 2 ° 2 4 6
I! Hkl I4~,vl
8
4
0
4
8
f~NfQJJJJ#f1
°12
8
4
0
4
8
Fig. 6 (AboveL Sync:hronizing impulse generator (RCA photoL
Fig. 6 shows a view of the synchronizing pulse generator which generates
the pttlses for' both horizontal and vertical synchronization.
The required
regulated power supplies arid amplifiers
are included within the other cabinets.
Television Transmitting Antennas
The antenna to be used with a television transmitter presents a problem 'in
the relative difficulty in attaining constant characteristics over the necessary
frequency band. Attaining these constant
characteristics over a given band width
becomes easier the higher the frequency
of operation. Therefore, we can expect
considerable simplification of vision antenna structures between the 44-50 mc
channel and the 102-108 mc channel. As
Fig. 9. Optimum proportions of
lingle radiator modified for IUp- .
porting brac:ket.
• Section 8
Fig. 7. Television transmitting antenna atop Empire State Building.
the trend is toward the higher frequencies, the extent of the experimental work
that has been done is highly justified.
Fig. 7 shows a novel approach to the
problem of attaining constant characteristics over a wide frequency band. This
is a photograph of the vision and sound
antennas atop the Empire State Building. The vision antenna is of particular
interest and the neat experimental evolution of the final shapes as reported by
Lindenblad is illll5trated in Fig. 8,
which is taken. from his paper. In general, elliptical shapes of all of the radiator surfaces seemed to give the most
constant impedance characteristics. In
order that the protruding portion of the
ellipsoid and the collar radiate equally,
their relative lengths should be in the
ratio of 7 to 5 as illustrated in Fig. 9,
which is also taken from Lindenblad's
paper. This gives an input impedance
in the order of 110 ohms. The best ratio
between major and minor axes of the
ellipsoid is 15 to 6. The optimum ratio
of mean collar diameter to ellipsoid
diameter was found to be 3 to 2. The
e,llipsoid is bonded to the collar by a
~pecially designed bracket for lightning
protection. For vertically polarized
waves, a single unit could be mounted
vertically. For the desired horizontal
polarization, 4 units were arranged
Fig. 10. Cutaway view of c:oaxlal
transmission line (RCA photo).
12
!Ffli fI° ffl
,8
4
4
8
f~II13{11
°6 4 2 ° 2 4 6
0(0 Frequency Deviation
243
Section 8 •
THE
Fig. 4 (Above). The video e:ontrol
desk of the NBC television studios.
around the tower excited in progressive
phase quadrature as a "turnstile" antenna. It was found upon completion
that this antenna had uniform characteristics over the range of about 30 to
60 mc, or 6 to 10 times that obtainable
with other conventional designs with
complicated correction networks. This
truly represents a real advance in antenna technique.
MYE
TECHNICAL
MANUAL
Fig~ 5 (Below). Monitoring Image
and wave shape of video signal.
See tubes above e:ontrol panel of
Fig. 4.-
mile trial section between N ew York
and Philadelphia. A lead sheathed coaxial cable suitable for such purposes is
shown in Fig. 10.
The second approach to the problem
is that of ultra-high-frequency radio link
transmitters. At high frequencies very
efficient and highly directional antenna
structures can be cheaply constructed.
By the use of such antennas for both the
receiving and ttansmitting functions,
low transmitter power acquirements and
a minimum of interference may be attained. It is conceivable that an extensive network could be built up of many
such units located on strategic geographical points at distances depending
upon the line-of-sight range obtained. Itis also possible that sufficient reliability
could be realized in an unattended station or at least by remote control.
Fig. 11 shows an experimental link
transmitter operating on a frequency
of 177 mc. It is located on the 10th floor
Interconn,ecting Links
In the near future the problem of simultaneous network operation of a multiplicity of local television stations must
be faced. This will be a particularly difficult economic problem in the United
States because of the great distances and
relatively low population density in most
areas. The economic phase is even a
Fig. 11. 117·me: u-h·f transmitter
linking Radio City studios with
Empire State Building transmitter.
limiting factor in bringing to reality the
proposed Birmingham provincial station
outside of London in a relatively highly
populated area.
At the present time there seem to be
two general methods of approach to the
interconnection problem. One is the use
of transmission lines. Over relatively
short distances a selected pair in an
ordinary telephone cable has been used
with correction for remote television program pickups. The coaxial cable is well
adapted to the transmission of video signals ~cause the attenuation is faIrly low
and quite uniform over a wide frequency
range. Unattended amplifying units located in manholes at proper intervals
have been used successfully in a 100-
244
of the RCA building and serves as an
alternate to a coaxial transmission line
between the NBC television studios in
the RCA building and the -television
transmitter located in the Empire State
Building, a distance of somewhat less
than a mi,le. It will be noted that such
transmitters can be made compactly.
Bibliography
(1) Radio Transmission Considerations"
Smith, COMMUNICATIONS, March 1939,
page 30.
(2) "Televison Station W2XAX"-Part 1
-Goldmark, COMMUNICATIONS, No-vember 1938, page 7.
\
(3) "Television Station W2XAX"-Part
2 "- G 0 I d mar k, COMMUNICATIONS,
February 1939, page 27.
H
I
II
i'
I'
,I
fUNDAMENTALS Of TELEVISION ENGINEERING
Transmittet;s,"
(4) "Television
tronics, March 1939, page 27.
RCA Review, April 1939, page 387.
(6) "Television Radio Re1ay"-Trcvor and
Dow, RCA Review, October 1936,
page, 35.
Elec-
)
(5) "Experimental Studio Facilities for
Television"-Hanson, RCA Review
April 1937, page 3.
'
(7) "Television Transmitting Antenna for
Empire State Building"- Lindenblad,
• Section 8
(8) "Equipment Used in the Current
RCA Television Field Tests"-Beal,
RCA Review, January 1937, page 36.
Part IX: foreign Developments
B
ECAUSE of the old American custom of believing that little, if anything worth while is ever done outside
the bounds of these United States, it
would seem appropriate in this series to
pause long enough to take a hurried
glimpse at the development work in
'television in other countries. While
such a study does not fit any too well
into the main title of the series, an
appreciation of foreign television activities is absolutely necessary to view
our domestic developments in their
proper perspective.
Fig. 1. Radiating Iystem of
Rome - Mount Mario television
transmitter.
England
The television acttvittes in England
are perhaps the most intensive of any
foreign country. The British authorities have led the world in providing an
ambitious program service. The radio
listener fee of ten shillings per year
was the source oHhe funds which made
this possible. At the outbreak of the
war there were reported to be about
25,000 television receivers in use with
others being purchased at the rate of
1000 to 1500 per month. The television
broadcasts of one hour each afternoon
and two hours each evening were
abandoned "for national defense purposes" when the war began, and at this
writing have not been reestablished.
The London transmitter is located at
the edge of the city in Alexandra Palace where broadcasts began in August,
1936. The standards adopted are 405
lines, 50 frames interlaced, giving 25
complete picture scans per second. The
equipment in use was provided by the
Marconi-E. M. I. company and is built
around the "Emitron" camera which is
basically a mosaic-storage tube patterned after the iconoscope. The transmitter has a peak output power of 17
kw corresponding to "full picture
white," and is modulated by the conventional grid system. Double-sideband
amplitude modulation, "infra-black"
synchronizing pulses, and positive
modulation are used.
Outside broadcasts are accomplished
by mobile units utilizing radio-link
transmitting special balanced-pair lowcapacitance cables primarily designed
for television signals, and a limited use
of ordinary telephone-cable pairs suitably equalized for short distances. A
line utilizing the special balanced pair
n111S past points from which many
broadcasts emanate, such as Buckingham Palace, Trafalgar Square, and
Piccadilly Circus. The British system
has been covered quite thoroughly in
several recent articles published in the
United States.
Italy
A relatively insignificant amount of
Fig. 4. Rotary converter and
automatic anode voltage regulators of Italian transmitter.
Fig. 2. (Left) Safar standard type
television transmitter for Italian
statlonl.
Fig. 3. (Rlgbt) The
Safar transmitter
with cover plates
removed.
245
Section 8 •
THE
MYE
TECHNICAL
MANUAL
Front (Fig.
5. left)
and rear
(Fig. 6. right)
views of
Safar
c:ontrol desk.
Fig. '.(Above) Sync:hronlzing
opparatus. mixer and c:ontroll
of Safar television c:ameras.
Fig. 10 (Below) Stage in the
Safar television theatre.
_._P4.(".
Fig. 11. (Above) Safar Type B
Telepantosc:ope. a mosaic: devlc:e
used in telec:ameras.
Fig. 14. (Below) A40.1cv Safar
tube for prolec:tion rec:elver•.
246
information on the Italian television
activities has appeared in the Englishlanguage press. A consistent, though
limited, program of research has been
conducted by the Societa Anonima Fabbricazione Apparecchi Radiofonici (the
"Safar") in Milan, the efforts of Mr.
Arturo Cas~ellani being conspicuous.
Outstanding in their list of accomplishments is the Rome station. This station
is built on the top of Mount Mario so
that the transmitting dipoles are at a
height of about 500 feet over the city.
This hilltop location is situated at the
periphery of Rome and, naturally, has
the greatest field strength direct toward
it. A signal of at least 200 microvolts
is delivered to the receiver terminals
by the usual dipole in all parts of the
city. This Mount Mario antenna structure is