Experimenters Handbook 1966 Fall

User Manual: Experimenters-Handbook-1966-Fall

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BUILD FROM COMPLETE PLANS

Panic Alarm- CD Ignition System
Smoke Detector-99c Speaker B
TV Tube Tester Electronic St
and dozens more

ELECTRONICS TRAINING

Home Study vs Resident Schools

UIJIta
;

AIWIPLIFIER

SCOTTICIT.

Cc or

rgaii

BETTER
THAN
EVER
1967
670

Mail the Card Today for
Your FREE Catalog
No Money Down
Easy Pay Terms
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LAFAYET
RADIO ELECTRONICS

CATALOG NO.

Over 500 Pages

FIVE BETTER ELECTRONICALLY WITH
LAFAYETTE

1967
OUI 45th

,at

ERE E

VIII
SIS

TV Tubes and Parts

' ...Kï

......,

r:: S' ;:'

\ U..,

a,,,

Electronic Parts
Test Equipment
C.B. 2 -Way Radio
Tools
Ham Gear
Stereo Hi -Fi
Tape Recorders
Walkie- Talkies
Auto Accessories

,...
_

,...

LAFAYETTE'S
MAIL ORDER &
LONG ISLAND
SALES CENTER

Featuring Everything in Electronics for
HOME

from the

INDUSTRY

LABORATORY

"World's Hi -Fi & Electronics Center"

LAFAYETTE Radio ELECTRONICS
Dept. EHJ -6, P.O. Box 10
Syosset, L. , N.Y. 11791

....... - - - - - - Send me the Free 1967 Lafayette Catalog 670

111 Jericho Turnpike
Syosset, L. I., New York 11791

OTHER LOCATIONS

Dept. EHJ -6

NEW YORK
Bronx
Brooklyn
Jamaica
Manhattan
Scarsdale
Syosset

Name

Address

City
Zip

________ .....

- ______________

State
PENNSYLVANIA

(Please Give Your Zip Code No.)

1
,

Pittsburgh

Newark
Paramus

MASSACHUSETTS
Boston
Natick

Plainfield

Saugus

NEW JERSEY

WASHINGTON, D.C.
(Area)
Falls Church, Va.
Mt. Rainier, Md.

CONNECTICUT
Hamden
W.

Hartr ^r

CIRCLE NO. 18 ON READER SERVICá CARD

Introducing EICO's New "Cortina Series "!
Today's electro-technology makes possible near-perfect
stereo at moderate manufacturing cost: that's the design concept behind the new EICO "Cortina" all solid state stereo components. All are 100% professional,
conveniently compact (31/2"H, 12 "W, 8 "D), in an
esthetically striking "low silhouette." Yes, you can pay
more for high quality stereo. But now there's no need
to. The refinements will be marginal and probably
inaudible. Each is $89.95 kit, $119.95 wired.
Model 3070 All- Silicon Solid -State 70 -Watt Stereo

Amplifier: Distortionless, natural sound with unrestricted bass and perfect transient response (no inter stage or output transformers); complete input, filter
and control facilities; failure -proof rugged all-silicon
transistor circuitry.
Model 3200 Solid -State FM /MPX Automatic Stereo
Tuner. Driftless, noiseless performance; 2.40 for 30db
quieting; RF, IF, MX are pre -wired and pre -tuned on
printed circuit boards
you wire only non -critical power
supply.

7 New Ways to make Electronics more Fun!
Save up to 50 % with EICO Kits and Wired Equipment.
CRAFT

New

EICOCRAFT

easy -

to-build solidstate electronic TruRitsr. great

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only the complexity Is
reduced to make kit building faster, easier,
You hear
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NEW ctOO 623 S oiic

F-

NEW

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Engine Analyzer

ship-to-shore, aircraft,
Coast Guard, and the full AM band. 550KC to
30MC in four bands. Selective, sensitive superhet, modern printed circuit board construction.
Easy, -fast pinpoint tuning: illuminated slide rule dials, logging scale; "S" meter, electrical
bandspread tuning, variable BF0 for CW and
SSS reception, automatic noise limiter. 4"
speaker. Headphone jack. Kit $49.95, Wired
plus ham operators,

Now you can tune -up, troubleshoot and test your own car or
boat.
Keep your car or boat engine in
tip -top shape with this completely

lower cost. Features:

pre -drilled copper plated etched printed
circuit boards; finest parts; step -by-step instructions; no technical experience needed
just soldering iron and pliers. Choose from: Fire

Alarm; Intercom; Burglar Alarm; Light Flasher;
"Mystifier "; Siren; Code Oscillator; Metronome;
Tremolo; Audio Power Amplifier; AC Power Supply. From $2.50 per kit.

portable, self- contained, self powered universal engine ana-

$69.95.

lyzer. Completely tests your total

ignition /electrical system. The
first time you use it just to tune
for peak performance
it'll have
paid for itself- (No tune -up
charges, better gas consumption,
longer wear) 7 instruments in
one, the EICO 888 does all these

for 6V and 12V systems; 4, 6 &
8 cylinder engines.
The EICO 888 comes complete
with a comprehensive Tune -up
and Trouble- shooting Manual including RPM and Dwell angle for
over 40 models of American and
Foreign cars. The Model 888 is
an outstanding value at $44.95
kit, $59.95 wired.

"the best ham
Radio TV Experiby for 196e"
menter Magazine. 200 watts PEP on 80, 40 and
built -in VOX,
Receiver
offset
tuning,
20 meters.
high level dynamic AEC, silicon solid -state YFO.
Unequaled performance, features and appearance. Sensationally priced at $199.95 kit,
$299.95 wired,

transceu"r

15.

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PUNCH ,r

new EICO

Pro" 23- channel Dual Conversion

Sentinel -

-wait

Transceiver. New advanced Big -Reach "Range
Plus" circuitry lengthens "talk- power" reach.
Automatic noise limiter super- sensitizes for weak
signals. "Finger Tip" antenna loading and transmitter tuning controls. 23 crystal -controlled
all crystals
transmit and receive channels
supplied. Rear -illuminated S /RF meter. Transistorized 12VDC and I17VAC dual power supply.
Wired only, $169.95. Positive- Negative Ground/
Mobile Marine Modification kit (optional 55.95).

rFREE 1967 CATALOG
EICO Electronic Instrument Co., Inc.
131 -01 39th Ave., Flushing. N. Y. 11352

Send me FREE catalog describing the. full EICO line of
200 best buys, and name of nearest dealer- I'm inter
ested in:
ham radio
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D Citizens Band radio
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Name

Model 460 Wideband Direct -Coupled
5" Oscilloscope. DC-4.5mc for color
and 85W TV service and lab use. Push pull DC vertical amp., bal. or unbal.

input. Automatic sync limiter and amp,
$99.95 kit, $139.50 wired.

City

Zip

State

CIRCLE NO.
1966 Fall Edition

Model 232 Peak -to -Peak VTVM. A must
for color or B &W TV and industrial
use. 7 non -skip ranges on all 4 func.
tions. With exclusive Unl- Probe.®
$29.95 kit, $49.95 wired.

Addre

7 ON

READER SERVICE CARD
1

NO SPECIAL TOOLS REQUIRED

LIGHT UP THE NIGHT
With RCA's EXPERIMENTER'S KIT
Build Your Own Light -Operated Switch
for Dozens of Applications Around the House
Just let your imagination soar-and you'll trigger your
own application ideas for any of the 14 control circuits
you can build with only three RCA Experimenter's Kits.
For instance, you can build a light- operated switch for a
garage light, a yard or path light, or even an advertising
sign that can be activated with lights from an approaching automobile! You can also build a model race car
speed control, an electronic heat control and other interesting circuits with hundreds of applications. All these
circuits with easy -to- follow directions are described in
the RCA Experimenter's Manual, KM -70, available from
your RCA Semiconductor Distributor.

HERE IS WHAT YOU NEED...
Basic Experimenter's Kit (KD2105). Containing
one silicon controlled- rectifier; two transistors; five
RCA

rectifiers.
RCA Experimenter's Manual (KM -70). 80 pages profusely illustrated; 14 circuits -how they operate and
how to build them.
RCA Add -On Light Sensor Kit (KD2106). Containing one
photocell for light- operated circuits.
Heat Sensor Kit (KD2110). Containing
three thermistors for different temperature ranges;
special solder for heat control circuits.
Readily available passive components and hardware.
RCA Add -On

HERE IS WHAT YOU CAN MAKE...
Electronic Timer. 2. Electronic Time Delay Switch.
3. Electronic Flasher. 4. Battery Charger (12 Volts). 5.
Battery Charger (6 Volts). 6. Model Race Car and Railroad Speed Control. 7. Light-Operated Switch (Turn -On).
8. Light- Operated Switch (Turn -Off). 9. Electronic Heat
Control (Turn -On). 10. Electronic Heat Control (Turn -Off).
11. Overload Switch, 12. Electronic Synchronous Switch.
13. Universal Motor Speed Control, 14. Lamp Dimmer.
1.

d..
!

tSflJS1N11kII

easuu

roi
If you want to build one circuit or all 14, check with your
RCA Distributor where kits and RCA Experimenter's Man
ual are on display. He'll be glad to help you select the
kit or kits for the solid -state circuit you have in mind.
Do it today!
AVAILABLE FROM YOUR RCA SEMICONDUCTOR DISTRIBUTOR
RCA Electronic Components and Devices.

Harrison, N.J.

The Most Trusted Name in Electronics

CIRCLE NO. 22 ON READER SERVICE CARD
2

ELECTRONIC EXPERIMENTER'S HANDBOOK

PHILLIP T. HEFFERNAN
Publisher
OLIVER P. FERRELL
Editor

ROBERT CORNELL
Managing Editor
JOHN D. DRUMMOND
Technical Editor

WILLIAM GALBREATH

FALL EDITION
19660
R6N6ELECTRONIC

POPULAR
EL

EXPERIMENTER'S

Art Editor

MARGARET MAGNA
Associate Editor

ANDRE DUZANT
Technical Illustrator

NINA KALAWSKY
Editorial Assistant

PATTI MORGAN
Editorial Assistant

LAWRENCE SPORN
Advertising Soles Manager

ARDYS C. MORAN
Advertising Service Manager
ZIFF-DAVIS PUBLISHING COMPANY
Editorial, Circulation, and Executive Offices
One Park Avenue, New York, New York 10016
212 679 -7200
Eastern Advertising Manager, RICHARD J. HALPERN

Midwestern Office
307 North Michigan Avenue, Chicago, Illinois 60601
312 726 -0892
Midwestern Advertising Manager, JAMES WEAKLEY
Western Office
9025 Wilshire Boulevard, Beverly Hills, California 90211
213 CRestview 4 -0265; BRadshaw 2 -1161
Western Advertising Manager, BUD DEAN

IN VIEW OF THE PRESSING DEMAND
FOR TRAINED ELECTRONICS TECHNICIANS, A SPECIAL TWO -PART STORY
HAS BEEN ADDED TO THIS EDITION

-THE

TWELFTH -OF THE ELECTRONIC
EXPERIMENTER'S HANDBOOK. THE UNDISGUISED PURPOSE OF THIS PARTICULAR STORY IS TO ENCOURAGE MORE
ELECTRONICS HOBBYISTS TO SERIOUSLY CONSIDER A FULL -FLEDGED CAREER
IN THIS EXPANDING FIELD. THE STORY
DISCUSSES HOME -STUDY TRAINING VS.
ATTENDING A RESIDENT ELECTRONICS
TRAINING INSTITUTE.
URGE YOU TO
READ THIS IMPORTANT STORY. FURTHERMORE, THERE IS A FOLLOW -UP
STORY BY THE SAME AUTHOR IN THE
OCTOBER, 1966, ISSUE OF POPULAR
ELECTRONICS. THIS LATTER STORY IS
AN ANALYSIS OF JOB OPPORTUNITIES
FOR HOME -STUDY AND RESIDENT
IF YOU ARE INSCHOOL GRADUATES.
TERESTED IN ESTABLISHING A WELL PAYING TECHNICIAN'S CAREER IN ELECTRONICS, THESE ARTICLES WILL TELL
YOU HOW MUCH TIME AND MONEY
YOU CAN EXPECT TO SPEND AND WHAT
YOUR EARNING POTENTIAL WILL BE
AFTER GRADUATION.
AS ALWAYS, THE EDITORIAL STAFF
OF THE ELECTRONIC EXPERIMENTER'S
HANDBOOK WILL APPRECIATE YOUR
COMMENTS AND SUGGESTIONS FOR THE
NEXT EDITION.
OLIVER P. FERRELL
EDITOR
I

Japan: James Yogi
c/o Sekihara
1,

William

Sakamachi, Shinluku -ku
Tokyo, Japan

Ziff, Chairman of the Board (1946-1953)
William Ziff, President

W. Bradford Briggs, Executive Vice President
Hershel B. Sarbin, Vice President and General Manager
Philip Sine, Financial Vice President
Walter S. Mills, Jr., Vice President, Circulation
Stanley R. Greenfield, Vice President, Marketing
Phillip T. Heffernan, Vice President
Frank Pomerantz, Vice President, Creative Services
Arthur W. Butzow, Vice President, Production
Edward D. Muhlfeld, Vice President

Member Audit Bureau
of Circulations
1966 ELECTRONIC EXPERIMENTER'S HANDBOOK, Fall
Edition, published by the Ziff -Davis Publishing Company, One Park Avenue, New York, New York 10016.
Also publishers of Popular Electronics, Electronics World,
HiFi /Stereo Review, Communications Handbook, Tape
Recorder Annual, Stereo /Hi -Fi Directory, Electronics
Installation and Servicing Handbook.

1966 Fall Edition

INTERNATIONAL
CRYSTALS
the first

choice
of the
Radio
Amateur

THE AMATEUR WHO SELECTS INTERNATIONAL CRYSTALS FOR HIS
COMMUNICATION GEAR PROBABLY KNOWS THESE IMPORTANT FACTS:
International customers include broadcast
stations, airlines, military services, Civil Air
Patrol, taxicabs.

Every amateur crystal is manufactured by
the same skilled craftsmen who make International commercial crystals.

International crystals are the product of a
continuing research and development pro-

International crystals and electronic components are used in the United States missile and space research program.

gram.

International crystals are designed and manufactured to operate under all types of field
fixed or mobile.
conditions . .

All International crystals are guaranteed
against defective materials and workmanship for an unlimited time when used in
equipment for which they were specifically
made.

International crystals are used in all major
makes of commercial two -way radio equipment.

Whether you're an amateur building your first transmitter or an engineer with special
crystal requirements, you can look to International for precision frequency control.
KEEPING

YOU

ON FREQUENCY

OUR BUSINESS!

INTERNATIONAL

Write today for a FREE CATALOG of International
precision made crystals and quality electronic equipment.
International Crystal Mfg. Co., Inc.
18 North Lee
Oklahoma City, Oklahoma 73102
NAME

CRYSTAL MFG. CO., INC.
1E3

NO. LEE

OKLA_

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CIRCLE NO. 11 ON READER SERVICE CARD
4

ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER
1

USEFUL
PROJECTS

2
AUTOMOTIVE
ELECTRONICS

PICTURE TUBE TESTER AND REJUVENATOR
LUMEMIN STEALS THE SHOW- FAIL -SAFE TRANSISTOR
POWER SUPPLY -CHRISTMAS LIGHTS TWINKLE TO
MUSIC -SMOKE ALARM FOR YOUR HOME- SUPERSENS-FREEZE MOTION WITH SOUND -LET THE SUN
POWER YOUR PORTABLE- SUPER -X PULSE POWER
PACK FOR HO RAILROADING -LI'L DUSKER: THE LIGHT
WATCHMAN -SOLID -STATE SLOT CAR SPEED CONTROL
-ELECTROLOCK -DON'T PANIC
PUSH THE BUTTON
TV

...

63
-PROTECT YOUR
CAR'S ELECTRICAL SYSTEM -HEADLIGHTS -ON ALARM
-AUTO VOLTMETER SHOWS YOU'LL GO
A UNIVERSAL CD IGNITION SYSTEM

3
ELECTRONICS
SCHOOLS

75
1-

OPERATION ACTIVATE: PART
GETTING YOUR TRAINING IN RESIDENT SCHOOLS; PART 2 -HOME -STUDY
TRAINING

4
AUDIO
STEREO
HI -FI
PROJECTS

TOTEM POLES FOR STEREO -HI -FI A GO -GO LAMPS
"CINDERELLA" -SOLID -STATE 6 -WATT AMPLIFIER FOR
10 BUCKS -UNIQUE 99¢ SPEAKER ENCLOSURE

5
COMMUNICATIONS

SWL
CB
HAM

115
CAMPER'S SPECIAL -SUPER SELECTIVITY FOR YOUR
RECEIVER -"WATCHDOG" MOBILE MONITOR -DUALSENSITIVITY FIELD STRENGTH /ABSORPTION METER

TIPS
AND
TECHNIQUES

129

ELECTRONICS
MARKETPLACE

151
Copyright i[ 1966 by Ziff-Davis Publishing Company.
All rights reserved.

3
more

features

-all
new

Here is RCA's new WR -50B RF Signal
Generator -wired or kit. It looks just
like the old WR -50A, but the resemblanceends there. It has all the features
you liked in the older model...plus 3
new ones you'll find in red below:
Wide frequency range from 85kHz to
40MHz in 6 overlapping ranges plus
harmonics for higher frequencies
Built -in crystal calibrating oscillator
circuit with front panel crystal socket
Internal 400 Hz audio oscillator
NEW -Sweep output at 10.7 MIL with
return trace blanking for sweep alignment of FM receivers
NEW -Sweep output at 455 kHz with
return trace blanking for sweep alignment of new transistorized AM radios
Individual inductance and capacitance
adjustments for each range
Modulation level control
Two -step RF attenuator switch plus a
continuously -variable attenuator control
NE,1V- additional switch for further
attenuation of crystal oscillator Output
The Optional Distributor Resale Price
is only $65.00. Kit Form, $45.00, includes
pre -assembled range switch with pre aligned coils and trimmers. See the RCA
WR-50B at your authorized RCA Test
Equipment Distributor.
RCA ELECTRONIC

COMPONENTS AND DEVICES, HARRISON, N.J.

The Most Trusted Name in Electronics

CIRCLE NO. 23 ON READER SERVICE CARD

CHAPTER
1

USEFUL
HOUSEHOLD
PROJECTS

It is not unlikely that the arbitrary definition of "Household" projects has been stretched out of shape in this edi-

tion of the ELECTRONIC EXPERIMENTER'S HANDBOOK.
However, the common denominator in selecting these
projects is still valid -they are all things that might be
seen around the electronically -oriented household. The
projects have been mixed so that there is something here
for father or brother in his workshop, a couple of pre -teen
projects, at least two that should delight your mother,
and a couple that are just plain general -purpose units.
Our cover photo shows the very popular version of the
hi -fi color organ designed and constructed by Leon Wort man ( "Christmas Lights Twinkle to Music "). Unlike the
lights for many other color organs, these are not something you buy extra -they're the lights on your Christmas
tree. If you're looking for something novel and attractive,
we urge you to give this particular project consideration.

8
Jeff H. Taylor

TV PICTURE TUBE TESTER AND REJUVENATOR

14
LUMEMIN STEALS THE SHOW

Louis

Garner, Jr.

18
FAIL -SAFE TRANSISTOR POWER SUPPLY
Edward Nawracaj and Fred Forman

21
CHRISTMAS LIGHTS TWINKLE TO MUSIC

Leon A. Wortman

25
H. St.

SMOKE ALARM FOR YOUR HOME

Laurent

29
Louis

SUPER -SENS

Garner, Jr.

39
FREEZE MOTION WITH SOUND

Roy E. Pafenberg

43
LET THE SUN POWER YOUR PORTABLE

Homer

Davidson

45
SUPER -X PULSE POWER PACK FOR HO RAILROADING
Woodrow Pope

51
LI'L DUSKER -THE LIGHT WATCHMAN

Don Lancaster

55
SOLID -STATE SLOT CAR SPEED CONTROL

James Fishbeck

58
Murray

ELECTROLOCK

60
DON'T PANIC
1966

Fall

Edition

...

PUSH THE BUTTON

Bruno

Coultes

M. Larsen

BUILD A
TV PICTURE TUBE
DOES YOUR TV set "smear" when
you try to turn up the brightness to

a comfortable viewing level ? Do the
whites seem to become silvery? Is your
picture so dim that you have to pull the

shades or wait for nightfall to watch a
program? Does it take a long time for
the brightness level to come up? Is it
impossible to vary the brightness level?
Does the picture tube seem to go on and
off? If the answer is yes to any or all
of these questions, you probably have a
"sick" picture tube.
While there are many different types
of tests performed by the picture tube
manufacturer, three types are usually
made in the field: open -short, emission,
and grid control tests. You can make
all of these tests reliably and quickly,
and also "rejuvenate" a "tired" picture
tube with this easy -to -build TV Picture
Tube Tester and Rejuvenator. The parts
are inexpensive and readily available.
HOW IT WORKS

The open-short test
is shown in the simplified diagram in
Fig. 1. In this test a.c. voltage is applied to the cathode, and to each element
in the tube, one at a time, through a
neon lamp. Each of the elements acts
like an anode with respect to the cathode,
as in an ordinary diode. Since half the
a.c. voltage waveform is passed by the
diode so formed, only one half of the
neon lamp will glow.
Should the element be shorted to the
cathode, current will flow in both direcOpens and Shorts.

tions and both halves of the lamp will
glow. Should the element be open, no
current will flow and the lamp will not
glow.
In the heater -cathode check, however,
the lamp will not glow even on one
side when conditions are normal. The
inside of the cathode cylinder is not
coated with the activated emitting material and very little current will flow.
A shorted condition will be indicated as
in the other tests
both halves of the
neon lamp will glow.

...

Emission. The emission check is shown
in the simplified diagram in Fig. 2. The
control grid is tied to the cathode and
an a.c. voltage is applied to G2 through
a d.c. ammeter and series resistor. The
amount of current that flows (during
each positive half cycle) is a relative
indication of the electron emission
capability of the cathode.

Grid Control. The grid control test is
similar to the emission test except that
instead of having a zero grid bias as
used in the emission test, a negative
voltage is applied to the control grid as
shown in Fig. 3. As the control grid
voltage is made more negative, less G2
current flows. When the control grid
(G,) voltage is made sufficiently negative, no current will flow and the tube
will be cut off.
The amount of negative voltage required to achieve cutoff indicates the
relative contrast range of the picture
ELECTRONIC EXPERIMENTER'S HANDBOOK

It's easier to plug in
a tester than it is

to change a picture tube
By JEFF H. TAYLOR

TESTER AND REJUVENATOR
SIMPLIFIED CIRCUITS

tube. A tube that will cut off with a
small voltage will produce a more con trasty picture than one that requires a
larger voltage. In a 3 -gun color tube, it
is possible to determine if all the guns
will cut off at the same potential, or the
degree of imbalance, if any.

Fig. 1. Neon lamp indicator shows leakage, shorts,
and opens between each element and the cathode.

Rejuvenation. The cathode of a picture
tube is a small metal cylinder with an
external coating of emitting material.
The heater is essentially a coiled wire
and is placed inside the cathode cylinder. As the picture tube is used, the
outermost activated material on the
cathode becomes deactivated and its
ability to emit is reduced accordingly.
The process of rejuvenating the picture
tube removes some of the deactivated
coating from the cathode and allows the
unused material beneath this "scab" to
once again emit a good electron beam.
This is accomplished by causing a heavy
current to flow from the cathode to G1-by placing a relatively high potential
across the control grid and the cathode,
for a very short period of time, as shown
in Fig. 4.
If the tube is very weak, sufficient
current may not flow to rejuvenate the
cathode. Increase the filament voltage
one step and try again. When the
REJUVENATE button is depressed, you
may see sparks fly inside the picture
tube in the vicinity of the cathode. This
is caused by the "dead" material being
"stripped" off the cathode.
In a 3 -gun color CRT, each gun in

Fig. 2. Meter reads relative emission. Tests made
at 1- minute intervals show warm -up characteristics.

Fig. 3. Grid control is determined by the amount of
negative voltage needed on G1 to obtain cutoff.

T
Fig. 4. Momentary application of a high d.c. potential across the cathode and G1 can boost emission.
1966 Fall Edition

mIN2071
R3

NIN2071

MEG.

6.8K

NE48

S3A

S3C

10K

0- 5O0ya

117 VAC

HTR
GRIDI

GRID2
S3

536

EMISSION

03
IN2071

S3D

68K

CUT -OFF
REJUVENATE

CI
.I

-J
T

.5°f.

Fig. 5. When testing tubes, follow the sequence shown on S3,
starting with HTR. Do not rejuvenate unless you have to. The

6.3V

first three positions help 12
"look" for opens, leakage, and

shorts, and should be used
when the tube is cold and again
when the tube is hot. Push -torejuvenate switch S4 is used
only when S3 is in the rejuvenate position. Wiring of the filament circuit is shown in Fig 7.

1.2R
R6
1.5f1

PARTS LIST
1000 -volt paper capacitor (two 0?µf., 600 -volt capacitors in series or two 0.05µf., 1600 -volt capacitors in parallel)
C2- 0.5-µf., 600 -volt paper capacitor
D1, D2, D3-1N2071 silicon rectifier
F1-11/2-ampere fuse
11- .VE -51 neon lamp

12-.VE -48

neon lamp

-0 -500 microampere meter (Simpson
27 or equivalent)
resistor
RI- 10,000-ohm, % -wattresistor
% -watt
M1

R2- 6800 -ohm,
R3- 1000 -ohm. V2-watt resistor
R4- 68,000 -ohm, % -watt resistor
R5-1? -ohm, 2 -watt resistor
R6-1.5 -ohm, 2 -watt resistor
R7- 100,000 -ohm potentiometer
S1- S.p.s.t. toggle switch

-4 -pole,

9- position rotary switch
P.4 2013 or equivalent)
S3-4 -pole. 6- position rotary switch
P.1 2011 or equivalent)
S2

,Model

(Centralab
(Centralab

S4- Normally -open push- button switch (Grayhill
23 -1 or equivalent)
TI -Power transformer: primary, 117 volts; secondaries, 470 volts CT 3 40 ma.; 5 volts
2 amp.; and 6.3 volts CT n 2 amp. ( Stautor
PC 8401 or equivalent)
Cabinet (Bud WA 1540 or equivalent)

-2"

x 5" x 7" chassis
1
Misc. -CRT sockets and adapters, fuse holder,
line cord, knobs, etc.

Fig. 6. Nothing is critical here, except for meter po-

larity. Most of the components are panel- mounted.
10

ELECTRONIC EXPERIMENTER'S HANDBOOK

turn can be treated in this manner. Appropriate adapters and switching arrangements to accommodate multi -gun
tubes, or any tube having a different
base or basing arrangement, can be
added to the tester. If you are careful,
and if you don't have an appropriate
socket, you can use clip leads or patch
cords to make connections to the CRT
pins.
CONSTRUCTION

Any convenient layout of parts can be
used in building the tester /rejuvenator.
The wiring is straightforward, except
for the filament wiring. The phase of

6.3v

the transformer's filament windings
must be determined before the filament
switch can be wired.
To determine the phase, first tape the
leads from the high -voltage secondary
winding to avoid accidental contact, and
do the following:
(1) Connect one of the 6.3 -volt leads
(not the C.T.) to one of the 5 -volt leads.
(2) Connect the primary to 117 volts.
(Be sure that the other transformer
leads are not touching each other.)
(3) If an a.c. voltmeter is available,
measure the voltage between the two unconnected (not the C.T.) filament leads.
If this voltage measures about 11 or 12
volts, label the 6.3 -volt lead to which
the meter is attached "A "; label the 5volt lead to which the meter is attached
"G"; label the other 6.3 -volt lead "C ",
and the other 5 -volt lead "F ". If the
meter voltage measures 1 or 2 volts,
label the 6.3 -volt lead to which the meter
is attached "A "; label the 5 -volt lead to
which the meter is attached "F"; label
the other 6.3 -volt lead "C ", and the
other 5 -volt lead "G ".
In the absence of a voltmeter, a 12volt panel lamp can be used as a voltage
indicator. The bulb will glow brightly
when the winding phase produces 11
volts, and will glow almost imperceptibly-if at all -when the winding phase
produces 1 volt.
Wiring is considerably easier if the
switches are wired before installation.
The neon lamp is supported by its
terminals.

POSITION VOLTAGE
I

1.3

1.85

2.25(600mo.)

2.61(450mo.)

3.15
5

6
7

6.3

8.15

11.3

to aid or oppose each
other to obtain six more filament voltage levels.
Fig. 7. Windings are made

1966

Fall

Edition

Fig. 8. Observe polarity of D3 or you'll put a posiG1 and possibly ruin your meter.

tive voltage on

one side of the neon bulb will glow. If it
is shorted, both sides of the lamp will
glow. If it is open, or if cathode emission is extremely low, the lamp will not
glow.
(6) Turn the selector switch to GRID
2. If grid 2 is normal, one side of the
neon lamp will glow. If this grid is
shorted to the cathode, both sides of the
lamp will glow. If grid 2 is open, or if
cathode emission is too low, the lamp
will not glow.
Emission Test

Fig. 9. Test cable can be fed through the panel,
or plugged into a front -mounted octal socket. Picture tube socket adapters can be added as needed.

The on -off switch, panel lamp, and
grid -bias potentiometer are mounted
through the front panel and the chassis, and serve to hold the panel and
chassis together. The filament and function switch are mounted on the front
panel and are held securely in place
with lock washers.
OPERATING INSTRUCTIONS

(7) Turn the selector switch to
EMISSION. The meter should indicate
approximately 300 microamperes or
more for a good tube; however, a tube
that conducts 100 microamperes or
more will probably produce an acceptable picture. (Some of the newer type
picture tubes designed to use higher G2
voltages may indicate "weak" when
they actually are not.)
Grid Control Test

(8) Turn the selector to CUT -OFF.
With the GRID CONTROL knob turned
fully counterclockwise, the meter should
indicate the same value as it did on the
emission check. Now advance the control clockwise until the meter registers
no current (or an extremely small current). If the potentiometer has not advanced beyond the vertical mark, the
tube cutoff characteristic is acceptable.
In most cases, the tube will cut off well
below this mark.

Open and Short Tests

Rejuvenation

(1) Select proper filament voltage.
(2) Connect the socket to the CRT.
(3) Turn the power switch to ON and
allow approximately 30 seconds for the
tube to warm up. Look at the neck of
the tube to see if the heater is glowing.
If it is not, the problem may be a loose
connection in the picture tube base.
Often this condition can be corrected
by resoldering with solder containing
noncorrosive flux.
(4) Turn the selector switch to HTR.
If the heater is not shorted to the
cathode, the neon lamp (12) in the center of the tester will not glow. If it is
shorted, both sides of the lamp will

(9) If the emission check indicated a
weak tube, turn the selector switch to
REJ. Depress the REJUVENATE button for approximately 1/2 second and release, then turn the SELECTOR switch
to EMISSION. If the tube now appears
normal, remove the tester. If the tube
still appears weak, increase the filament
voltage to the next higher voltage and
rejuvenate again. Reduce the filament
voltage to its normal value, wait about
a minute, and retest. If it does not now
appear usable, increase the filament
voltage one step higher and rejuvenate
again. If this all -out try doesn't help,
check emission with a higher than normal filament voltage. If this works, but
rejuvenation doesn't, install a picture
tube brightener.

glow.
1.
12

(5) Turn the selector switch to GRID
If grid 1 is not shorted to the cathode,

ELECTRONIC EXPERIMENTER'S HANDBOOK

TRAINS

NOT ONLY
YOU GET
BUT HELPS
YOU
COST IN
NO EXTRA
AT
STARTED
OF

DORY
,

THE

TECH

HOME LABORATORY EQUIPMENT
YOURS TO KEEP!

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VPREPARE AT HOME

Whether you want to prepare for a good -paying new
job or for advancement in Electronics with your present employer,
DeVry Tech offers specialized educational programs designed to
meet your needs. You set up your own HOME LABORATORY
and work over 300 construction and test procedures to develop
on- the -job type skills. You build a quality Transistorized Meter,
a 5 -inch Oscilloscope and a special Design Console. DeVry also
includes modern "programmed" texts, instructive motion pictures, Consultation Service. Effective? Yes!

VRESIDENT SCHOOL
If you prefer you may get all of your training in DeVry's
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in Communications, Microwaves, Radio -Television, Automation,
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provides part-time job placement service to those who wish to
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Meet W. E. Bartz, who has helped thousands of DeVry
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AVAILABLE IN CANADA

CIRCLE NO. 6 ON READER SERVICE CARD
1966 Fall Edition

THE CURTAIN RISES and the spotlight falls on the slender girlish figure
of the performer as she strolls gracefully towards the center of the stage. She
stops behind a thin narrow box perched
atop a microphone stand and turns to
face the audience. Like a symphony conand on
ductor, she raises her hands
the downbeat rich musical tones, changing in pitch and intensity with each wave
of the hand, fill the auditorium. She
plays marches, polkas, and operatic
themes without once ever touching the

...

music box.
Magic ? No. "Lumemin" is the word.
Using a pair of sensitive photocell "eyes,"
the Lumemin "sees" our performer as
she moves her hands up and down, causing varying amounts of light and shadows to fall on its "eyes." In operation,
one photocell controls loudness while the
other controls the musical tones which
are rich in harmonics and sound somewhat like conventional brass, woodwind,
and string instruments.
14

The UJTO Circuit. The heart of the
Lumemin is a versatile UJTO (Unijunction Transistor Oscillator) module (Fig.
1), driven by a power supply and its
photoconducting circuit. The UJTO pro-

r
a

Fig. 1. Modified sawtooth signal across points B
and E is fed to an external amplifier and speaker.
ELECTRONIC EXPERIMENTER'S HANDBOOK

LUMEMIN
STEALS
THE

SHOW
This easy -to-build
musical instrument
reads your hands
like a Gypsy
By LOUIS E. GARNER, JR.

duces square -wave pulses as well as a
modified sawtooth signal rich in harmonics. The latter is fed to an external
audio amplifier and speaker.
Referring to Fig. 1, an a.c. input applied across D and E is rectified by diode
Da and smoothed out by Ra and a 500 pf. capacitor (Ca) in the power supply
circuit. Zener diode Db limits any voltage surges from the power supply to
maintain a constant potential at the
unijunction transistor (UJT) base electrodes through Rc and Rd.
Without emitter bias, the UJT is in a
nonconducting (high- resistance) state.
Capacitor Ca charges up through Rb and
a resistor in the power supply circuit
that appears effectively across A and B.
As Ca begins to charge, the emitter voltage increases gradually until its point of
conduction is reached. At this time, the
UJT is triggered and switches from its
nonconducting to a conducting state.
As the UJT conducts, Ca discharges
rapidly through the UJT and Rd, developing a positive -going pulse at B1
across Rd, and a negative -going pulse at
B2 across Rc. At the same time, a modified sawtooth waveform appears between
terminals B and E. With Ca discharged,
the UJT reverts to its high- resistance
(nonconducting) state and the entire
cycle is repeated.
The frequency (or repetition rate) of
the circuit is dependent on the RC time
constant of the components in the UJT
emitter circuit. Basically, this boils down
to the values of Ca, Rb, and the external
resistance between A and B, as mentioned earlier. The output appears across
points B and E.
The Other Components. Now,

let's look

at the rest of the Lumemin's circuit

(Fig. 2) . The major components are an
isolating transformer (T1) and photocells PC1 and PC2. Photocell PC1 is part
of the UJTO's timing network. It is
shunted by R1, and this shunt combination is in series with R2. Therefore, PC1
serves as the external frequency control
resistor. As PC1's resistance changes
with different light intensities, corresponding changes take place in the
UJTO's frequency. Thus, the instrument's tone is controlled essentially by

Fig. 2. Diagram of power supply and timing network
shows wiring connections to UJTO plug-in module.
1966

fall

Edition

PC1.
Recall from Fig. 1 that a modified
15

Fig. 3. Rear view of box used by author
shows attractive slide cover design finished
in gray aluminum. However, the builder
can select practically any size or shape
enclosure consistent with good appearance.
TOP

Fig. 4. If you use the enclosure specified,
lay out the chassis and drill holes as shown.
17"

I-1/4"

5 /e"
DIA

DIA

3/32"
DI4

I-I/2"

+-IJ8"

I-1/2'

7/16"

3/16 "DIA

13/32"

3/4"

TOP

5 1/2"

3/4"

2 -1/2"

-4
_

3/IG'

1/2"
I

DIA

13DÌÁ'

\1/6 "014(4)

I-1/2"

3/4"

MOUNTING HOLES

7/16"

cf 3/4

T
I

I/2,

-1/2'

o
1/2"

-1.13/4"1-.1

sawtooth signal appears between terminals B and E. It can be seen from Fig.
2 that this signal appears across R3 and
PC2 which are in series. The signal
across PC2 is coupled through C2 to
output jack JI which feeds an audio amplifier. Operation of PC2 is such that its
resistance decreases with the intensity
of the light shining on it. Therefore,
the amplitude of the output signal is
directly proportional to PC2's instantaneous resistance, and thus inversely
proportional to the light falling on the
device. Accordingly, maximum volume
is obtained with reduced lighting, while
a strong light produces little or no output.
Although the UJTO can be powered
PCI

PC2

directly by the a.c. line, isolation transformer Ti is used to insure greater safety and shock -free operation. Terminals
C and F on the UJTO's circuit board
(Fig. 1) are not used in this application.
Construction. Although the model shown
in Fig. 3 has been designed around an
attractive slide cover gray aluminum
box, and all layout and construction details are centered around this design,
the instrument can be housed in practically any type of enclosure, including
a wooden cabinet or plastic box.
Remove the cover and drill the holes
in the box following the layout and hole
dimensions given in Fig. 4. Mount J1,
Si, T1, PC1 and PC2 on the chassis as
STANDOFFS

(4)

Fig. 5. Electrical components are

first mounted on the perforated
phenolic
mounted
standoff
must be
RUBBER FEET

UJTO PLUG -IN MODULE

board which is then
on the chassis with four
Orientation
spacers.
as shown in diagram.

ELECTRONIC EXPERIMENTER'S HANDBOOK

TOP

-0

TO PCI

PCI

2.v6

501
6

TO PC2

TO Ti

-3/1.

SOT TOM

TO PCI

SOI

Fig. 6. Phenolic board showing components mounted
on one side (top) and wiring details on other side.

PARTS LIST

C1- 500 -12f.,

-2-

15 -volt electrolytic capacitor

C2
o/., 200 -volt paper capacitor
11 -Open circuit phone jack

PC1, PC2 -CdS photocell (GE Type X6)
R1- 10,000 -ohm, % -watt resistor -see text
R2- 1000 -ohm, A -watt resistor-see text
R3- 470,000 -ohm, % -watt resistor-see text
S1- S.p.s.t. toggle switch
S01- Cinch -lanes bifurcated -contact edge connector, Series 250, Type 50 -6A -20 (Newark
Electronics Stock No. 29F952 or Allied Electronics Stock No. 40 H 319)
T1 -115 -volt isolation transformer (Lafayette
Stock No. 33 G 7502)
CITO- Unijnnnction transistor oscillator module
(MS Type 5100 -4A- available for $5 from
Midland Standard, 161 E. Chicago St., Elgin,
Ill. 60120)
1 -3%" x 2%" x 17" slide cover utility box
1

(LD1B No. 19)
x 2 'A" perforated phenolic board

-6%"

Mise.-Line cord and plug, rubber feet (4),
standoff spacers (4), push -in terminals, rubber
grommets (3), machine screws, nuts, wire,
solder, etc.

Fig. 7. When installing the UJTO module
in the Cinch -Jones

connector

(SO1),

make sure it is positioned with foil side
of the board facing
the chassis rim as
shown in Fig. 5, or
circuit will not work.

1966 Fall Edition

shown in Fig. 5. The photocells are
mounted in tight- fitting rubber grommets, and the rubber feet can be put on
at this time. Use No. 6 self- tapping
screws, or if you prefer, machine screws
with nuts and flat washers. Transformer
T1 can be mounted with the same size
hardware. Then put the chassis aside,
temporarily.
You can now begin to assemble the
electronic components on the phenolic
board as shown in Fig. 6. On one side
of the board, mount the Cinch -Jones
socket (201) , and capacitors Cl and
C2, as shown in the top view. Wire the
other side of the board as shown in the
lower view. Refer to Fig. 2 for detailed
wiring information.
The only thing left for you to do is
to plug the UJTO module (Fig. 7) into
socket SO1 (Fig. 6) , and mount the electronic component board on the chassis
using four standoff spacers ( Fig. 5) .
Be sure to insert the module with the
foil side facing the chassis rim. Then
complete the interconnection wiring.
As a final touch, you can use decals
to label the controls and thus give the
instrument a commercially built appearance. After the decals are put on, they
should be protected with two or three
coats of clear lacquer or acrylic plastic.
Using the Instrument. For personal
use or individual practice, a pair of
high- impedance magnetic or crystal
headphones can be plugged into J1. For
parties, or audience entertainment, you
will need a suitable audio amplifier/
loudspeaker system such as a guitar amplifier, a public address system, or a
standard hi -fi system. Simply connect
a suitable cable between J1 and the amplifier's high- impedance microphone jack.
The Lumemin should be placed in an
area where a moderately strong light
will fall on its photocells. The light
source can be an overhead lamp or a
sharply focused spotlight, as you prefer.
Since no warm -up is required (except

for the reproduction equipment used),
the moment you turn the instrument on
you can play individual notes by using
your hands to cast appropriate shadows
on the photocells. The lowest frequency
note is obtained when the tone photocell
(PC1) is in complete darkness, and the
(Continued on page 138)
17

BUILD A

FAIL-SAFE TRANSISTOR
POWER SUPPLY
By EDWARD NAWRACAJ and FRED FORMAN

It halts runaway transistors
restores itself instantly

COMBINING a transistorized series BYregulated
power supply with a light dependent resistor (LDR1) it is possible
to obtain a fail -safe power supply that
is regulated, short -proof, and self-restor,

ing. There are no fuses to replace or circuit breakers to reset. Even a dead short
across the load line cannot damage this
power supply.
keep
Before you say, "So what ?"
-reguseries
-circuited,
short
that
in mind
lated power supplies generally cause the
base -emitter junction of the series transistor to rupture, and end further use of
the supply until the transistor is replaced. This does not happen with the
fail -safe supply.
The components selected enable this

...

... eliminates batteries ..

... and dead shorts can't kill it
supply to provide you with a 9 -volt output at 0 to 100 milliamperes. It is ideal
for transistor projects, radios and other
9 -volt battery- operated devices whose
current requirements do not exceed 100
ma.

In addition to the fail -safe feature, the
supply tends to protect the devices being
powered. Suppose you had a defect
which could cause a runaway condition
in one of your transistor projects . . .
chances are that with a battery supply
your transistors would draw destructive
currents. With the fail -safe supply,
maximum current is 100 ma. And, of
course, a big advantage is that the power supply serves as a battery eliminator:
it works off the 117 -volt line.
ELECTRONIC EXPERIMENTER'S HANDBOOK

DI
1N4001

An overload brightens 11
and darkens 12. You see I1
and LDR1 "sees" 12. If you

don't remove the overload,
the LDR biases Ql to cut
down the output current.
Removal of overload darkens 12 and output voltage jumps back to normal.

12V

loon

I7 VAC

02
IN3020A

An overload indicator quickly alerts
you to operating conditions. Here's what
happens. Under normal load conditions

the indicator light Il, protruding through
the top of the cabinet, is off and the output voltage is correct. Under excessive
load conditions, IZ glows and the output
voltage is down sharply. When you remove the excess load, 11 will stop glowing and the output voltage will come up
to normal almost instantly.
How It Works. Diode D1

rectifies, and

Cl filters the 12 -volt a.c. output from Ti.
The main current path can be traced
from the bottom of the secondary winding of T1 through the parallel path of

and the load, through the emitter collector circuit of Q1 through R2,
through the parallel paths of Il and
LDR1, through DI, and finally back to
12

T1.
A

small secondary current path
through R1 and zener diode D2, which is
dependent upon the total effective resistance of all the other components and
the load, establishes and varies QI's base
bias, which in turn varies Q1's dynamic
resistance, the main current flow, the
respective voltage drops across the various components in the circuit, and the
load. Output voltage variations due to
larger or smaller loads are compensated
for by these changes in bias, so long as

TO NEGATIVE POWER

OUTPUT LEAD
RI
02

FROM SECONDARY
CI

TI
DI

PARTS LIST
elcetrelrlir capacit,u

C1- 1000 -11f., 25 -volt
D1-50 -PlV, 300 -ma.

diode 1.A 2482, 13`40!)1,
or 1.V2610)
D2-10 -volt, 1 -watt, 10% :c,er diode

(1N3020A)

-18 -volt miniature
equivalent)
12 -10 -volt miniature
11

equivalent)

lamp (Sylvania 18ES or

lamp (Sylvania 10ES or

LDR1- Light- dependent resistor,

100 footca,dle-

100 ohms, (Sigma 4116 or equivalent, 1 -watt,
300 -volt r.m.s. rating)
QI-2,697, 2.V1420, or 23'1613 transistor
R1- 100 -ohm, % -watt resistor
R2- 15-ohm, 2 -watt resistor
S.p.s.t. slide switch
T1- Filament transformer: primary, 117 volts;
secondary, 12 volts, 1 amp. or greater ( Stancor
P8130 or equivalent)
1 -4" x 23" x 2" aluminum box
1
%" x 2%" perforated circuit board
11isc.- Transistor heat sink for TO -5 transistor
housing (Thermalloy 2211 or equivalent),
grommets (3), right-angle brackets (2), color
cap for 11, line cord, output leads, wire, screws,

SlTO

POSITIVE
POWER

OUTPUT LEAD

LORI

INSIDE
HEATSINK

Press-fit 12 into a grommet and position the assembly close to and "facing" LDR1. A wire loop holds
the grommet in place. Observe polarity of diodes.
1966 Fall Edition

-1

etc.

the load does not demand more than the
maximum 100 ma. of current.
Excessive loads reduce Q1's forward
bias to a very low value and sharply limit the amount of main current flow. The
resulting drop in voltage across the load
extinguishes 12. The loss of light on
LDR1 increases its resistance and further limits the main current flow. The
voltage drop across LDR1 is now sufficient to light Il and alert you to the
overloaded condition.
When the excessive load is removed,
current flow through 12 will increase
sufficiently to once again illuminate
LDR1, reduce LDR1's resistance, and increase Q1's forward bias. This servo-like
action has a regenerative characteristic
and quickly responds to almost instantaneous load variations.

3/d'01A
2-3i4"

7/8"

1/2"

3/8 "DIA

1/8"
DIA

o
- --7/e "

7/8

Construction. Prepare a 2" x 2 3'i" x
4" aluminum box as shown and install

the three grommets, switch, transformer
and 11. Preassemble all the other components on a 134" x 21/2" perforated
phenolic or other suitable circuit board.
Transistor QI should be enclosed in its
heat sink before you mount it on the
board.
Pressure -fit 12 into a grommet and
position it close to and "facing" the
sensitive side of LDR1. Stand the grommet upright on the board and tie it into
place with a small length of bare wire.
Now attach two small right -angle
brackets to the edge of the board as
shown. Because some of the negative
leads are connected to one bracket and
some to the other, this circuit is corn-

I-v2"
1/2 "DIA
2

-3/"

Drill holes in the outer portion of the aluminum
box as shown. The size of the rectangular opening
can be modified to accommodate any s.p.s.t. switch.

pleted when the board is fastened to the
box. Therefore, you should avoid contact between the box and the positive
lead or the load.
Install the subassembly in the box,
and hook up the transformer, line cord,
and output leads. Double-check to see
that all wire and components are properly arranged so that there are no un-

Preassemble the circuit board and install after Sl,
Il, and Tl (in that order) are mounted. Connect all
leads and check the circuit before closing box.
20

wanted short circuits.
You can now plug in the unit and
check its operation. Touch the output
leads together and watch the action. Do
the same with the leads apart. If you
followed instructions, the action will be
-Cas described.
ELECTRONIC EXPERIMENTER'S HANDBOOK

COVER STORY

Add a new dimension to your holiday

lighting -just use any radio
or record player and the "Rhythmicon"

HERE'S a little project we have dubbed

the "Rhythmicon," for with it you
can make your Christmas lights twinkle in time to the music from your radio,
phonograph, hi -fi or p.a. amplifier. The
possibilities the Rhythmicon offers are
endless Use it to control tree lights,
floodlights, spotlights, or conventional
electric bulbs-indoors or out.
Simply connect the two clip leads from
the Rhythmicon to the loudspeaker
leads of the sound source, and play
carols or other seasonal material
through it. The lights plugged into the
socket on the box will automatically fol111.

1966

Fall

Edition

ICnristmas

fights
bu inhk
to Ilitusic

By LEON A. WORTMAN

Christmas
!Tgbts

twinkle
to Music
ers. A solder lug is placed under the
mounting nut of D2 to connect the cathodes of D2 and D3 directly to the lamp
socket, S01. Diodes D4 and D5 (as well
as SCR1) must be electrically insulated
from the heat sink with mica washers on
on,
full
to
from
off
going
low the sounds,
getting instantly brighter and dimmer either side. Between the mica washers
as the music gets louder and softer; go- and the bodies of these three semiconing off completely when the music stops. ductors, use solder lugs as shown in the
The music plays, and the lights dance upper photo on page 23. Use heavy metal
washers between the outer mica washers
automatically.
and the mounting nuts. When SCR1 and
Construction. Basically, the Rhythmicon makes use of the ability of a silicon D4 and D5 are mounted, check with an
controlled rectifier to act as a "rheo- ohmmeter to insure that their cases are
stat," controlling large amounts of cur- not shorted to the heat sink.
The heat sink must be electrically isorent in a circuit in response to pulses
from the Minibox. In the author's
lated
Uniapplied to its "gate" electrode.
junction transistor Q2, in combination unit, 6 -32 holes for machine screws were
with Q1, acts as a pulse generator to drilled and tapped into opposite sides
turn SCR1 on. The pulse frequency of a 3' +" x 1/2" x 1/2" bar of Bakelite. The
(and, consequently, the brightness of heat sink was mounted on the Bakelite
the lamps controlled by SCR1) depends through holes in the 1/1" flange made preon the amplitude of the audio signal ap- viously, and the Bakelite was then seplied to TI (see "How It Works," page cured to the inside of the Minibox in
the same way. Polystyrene or any simi24).
A 3" x 4" x 5" Minibox holds all of lar insulating material can also be used
the circuitry and components for the for this, or the heat sink can be mounted
Rhythmicon. The SCR and the four sili- with machine screws using extruded
con rectifier diodes must be mounted on shoulder washers to insulate it.
As shown in the top photo, most of
a heat sink. First, fabricate the heat
remaining components are mounted
the
cutaluminum,
1,46"
sink from a piece of
ting it to 212" x 334 ". A 'I" flange is to a 21/4" x 32" piece of perforated cirbent along the 331" dimension for mount- cuit board (with the exception of S01,
ing the heat sink, and five holes are Fl, Tl, S1, and Rl, which are mounted
drilled in it for mounting SCR1 and at the ends of the box) . "Flea clips"
D2 -D5. The holes must be large enough are inserted into the perforated board
for complete clearance of the mounting at suitable points to provide rigid termi-

studs.
Referring to the photos on page 23,
mount D2 and D3 directly in the two
center holes without insulating wash22

nals for connecting the transistors and
other components. The perforated circuit board is mounted to the box with
several machine screws and 1/" standELECTRONIC EXPERIMENTER'S HANDBOOK

%x5Xsg5SxZ1s:5AWAIiislZVZx5XWME3t;3x3t5Slagxagxfi.4x*A5a5A5:43WA
SOI

SCRI

5,-sSx:4stgxZ;Astgx::FAVS

Aluminum heat sink is mounted
to one side of box on a Bakelite strip; PC board is mounted
on /2" spacers. Only rear of
S01-the socket for lights -is
1

seen. Heat sink and components
should not contact metal box.

R2 R3

offs to provide clearance for the tips of
the "flea clips" which protrude through
the board.
Before mounting the circuit board and
heat sink, drill holes in the Minibox for
the remaining components. At one end
of the box, mount SOI, F1, and Tl; at
this same end, drill holes for the a.c.
line cord and audio clip leads (these
can also be made with a.c. lamp cord) ,
and line them with rubber grommets.
Drill holes for Si and R1 in the opposite
end of the box.
Final Wiring. Because some of the components of the Rhythmicon are at the
potential of the a.c. line, it is essential
that no part of the circuit makes electrical contact with the Minibox. The one
exception to this is the audio lead which
is connected to the bottom end of R1;
connect this lug of RI to the box by
placing a solder lug on the control shaft.
Also, connect the ground terminal of Cl
directly to the box (rather than to the
lower terminal of R1) using a lug under
one of the nuts holding the perforated
circuit board.
Transformer Ti, a universal push -pullplates-to- voice -coil audio output type,
is used to couple the audio source to the
Rhythmicon. It is connected so the
secondary or voice coil side becomes the
input. Connect the center lug of R1
1966

Fall

Edition

Studs at left (below) are D4D5. Mount with mica washers
on both sides of heat sink; use
same method for SCR1 seen at
right. At center are D2 -D3; no
washers are needed for them.

and the positive terminal of Cl to the
transformer terminals that give the
highest impedance -with the unit used
by the author, terminals 1 and 6. Connect the push -pull plate side as shown
in the schematic; the center tap is not
used and can be cut short.
Since transistors QI and Q2 are soldered into the circuit, be sure to use
alligator clips or other heat sinks to
avoid heat damage. Observe similar precautions with the diodes and SCR1. Component values are not critical, and may
vary plus or minus 10(, it is desirable
to select a resistor for R6 that is within 5% of 3000 ohms, however.
Operation. It takes less than half a
watt of audio at 4 ohms impedance to
operate the Rhythmicon, and even a
transistor radio can be used to demon;

i5?.'i^'C>.:

`.9.FSFA^.a5*c5^'9.45a9.%X547Z:eti9Eix..:M.45:55 .S'53T.e..`9.4SZ:Fíae}t"9.4FvF65.. .7"gMU9Fr.^

(pm
4.7K

R6
3K

R3
3.3K

33011

14
02
T1
VAC

2N2160

FI
D61

Z4XL20
BI

CLIPS
TO
SOUND'

.0475f.

SOURCEI

390

(SCR1)
Rhythmicon consists of bridge rectifier, audio pulsing circuit (Q1 -Q2), and power control

PARTS LIST

-100 µf., 50 -volt electrolytic capacitor
C2 -20 µf., 25 -volt electrolytic capacitor
C3 -.047 µf., 200 -volt paper capacitor
D1 -1N34A germanium diode
D2-D5- Silicon diode rectifier (GE -X4 or Lafayette
C1

Stock No. 19G4208 or equivalent)
D6-20 -volt, 1 -watt zener diode (GEZ4XL20 or

equivalent)

F1- 5-ampere, 125 -volt "slow- blow" fuse and fuse holder (Littlefuse Type 3AG or equivalent)
Ql-GE-X9 pup transistor
Q2- 2N2160 unijunctioz transistor (GE)
R1 -10 -ohm, 5 -watt wire -wound potentiometer
R2 -4700 -ohm, Y,-watt resistor
R3-3300 -ohm, % -watt resistor
R4-330 -ohm,

V2-watt resistor

strate its functioning. No modification
is required at the audio source simply
;

connect the clip leads to the amplifier
speaker terminals, or to the voice coil
leads of a speaker. Any impedance between 4 and 16 ohms will do, with 8
ohms as optimum.
Potentiometer RI is the sensitivity or
light amplitude control for the Rhythmicon. After setting the audio amplifier
for the best listening level, adjust R1
to the point where the lights follow
variations in sound volume; turn it too
high and the lights will stay on with
little variation, going off when the sound
stops.
Lovely lighting effects can be created
by connecting up to four 100 -watt Par 38 lamps (available in red, blue, and
green) at the base of the Christmas
tree, or as part of an outdoor display.
Plugging in strings of conventional tree
lights further enhances the effect. The
24

RS-39 -olum,

% -watt resistor
5 -watt wire -wound resistor

R6- 3000 -o/zm,
or better

S1- S.p.s.t.

toggle switch

SCR1- Silicon controlled rectifier (GE -X1
equivalent)

10%

S01-Panel-mounting
Universal push -pull output transformer (Lafayette 33G7503 or equivalent-see text)
I -3" x 4" x 5" Minibox
Misc.-Sheet of 1/26" aluminum for heat sink; perforated circuit board; flea clips; Bakelite bar for
mounting heat sink; mica washers for mounting
SCR1, D4 and D5; solder lugs; 6 -32 hardware; %"
spacers; alligator clips; line cord; grommets; wire;
a.c. socket

TI-

solder. etc.

rating of SCR1 gives a total
of 450 watts of power handling capability-that's a lot of dancing, twinkling,
4.7- ampere

decorative light!

-®-

HOW IT WORKS
Audio is applied to Tl, and rectified and filtered
by Dl -C2; the resulting polarized voltage appearing across R2 biases Ql, following audio amplitude variations. Unijunction Q2, C3, R4, and R5
comprise a pulse generator. The frequency of the
pulses depends on the d.c. potential applied to
Q2's emitter by Ql. The greater the audio amplitude, the higher the pulse rate. Resistor R6 and
zener diode D6 form a voltage divider across the
output of the bridge rectifier (D2 -D5), and provide stable, low potentials for Q1 -Q2. The SCR
begins conducting when a pulse is applied to its
gate: current flows until the pulsating d.c. delivered by D2 -D5 reaches zero. At that point, another pulse from Q2 is required to again start
conduction. The greater the pulse rate, the higher
the average current through SCR1 and the lights
connected to S01.

ELECTRONIC EXPERIMENTER'S HANDBOOK

Where there's smoke,
there's fire ;
where there's fire,
it may be too late;
this detector
"sees" the smoke
and warns you

A
S
KE
LA
F R
OLTIt

E
SMOKE can cause as much as, or more,
loss of life and property damage than
fire. In many instances, smoke is present
long before a fire is actually detected.
Homes and business establishments are
often equipped with either simple or
elaborate fire alarms, but relatively few
1966

Foil

Edition

By H. ST. LAURENT

of them have any provision for smoke

detection. Early warning of the presence
of smoke can give you enough time to
either put out a fire and minimize damage,
escape.
Fortunately, most smoke is lighter
than air, and rises. It will accumulate

cr-

the presence of
smoke, light reflectlamp 11
ed from
reaches the photocell (PC1). Action of
PC1 fires VI., energizes
the relay, and sounds
the alarm. Sensitivity
can be adjusted to
allow for heavy cigar
In

PCI

47K

LENS

39011

and pipe smokers.
C2

5yf.

HORN

EXTERNAL
ALARM
TI

00Ipf.

R3
IO MEG.

on the ceiling and build down. A room
almost filled with smoke may have an
area close to the floor that will allow a

safe crawl space for escape. By the same
token, if a smoke alarm were located
near the ceiling, it would sound an alert
long before a dangerous concentration of
smoke accumulated. Here's a smoke detector you can construct complete with
a built -in alarm for about $10.00.
How It Works. A light source consisting
of a lamp, lens, and shield aims a narrow
beam of light about 1 inch in front of,
and at a right angle to, the "line -of-

2 1/8

13/16
W16"

conditions.
When smoke enters the chamber, it
interferes with the light beam and causes
the light to be reflected in many directions. Some of these reflections strike
the photocell. Under the influence of
light, the resistance of the photocell decreases and causes a higher voltage to
appear across R3 and on the starter electrode (pin 4 of V 1) When the starter
.

STOCK

'PIA.

3/8

'BTOCK.

9/16"

3/16 "DIA

sight" of a cadmium sulphide photocell.
The cell is recessed in a lighttight cylinder and does not "see" enough of the
light to trigger the alarm under normal

DIA

1/2"

IJ2°

{

--.I 5/8"

BOTTOM

REAR

SIDE
1/2

y /2 "DIA
1

---1_
T/I6

LENS

Light- source barrel is made from a block of wood.
Size of lens opening can be varied to accommodate
your lens. Use a cardboard tube as an extension.
26

"AROM"TOP

Photocell is mounted at right angles to the sharply
focused light. Paint inside of the wooden smoke
chamber flat black to minimize light reflections.
ELECTRONIC EXPERIMENTER'S HANDBOOK

electrode voltage reaches the firing point
(approximately 50 volts) , the tube conducts, energizes the relay, and activates
the alarm. The alarm will shut off when
the smoke has cleared the chamber in
the smoke detector.
Potentiometer R3 serves as a sensitivity control and is usually adjusted to
require a fairly large volume of smoke to
trip the alarm in order to prevent a false
alarm, which could be caused by a number of people smoking in a confined area.
Transformer Ti provides 6.3 volts to the
lamp (11) and to the horn; RI is a current limiter, and tends to protect and
increase the life of II; R2 serves as a
makeup resistor and prevents the resistance divider network across the 117 volt line from drawing too much current
in the event that R3 is inadvertently adjusted too close to minimum resistance ;
capacitors Cl, C2 and resistor R4 are

KI¡aLINE

the lens block to allow the lens and
photocell to fit properly. The distance
between the lens and the lamp will vary
in accordance with the focal length of
the lens, and should be adjusted to give
the sharpest beam of light possible.
Attach the lamp socket to the lens
block with a small 1" wood screw. A
green or red plastic window can be placed
over the front opening of the lens block
to cut down some of the glare from the
lamp. This light from the front opening
only serves as a pilot to let you know
that the lamp and power are on. Cover
the smoke chamber and other internal
surfaces with a flat black paint to minimize stray reflections.
The cabinet is made of standard 21/2"
x %" pine panel stock. A slot cut about
1/2" from the edge of the panel stock,
and about ',is" deep holds a metal grille
in place when the sides are assembled,

PARTS LIST

C1- 0.001 -14, ceramic capacitor
C2 -4- or 5 -nf., 50 -volt electrolytic capacitor
11 -Pilot lamp (GE 12 or equivalent)

K1-3500-ohm, s.p.s.t., N.O., miniature relay

(Guardian E -3772 or equivalent)
sulphide cell (Clairex Cl -504 or
equivalent)
R1 -10 -ohm, % -watt resistor
R2- 47,000-ohm, 1,A-watt resistor
R3- 10- megohnz potentiometer, linear taper
R4-390 -ohm, Y2-watt resistor
T1-117 -volt to 6.3 -volt, 1- ampere filament
transformer
V1 -5823 glow tube
1 -Horn (imported type used on bicycles)
1 -14 -nun. x 34 -mm. focal- length lens (any double convex lens that fits is suitable)
1 -Lamp socket (Dialco 19 -07 or equivalent)
Misc. -Tube pin sockets (3) removed from miniature socket, wood, 4" x 8" ¡octal grid, quick setting glue, wood screws, etc.

PC1- Cadmium

UNE

To K1

Remove unused tube pins and use a drop of cement to hold the tube in place. Lamp 11 is inside the
barrel. A cardboard tube holds the photocell (PC1).

uncritical circuit stabilizing components.
Construction. The smoke chamber is
made of wood stock lattice strips or other
suitable 1/}" x 13/4" lçlmber and 1/8"
Masonite or other tempered board. The
lens and photocell holders are made of a
heavy manila paper and glued in place.
If necessary, you can modify the diameter of the holders and the openings in
1966

Fall

Edition

The electronic components including the smoke
chamber complete (not wired), machined cabinet
parts, grille, base and cover, hardware, line
cord, wire, etc., are available for $15 postpaid in
the U.S.A. from Lectromek Co., 166 Wendell Rd.,
Warwick, Rhode Island 02888. No C.O.D. Price
list for individual parts available,

and dresses up the appearance of the
cabinet. An alternate method is to rabbet
the top edge of the four sides so that
the grille can be set flush, then topped
off with 1/2" half-round molding. All
cabinet and smoke chamber parts are
glued in place, with the exception of the
back cover which has a %" hole near
the top, center, to accommodate a hook
27

The smoke chamber should be as
lighttight as possible to keep

the detector immune to outside
light. The plastic window lets
you see if the lamp and power
supply are in working order.

or other wall hanger for holding the finished smoke alarm. Complete all wiring
and mounting of parts before you screw
down the back cover.
When the back cover is secured, slip
the unit into the cabinet. It should fit
snugly. Two 6 x 3/4" half -round head
wood screws on each side of the cabinet
will hold the alarm in the cabinet.
Installation and Adjustment. Installation is simple -you just hang the unit in
an upright position, as high as you can
on a wall of the area to be protected,
and plug the line cord into the nearest
117 -volt a.c. outlet. Be sure smoke chamber inside cabinet is pointing up.
Before adjusting the unit, set the

Completed unit is mounted vertically, as close to
the ceiling as possible. Rising smoke enters smoke
chamber through metal grille to set off the alarm.
28

sensitivity control in the minimum position (counterclockwise) to keep the
alarm off, and allow about five minutes
of warm -up time for the detector to
stabilize itself. Then all you have to do
is rotate the sensitivity control until the
alarm sounds, and back off slowly until
the alarm stops. That's all there is to it.
You can check this setting by blowing
some smoke through the lower half of
the metal grid and waiting for the smoke
to reach the chamber if all is well, the
alarm will go on.
Sometimes line voltage variations will
modify the sensitivity characteristic
after you have set the sensitivity control. So, from time to time, blow some
smoke into the unit to see that it is
working. If the unit tends to "false
alarm" because of a normally smoky
room condition, or because of upward
line voltage variations, densensitize the
detector a bit by a slight counterclockwise adjustment of the control.
Another way to adjust the detector is
to use a Variac and step up the line
voltage to 125 volts, then slowly rotate
the control until the alarm just sounds
off. With the control in this position, the
alarm should function properly over a
line voltage range of 105 to 120 volts.
If, for some reason, line voltages in excess of 125 volts are regularly encountered, the Variac voltage should be
-®
adjusted accordingly.
:

ELECTRONIC EXPERIMENTER'S HANDBOOK

By LOUIS

GARNER,

JR.

SUPER -SENS

Versatile electronic relay provides unlimited control functions
need a burglar alarm, a fire
alarm, an automatic fan control, an
automatic light switch, a liquid level
control, an automatic dehumidifier control, a photoelectric counter, a radio remote control, a lawn sprinkler control,
an automatic door opener, a time delay
relay, an electronic latching relay, or a
sound -actuated relay ?
Would you like to amaze your friends
and neighbors, gain the respect of your
teachers or co- workers, assemble a
Science Fair project that is different,
or build a basic control that can be
used in hundreds of applications ?
If you can answer yes to any of these
questions, you'll enjoy building and
using ' Super -Sens, an easy -to -wire, inexpensive electronic relay so sensitive
that it can be tripped by a pencil line
drawn on a piece of paper.
Electronic relays are not new. They
have been designed and manufactured
for years. You can purchase a variety
of types at prices ranging from $20 to
$50 or more, or you can build Super
Sens for less than $10.00.
One popular "supersensitive" electronic relay offered by a leading laboratory
supply house requires a signal current
DO YOU

1966

Fall

Edition

of 50 microamperes at a little under 10
volts. Super -Sens, in contrast, will trip
with a miniscule control current of
about 0.2 µa. at approximately 1 volt.
Using its built -in bias circuitry, the device can trip with as much as 50
megohms between its input terminals.
Super -Sens can be actuated by many

input devices: photocells, humidity

detectors, microswitches, thermostats,
magnetic contacts, pressure switches,
thermistors, and almost any high or low
resistance type of sensor or probe, as
well as the comparatively low level signals obtained from a carbon microphone
or a simple radio receiver.
Super -Sens, in turn, can be used to
actuate almost any type of electrically
operated equipment: lamps, solenoid
valves, buzzers, bells, power relays, fan
motors, pumps, door openers, heating
systems, etc.
HOW IT WORKS
is essentially a two -transistor, high -gain, direct -coupled d.c.
amplifier driving a standard sensitive type electromagnetic relay. See Fig. 1.
Transistors Q1 and Q2 are connected in
a modified Darlington circuit. (A Dar-

Super -Sens

ARM

f-r---®N.O.

10K

little as 0.2 µa. at 1 volt is enough to
trigger relay; up to 50 megohms can be sensed.
Fig. 1. As

lington circuit is a circuit having two or
more transistors connected in such a
manner as to have a single input, a
common load and a current gain which
is the product of the current gain of
each transistor.)
Series resistor RI tends to limit base
current to prevent accidental damage to
the transistors by excessively strong in-

SENSOR
D.C.

VOLTAGE

OUTPUT

put signals. Unbypassed emitter resistor R3 stabilizes circuit operation, and
provides a degree of temperature compensation. Sensitivity control R4 and
current limiting resistor R2 are parts of
a bias and control circuit to permit the
use of external resistive -type and switch type sensors. Circuit power is supplied
by BI and is turned on and off with
s.p.s.t. switch S1.
When a signal or bias voltage of proper polarity (base positive with respect to emitter) is applied to the base
emitter circuits of QI and Q2, the transistors conduct and energize Kl. Bias
voltage can be taken from the internal
R2, R4, B1 circuit (B terminal) or it
can be derived from an external circuit.
There are essentially three basic types
of input circuit control devices that
Super -Sens will cater to: those that
look like a voltage source, those that
look like a resistor, and those that look
like a switch. The voltage source devices are hooked up to I and G.
The resistor control types are given
special consideration: high-resistance
devices are connected across terminals
I and B (in series with the internal

SENSOR
HIGH

RESISTANCE
SUPERSENS

RESISTANCE

SUPER-

SUPER SENS

SENSOR
LOW

SENS
B

that look like a voltage such as a
photovoltaic cell, etc.; those that look like high or low resistors; and those that act like a switch.
Fig. 2. Any one of three basic types of sensors can be used: those

LOAD A

LOAD
N.

N.C.®

SUPERSENS

ARM

N. O.

N.O.

SUPER SENS

SUPERSENS

111111i
EXT. POWER SOURCE

LOAD B

TO EXT.
POWER SOURCE

-D
EXT. POWER SOURCE

Fig. 3. Controlled external load circuit can utilize almost any source of power. If power requirements exceed the relay contact's rating, a power relay can be added. One or two loads can be switched.
30

ELECTRONIC EXPERIMENTER'S HANDBOOK

Fig.

4. Etched circuit
board construction provides a mounting base for
all the components, including the relay. Conventional chassis -type con-

struction is also quite
suitable. If you want to
make your own printed
circuit board, you can use
these actual size photos
as guides. All components
are mounted on one side
of the board (top). The
foil side (bottom) must
be clean to prevent leakage between conductors.

bias circuit) and low- resistance types
are placed between terminals I and G
PARTS LIST
with a jumper from terminals I and B,
BI -6 -12 volt battery
as shown in Fig. 2. Actually, the reKI -Relay (1AICO GS -100 or equivalent)
Q1, Q2-T1416 transistor
sistive devices are made to function like
R1- 1000 -ohm, % -watt resistor
a voltage source, since terminal B has
R2- 10,000 -ohm, % -watt resistor
R3 -47 -ohm, % -watt resistor
sufficient voltage of proper polarity to
R4- 1- megohm potentiometer, linear-taper
forward -bias the transistors.
SI- S.p.s.t. toggle or slide switch
1circuit board*
Switch -type devices can be connected
1- Etched
Cabinet (Minibox 2102)
between points I and B, and R4 adjusted
Misc.-Small knob, screws, nuts, hardware, wire,
solder, etc.
to provide just enough voltage to pull
in the circuit when the switch is closed.
*A pre- etched circuit board on an epoxy -glass
base is available from DE\ICO, Box 16041, San
Conversely, these switches can also be
Antonio, Texas 78216 for $2.00. This firm can
made to drop out the circuit. A jumper
also supply: a "basic" kit (board, relay, tranbetween I and B, and R4 adjusted to pull
sistors) for $7.50; a complete kit for $9.50; and
a pre -etched moisture sensor for $1.50.
in the circuit, will keep the circuit on
until a switch across I and G causes the
circuit to drop out when it is closed.
The relay can be hooked up to provide
If you
your own board, follow
either a normally open, or normally the actualetch
size layout shown in Fig. 4.
closed control circuit, or both, as shown Wiring is not critical, but
special prein Fig. 3.
cautions should be taken. First, be sure
there is ample separation between the
CONSTRUCTION
I, B, and G terminals. Second, use an
Since the basic unit is the same for epoxy -glass rather than a paper -base
all applications, let's put the thing to- phenolic copper -clad base board, (moisgether, and then we'll consider some of ture absorption in the latter material
the many applications. All components may cause erratic operation) Third,
be
are standard and readily available sure to remove all of the unused copper
through most electronics supply houses. during the etching process, for an al.

1966 Fall Edition

N.C.
SUPER - SENS
ARM

CII

BATT
+

N.O.

&®

C13

FOIL

Ti, T2. Door and
Fig. 5. Fire alarm circuit has fusible links Fl to F4, and thermostatic contacts
locations.
window contacts C1 to C3 and foil patterns make up burglar alarm. Place sensors in strategic

most invisible, microscopically thin layer
of copper can provide sufficient conduction to actuate the relay.
To
avoid accidental mechanical
damage, mount the relay last. Heat sink the transistor leads with a pair of
long -nose pliers to prevent heat damage
when soldering. The Sensitivity control
can be mounted on either side of board.
The completed board can be mounted
in a small Minibox as a self- contained
instrument, or in another piece of equipment, depending on the device's ultimate
use. Mount the board on spacers to provide air space between the board and
the cabinet. Power supply B1 can be
built in or externally connected.
A number of component changes can
be made to meet individual needs. General Electric GE -10 transistors will
serve as direct replacements for the

specified TI units. A Sigma 4F-1000 /SSIL relay can be used in place of the
JAICO type, although a new layout and
larger circuit board would be required.

If maximum sensitivity is needed at all
times, omit R.ç and connect R2 directly
to the Si, K1 junction.
A variety of power supplies can be
employed. The total current drain when
the relay is closed is only a few milliamperes, permitting the use of small
transistor -type batteries.
As might be expected, the instrument's ultimate sensitivity depends on
supply voltage, component tolerance,
and the gain of the transistors. With
the components specified in the Parts
List, the current sensitivity (for relay
closure) will vary between 0.15 and
0.45 pa., using a 9 -volt power supply.
(Continued on page 36)

(A) and (B) stay on for a
Fig. 6. An RC network can be added to make a time-delay relay. Circuits
switch is closed.
desired time after the switch is opened. "Turn on" is delayed in circuit (C) when the
32

ELECTRONIC EXPERIMENTER'S HANDBOOK

to
tes.
ling.
ARD
)K.

SEND CARD FOR RCA'S

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CAREER BOOK TODAY
YOUR CAREER IN A WORLD OF ELECTRONICS

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EE -96

350 West 4th Street, New York, N. Y. 10014

Institutes also offers
Classroom Training.
RCA

Catalog free on request.

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(Courses also available in Spanish)

CIRCLE NO. 24 ON READER SERVICE CARD
1966 Fall Edition

If higher gain transistors are used, the
overall sensitivity may be as great as
0.1 (or less) µa., while lower gain units
may provide a sensitivity of 0.75 µa.
APPLICATIONS

Burglar and Fire Alarm. An easily in-

stalled alarm system, suitable for a
home or place of business, is shown in
Fig. 5. It offers fire alarm protection
during the day, and both fire and bur-

glar alarm protection at night.
A break in any part of the external
series circuit will trigger the alarm.
A "push -to- test" switch (S3) , when depressed, will sound the alarm if the relay
circuit is in working order.
Fire protection is afforded by fusible
links Fl to F¢ and by thermostatic contacts T1 and T2 placed on ceilings in
strategic locations. Door and window
contacts Cl to CS, together with the foil
patterns, provide burglar protection.
Any combination of switches, contacts,
or links can be used, so long as the circuit forms a closed loop and the total
resistance of the loop isn't great enough
to prevent an adequate amount of voltage from terminal B to be applied to
terminal I. The sensitivity control can
be adjusted to compensate for loop resistance and battery conditions.
Switch S2 skips the door and window
detectors during the day, and Si, which
can be lock -protected, serves as a master
on /off control. If switching S2 from
night to day or day to night causes a
momentary but undesirable alarm, connect the Night side of the switch to the
switch's center arm. In this mode of
operation, Super-Sens is on all the time,
the relay is energized, and the normally
closed contacts are held open.
Occasionally, a latch or alarm-hold
type of operation is desirable . . . that
is, once the alarm is triggered, it sounds
continuously even after a break in the
loop is restored. In this type of operation,
the alarm can be reset only at the main
panel, which could be located inside a
locked cabinet. To build in the latch feature, connect a 1- megohm, 1/2 -watt resistor in series with terminal I and S2.
Adjust the Sensitivity control until the
relay just pulls in (silencing the alarm),
then back off slightly. Use the test
switch and control alternately, and adjust until the desired action is achieved.
36

Time Delay Relays. Controls which can
switch a circuit "ON" or "OFF" for preset or adjustable periods of time are used
extensively in experimental work, photography, laboratory tests, chemical
processing and manufacturing. Super Sens can be used in such applications by
adding a relatively simple "time delay"
accessory. Typical circuit arrangements
are shown in Fig. 6.
A 20-megohm resistor connected in series with a 0.25 -4 capacitor in Fig.
6 (A) sets up a time delay on the order
of 3 to 9 seconds, depending on the setting of the Sensitivity control. A momentary normally open contact switch
connected across the capacitor allows the
circuit to conduct when the switch is
pressed and released. The relay closes
and remains closed until Cl is charged
up and stops drawing current.
The circuit in Fig. 6 (B) permits a
wider range of control. When SI is de-

SHORT LENGTH
OF CO -AX

CLAMP

(A)

TANK

INSULATED
BUSHING

SUPER
SENS

(B)

METAL TANK

Fig. 7. Levels of low- and high -conductive liquids
can be monitored by easily made probes.
ELECTRONIC EXPERIMENTER'S HANDBOOK

-®I

®G

__J

SUPER -SENS

SUPER -SENS
B

MOISTURE
SENSOR

MOISTURE

(A)

SENSOR

(B)

Fig. 8. These circuits can be used to control humidifiers and lawn sprinklers. Just a drop of rain
on the sensor will release the relay in circuit (A). Circuit (B) can detect slightest trace of moisture.

pressed and released, Cl is charged by
the bias supply and then discharges
slowly through the instrument's input
circuit, holding the relay closed until Cl
loses most of its charge. The time delay
varies with R1's setting, and ranges from
about 25 seconds with RI set at 0 resistance to as much as 1 minute and 45
seconds when RI is set at 1 megohm. The
timing range can be changed if you use
different values for Cl and R1. The
larger the time constant (R1 x Cl) the
longer the time delay.
In Fig. 6 (C) , a delay in "turn on"
time takes place after the slide switch
is thrown. When S1 is switched to the
"ON" position, the relay does not close
until the current through R1 and Cl falls
off enough to reduce the voltage drop
across R1.
Liquid Level Control. Farmers, chemical
engineers, food processors, electroplaters, beverage manufacturers, industrial
plant operators and others need to check
or maintain liquid levels in large tanks
or vats from time to time. Super -Sens
can do an excellent job in such applications when used with suitable sensor
probes. Typical techniques are shown in
Fig. 7.
A short length of rigid coaxial cable
can be used as a simple liquid sensor
probe if clamped to the side of a tank.
If the cable's shield is connected to the
instrument's B terminal and the center
conductor to the I terminal, the relay
will close when the liquid reaches the
exposed lower end of the cable. Connections are as shown in Fig. 7 (A) .
If a metal tank is used, the sensor
probe may be a short length of conductor
mounted in an insulated, liquid -tight
bushing at an appropriate point on the
side of the tank, as illustrated in Fig.
,

1966

Fall

Edition

(B) If the liquid is highly conductive,
connections can be made to the I and G
terminals, with a jumper between the I
and B terminals. With these connections,
the Sensitivity control is adjusted until
the relay just closes. The relay will open
when the liquid level reaches the probe.
Other types of probes can be used, of
course, including insulated metal strips
cemented inside the tank or short parallel metal rods mounted on an insulating
block and attached to the tank. Regardless of the probe used or the type of
liquid handled, Super -Sens can control
pumps or solenoid valves, or activate remote signaling devices.
Rain Alarm. A standard moisture sensor plate will make Super -Sens serve as a
rain alarm. The sensor plate leads are
connected as shown in Fig. 8 (A) and
operate in the same way as the level control in Fig. 7 (B). Just a drop or two of
rain on the sensor plate is enough to
cause the relay to open.
Humidity Control. A modification of
the "rain alarm" circuit is shown in Fig.
8 (B) Here, the moisture sensor plate
is connected and operated in the same
manner as the circuit shown in Fig. 7
(A). With this arrangement, Super Sens' high sensitivity will respond to the
slightest trace of moisture and close the
relay. It can detect the small amount of
moisture condensed from a person's
breath and can be used, among other applications, for controlling a dehumidifier.
Lawn Sprinkler Control. If the moisture
sensor plate used in the "rain alarm"
and "humidity control" circuits is replaced by a pair of semi -insulated spiketype probes driven into the ground, Super -Sens will serve as an automatic lawn
sprinkler control. Its output terminals
(ARM and either N.O. or N.C. contacts)
7

are connected to switch an appropriate
solenoid valve in the automatic sprinkler
system.
Either the low- resistance connections
or high-resistance connections can be
used, depending on soil conductivity,
electrode (probe) spacing, and desired
soil moisture content. In any case, the
instrument's Sensitivity control can be
finely adjusted to achieve the desired
operating characteristics.
Acoustic Relays. Add an easily -built,
low -cost accessory, and Super -Sens becomes a sound -operated relay. Three
types of circuits are shown in Fig. 9.
In Fig. 9 (A), a low- impedance single -

button carbon microphone (Shure R10),
a 6 -volt battery, an 8 -ohm to 500 -ohm
output transformer (Argonne AR-164),
a 1N34A general -purpose diode, and a
2 -4, 15 -volt electrolytic capacitor apply
a positive -going signal to energize the
relay.
A single-transistor amplifier, in Fig.
9 (B) enables the use of a high- impedance (Philmore M-55) , or a low- impedance carbon microphone. A 1- megohm
resistor (R1) is used with high- impedance microphones and a 47,000 -ohm resistor for low impedance types. The Sensitivity control is adjusted until the relay
closes and is then backed off slightly.
Thereafter, a sudden sharp sound will
cause the relay to "latch" open.
A crystal microphone cartridge, or a
magnetic headphone element can be used
as a microphone with the circuit shown
,

Fig. 10. Radio control can be achieved with simple detector. Tune Cl, Li to desired frequency.

in Fig. 9 (C) The diode and transistor
are the same as in the previous circuits.
The Sensitivity control is set in the
same manner as in the circuit in Fig.
.

(B).

The acoustic relay circuits shown here
are moderately sensitive, requiring a
fairly loud signal for operation. Where
extreme sensitivity is needed, Super Sens can be coupled to a 3- or 4- transistor audio amplifier. The hookup would
be the same as in Fig. 9 (A) .
Radio Control. Super -Sens can be operated by remote radio signals provided
that a suitable control circuit is connected to its input terminals, as shown

in Fig. 10.
The values of tuned circuit LZ and Cl
are chosen to resonate at the desired
control frequency. A general-purpose
(Continued on page 141)

Sound -actuated relays can be made. If microphone is low- impedance type, use circuit (A);
high- impedance pickups work well in circuit (C); a low- or high -impedance unit can be used in circuit (B).
Fig. 9.

ELECTRONIC EXPERIMENTER'S HANDBOOK

FREEZE
MOTION

WITH

SOUND

Like to

try your hand at the

fascinating field of high -speed

photography? All it takes
a

Sound -actuated unit (lower right) flashes strobe as
first balloon, hit with dart. bursts. Insert shows
drop of milk hitting black background; mike was 10"
away, sensitivity of trip unit reduced to just half.

simple trip unit and a strobe

By ROY E. PAFENBERG

HAVE YOU ever wondered just exactly how glass breaks, liquids splash,
balloons burst, or a ball bounces? The
electronic flash trip unit featured here
will answer these and a host of other
intriguing questions that can only be
explored through the use of high -speed
photographic techniques.
Adaptable to almost any camera and
electronic flash, this simple sound -actuated unit provides a means of obtaining
1966

Fall

Edition

unusual and striking photographs. The
experimenter, research worker, or technician will find it a valuable low -cost
laboratory accessory, and the student
can use it as the ideal basis for a
science project and /or science fair exhibit.
Although the fact is not widely known,
the 1 /1000 to 1/2000 second flash duration of the conventional hobby or professional electronic flash unit is fast
39

Trip unit fits neatly in 2%" x 21/4" x 5"
box; since layout is compact, it's best
to copy author's model. Strobe light is
the inexpensive unit described in text.

PARTS LIST

enough to capture all but the highest
speed events on film. The problem is
one of timing. With the method described here, sound produced by, or
associated with, the event to be photographed is used to trigger the electronic
flash. Since the camera shutter must be
open, photography is done in subdued
lighting or in a darkened room. After
the flash captures the high -speed event
on film, the shutter is manually closed.
The exact instant the flash occurs
relative to the noise that actuates it
can be controlled by the way in which
the microphone is positioned. Since
sound travels relatively slowly, placing
the microphone close to, or away from,
the object will introduce an adjustable
time delay.
Construction. In essence, the flash trip
unit incorporates two stages of audio
amplification (a single 12AT7) that
triggers the 2D21 thyratron in response
to sounds picked up by the microphone
see "How It Works," page 42 ) Since
a thyratron acts like a switch or short circuit when it conducts, it fires a flash
unit connected to J2.
Although the sound -actuated trip unit
may take any form that gives due consideration to layout, wiring, and the
shielding requirements of high -gain am(

Cl, C2,

C4- 0.005 -14.,

500 -volt ceramic disc

capacitor

C5- 10 -µf., 25 -volt electrolytic capacitor
C6-20 /20 -µf., 150 -volt dual electrolytic capacitor
D1- 500 -ma., 400 -P1V silicon diode
11, 12 -Phono jack, single -hole mounting type
R1- 2.2-megohrn, % -watt resistor
R2, R5- 220,000 -ohm, ;4-watt resistor
C3,

500,000 -ohm potentiometer, audio taper,
with s.p.s.t. switch S1
1000 -ohm, Y2-watt resistor
R4,
R6- 470.000 -ohm, % -watt resistor
R8-47,000 -ohm, ;-watt resistor
R9 -27 -ohm, V2-watt resistor
R3

ñ7-

R10-2200-ohm, ;4-watt resistor

SI-S.p.d.t. switch;

part of R3
TI -Power transformer: primary, 117 volts;

secondaries, 125 volts a 15 ma., and 6.3 volts
(rig 0.6 amp. (Staneor PS -8415 or equivalent)
V1 -12AT7 vacuum tube
V2-21)21 thvratron tube
1
x 2',-.i" x 5" Minibox
1
-pin miniature tube socket with shield
1
-pin miniature tube socket with shield
Crystal lapel microphone (or similar)
Misc. -Knob, terminal strips, solder lugs, hardware, grormnets, a.c. line cord, wirr, solder, etc.

-2W
-7
-9
1-

plifier circuits, the prototype unit is
neat, compact, and rugged. The two
tubes (V1 and V2) and tab -mounting
filter capacitor C6 are mounted on top
of the 21/4" x 21/4" x 5" Minibox used
as a chassis, while the power transformer fits inside and as close to the back as
possible. Sensitivity control R3 and mike
input jack J1 are at the front of the box;
output jack J2 (for connection to the
ELECTRONIC EXPERIMENTER'S HANDBOOK

{

VIA

vlB

125T 716

2021 6

.005yf.

5,7

y f.

J2(

STROBE

SHUTTER
CABLE

¿5¿R1

SM G

220K

S00

220

25V

R9
2711

105 í

470

IOUf.

25V

47K

RIO

2.2K

TI
IW

C6A

C6B

150V

20yf.

VI
4

Two stages of audio (Vla and

Vlb) amplify mike input to trigger 2D21 thyratron (V2).
RI

RIO

R5 R6 R7

Locate T1 as close to the back of box as possible; note location of tube sockets, and
mounting hole for C6. Jack J2 (for strobe connection) is hidden at rear of box.

strobe shutter cable) and the a.c. line
cord entry are at the rear.
Two two -lug terminal strips are used
one for mounting silicon diode DI and
the other for terminating the a.c. line
cord. Chassis ground connections are
made to soldering lugs installed under
the tube socket mounting screws. Use
insulated hookup wire for connecting
the a.c. switch and filament circuits;

1966 Fall Edition

the balance of the wiring can be done
point -to -point using component leads.
It's a good idea to use spaghetti on the
leads as required to avoid possible
shorts.
With the components mounted and
wired, carefully check your work before
installing the tubes and applying power.
Check to see that the tube filaments
light, and measure the B -plus at the
41

+300V

FLASH TUBE
RI

4MEG.

TRIGGER

TRGNçç,
10001f.

;

.020

TO
3 MEG?

CAMERA

SHUTTER
CONTACTS

-300V

Flash shutter contacts are polarized. Check with a
voltmeter, and connect positive side to V2's plate.

R1O-C6b. It should be slightly in excess of 150 volts. Finally, check
for a reading of approximately 3 volts
at pin 2 of the 2D21. Secure a crystal
microphone such as the Lafayette Radio
99 G 4510 and terminate its cord in a
phono plug.
The Flash Unit. The small schematic on
this page is a simplified diagram of a
typical electronic flash. Normally, the

junction of

camera shutter discharges capacitor C2
-charged through isolating resistors R1

Mike was one foot away for photo of golf ball falling into bowl of water. Fracture pattern of bulb is
seen below; despite its looks, it exploded violently.

and R2- through the primary of trigger
transformer Ti. The very high voltage
pulse produced by TI's secondary is
applied to the external starter anode
of the flash tube, partially ionizing the
gas inside it. The energy stored in Cl
flows through the ionized gas, producing
an intense flash of light. In this application, the shutter leads from the flash unit
are connected to J2 of the trip adapter.
The cord and connector are wired so
that the positive terminal from the flash
is connected to the 2D21 plate.
Almost any electronic flash unit will
work with the trip unit, so if you already own one or can borrow one, you're
in business. If you must buy one, remember that a.c. power will be required

HOW IT WORKS
As shown in the schematic on page 41, the in-

put signal from a high -impedance crystal microphone is amplified by a conventional 12ÁT7 (V1)
twin- triode audio amplifier. A sensitivity control,
R3, is provided between the first and second
audio stages, and serves to determine the input
signal level required to trigger V2, the 2D21
thyratron trigger stage. This stage serves as an
electronic switch to close the contacts of the electronic flash unit. The firing circuit voltage developed in the flash is used as the plate supply
voltage for the 2D21. Resistance network R7 -R8
biases the cathode of the 2D21 to a positive value
of approximately 3 volts. When the positive peak
of the audio signal applied to the control grid of
the 2D21 appreciably exceeds the cathode bias,
the tube conducts or fires, triggering the flash unit.
The power supply is entirely conventional. The
6.3 -volt winding of Tl supplies filament voltage
to V1 and V2, while the output of the 125 -volt
winding is rectified by D1 and filtered by C6 -R10
to supply bias voltage and 150 volts of B -plus for
the audio amplifier plate circuits.

for the trip unit, so it would be foolish
to pay extra for a battery -operated
flash. Small but adequate a.c.- operated
flash units are quite reasonable-the
unit shown in the photo on page 40 is
available from Spiratone, Inc., 135-06
Northern Blvd., Flushing 54, N.Y., for
$12.95 plus postage.
Take a close look at the camera shutter on your flash unit, and secure an
extension cord to fit it. Cut the camera
fitting off of the other end, strip the
wires, and turn the flash unit on. Touch
a voltmeter set to a high range to the
bared leads, and observe the polarity.
Connect the positive lead of the cord
(Continued on page 142)
ELECTRONIC EXPERIMENTER'S HANDBOOK

Why depend on batteries
when you can get
all the energy you need
free of charge? How?

LET THE SUN POWER YOUR PORTABLE
By HOMER L. DAVIDSON

YOU CAN USE the sun to power your
small transistor radio -or, if it's

raining, you can use a 100 -watt light
bulb. The only other element you really
need is International Rectifier Corporation's "Solar Pac," which can be hooked
up to charge the radio's battery, or to
operate the radio, or to do both. The
"Solar Pac" comes in two models:
SP5C26C (4.5 volts at 26 ma.) and
SP9C13C (9 volts at 13 ma.) , and is
available from electronic supply houses
for $9.95.
There are many ways you can connect
the solar pack to your radio. You may

1966

Fall

Edition

want to add a switch (see schematic) to
provide a choice of either solar or battery power. Or you can simply connect
the pack's 6" leads to the battery connections inside the radio. You can even
use the solar pack as a plug-in supply
by connecting an earphone jack and
cord to the pack, removing the existing
wires from the radio's earphone plug,
and running a pair of wires from the
plug to the battery connections.
Mounting the pack is no problem as it
is supplied with mounting pads which
can be attached easily to any radio case

Hook up a couple of alligator clips to the leads of
the solar pack to make easy -to- connect power supply.

SOLAR PAC
TO
RADIO

SLIDE SWITCH

Li! IET
9V

Your portable can be switched to either battery or
sun operation by adding a slide s.p.d.t. switch.

or cover. But for a more permanent installation, place the pack against the
plastic back of your radio, outline its
shape with a scribe, carefully cut out
the required area with a knife -tipped
soldering iron or jeweler's saw, fit the
pack into place, and seal around the
edges with cement.
If you plan to use the solar pack as
a universal power supply for more than
one radio or transistor project, add
alligator clips to the pack's leads for
easy handling. Should circumstances require lower voltages than that provided
by the solar pack, insert an inexpensive
100 -ohm potentiometer in series with the
output to reduce the voltage.
Once you know how much resistance
you need in a given circuit (by measuring the pot's resistance in the circuit),
you can substitute a fixed resistor. Add
a resistor only when no battery is in
the circuit, and only when the unit is
to be used out -of- doors. A resistor is
not required indoors as you can move
closer to or further away from the light
source to obtain a desired voltage. -J-

By connecting the solar pack in parallel with the

battery, you can charge the battery while operating
the radio, or run the radio without the battery.

The earphone jack connections of your transistor radio can be modified to accommodate the solar pack.

The solar pack can be cemented to the radio case,
and the leads can be slipped under the case flap.
ELECTRONIC EXPERIMENTER'S HANDBOOK

BUILD...
THE $UPERX PULSE POWER

PACK FOR NO RAILROAOT G
...ail.' pet the feel ,)r the rezl thin j

By KOODROW POFE
Design Er,g'ne3r,
Z_ollins Radio Canpcny

?ailroad Engineer, can
atnrt your 10 o without jamping
to 1.) _cole miles psr hour? You can, you
know, without ecui ping your .oconDtive with eywtee.s Dr high gear ratios.
How? Easy . . just build and use a
new transistor tl-_rcttle power pack on
your pike for the ulïimate in mo lei railroading
With it ycu get pulse *Dower for
smoother stall -free starts, and your loco

S AY

Mr. Mocel

yoga

can crawl, or hi -ball, or couple -without
crashing. You also get lots of power to
operate signal lights, switch machines,
or other accessories
all with circuit
overload protection.

...

Just What is Pulse Power? To understand pulse power, you must first understand the nature and operation of the
conventional d.c. power pack. Your loco
is equipped with a tiny d.c. motor that
operates off power supplied to the tracks
by the power pack. When you man the
throttle, which is nothing more than a
rheostat, you are regulating the voltage
across the track, and hence the motor

speed.
Assume your throttle is turned all the
way down and your loco is sitting still.
You now begin to turn up the throttle,
gradually increasing the voltage applied
across the tracks. But notice, your loco
does not start immediately; it waits
until the proper operating voltage is
reached, and until all magnetic and
mechanical locking has been overcome.
By this time the voltage is too high for
a slow, smooth start, so the loco lunges
ahead.
Figure 1 shows, graphically, how late
a typical loco might start after you begin cranking up the throttle. You will
note that a certain minimum voltage
must be reached to overcome the inertial
load on the motor before it will even begin to turn.
Now let's assume you are using one
of the latest power packs to hit the
scene -you know, like the one we're telling you about right now -your loco will
start to crawl, like real trains do, the
moment you hit the throttle. How come?

Fig. 1. The ordinary power pack is nothing more
than a full -wave rectifier whose output is a pulsating d.c. voltage with peaks that look like the waveform above. For most locos, the average power required for starting is much too high for a smooth
start, and the trains pull out with a sudden jerk,
and at a speed not akin to real railroading.

Well, with pulse power you get maximum voltage in the form of narrow
pulses the instant you flip the primary
power switch. This is shown, graphically, in Fig. 2. Here the average power
consumed by the motor is a direct func-

PARTS LIST

Cl-1000 -µf.,

capacitor
15 -volt electrolytic
(Sprague TVL 1165 or equivalent)
C2, C3- 0.47 -µf., 35 -volt capacitor (Kernet
KR47C35K or equivalent)
C4- 1 -µf., 35 -volt capacitor ( Kemet K1C35K,
or equivalent)

Dl, D2, D3, D4, D6,

D7- 1N2069

silicon diode,

or equivalent)
D5-1N276 diode, or equivalent

FI -1-ampere fuse
11

-#47 lamp, 6 -8 volts, 0.15 -amp.
-12 -volt, 1.2 -amp. automobile dome lamp,

12, 13

or equivalent (two required)
Q1, Q2, Q3, Q7 -2N404 transistors
Q4, Q8- 2N1382 transistors
Q5, Q6- 2N456A transistors
-watt resistor
RI,
2200 -ohm,
R2,
22,000-ohm, % -watt resistor
R4 -Not used
6800 -ohm, ,A-watt resistor

R6R3R5R7- 10,000 -ohm, 2 -watt carbon
linear taper
R8-390 -ohm, 1/z -watt resistor

potentiometer,

R9, R15, RIO- 1000 -ohm, % -watt resistor
R10, R14- 10,000 -ohm, % -watt resistor
R11-10 -ohm, 1/2-watt resistor
R12- 1000 -ohm, 2 -watt carbon potentiometer,
linear taper (with switch S3)
R13- 330 -ohm, V2-watt resistor
D.p.s.t. slide switch
S2- S.p.s.t. slide switch
S3- S.p.s.t. switch (mounted on R12)
S4- D.p.d.t. slide switch
TI -Power transformer: primary, 115 volts; secondary, 12.6 volts with center tap, (Stancor
P -8130, or equivalent)
Cabinet (Bud AC- 1613 -A or other suitable
sized cabinet)
Alisc- Fuse clip; pilot light holder; red lens
(Dialco series 1006); binding posts (4
red, 2 black); throttle knob (Raytheon
175- 6 -2G); crawl adjust knob (Raytheon
90- 3 -2G); power transistor mounting kit (Motorola 31K -15)

SI-

I-

-2

Fig. 2. The pulse power pack produces a train of
narrow pulses in addition to variable d.c. power.
The pulses are fully visible when the throttle is
turned down, but disappear gradually as the throttle voltage builds up to full power. Instant rise

of pulse from zero to maximum provides immediate
power to operate train when crawl knob is turned up.
ELECTRONIC EXPERIMENTER'S HANDBOOK

251382

254564

FM.

NOTE
AT

4LL 5E5J57055 ±10X1/25

2 N4 INTENTION4L.'.r OMITTED

CONTROL <<

-oo6Ò66boo
-

PJN,

Fig. 3. Crawl control R7 adjusts pulse width to give desired crawl speeds when S2 and S3 are turned
on. Throttle R12 is part of a voltage divider that drives emitter followers Q7 and Q8 with varying d.c.

tion of the pulse width which you adjust with a crawl control. This varies
the circuit RC time constant.

i2v

ov-

i2v
1

_L_
3v

Fig. 4. Pulses rise to maximum as soon as power
is turned on (a), providing immediate train start.

Crawl knob adjusts pulse width for varying train
loads and desired crawl speeds. Throttle adjusts d.c.
at emitter of Q8 (b) to run train at desired speeds.
With throttle turned down (c), pulses appear prominently, then fade away as d.c. is turned up.
1966

Foll

Edition

How It Works. From Fig. 3 it is apparent that pulse power, which makes
your trains run like a dream, calls for a
rather sophisticated circuitry. Let's give
the circuit a once -over and see what we
mean. First, we have transformer T1
stepping down the 117 -volt a.c. primary
power to approximately 12.6 volts. This
12.6 -volt supply branches off to jacks
J1 and J2, where it is available to operate switch machines, signal lights, and
other accessories. Some of this power is
also tapped off and applied to the bridge
rectifier circuit (D1 through D4), from
where it will eventually operate your
trains.
The 6 -volt #47 pilot lamp (11), wired
from the center tap to one side of the
transformer secondary winding, is merely an indicator to tell you when the
power is on. You can break down the
rest of the power pack into its pulse
forming and control circuits. the variable d.c. circuit, and the short -circuit
protection circuit. If you care to, you
47

can throw in polarity switch 84 (forward
and reverse) for good measure.
The Pulse Circuits. These circuits begin with Q1 and Q2 which comprise a
free -running multivibrator. The collector
of Q2 puts out a 60 -cycle square wave
which is fed through S2 and S3 to pulse
generator Q3 for conversion to narrow
pulses. These pulses are then amplified
by Q4 and appear as shown in Fig.
4(a). CRAWL ADJ potentiometer R7
adjusts the pulse width to suit varying
train loads and desired crawl speed. The
CRAWL ON -OFF switch (S2) is used to
disable the crawl feature, if desired.
Switch S3 is ganged to the main throttle
so that it cuts off the pulses when the

throttle is turned all the way down to
where you hear a "click."
Variable D.C. Circuit. In the variable
d.c. function generator circuit, R12 and
R13 form a variable voltage divider, the
output of which is fed to emitter followers Q7 and Q8. The emitter followers
provide a low impedance source for the
voltage. The output voltage at the emitter of Q8 is variable from about 3 volts
to 12 volts, as shown in Fig. 4(b), depending on the setting of R12, the speed
control potentiometer.
Diodes D6 and D7 are used to mix the
two functions (pulse and variable d.c.)
together. The pulses and variable d.c.
are fed to emitter followers Q5 and,.Q6

5/8"

3/8 "DIA

3/8"
DIA

1/6"

I-3/8"

DIA

1/4
DIA

3/8"

I/4"

DIA

3/8
DÌÁ

s/e"
1

Fig. 5. This layout and accom-

panying dimensions are valid
only if the recommended Bud
cabinet is used. Lay out, drill,
and punch all holes as shown.
If you use another cabinet,
this layout can still serve as
a guide. The transistor mounting holes remain the same, regardless of cabinet dimensions.

1/2'X I/4'

7/16
DIA

1/4"

I-3/4'
rn

I-7/Ifi'-.i

3/8"

DIA

3 -3/4'

7/8"

-a

(k.1/8.

I/2'7(1/4'

DIA

11/16"

1/8
DIA

DIA

ELECTRONIC EXPERIMENTER'S HANDBOOK

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ampere of current from the power
pack, the lamps begin to glow and their
filament resistance goes up rather sharply to form a protective load for the
power pack. Thus, even if the output
leads at J3 and J4 were to be shorted
together, no damage would result to the
power pack. But because one of the
lamps is mounted under the red jewel,
you would know there was an overload
when it lit up.
The FWD -REV switch (Si) is an
ordinary d.p.d.t. switch wired to reverse
the polarity of the d.c. voltage as it is
flipped from one direction to the other.
1

Rear view of transistor power pack showing location
of power transistors Q5 and Q6. Be sure to use a
rubber grommet to protect line cord from damage.

which provide a high current output.
Their output waveform is as shown in
Fig. 4(c).
Short Circuit Protection. Lamps 12
and 13 in the emitter circuit of Q6 pro-

tect the entire unit against accidental
short circuits or overloading. Together
with a red jewel mounted on the front
panel, they also double as a track short
indicator. These lamps are of the ordinary 12 -volt auto dome light type,
each rated at 1.2 amperes. Putting them
in parallel, however, increases the circuit capacity to 2.4 amperes.
When the filaments are cold, the lamps
exhibit a very low resistance, and therefore act like a piece of wire. When your
loco or other load begins to draw about

Construction. Assuming you have obtained the Bud cabinet called for in the
Parts List, you now proceed to lay out
and drill the holes as shown in Fig. 5.
After drilling all holes and deburring
them, mount the power transistors on
the back panel, making certain you use
the mica strip and washers supplied
with the mounting kit to insulate the
transistors from the case.
Figure 6 shows the general layout of
the wiring and other circuit components.
Electrolytic capacitor Cl should be
wrapped with electrical tape to insulate
it from the case. Notice that it is
mounted with a plastic clamp.
The circuit board is made from a
piece of 23/4" x 63/4" Vectorbord. Observe the location and mounting position
of 11 and 12. Bring out long leads to the
panel mounted components, and use a
(Continued on page 137)

With bottom plate removed, laced wiring
harness can be tucked away to one side
during repair or maintenance of the unit.
The component circuit board is supported
with metallic or insulated standoffs. To
install the line cord, thread free end
through grommet at rear of cabinet. Separate ends of cord back 12 inches and tie
into a knot to take up any strain on cord.

STANDOFF

CIRCUIT
BOARD

ELECTRONIC EXPERIMENTER'S HANDBOOK

BUILD THE LI'L DUSKER

This light sensor turns your lights on
at dusk, and off at dawn,
automatically- without a timer
By DON LANCASTER

HERE'S

A CLEVER, useful, and economical photoelectric controller you
will want to build. Li'l Dusker, the "light
watchman," will earn its keep turning on
lights for you in dark driveways, stairways, and halls at night, and then turning them off at dawn when they are no
longer needed. And while you are away
from home, Li'l Dusker will turn on that
important "there's somebody home" light
that will deter all but the most persistent

intruder.
But Li'l Dusker has many more talents. It can serve as an automatic door
opener, or a light- operated relay. And
if you want an automatic flasher with
adjustable frequency, or a low -cost touch
control for a desk or table lamp, call on
Li'l Dusker.

About the Circuit. Although Li'l Dusker
acts like a magician, the circuit is really
1966

Fall

Edition

a simple one, as Fig. 1 shows. It is just
a d.c. power supply (R1, Dl, and C1)
and a limiting resistor (R2) , a cadmium
sulfide photocell (PC1) and a d.c. relay
(K1) all connected in series.
The cadmium sulfide photocell has a
low resistance in the presence of light
and a high resistance in darkness. This
,

characteristic enables the Dusker to tell
night from day. Therefore, as light increases with the break of dawn, the
photocell resistance decreases, increasing
the current in the relay coil, and causing
the relay to pick up.
The relay sensitivity -the light intensity that will cause the relay to pick up
-is established by the value chosen for
the current -limiting resistor (R2) . The
circuit application determines which set
of relay contacts is used. For dusk -todawn control, the NC ( normally closed )
51

LINE

SOI

100W

FEET

CORD

MAX. LOAD

WINDOW

(A)

1. For dusk -to -dawn control, connect load
circuit to the NC relay contacts; for photocell relay application, connect load to the NO contacts.

SILL

BX OR ROMEX

Fig.

PARTS LIST

electrolytic capacitor
CI-4 -µJ., 250 -volt-P1V
rectifier (RCA 40265

D1- 130-ma., 400
equivalent)
K1- Phillips -Advance

#1524-1C relay, 24 -volt,

1100-ohm coil, 1 amp contacts (Newark 60 F
1749 or equivalent)
PC1- 200 -volt, % -watt radium sulfide photocell
(RCA 4403- Allied Radio 7 Z 435 or Polaris
Maj -1- Allied Radio 7 Z 565)
PL1 -100 -volt, 2 -pole standard plug (Amphenol
61 -M or equivalent)
R1 -15 -ohm, Y2-watt resistor
R2- 10,000 -ohm, 2 -watt resistor
S01 -110 -volt, 2 -pole universal receptacle (Amphenol 61 -F or equivalent)
1--Case made from Millen 74400 octal base and
shield (Newark 40 F 734)
Misc. -"Pop" rivets (4), 17 "-square piece of
1/16" single -sided PC board, funnel eyelets
for PC board (24), %" x %" aluminum sheet
(2), 2" x 11/2" plastic sheet or film, glue or
sealant, wire, solder

contacts are used; for door -opening operation, the NO (normally open) contacts are employed instead.
Construction Pointers. Li'l Dusker can
be encased for mounting on a windowsill
or anywhere outdoors, and can be plugged
into a standard wall receptacle or octal
socket. In Fig. 2(A), the Dusker has its
own line cord and is mounted on a windowsill where it can "look" outside. For
general outdoor use, BX, ROMEX, or
other approved wiring can be brought in
through the top of the unit. To make
the Dusker weatherproof, the outlet can
be recessed and the entire unit mounted
as shown in Fig. 2 (B) in a sheltered
area.
If Li'l Dusker is to serve as a door
opener, the case is used as it comes, with
only slight modification. You can then
make a companion light source, perhaps
with a 6.3 -volt filament transformer and
an automobile 6 -volt lamp bulb and socket. You might want to add a low -cost
52

(B)

RECESSED SOCKET
OUTDOOR
LIGHT

SOURCE

_OCTAL

(C)

PLUG
INTERRUPTED BEAM CONTROL

(D)

PLUG

Fig. 2. Select one of these four case configurations
for the Dusker. For table or desk lamp touch
control applications, the outer casing is not used.

lens to focus the beam and thus provide
for greater separation between the
Dusker and the light source.
For touch control applications, you
can omit the case altogether and mount
the circuit directly inside the base of a
table or desk lamp.
Construction Details. Using a Millen
#74400 octal base and shield, cut the
case for the plug -in configuration following the details given in Fig. 3. In addition, two mounting brackets will be required. These can be made out of a small
strip of aluminum sheet cut as shown in
Fig. 3 (D) . Drill the holes first, then
ELECTRONIC EXPERIMENTER'S HANDBOOK

bend the bracket into shape using long- * /16" DRILL(4) MATCH
TO BRACKETS
nose pliers, or a vise, if one is available.
DO NOT EYELET
You will also need a piece of tough
UNTIL ASSEMBLED
plastic film to serve as a protective window for the photocell. Acetate, Mylar,
I)
or anything similar will do. Avoid using
brittle material that will crack or break. *USE 5/64'
The parts are mounted on a small DRILL (5)
DO NOT -10.
(1%- inch-square) printed circuit board
EYELET
*
laid out, drilled, and cut as shown in
Fig. 4. Eyelets are used in the holes
where shown to give the circuit board
some extra ruggedness. The aluminum
brackets are riveted to the circuit board
I

/16 "DRILI(15)SET
WITH
UNNEL EYELETS
I

-3/4"

3/4"

Fig. 4. This is foil side of printed circuit board.
Numbers in parentheses indicate holes required.
SHIELD

3/4"
°

3/4"

FOIL SIDE

3/4"
1/8° DRILL(2)
MATCH DRILL
TO ORIGINAL
BASE HOLES

PUNCH
I

/8'

DRILL
(2)

(

J
PLASTIC

ORIGINAL UNIT)

I/4-*-1

BASE
(IF NOT REQUIRED
DISCARD OCTAL PLUG
AND MTG. FROM

WINDOW

(B)

I/8"DRILL

.(21

I/2"-H

1-9/64" PUNCH KEYED
1-5/32" ROUND

ALUMINUM BRACKET
(2 REQUIRED)
8

1/16"
DRILL

(2)

1/4
7/8

(D)

Fig. 3. The base and shield of case are cut and
punched as shown. Then they are finished with
lacquer or paint, or are anodized. The two brackets at bottom are made from 1/32 -inch aluminum sheet. Window is made from heavy plastic
film such as Mylar; avoid using brittle material.
1966 Fall Edition

Fig. 5. Here's the component layout. Photocell PC1
is mounted on the foil side of the circuit board as
shown in (A). All of the other parts are mounted
on the bare side of the board as shown in (B).

in the locations indicated in Fig. 5, again
using eyelets.
The photocell is glued to the back of
the printed circuit board with silicone
53

9lIImIUIIAIIImllllnm1u1lllRnw
ollllnllmlllll

luullu0l11111u1

immateliMMAMMINI

ALUMINUM
BRACKETS
EYELETED TO

IlIIlIIfiNU
N

S01

BOARD AND
POP RIVETED
TO CASE

7PO

1011,

PLASTIC WINDOW
GLUED AND THEN

RIVETED
PLACE

ducing the amount of light reaching the
photocell. A filter made of colored cellophane, Polaroid material, or tinted acetate placed over the light window will
work well.
Once you have obtained just the right
sensitivity for the particular application,
complete the assembly by "pop " -riveting
the circuit board and bottom plate to the
case. Once pop- riveted, the Dusker becomes tamperproof and there's no way
to take the case apart without using an
electric drill. If it becomes necessary to
open the case again, use a ', " high -speed
bit to drill out the rivets.
Once assembled, operation of the
Dusker is a snap. Just plug it into a
convenience outlet, plug the load or lamp
into its receptacle, and away you go.
Special Applications. For operation as a
light flasher, the Dusker must be wired
as a dusk -to -dawn control. This makes
it essentially an oscillator with negative
feedback. The Dusker must be positioned
25-100W
BULB

COM
117 VAC

S0 -60C PS
LINE CORD

Fig. 6. After all the parts are preassembled on
the circuit board, and the unit has been fully
wired and tested, install the plastic window and
pop -rivet the aluminum brackets to the case shield.

rubber sealant (Fig. 6) The plastic
window is glued in place and allowed to
dry before the aluminum brackets are
riveted on.
Before making connections to the relay, refer to the Special Applications
section at the end of this article to determine the proper relay terminals to employ. In general, the NC contacts are
used when decreasing light must energize the load, and the NO contacts are
used when increasing light is to energize
the load.
Checkout and Final Assembly. Before
final assembly, you will want to check
out the circuit to make sure it works the
way you want it to. For this you can
use a flashlight or other suitable light
source. If it becomes necessary to change
the sensitivity of the unit, change the
value of R2 as necessary. But you can
decrease the sensitivity by merely re.

PCI

Le,

NOTE

SI IS

SPST

MICROSWITCH

Fig. 7. This low -cost touch control circuit can
easily be wired to any desk or table lamp by adding
a microswitch across PC1. To turn on lamp, touch
Si gently. To turn off lamp, bring hand near PC1,
shielding it from light. For proper operation, PC1
must be shielded from other strong light sources.

in such a way that the light shines in its
"eyes." Initially, when the light is off,
the photocell turns it on: the Dusker

"sees" it and turns it off again. This
cycle can go on as long as the unit is
plugged in. To adjust the on-off rate
(frequency), adjust the amount of light
that gets fed back. Changing the bulb
size will usually do the trick.
For "touch control" operation, mount
the circuit board (less case) in the base
of a lamp so that only the lamp light
(Continued on page 139)

ELECTRONIC EXPERIMENTER'S HANDBOOK

BUILD

SOLID -STATE SLOT CAR
SPEED CONTROL
Turn your slot racing car into a
mighty fast cat, yet maintain absolute
speed control every inch of the way

S IMPLE

TO BUILD, inexpensive to
own, a dream to operate! We're

talking about a transistorized slot racing speed controller that lets you run
your model racing car almost like the
pros do at Le Mans. From the instant
you start, all the way through the sloping, winding, pretzel- shaped speedway,
till your car zooms across the finish
line, you'll enjoy the full pleasure of in-

By JAMES FISHBECK

stant and complete control over your
racing car's speed and performance.

Because the push- button type of speed
controller controls the car's speed by
applying a series of pulses, the acceleration is in steps, rather than through a
smooth, linear variation from low speed
to top speed. This new solid -state speed
controller uses a carbon potentiometer
wired to a d.c. amplifier to provide a

smooth variation in resistance, which
gives your car finger-tip speed control
and all the power it needs to perform
with style and class.
How It Works. The speed controller
consists of a dual amplifier and two
separate potentiometer throttles -one
for each amplifier (Fig. 1) . Each amplifier output drives a separate lane of
the speedway.
Potentiometer R1 is shown connected
across the d.c. power pack supplied with
the racing car set. Its center tap is wired
to the base of emitter follower Qi, thereby controlling the output of this stage.
The output of Q1 is directly coupled to
the base of Q2, the power output stage,
which supplies power to the track
through Fi. The other amplifier operates in the same way.
Since the power pack is nothing more
than a step -down transformer feeding
into a full-wave rectifier, it puts out an
unfiltered d.c. which is quite suitable to
run racing cars. Because the transistor
amplifiers do not perform well with pulsating d.c., a filter capacitor (C1) is put
across the power pack output to filter
out the ripples before they get to the

amplifier.
If you operate a speedway with more

Fig.

than two lanes, you can build a separate
amplifier for each lane with no degradation in performance (as long as you
don't exceed the wattage rating of the
power pack) . Just be sure you use identical components in all the amplifiers and
speed control potentiometers.
Construction. Except for the two speed
controller potentiometers, all parts, including the power pack supplied with
the slot racing set, are mounted on a
2" x 5" x 7" aluminum chassis (Figs.
2 and 3 ) The two speed controller po.

PARTS LIST
500 -µf., 25 -volt electrolytic capacitor (1
null Dubilier BBR 500 -25 or equivalent
Fl, F2-1-ampere fuse (Littelfuse 3AG)
(.1

Ql, Q3 -2N109 transistor
Q2, Q4 -2N554 transistor
RI. R3- 5000 -ohm carbon potentiometer, linear
taper (IRC -CTS 011 -114 or equivalent)

R4- 1000 -ohm,

1 -watt, 10% resistor
screw -type terminal strip
(Cinch -Jones 17 -4 or equivalent)
s' 5" .c 7" aluminum chassis base (Bud
1 -2"
AC-402)
c 2
.e I ! s" aluminum Miniboxes
Pod CU-3017A)
Misc.- -Two miniature fuse posts (Littlefuse
342014), multiple-conductor intercom cable,
power pack from existing racing set, two
knobs, mounting hardware, transistor sockets.
rubber grommets, hookup wire, etc.

R2,

TS1- 4- terminal

this two -lane

speed controller, each channel is a mirror image of the
other. The speed control potentiometers are mounted
on individual chassis, and
are connected to the amplifier circuit by long cables.
For compactness, mount the
slot racer power pack on top
of the amplifier chassis.

ELECTRONIC EXPERIMENTER'S HANDBOOK

Large chassis allows plenty of room for
mounting the power pack. Use mounting kit for Q2
and Q4, and be sure to mount Ql and Q3 on sockets.
Cables at sides of chassis go to speed controllers.
Fig. 2.

tentiometers are mounted on individual
31/4" x 21/s" x 11%" aluminum Miniboxes.
After drilling, punching, and deburring
the chassis, insert rubber grommets
through all cable entrance holes.
If your power pack is too large to fit
on the size chassis recommended, get a
bigger chassis. The size suggested happens to be convenient, but you have
complete freedom to select the packaging that best suits your needs. Incidentally, the layout of components is not
critical, either. Just use good practices
to come up with a professional looking
job. You must mount the two small
transistors (Q1 and Q3) on sockets,
however, and you must use mounting
kits for the power transistors (Q2 and
Q4).
After you have mounted each potentiometer on its Minibox, wire it up as
shown in Fig. 1 using the three -conductor flexible cable ( you can make the
cable any length you wish) Connect
the other end of the cable to the main
chassis.

don't, yet. You'd better go over all the
wiring, very carefully, and check it out
against the schematic. Above all, you'll
want to make certain you haven't reversed any of the leads to the power
pack, as this could play havoc with your
transistors. If everything's okay so far,
wire the output terminals to the track
and plug the unit in.
If either car runs in the wrong direction, reverse the track leads to that
lane. Do not reverse the leads at the
power pack to correct this condition.
Should either controller potentiometer
work backwards, that is, if the car increases speed when the knob is rotated
counterclockwise, reverse the two cable
leads across the potentiometer end terminals.
If one car tends to run slowly when
the potentiometer controlling that car is
all the way off, one of the transistors
in the amplifier associated with that
lane is defective. To determine which
transistor is at fault, remove the smaller
transistor (Q1 or Q3) from its socket.
(CAUTION: always turn the power off
when removing or inserting any transistor.) If the car still runs slow with the
transistor removed, replace the larger
transistor. If the car doesn't run at all
now, replace the smaller transistor. -MI-

Having completed
all your wiring, you are now itching to
fire up the unit and race away .
but
Check It Out First!

1966 Fall Edition

Fig. 3. This underchassis view shows parts layout
and wiring. Capacitor Cl is wired across the power

pack output to provide filtered d.c. to the amplifiers. Use rubber grommet at all cable entrances.
57

BUILD THE

ELECTROLOCK
By MURRAY E. COULTES

A keyless wonder

you just dial
the secret combination
to open it
SAY daisies don't tell. Perhaps
of the "Electrolock." Unlike conventional locks which
give tell -tale sounds when the right combination registers or which can be easily
jimmied, the Electrolock is electronic and
can't be opened by anyone but yourself.
It uses no key; instead, you dial the four
opens.
correct digits, and presto
As seen in Fig. 1, the Electrolock is a
series circuit consisting of a battery, a
solenoid, a push- button switch, and four
rotary switches. The plunger of the solenoid is connected to a small barrel bolt,
and a small spring holds the bolt closed
when the solenoid is not activated. But

THEY
the same can be said

-it

when you dial the right four numbers
and depress the push button, you complete the circuit, current flows through
the solenoid, and the plunger pulls back
the barrel bolt. When the push button is
released, the spring pulls the bolt into
the closed position again.
There are many ways in which you can
construct the Electrolock. The combination that will open the lock depends
on the switch connections you use. Usually, a 4.5 -volt battery suffices, but for
more snap you could try a 6- or 9 -volt

battery.

Drill a hole through the barrel bolt
the same size as the hole through the
plunger of the solenoid, and fasten them
together as shown in Fig. 2. Be sure to
drill the hole parallel to the knob so that
the bolt will not be turned down when
the plunger is connected to the bolt. The
spring is fastened between the screw
connecting the solenoid plunger and barrel together to another screw mounted
58

External battery can be connected to the banana
jacks to overcome a weak internal battery. However,
the lock cannot be opened without the combination.

on the barrel lock frame. If you can't
find a suitable spring, use two or three

smaller ones tied together.
To operate the Electrolock, dial the
correct combination and depress the
push- button switch. The bolt should
ELECTRONIC EXPERIMENTER'S HANDBOOK

S5
12

SOLENOID

100

90
8
7

2
03
4
5

its

/22-3
87
4
5

100

O S3

941

12
11

9QS2 53
87 54

90
J^2
81

2
3
4

4.5V

Fig. 1. Any combination can be made by selecting
different switch positions. As there are more than

20,000 possible combinations, chances of "picking"
the lock are discouraging. Furthermore, if you add
a fifth switch, you can get 248,832 combinations.

PARTS LIST
B1 -4.5-volt battery
11,
Banana jack
S1, S2, S3, S4-12- position rotary switch
SS- Push -button switch, normally open
1
-volt d.c. type solenoid (Guardian Model 11
or equivalent)

12-

-6

Misc.-Barrel bolt, aluminum strip battery
mount, machine screws, hookup wire, solder

-40

BARREL BOLT

MACHINE SCREW
SOLENOID

Fig. 2. Spring holds barrel bolt in closed position.
Solenoid retracts the bolt when the proper combination is dialed and the push button is depressed.

Fig. 3. Align barrel bolt with solenoid to obtain
smooth action without bolt rotation. Battery and
switches can be mounted in any convenient position.

snap open. If it doesn't, check your wiring, particularly the switches. You may
have to adjust alignment and spring
tension to get smooth, positive action.
You've probably guessed the reason for
putting the two banana jacks on the

front panel. In case the battery inside
the unit hasn't the energy left to open
the lock, you just connect a fresh battery
across the terminals and dial the combination. Remember, you can't open the
lock if you forget the combination. -[3

1966

Fall

Edition

DON'T PANIC...
PUSH
THE BUTTON!

venturous soul will be tempted to
Don't you dare some
throw that switch. And when he does,
build this box you are sure to see a panic in the making.
Once the main switch is thrown, and
.... unless you want to after
a one- or two -second delay, the
create pandemonium box lets out a wailing sound akin to that
By BRUNO M. LARSEN

PANIC siren is guaranteed to set
TS
he most blasé individual or "stuffed
unwit1

shirt" on his ear, and cause the
ting "victim" who sets it off a moment or
two of embarrassed concern. For it is a
certainty that if this box is left alone
60

of a fire engine, ambulance, or police
siren. Lights go on and, within a second or two, start to blink like mad. The
"victim" will snap the switch back to
OFF, only to find, to his chagrin, that
the switch has no effect whatsoever on
the rising siren wail, or on the lights.
If the switch thrower can keep a cool

head, he'll "push the panic button" -the
one innocently labeled SQUELCH -and

ELECTRONIC EXPERIMENTER'S HANDBOOK

sigh with relief as the siren starts on its
downward wail. If he releases the button while the siren is dying down, as he
probably will, the siren immediately
starts up again, whereupon the "victim"
quickly presses the panic (SQUELCH)
button again. But this time he isn't taking any chances-he's going to keep his
fingers on that button until the sound
ceases completely. As it does, he smiles
triumphantly. (All this time the lights
are still blinking-the squelch button
has no effect on the lights.) Once again
he releases the button -and once again
the siren starts.
What the "victim" doesn't know is that
the contraption will go off by itself once
the main switch is thrown to OFF and
a preset time has elapsed. Every time
he throws the switch he recycles the
panic box, and when he presses the button he only interrupts the sound, without affecting the cycle.
How It Works. The secret of the panic
box is a delay incorporated in the ON-

OFF switch that causes the siren and
light circuits to remain activated for
from 60 to 90 seconds after the switch
is turned off. Pressing the SQUELCH
button is the only "known" action that
can be taken to start the siren on its
downward wail.
The heart of the panic box is a siren
module (Fig. 1) connected to a speaker
and a battery. The module contains a
relaxation oscillator (Q1) and a direct coupled output stage (Q2) . The oscillator creates a tone which rises from 5
to 3000 cycles within 30 seconds, and
creates a downward wail after the delay
switch shuts itself off.
Switch S1 is a concealed slide switch
that is normally left ON. It is used only

SPKR
GRN
GRN
RED

SIREN
MODULE

BLK
YEL
YEL

S3
SQUELCH
PUSH BUTTON-El

SLIDE SWITCH

Fig.

Observe

color -coded leads
coming from the siren module, and
connect as shown.
The lamp circuit
and its batteries
are optional and
can be omitted. r
This circuit has
been included only
for
psychological
effect. Lights have
built -in
blinkers. L

52
ON-OFF
BI

--'

+1-KD

11--1

+FL2

-J

NOTE:CIRCUIT WITHIN DOTTED LINES
MAY BE OMITTED WITHOUT
AFFECTING OPERATION OF
SIREN MODULE

by those in the know to shut the works
down. You can have fun in another way
-leave the switch off and your "victim"
won't be able to victimize someone else.
An 8 -ohm, 21, PM speaker serves as
the siren horn, and the entire unit is
powered by two or four 9 -volt batteries,
as shown in Fig. 2. Two of these bat -

teries-in parallel-provide

power for
the siren, and the other two-also in
parallel -provide power for the lights.
Construction. The box, a 61'16" x 5932"
x 2 íI" plastic meter case, houses all the

components, including the speaker and
the batteries. The box also functions as
a resonant cavity and greatly amplifies
the siren sound. What's more, the same

r
Secret of continuous panic making noise output is the built -in
delay in switch S2; outwardly it
seems to be an ordinary on- and -off
toggle switch. Switch S1 is concealed
and normally left on. Only you know
where to find it and shut the thing
off in case of panic. Panic button
S3 has no effect on the delay action
of S2 and opens the siren circuit
only as long as it is held down. If
the victim's patience runs out before
the delay cycle is completed, he is
most likely to recycle the unit so
that it will not cut out by itself.
Fig.

1966 Fall Edition

loudness is maintained during the upward and downward wails of the siren.
Other types of enclosures can be used,
provided care is taken to select a box
that will resonate properly. Metal boxes
are generally poor resonators, while
wooden boxes make ideal resonators. The
SLIDE

SPEAKER

SWITCH
SI

TIME
DELAY
SWITCH

PANEL
LAMPS
SALCIA'

PUSH BUTTON
S3

SIREN
ODULE

IDE

SWITCH
sl

SPEAKER
CLAM P

BAI SERIFS

12 OR 4
(SEE TEXT)

SPEAKER

Parts layout and box dimensions are not critical.
Paint the outside fireman's red and use large bold
letters. Battery mounting brackets are optional.

Speaker and "hidden switch" are mounted on back
of box. Better chain the box in place lest your victim
heave it out the window when the alarm sounds off.

arrangement of the components is left to
the discretion of the builder.
The slide switch (Si) can be wired so
that it opens only the siren cycle, or
both the lights and the siren. To make
this switch less conspicuous, the proPARTS LIST

Bl, B2, B3, B4-9 -volt transistor radio battery
(Eveready 216, or equivalent)
0.3 -amp. flasher bulb (GE -407
or equivalent)

Li, L2-4.9 -volt,

slide switch
Sl- S.p.s.1.
60- second delayed action light

switch (LafaS2yette Radio 34 R 3805, or equivalent)
S3- Normally- closed momentary push -button
switch
SPKR -2;_ ", 8 -ohms speaker (Philmore TS -25,
or equivalent

-Siren

module (Lafayette Radio 19 -0105, OlIii -iron Model
IIS available at parts distributors)
1
15/16" x 5 -9/32" x 2- 5/16" plastic meter
case (Allied Radio 87 P 886 or equivalent)
Matching panel (cover) for above case (Allied
Radio 87 1' 888 or equivalent)
2 -Bulb sockets with red-faceted jewel lenses
(DIALCO 510M or equivalent)
4 -Type 5D battery clips (Cinch -Jones, or
1

son Radio TR 71, or Saxton

-6-

4-equivalent)
Battery brackets (Keystone No.
alent)

95, or equiv-

Misc.-Rubber feet, wire, solder, hardware and
terminal strips

truding stem can be cut off flush with
the plastic box. You can use 6 -32 hardware to mount the components, or you
can fasten them permanently to the box
cover with pop rivets.
The small speaker has no mounting
holes or flanges (actually, there are a
number of speakers available with
mounting holes) but you can use a couple of mounting clips with washers to
secure the speaker to the back cover of
the meter case. Before mounting the
speaker, drill a number of holes in the
mounting surface to vent the speaker
cone to the outside of the enclosure.
Size of the holes is not critical. Also,
to make certain that the batteries clear
the main ON -OFF switch and the light
sockets, install battery mounting brackets near the edge of the box cover.
There is nothing critical in the wiring. Nor is there anything functional
about the blinking lights, which are included purely for psychological purposes
-you can omit this circuit if you wish.
The outside of the box can be finished
and stenciled in any manner you wish.
For example, the SQUELCH button can
be labeled PRESS HERE, or PANIC
,

BUTTON. Or WARNING, DANGER,
etc., can be substituted for CAUTION.

Setting the Trap. Make sure that the
concealed slide switch is in ON position,
and the master ON -OFF switch Is set to
OFF. Then lay the box in a conspicuous
place, and be ready when the fun starts.
-®Happy panic
!

ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER
2
AUTOMOTIVE
ELECTRONICS

Only 21/2 years ago, when POPULAR ELECTRONICS
published a product -by- product analysis of the transistorized ignition market, there were about 30 different manufacturers in business. And they were offering products
based on 11 different designs. Thirty months later there
appears to be only a half dozen active manufacturers
selling three or four different designs. What happened?
The answer to the above question is plain and simple
the 1964 transistorized ignition systems were dropped
like the proverbial hot potatoes. Some systems were so
poorly designed as to be almost unbelievable. One or two
apparently unscrupulous manufacturers turned in a "fast"
buck and got out of business. The good products suffered because of class association and several manufacturers switched to the production of other goods. But
possibly the one major contributing cause to the downfall
of transistorized ignition was that many 1964 circuits
weren't the very best.
The Editors of EEH have had the opportunity to exhaustively test the only logical answer to the transistorized
ignition problems -the capacitive discharge circuit. In the
pages that follow are the plans for one of the best ignitions systems we have ever published. Although specialized components are called for, this is one system (among
the two or three that survived from 1964) that we feel
deserves your unqualified attention.

64
NOW! A UNIVERSAL CD IGNITION SYSTEM

Murray Gellman

69
PROTECT YOUR CAR'S ELECTRICAL SYSTEM

Charles Erwin Cohn

70
HEADLIGHTS -ON ALARM

Thomas

Yocom

71
AUTO VOLTMETER SHOWS YOU'LL GO
1966

Fall

Edition

Joseph Tartas
63

NOW! A UNIVERSAL
CD IGNITION SYSTEM
By MURRAY GELLMAN

Modified unit fits
12- or 6 -volt cars,
including
positive ground ignition
Because of the excellent response to the
article on a "Transistorized Capacitor
Discharge Ignition System" by Murray
Gellman (in the 1966 Spring Edition
Of ELECTRONIC EXPERIMENTER'S HAND-

the author has provided construction details to modify the basic 12 -volt
negative ground circuit for operation
with 6- or 12 -volt positive, or 6 -volt
negative ground ignition systems. On
page 66 you'll find some representative
excerpts from our reader mailbag, with
the appropriate answers.
THE EDITORS
BOOK),

WHETHER YOU ARE the owner of a
foreign car with a 6 -volt ignition system, or an American car with a 12 -volt
positive or negative ground ignition, you
can now enjoy the advantages of increased gas mileage, quicker starting
even in cold weather, longer life for
breaker points and spark plugs, and
more power at high speeds with a tran-

sistorized capacitor discharge ignition
system. You can build the system from
scratch for the car you presently own,
and modify it later, if you wish, to fit
any other car you might buy. The 12volt negative ground system (and how
to build it) was described in the 1966
Spring Edition of the ELECTRONIC ExPERIMENTER'S HANDBOOK. The following
instructions tell you how to modify the
basic design to fit your car.
Six -Volt Negative Ground Ignition.

The

basic 12 -volt transistorized capacitor
discharge ignition system can be modiELECTRONIC EXPERIMENTER'S HANDBOOK

1N2615

H.V.

TO
DIST.

Iyf.
03
MCR1605-6

660K

1N2615
G

2NI100
ICI

4yf.

IN463

IGNITION
SWITCH

226f.
T

50y

2 5611

RESISTORS
IN

PARALLEL

132yf.

R7
100f1

TC5
OyI.

1.81<

TO POINTS

.OND

IN DISTRIBUTOR

Fig. 1. In this positive ground ignition system, the d.c. resistance of pulse transformer T2 replaces resistor
R6 in negative ground circuit. Also, positions of R1 and R2 are reversed, as is polarity of diode Dl.

Positive Ground Ignition. To convert
the 6- or 12 -volt negative ground system
to positive ground (see Fig. 1) using the
same printed circuit board, the collector
center tap must be removed from ground.
This can be done by cutting the copper
strip above and below the letter G with
a single-edge razor blade. Hold a clean
soldering iron-one having no solder on
the tip -on the copper strip next to the
letter G. Remove the strip using the
razor blade. Drill a hole (using a x$52

Component side of positive ground circuit board
showing parts location and orientation. All components are color- coded, and the appropriate colors
marked on the circuit board to facilitate assembly.

fled to operate on six volts by making

the following changes (1) add another
10-ohm resistor in parallel with R1; (2)
add another 820 -ohm resistor in parallel
with R2; (3) short out R6 (27 ohms)
by connecting a heavy jumper wire across
it; and (4) replace the SPC-4 transformer (T1) with six-volt transformer
SPC -4A (available from SYDMUR, P. 0.
Box 25A, Midwood Station, Brooklyn,
N.Y. for $14.95).
:

1966

Foil

Edition

TOROID CORE
Fig. 2. Fabrication details of positive ground pulse
transformer. Shown are a completely assembled
unit, the ferrite toroid core, and coil assembly forms.
65

MORE ABOUT CAPACITOR DISCHARGE IGNITION SYSTEMS
Q

I substitute a new ignition coil with
250:1 turns ratio for my 100:1 coil now
in the car?
Yes, but you wouldn't gain enough to
merit the extra cost. Your present coil
used with a CD system will produce adequate voltage at all engine speeds.

the ambient temperature under the hood,
and, besides, the metal box acts as a heat
sink.

Can
a

Q
A
Q

Must the "condenser" across the breaker
points be removed?
No. It does no harm -leave it there.

want to wind my own toroid transformer.
How about revealing the winding details?
Sorry, but this transformer is something
special and a patent has been "applied
for" to cover its construction.

Q
A

What temperatures will the CD system
withstand?
It has been tested at 60 degrees below
zero (F) and 200 degrees -plus under the
hood.
Why no heat sinks on the transistors?
The transistors are rated to operate above

FERRITE
TOROID
CORE

Fig. 3. Pulse transformer
is wound on ferrite toroid

with 300 turns of
bifilar -wound #40 Polyurethane insulated wire. Wire
terminals are soldered to
the lugs on the coil form.
core

RED

GRN

2CT

TI
CENTER

TAP

BARRIER
STRIP

Fig. 4. Wiring details of transistors and barrier strip
connections for positive ground ignition system.
Terminal marked A- connects to ignition switch.
66

Must I replace the distributor cap and ignition wiring harness?
You might find it advisable to clean out
the cap and check the harness for breaks
or worn spots. Replacement is not a prerequisite.
Do

change the engine timing?

No. Just be sure it meets the manufacturer's specs. The CD system will not up-

set the timing.
Q
A

Must I use a printed circuit board?
Why not? What have you got against
space -age engineering?
used your transformer in another CD
circuit that saw published this year. The
transistors gave up the ghost. What hapI

pened?
The toroid in this CD system was designed
to match the transistors. Substitution
could lead to a lot of headaches.

bit) in the copper strip ?!I -inch away
from the end that was cut, and another
hole near the letter Y in the ground
strip. Then, using a #42 bit, drill a hole
above the letter U on top of the printed
circuit board; this hole is used to mount
the pulse transformer (T2).
The pulse transformer is made by
winding 300 turns of bifilar -wound #40
Polyurethane insulated wire on a ?í, -inch
ferrite toroid core. (See Fig. 2.) After
the wire is wound, it should be placed in
a form and the leads connected to the
lugs (see Fig. 3) The wire leads can be
wrapped around the lugs without removing the insulation (the heat melts away
the insulation), and then soldered. After
this is done, the form is placed in a
small cup form and filled with epoxy
cement. (SYDMUR will supply the toroid, form, and cup form for $2.50, or the
completed pulse transformer for $4.50.)
The pulse transformer reverses the
polarity of the incoming negative pulse
to the positive pulse that is required at
the gate to make the SCR conduct. No
attempt should be made to drop the B+
(Continued on page 74)
.

CIRCLE NO.

ON READER SERVICE

CARD---31.

By CHARLES ERWIN COHN

PROTECT
YOUR CAR'S

ELECTRICAL SYSTEM
Forty -five -cent

1111k

pPov ides ¡ der-the-hood fire protection
e

M OST

VEHICLE lighting and electrical accessory circuits are well protected by fuses or circuit breakers.
However, the main feedline which connects the battery to the generator and
to all circuits, except the starter, and
the circuit wiring up to the fuse block
or circuit breaker very often go unprotected. Should a short occur at a point
ahead of the protective devices, the high
currents would cause extensive wire
damage, battery damage, and possible
fire.

At a cost of only 45 cents, it is now
possible to minimize this hazard. A fusible link introduced by Chrysler Corporation on its 1965 autos can be adapted
for use in any car equipped with a 12volt battery system. The part number
is 2580389, and it can be obtained from
any Chrysler dealer.
The link is a short length of 16 -gauge
wire which behaves like a fuse. Because
the regular wiring in the car is much
FEED LINE

FUSIBLE
LINK

STARTER
SOLENOID

=12v

STARTER

Insert fusible link between battery
and main electrical feedline. Should
the link fail for any reason, you can
reconnect the main feedline as before.

1966 Fall Edition

heavier, the link will burn out before the
regular wiring has a chance to do extensive damage in the event of a short. At
30 or so amperes, the link runs hot ; and
at about 40 amperes, it quickly melts.
Normal total current requirements in a
car rarely exceed 30 amperes. For the
system to operate again, once the link
fuses, it must be replaced. Special heat resistant insulation is used to safely contain the hot link.
As shown in the diagram, the link is
connected as close to the battery in the
electrical system as possible. It should
not be inserted in the starter circuit.
Usually, the link can be attached to the
"hot" terminal of the starter relay. As
a safety precaution, disconnect the battery before you install it, and reconnect
the battery after the job is done.
Disconnect the feedline from the solenoid, and connect the end of the link
with the larger terminal lug to the solenoid and the other end to the feedline.
A small nut and bolt can be used to
connect both wires. All connections
should be firm. The junction of the link
and the feedline should be taped, and
positioned so that it will not accidentally
cause a short circuit.
In the event the link gives way when
you are miles away from a service station, reconnect the feedline as it was
originally -after you have cleared the
short circuit.
-C69

HEADLIGHTS -ON ALARM
)

Alarm sounds if thé lights are left on
after the ignition is switched off

By THOMAS R. YOCOM

HOW MANY TIMES have you jumped
into your car, turned on the ignition
switch, ready to go somewhere, only to

-a

dead battery!
have nothing happen
Why? Because the lights were left on
after the car was parked; during the
winter months the chance of this happening is greatly increased. You can put
this annoying situation behind you for
good by installing a "Headlights -On
Alarm." It is small enough to be tucked
under the dashboard, and it will sound
an alarm if you leave your lights on
when you turn off the ignition switch.
How It Works. A warning bell or buzzer
goes on when current runs through relay

Should you forget to turn off your lights when
you turn off the ignition switch, the alarm will
sound -unless you install a disabling switch (S1).

PARTS LIST

DI, D2, D3,

D4- 1Á'34A diode

or equivalent
K1 -5000 -ohm remote -control relay, s.p.s.t., pull
out
at
1.2
ma. (Lafayette
in at 1.4 ma., drop
99 R 6091 or equivalent)
R1, R2 -2400 -ohm, 1/2-watt resistor
S1- S.p.s.t. switch (optional -see text)
1 -12 -volt buzzer
70

K1. When the ignition switch is turned
on, a small current on the order of 5 ma.
will flow through R2. No current can
flow through K1 because D2 is reverse -

biased at essentially full battery voltage. The ignition system and any other
electrical devices connected through the
ignition switch operate in a normal
manner.
When the parking or driving lights
are turned on, current runs through the
lights as usual, and also goes through
R1. Current cannot go through K1 because of the reverse -biased condition of
D2. However, if the ignition switch is
turned off, the bias on D2 is removed,
and if the headlight switch is still on,
current will run through K1, D2, and R2,
and energize the relay to turn on the
alarm.
Diodes D3 and D4 prevent interaction
between the parking and driving lights ;
otherwise both lights would go on when
either light switch was closed.
Installation. Parts can be mounted on
a small chassis or clustered around the
relay. The alarm circuit shown in the
schematic is for cars having a negative
ground electrical system. For positive
ground systems, reverse the polarity of
all the diodes.
Should you want to operate the lights
without having the alarm sound off and
without having to turn on the ignition
switch, break the line at point X in the
diagram and add Si.
Another innovation is to use the taillight circuit instead of the headlights
and parking lights. Since the taillights
go on when either the parking or driving
lights are on, you only need to monitor
the taillights. In this case, eliminate D4
and connect the anode of D3 to the taillight bus instead of to the driving lights
circuit.
ELECTRONIC EXPERIMENTER'S HANDBOOK

AUTO
VOLTMETER

SHOWS
YOU'LL

Keep tabs on your

charging system
catch battery failures
before they happen
By JOSEPH TARTAS

EVER stop to wonder what your automobile battery voltage is? "Why
twelve volts, of course," you say (unless you have a 6 -volt system and answer "six ") . It seems like a silly question -until you examine it closely. The
fact of the matter is that battery voltage varies over a range centered around
12 (or 6) volts: Exactly what it is, and
when, are facts that can tell you a great
deal about the health of your car's electrical system.
If your car or boat is equipped with
an ammeter or indicator light, you
might automatically assume that you
need only be concerned when the "Battery" light stays on, or if the meter
shows discharge when the engine is running. While it is important to know,
as these devices indicate, that your generator is supplying a charging current
to the battery, it is equally important
to know the battery voltage under load
and no -load conditions, as well as the
voltages actually available at the starter,
ignition system, etc. Voltage drop
across cables can be enough to cause
trouble. The voltmeter can tell you
where your trouble is without "cutting" into any of the circuits. It can
also alert you to potential trouble.
1966

Fall

Edition

Storage Battery Theory. Let's review,
for a moment, the typical characteristics of a lead -acid storage battery. It
consists of several cells each having a
potential of about 2 volts. The exact
voltage of each cell will depend on the
proportion of acid to water in the electrolyte, and the condition of charge or
discharge of the cell.
One standard method of checking a
lead -acid cell is to measure the specific
gravity of the electrolyte. This electrolyte is a mixture of sulphuric acid and
distilled water with a specific gravity of
1.260 at 77° F for automotive service,
and ranging from 1.275 for heavy industrial uses to 1.210 for batteries in
standby or emergency service. The specific gravity is measured by means of a
hydrometer. The open- circuit voltage of
the cell is directly related to its specific
gravity
Voltage = specific gravity + .84
A voltmeter, therefore, can be used to
continuously monitor the specific gravity of the battery as a whole.
Because the proportion of water to
acid is increasing as the cell discharges,
the specific gravity is gradually reduced
(water alone has a specific gravity of
:

is an output from the generator. When
it is lit, the generator output is nil or
inadequate. When the light is out, the
generator output exceeds some preset
current level at the generator terminals.

This illuminated voltmeter is one of several
types for use in cars. Panel meters will also
serve; in some cars, they can be mounted in
dash. Meter above is sold by Lafayette Radio.

1.000) and the relative state of charge
will be indicated by the hydrometer
reading. For the sake of accuracy, the
correct specific gravity is designated at
77° F, with a small correction factor of

about 15 points for temperature variations over the usually encountered
range of 32 to 110 °. Some hydrometers
have a built -in thermometer with the
necessary correction indicated.
As a cell discharges, the terminal
voltage begins to drop due to internal
resistance. The heavier the current,
the greater the internal voltage drop
and the lower the terminal voltage due
to the heating effect on the battery resistance. If there is excessive resistance
in the battery cables due to broken
strands in the conductors or poor terminal connections (due to loose or corroded joints), there is a further drop
under high current drain conditions,
and little voltage appears at the starter
terminals or at other equipment such
as the radio or lights.
One voltage appears at the battery
terminals under no -load conditions, a
lower voltage under starting conditions
(or with the lights, heater, or radio
on) and a still lower voltage at the
starter or equipment due to the normal cable drop. When an ammeter is
used as the indicator, it will show at a
glance whether or not there is a load
on the battery by its discharge rate,
but it does not give any indication of
the battery voltage or its condition of
charge, nor does it indicate excessive
IR drops.
The "idiot light" does not even give
this amount of information, but usually
tells no more than the fact that there
72

Neither the ammeter nor the light
necessarily show battery condition.
Enter the Voltmeter. A d.c. voltmeter
connected directly to the battery terminals will tell you at a glance the charge
condition of the battery, the condition
of your voltage and current regulator,
and if the generator is functioning
properly.
A typical 6 -volt battery will read 6.3
volts with no load when fully charged.
If it reads below that, the percentage of
charge left will depend upon current
drain, the length of time the discharge
occurs, and the final voltage acceptable
(the point at which the battery is considered discharged but not damaged)
The final voltage, below which the cells
are considered exhausted, depends upon
the time and discharge current rate. This
final voltage may vary from 1.0 to 1.85
volts per cell, but the most used value
is 1.75 volts for typical applications.
Any of several voltmeters can be used
in an automobile or boat. An 8- or 10volt d.c. voltmeter is suitable for a 6volt system, and a 15 -volt meter for a
12 -volt system. There are a number
of special meters available from automotive supply and electronics parts
houses, some types already mounted in
brackets, with or without a panel light,
and some types that include troubleshooting charts. These meters have expanded scales to make it easy to read
battery voltage while driving.
One type that includes both illumination and trouble- shooting information is
the Lafayette Radio voltmeter (Stock
No. 11 R 8002) another is the Stewart Warner "Volt- Guard." The latter is advertised as a voltmeter and electrical
system analyzer, which, in effect, is
what it really is. The Stewart -Warner
meter has a meter bracket and light
socket, but these are sold separately as
accessories.
Unlike the regular d.c. panel voltmeter, the automotive types draw about
50 ma. of current, but this small drain
is insignificant compared to the current
capacity of a car battery. The normal
leakage across the top of the battery
.

;

ELECTRONIC EXPERIMENTER'S HANDBOOK

due to dirt and acid probably equals or
exceeds this drain. The meter is wired
directly to the battery terminals with
small -gauge insulated wire ( #20 is
more than adequate) ; alternatively,
the ground lead can be connected to the
engine block where the battery is connected. In either case, the meter leads
should be soldered to solder -lugs and
connections to the battery or block
should be clean and tight.
It is a good idea to check voltages at
the various terminals (battery, engine
block, voltmeter on panel) with a portable voltmeter or VOM to determine if
there are any undesirable voltage drops
in the cables or connections after the
meter is installed. You may avert trouble

later on.

Each time
you start your car you should check
your indicator lights and watch the voltWhat the Readings Mean.

Simple gadget for turning over engine consists
of two clip leads connected to normally -open
push -button switch. Leads are connected to
starter control terminals of starter solenoid.

meter for abnormal indication. Remember that the battery drain is heavier in
winter and the battery voltage (if you
keep your car outside) will be lower to
start with.
(Continued on page 147)

BATTERY VOLTAGE TABLE
BATTERY VOLTS!

Below

5.0

Below
10 or
no read.
ing

ENGINE STARTING

ENGINE RUNNINGS

IDLING2

(Battery Condition)

(Generator Condition)

Dead or disconnected

Disconnected, defective, or improperly wired
meter. If the engine will start, or run, the
battery is not at fault

battery, meter disconnected or not
wired properly

4.5.6.0 9.12

Normal range for
Undercharged battery;
Generator not charging,
engine might not start winter and summer regulator not working, or
current drain from equipment (lights, radio, etc.)
exceeds generator output

12 -12.8

6-6.4

ENGINE OFF OR

Battery fully charged, but
generator or regulator not
working properly

Fully charged
battery. Generator
and regulator operating properly

6.7.7.6 13.5.15.2 Normal for short
period after driving
due to battery "surface
charge," or meter reads

Normal when battery,
generator, and regulator
are working properly. Meter
reading varies with charge
in battery, engine speed,
temperature, and regulator
setting

high

Above

7.6

15.2

1. The

Voltage regulator contacts
stuck together, or voltage
regulator set too high.
File and clean contacts and
check battery fluid for level
and specific gravity

minimum voltage reading possible will depend upon the type of meter used.

2. Idling speed below that which causes the cut -out relay to pull in.
3. Normal driving speeds.

All voltages are approximate, and will vary with temperature, condition of regulator contacts,
accuracy of meter, and other conditions.
11111111

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1966 Fall Edition

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(Continued from page 66)

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Installation. The wired printed circuit
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placed in the cabinet. Wires from G as
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on the barrier strip. The wires coming
from H and the collector center tap go
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EEH-66

Address

With the pulse

replaces R2 and R2 replaces Rl. Capacitors Cl (4 µf.) and C3 (50 pf.) are reversed in polarity so that the plus (+ )
side of the capacitors are grounded.
Diode D1 (1N463) is reversed so that
the anode goes to the plus ( +) mark
on the printed circuit board. The 27 -ohm
gate current limiting resistor (R6) is
not required since the d.c. resistance of
T2 takes its place.
Cut two 11/2" long pieces of heavy wire.
Insert the end of one wire in the hole
vacated by R6, and the end of the other
wire in the remaining hole. Now, connect the free ends of the wires respectively to terminals 1 and 3 of transformer T2. The center lug ( white dot) on
the pulse transformer goes to the hole
in the ground strip (near the letter Y) .

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ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER
3

OPERATION

ACTIVATE
How to get
moving toward
a successful career
in the

field of electronics
PART 1:

GETTING YOUR TRAINING
IN RESIDENT SCHOOLS
(see page 83 for an analysis

of home -study training)

By KEN GILMORE

1966 Fall Edition

IN Whippany, New Jersey, Richard J.
Ewalt carefully checks out a complex
piece of computer test gear he helped design. The equipment will become part of
the Nike -Zeus anti -missile system developed by Bell Laboratories, Ewalt's
company.
In Edwards, California, Loren E. Hirman sets up a series of subcarrier oscillators in a telemetry system. The device is used to transmit data from planes
being tested by Hirman's company, General Dynamics.
In Albuquerque, New Mexico, Harry
F. Chaney shoves a batch of tubes
on a special test board into an oven,
checks their performance at different
heat levels to see how they'll operate
under extreme temperatures. He works
for the Electron Tube and Semiconductor Devices Division of Sandia Corporation, a leading company in atomic energy
development.

Photos taken at RCA Institutes by Christopher Sheridan

All three of these men -Ewalt, Hirman, and Chaney-are electronics technicians, vital members of today's electronics team. For men -and women
interested in electronics, it's a good team
to join. The industry is advancing rapidly; new people are needed badly. Pay is
good, working conditions usually top

rate, and jobs are almost universally
interesting.
But there's a catch. If you're untrained, don't bother to apply. A few
decades ago, a bright young man could
pick up enough know -how working
around the local radio repair shop to
qualify for a job chasing electrons. Or
he could work in a plant and with a
little study on the side eventually learn
enough to get promoted to an electronics
job. But no more. Today, you've got to
know what you're doing. That means
a good technical school education.
The first thing to decide is where you
want to fit into the electronics picture.
In general, today's technical school programs are designed on three different
levels.
Engineering Technology. To become
an engineering technician, you'll spend
two to three years at one of the top technical institutes, a junior college, or a division of a regular four -year college
that provides an engineering technology
program. In most cases, you'll end up
with an A. S. (Associate in Science),
an A. S. E. E. ( Associate in Science,
Electrical Engineering) , an A. A. S. (Associate in Applied Science) , or some
similar degree. The course will cover
virtually the same areas in math, the
sciences, and engineering that regular
electronics engineers study. And as with
engineers, you'll spend most of your
time- 60 to 80 percent of it -in class.
Lab courses account for the other 20 to
40 percent.
76

Toward the end of your training, you'll
have the opportunity to specialize. At
New York's RCA Institutes, for example, you can become an expert in communications or computers. At Capitol
Institute of Technology in Washington,
D. C., you might choose communications
engineering, nuclear instrumentation, or
control systems as your field of con-

centration.
The engineering technician's program,
while at college level, is designed for
the man who wants to work with hardware. "It depends on what he wants to
do after graduation," says Edward Norman, Capitol's Dean. "Does he want to
hold down a desk and let paper be the
prime result of his effort? Then he'd
probably be happier as an engineer. But
if he wants the more practical type of
employment where he can actually get
his hands on a few parts now and then,
he'd probably like being an engineering
technician better."
"There is heavy emphasis on math
and physics in an engineering technology
course," adds Mike Terzian, Dean of Administration at RCA Institutes. "Since
it's a college level course, a student can
get credit for most of the work he does
if he should later decide to go to college
for an engineering degree.
"Meanwhile, after a little over two
years, the man who finishes our T -3
course [RCA's program at the engineering technology level] is ready to go to
work. The majority of our graduates
get jobs in research and development.
A project engineer will design something -say a piece of data processing
equipment which is supposed to meet
certain specifications. Now it's up to
the engineering technician to build the
prototype from scratch. He punches out
the chassis, lays out the circuit, builds it
and tests it to see if it meets specificaELECTRONIC EXPERIMENTER'S HANDBOOK

"Just how far
you're able to get
depends on ..
how hard you're
willing to work"
.

tions. If not, he may recommend modifications."
"Engineering technicians also do other
types of jobs," says Richard Ungrodt,
Dean of Engineering of the Milwaukee
School of Engineering. "They might be
part of a team that works out production
techniques. And some of them work in
sales and maintenance. You'll frequently
find engineering technicians assigned
to computers, for example. In the old
days, you'd find an engineer doing this
job, and sometimes you still do. But a
lot of this work can be done by top -level
engineering technicians. So they're really
doing engineering level work."
Industrial Technology. "This program is
designed for the fellow who wants to do
service type work," says C. L. Foster,
president of Central Technical Institute
of Kansas City, Missouri. "He may
maintain two -way radios in a fleet of
trucks, or enter the broadcast field. Or
he may work for the same company as
the engineering technician, doing work
on a less complex level."
"There's not so much math in his
curriculum," says RCA's Terzian, "and
there's more lab work. His training is
aimed toward analysis and troubleshooting, rather than design. It's a good
course for the guy who doesn't have college in the back of his mind, and there's
a steady demand for people with this

training."
A man preparing for an industrial
technician's job may spend a year to a
year and a half in school. He'll get a
diploma or certificate when he finishes,
but if he ever decides to go to college,
he'll have to start at the beginning; his
credits won't be transferable.
Service Technology. A service technician may work in a service shop, troubleshooting radio and TV sets and hi -fi
gear. In industry, he might do routine
1966 Fall Edition

production testing or wiring on a production line. But because his skills
aren't up to those of the engineering or
industrial technician, he's not able to
compete for jobs as well as his more
highly trained colleagues.
"As the demands of industry have
increased in the last ten or fifteen years,"
says Mike Terzian, "technicians have
needed more training. The man with
only a service technician's background
isn't likely to be able to hold down more
than a routine job. And demand isn't
too strong; sometimes we have trouble
placing them."
"The only place we offer a radio and
television servicing course per se is in
our night school," says J. J. Gershon,
Dean of Chicago's DeVry Technical Institute. "We feel that competition being
what it is, our graduates need more than
just a background in radio and TV."
Of course, it's one way to get started
in electronics. If you can't afford to
take a longer course, you might become
a service technician, then go on with
further schooling on a part -time basis
after you get a job. Generally, a service technician's training takes 6 to 12
months of full -time schooling, up to two and -a -half years in night school.
prepare for a technician's job
through home study?
The answer to this controversial question depends on whom you ask. Generally, most schools agree that you
Can

can't reach the engineering technician's
level or get an associate degree through
the mail.
"There's no comparison between resident and home -study training," says
DeVry's Gershon. "Resident training is
certainly more desirable. But if a man
has a family or can't leave a certain
area, then he has no choice. He can
77

profit from home study, even though he
can't attain the same level that he could
in resident school."
"Home study is more oriented toward
radio -TV servicing and manufacturing
assembly line work-than residence
schools," says Harry Rice, Dean of RCA
Institutes home study division. "But
home study graduates also get jobs as
broadcast engineers and technicians in
industry, and they open their own businesses."
A different view is taken by one resident school official who asked that his
name not be used. "I don't recommend
correspondence training to any young
man who is seriously interested in a career in electronics," he says flatly. "If
he's lucky, he might get a job on a production line doing routine wiring or testing. But it would be very difficult for
him to get a real technician's job."
Some schools take another view. "The
main difference between residence and
correspondence schools is that in residence school you learn the material in
a much shorter time," says Norman of
Capitol Institute. "And, of course, the
lab work can't be the same." Capitol
Radio, a home study school formerly

affiliated with Capitol Institute, requires
that a home -study student be actively
working in the electronics industry.
Therefore, the reasoning goes, he
doesn't need the same laboratory work
as students fresh out of high school.
But this is a unique requirement on the
part of Capitol Radio.
Foster of Central Tech also claims
advanced standing for his home -study
curriculum. "Our home -study program
very closely approaches the engineering
technician's program," he says. "We
can't say it's absolutely equivalent, because we do not go into higher math and
practical laboratory work is limited.
But a home -study graduate is certainly
prepared for a job at the industrial
technician's level."
How's the job outlook?

If you're trained as an electronics technician, job finding won't be a problem.
The Technical Institute Division of the
American Society for Engineering Education estimates that some 16,000 engineering technicians are graduated each
year. But the Bureau of Labor Statistics
of the U. S. Department of Labor places
the demand at about 80,000 a year. That

Training You'll Need For Various Jobs In Electronics
TRANSFER CREDIT
TO COLLEGE

TRAINING
LEVEL

JOBS QUALIFIED FOR*

DEGREE OR
CERTIFICATE

LENGTH OF

Certificate

6 -12 months

Certificate

1.11/2 years

Certificate
or
Associate

2 -3 years

Service

Radio -TV service

technician

Communications troubleshooting, maintenance
Broadcast engineer
Sound system troubleshooter
Assembly line wiring
Routine production line
testing

Industrial
technician

Field service technician

Engineering
technician

Field service technician

TRAINING

Computer technician
Junior R &D engineering
technician
Communications installation, maintenance
Broadcast engineer
Production line testing
supervisor
Computer technician
R &D Engineering technician
Senior engineering
technician
Associate engineer

of credits transferable depends
on college)

Degree

There may be some overlap, but in general each level of technicia,
78

Yes (exact number

fitted for a certain range of duties.

ELECTRONIC EXPERIMENTER'S HANDBOOK

"The engineering technician's program ... is designed for the man
who wants to work with hardware."

than five jobs available for
each man trained.
Milwaukee School of Engineering says
it could easily place twice as many graduates if it had them. RCA reports that
90 percent of its industrial and engineering technicians have jobs lined up
even before they graduate. The other
ten percent aren't looking for jobs;
they're foreign students returning home,
young men going into the service, and so
on. Other top schools report a similar
means more

situation.
By the way, the door is open for girls.
"They can work in electronics as well
as men," says Terzian. "And in most
places they have no trouble getting a
job."
How much can

make?

Starting salaries vary, of course, in
different parts of the country, at different companies, and for technicians with
varying amounts of training. Generally,
though, an engineering technician might
start in the vicinity of $500 a month.
Some, of course, don't make that much
others make more. An industrial technician might earn $50 or $75 less to
start with; a service technician could
average about $325 a month.
There's almost no limit to how far
you can advance, and most technical
graduates tend to do well. DeVry made
a survey recently of 43 graduates picked
at random. They had graduated from
two to fifteen years earlier. About 35%
were in military service or just out, or
were in the process of attending other
schools, or just didn't answer. Of the
remainder of these 43 graduates, two
had become vice presidents of companies, three held the title of chief
engineer, one was a principal engineer
(assigned to handle projects other engineers couldn't), six were engineers, and
one was working toward his master's
degree. Other titles: one senior design
engineer, one supervisory engineer, one
district engineering sales manager, one
international marketing manager, one
field service administrator, four engineering assistants, two technical staff
;

1966 Fall Edition

assistants, and one senior technical
writer.
Sometimes technical school graduates
even reach top management positions.
Cyril J. Statt, who graduated from Central Technical Institute in 1940, is now
manager of manufacturing at General
Electric's computer plant in Phoenix,
Arizona. And Richard Wainwright, a 1954
graduate of Capitol Institute of Technology, is president of his own company,
I -TEL, Inc., of Wheaton, Md, which designs and manufactures microwave filters. Just how far you're able to get
depends on your ability, your training,
and how hard you're willing to work.
What does it take to qualify
for a technical school?
While schools vary somewhat in

their

admission requirements, most of them
that will train you to be a high -level
engineering technician accept only high
school graduates with at least a C average. They usually also require one or
two years of algebra, one of geometry,
and one of physics or chemistry.
Requirements do vary, though. Milwaukee wants a background with four
years of high school math through trigonometry; others have their own additional requirements. It's a good idea to
check with schools you're interested in
while you're still in high school, so your
courses can be tailored to meet the requirements. If that's not practical, then
get all the math and science you can. But
don't neglect English, either. Most
schools emphasize technical report writing.
Many schools give entrance examinations. If you're not up to the minimum
level in any subject, you may be required to take remedial courses before
you can enroll in the regular technician's
program.
If you enter industrial or service technician's training, some or all of these
requirements may be waived. Check with
the schools you're considering for entrance requirements at the various levels.
Incidentally, most physical handicaps
won't stop you in electronics. One that
HANDBOOK

"If you're trained

...

finding a job
won't be a problem."
will keep you out of some jobs: color
blindness. Many technicians must be
able to read the color codes on resistors

4,
%
r,a,
..

..,,
r

and other parts.
And don't think you have to be fresh
out of high school to qualify. Many
schools have older students who worked
for a while before deciding what to do.
RCA had one graduate in 1960 who had
been a locomotive engineer for 20 years
when he quit his job to become a technician. He has recently been promoted by
his company to the job of master technician, and was invited this year to read
a technical paper describing some of his
work at a conference of military electronics experts.
How much will it cost?

Generally, tuition for an engineering
technology course, lasting two to three
years, will cost anywhere from a little
under $2000 to almost $3000. You can
pay as you go along, by the week ($20$25) or by the month or semester. Twoyear courses, naturally, tend to cost less
than three -year programs.
Living expenses vary considerably, depending on the city. RCA Institutes, for
example, estimates that it costs students
$30 to $50 a week to live in New York.
Central in Kansas City, on the other
hand, says that students get along for
$25 a week. All schools will help you
find a place to room and board; some
have school dormitories.
Incidentally, the tuition at a given
school is generally the same, no matter
what level training you're taking. The
difference comes in length ; you'll spend
six months in some of the simpler service technician's courses, three years in
the more rigorous engineering technology programs.
If the total cost of going to school and
living in a city away from home is too
much for your budget, you might be able
ELECTRONIC EXPERIMENTER'S HANDBOOK

to work part time. "At least 75 percent
of our full-time students work," says
Foster of Central.
"If a student wants to work," adds
Gershon of DeVry, "we'll help him find
a part -time job. A student who works
can usually earn enough to pay for either
his tuition or his living expenses, but
not both. On a normal day, he'll spend
two hours in lab, four hours in class,
and have two or three hours of homework. That's eight or nine hours on
weekdays, and then we load him up
with homework for the weekend. So
anyone who wants to work in addition
to this heavy load is going to be a busy
fellow."
Terzian of RCA agrees. "It's very
difficult to work and complete the T-3
program. But some students do it."
Ungrodt of Milwaukee is more pessimistic. "It's really practical only if a
student is willing to take more than two
years to get through a two -year course.
If a student works half time -20 hours
a week -and is a very good student, he
might be able to carry a 14- credit load
instead of the usual 18 -20 quarter hour
credits. But he shouldn't plan to do it
on a regular basis."
If you do have to work, though, most
schools have facilities for helping you
find a part -time job that will interfere
least with your studies.
How about holding down costs by
starting your training through the mail,
then finishing up in residence? You'll
have to check with the individual school
here. Central has a regular program
designed to let you learn as much as
possible at home, some others will
work out such a schedule on an individual basis, others discourage it. But
if the school you want to attend does
offer such a plan, you can cut down the
total cost of your technician's training
by taking advantage of it.
1966 Foil Edition

How do

choose a technical school?

It isn't easy. There are hundreds of
schools across the country that teach

electronics ; some are excellent, others
barely passable. And it's not always
easy to tell which is which.
If you must stay at home, and if your
town has only one school, then you have
no problem. You'll take whatever is
available, and hope it's a good school.
But if you can pick and choose, here are
some guidelines.
First, if you're still in high school, go
to the guidance department. Chances
are they'll have detailed information
about many schools both in your neighborhood and farther away. Second, if
you're going to take an engineering technology course, find out whether the
curriculum at the school you're considering is accredited, either nationally or
regionally. Ask local educators -school
or college officials-about regional accreditation. For national listings, see the
Where To Write For More Information
section of this article. Lack of accreditation doesn't necessarily mean it's not a
good school, but you'll want to check
more carefully if the school isn't an accredited one.
Third, write the schools you're considering and ask for their catalogs. Compare the courses listed. You'll find that
some schools offer a far broader program and courses on a much higher
level -calculus, digital circuits, microwaves, telemetering and servomechanisms, for example -than others. Even
among accredited schools, some obviously give far more than others. Incidentally, you'll generally find that those
with broader courses take longer-and,
of course, cost more. Finally, check the
faculty listing. Faculty members of top rated schools have impressive qualifications, both in academic degrees and experience.
81

The man who finishes

...

ready to go to work."
Have got what it takes
for technical training?
I

WHERE TO WRITE FOR MORE INFORMATION

National Directory of Schools and Vocations. Miller &
Brown, State School Publications, N. Springfield, Pa.
One of the most complete lists of technical schools.
$12 in hard cover, or see at library or vocational
counselor.
List of Accredited Curricula Leading to First Degrees in
Engineering Technology in the United States. Engineers'
Council for Professional Development, 345 E. 47 St.,
New York, N.Y. 10017. 25 cents.
Characteristics of Excellence in Engineering Technology
Education. Professor W. Leighton Collins, Executive
Secretary, American Society_ for Engineering Education,
University of Illinois, Urbana, III. 61801. 25 cents.
The Engineering Technician. Secretary, American Society for Engineering Education, University of Illinois,
Urbana, Ill. 25 cents.
How To Choose Your Technical Institute, by Hartung.
Bellman Publishing Co., Cambridge 38, Mass. $1.00.
The following can be ordered from National Council of
Technical Schools, 1507 M St., N.W., Washington 5, D.C.:
Directory of Approved Technical Institute Courses. Free.
Admission Requirements for Approved Technical Institute Programs of Higher Education. A review of the
high school background best suited for success in
technical institute programs. 5 cents.

Code of Minimum Standards. This code sets forth the
requirements of the NCTS for approval of Technical
Institutes. 3 cents.
The Electronic Technician. Electronics has become a

major field of employment with electronic technicians
in great demand. This monograph details the work of
these technicians and the industry which employs
them. 5 cents.
The Engineering Technician: His Education, Entrance
Into Industry, and Place on the Engineering Team. A
set of charts placing the technical institute program
and the engineering technician in proper relations. 5
cents.
The Technician and the Engineer. Reprint of an address
by Dean C. J. Freund, University of Detroit. 3 cents.
The Technical Institute: Its Relation to Engineering
Education and Trade Training. Reprint of an address by
the late Dean C. W. Beese of Purdue University. 9 cents.

Experienced teachers and administrators at the best technical institutes can
tell almost at once whether an enrolling
student is going to complete his technological training successfully. Certain
characteristics show up in almost every
successful student. Here are the signs
some leaders in the industry look for:
Norman of Capitol Institute of Technology: "Good math background or aptitude. Inclination toward practical work.
And a great deal of motivation."
R. E. Baird of the Oregon Technical
Institute: "While in school, he will work.
If he doesn't understand, he will let you
know in no uncertain terms, and will
hound you until he does understand. He
really wants to learn."
Terzian of RCA Institutes: "First, a
sincere interest in the field. Second, self
discipline; the ability to sit down and do
the assignments, prepare the reports, do
the homework. He doesn't have to be
exceptionally brilliant, but it helps if he
enjoys math and physics and is good at
them."
Gershon of DeVry Technical Institute:
"Perseverance and desire are more important than high academic ability. I'd
rather give the poorer student who
wants to work a lot of help to bring him
up to the proper level than have the
gifted one who won't work or just isn't
interested."
Foster of Central Technical Institute:
"We look for a man who is primarily interested in technical rather than research
type employment. He'll have to like to
work with his hands."
Ungrodt of Milwaukee School of Engineering: "Ability to work and interest
in the subject matter. He should be a
good math and science student. But the
ability to work is the most important
thing. A man who wants to get something can really work. And he has something when he's through."
What he has, of course, is the key to a
career in electronics. Do you have the
qualifications? If so, pick out a good
school and prepare yourself for a lifetime of employment in one of the most
-ice
exciting fields on earth.
ELECTRONIC EXPERIMENTER'S HANDBOOK

OPERATION
IN

ACTIVATE
you can
only study at home,
you still can obtain
excellent training
to become an
electronics technician
If

PART 2:

HOME -STUDY TRAINING
By KEN GILMORE

electronics today, it's what you know
no room for the
half educated, the basement tinkerer,
the guy who isn't serious enough to prepare himself with a first-rate education.
And preparation is just the beginning;
learning doesn't stop once you're on the
job. One educational authority, borrowing the language of nuclear physics, estimates that the "half- life" of even the
best technical education is just ten
years. To put it another way, 50 percent of what you learn today will be as
out -of -date as the crystal set ten years
from now.
All of this adds up to one thing: If
you want to be a member of today's
fast -moving electronics team, you'll have
to get good basic electronics training,
then keep re- educating yourself from
there on out.

that counts. There's

There are two ways you can get a
technical education. One is to attend a
regular electronics residence school
trade school, technical institute, or college. It's a good way-especially for
basic training.
But suppose you can't. There's no
school in your town, or you have a family to support and can't leave your job.
Or you just don't have the cash to go to
a full -time school or college. These days,
you can get a first -rate electronics education at home. Scores of top -notch correspondence schools now offer an incredibly rich variety of courses, designed
to make you anything from a radio repairman to an expert in space communications. And once you're on the job, education through the mails is one of the
best ways to keep your knowledge up
to date.
Before you go rushing off to the nearest post office to get your application in,
however, you'll have to make a couple
of basic decisions: (1) Exactly what
kind of job -among the many fascinating ones available in the field of electronics-do you want to land, and (2)
Which school, which courses, will best
prepare you to reach this goal?
To make the right decision, you need
information. And that's what you'll find
in the following pages. The Editors
have talked to scores of education authorities across the country; we've
queried home -study school officials and
talked to their students and graduates.
Here are their answers to the questions
you'll be asking:

-a

What can

learn at home?

The answer is- almost anything. Vari-

ous schools approach the subject of
electronics in different ways, at different
levels. Some concentrate in one area.
Hollywood's Grantham School of Electronics home study division, for example, specializes in preparing you to
get an FCC First Class Radiotelephone
license-your ticket to a job in radio
or TV broadcasting or as a communications technician. Massey Technical Institute of Jacksonville, Florida, and
Chicago's Coyne Electronics Institute
emphasize training that will help you
go into the radio -TV service business on
your own.
International Correspondence Schools
84

(ICS) of Scranton, Pennsylvania, on the
other hand, offers a wide variety of
courses: electronics fundamentals, hi -fi
and stereo servicing, radio -electronic
telemetry, industrial electronics, and
many more. At Chicago's DeVry Technical Institute, you can choose among
all the standard courses and such up -tothe- minute fields as computer technology
and space and missile instrumentation.
Many schools offer courses on several
levels. "We advise beginners to take
courses in one of our career programs,"
says Jack W. Friedman, director of the
RCA Institutes Home Study School.
"These courses begin with basic electronics and lead through advanced
material in television, communications,
automation and industrial electronics,
transistors, or electronics drafting. Our
advanced courses, on the other hand,
serve more specific needs, such as helping a technician update himself or move
to a higher level."
Some schools offer only advanced programs. "Many courses are keyed for the
rank beginner," says G. O. Allen, president of the Cleveland Institute of Electronics (CIE) . "Courses of that type
serve a much -needed purpose, but we
prefer to leave the manual training to
them. For the man who has progressed
well beyond the intermediate level, we
offer a college-level course in communications engineering." Courses at Philco's
Technical Institute in Philadelphia and
Capitol Radio Engineering Institute in
Washington are also designed for the
working electronics technician or graduate engineer who wants to upgrade his
skills or keep up to date in this fast moving field.
What jobs can prepare for?
There's almost no limit. Home -study
graduates of Central Technical Institute
of Kansas City, for example, hold such
positions as engineering technicians in
aerospace research and manufacturing,
TV cameramen, studio and recording
technicians, maintenance and operating
technicians with airlines, police departments, railroads, and public utilities.
Some own their own radio -TV repair
shops. Virtually every major electronics
company in the country and many small
ones have on their staffs men working in
research and development, in manufacI

ELECTRONIC EXPERIMENTER'S HANDBOOK

you put in. Here are some typical examples.

Major programs at Capitol Radio Engineering Institute (CREI) in Washington, D. C., take about three years to
complete for the average student studying two to three hours a day. Costs
depending on the subject -hover in the
vicinity of $500 to $550 for the entire
course. DeVry estimates that the average student studying its $560 course
seven to ten hours a week can finish in
a year and a half. At CIE an FCC license course costs $325 and ordinarily
takes nine to ten months. Coyne's TV
servicing course costs $165, will occupy
turing, in testing-men who got their the average student a year and a half.
training or updated their skills through
National Technical Schools in Los
correspondence study.
Angeles offers a 150 -lesson master course
Take a few isolated examples from in radio, TV, and industrial electronics
one school -National Radio Institute in for $367. Each lesson takes three to
Washington, D. C. NRI graduate David four hours, and National Tech urges
F. Conrad of Reseda, California, is a students to finish at least one a week.
senior engineering aide for Litton Sys- Most, however, move faster and complete
tems; he checks out magnetic recording the course in one to two years.
devices for a living. Robert L. L'Heureux
All times quoted above are average;
of Southboro, Massachusetts, works for some students learn faster, some slower.
the data -processing division of Minneap- Put in twice as much time, and you'll
olis- Honeywell. Walter G. Higgins of finish twice as fast. Most schools have a
Portland, Oregon, was a mailman when time limit on finishing, too, but will
he studied electronics at home; after his grant an extension if you need it.
course, he transferred to the Department
One final point: Most schools give
of the Interior as an electronics tech- substantial discounts for speeded -up paynician and now maintains UHF and VHF ment, even lower prices for cash in adcommunications links. Jim Davis of vance. All prices given here are for the
Long Branch, New Jersey, troubleshoots most extended payment plans the schools
transistorized chopper -stabilized d.c. offer on a so- much-down, so- much -aamplifiers at Electronics Associates, Inc. month basis.
The list could go on endlessly.
By the way, you don't have to hesitate
Most schools claim that between 90% to pay in advance. All reputable schools
and 100% of their graduates obtain em- have fair refund policies if something
ployment in electronics. Says R. Parma happens to keep you from finishing.
of National Technical Schools in Los AnOnce I've received my diploma,
geles, "About 30% of our students are
are jobs easy to get?
currently employed in electronics. These
Will the school help me land one?
students feel that they lack the technical
skills to achieve advancement in their
If you don't already have a job in eleccompany. Another 60% of our students tronics (many home -study students do) ,
are employed outside of electronics, but most schools will help you find one. Many
desire to change their jobs because of have formal placement bureaus (some
the increasing opportunities in this invite you to use their services for the
industry."
rest of your life) ; others will simply
forward your grades and a letter of recHow long does it take, and how much
ommendation to prospective employers,
will it cost?
leaving the bulk of the job up to you.
Time to completion depends on three No reputable school, of course, guarmain things the contents of the course, antees you a job on graduation, any
how fast you learn, and how much time more than reputable universities do.

1966

Fall

Edition

Just how hard-or how easy- you'll
find it to land a job with good pay depends on several things. The training

happy to say the closed -door attitudes
exhibited by many employers in the past
have been cast out by progressive companies," says D. A. Lockmiller, ExecuNatuyou select is one of the big ones.
rally, you can't expect to get the same job tive Secretary, National Home Study
Council. "Now we hear this question:
-or the same pay-after finishingasa six
you 'What does he know and can he use it
month course in basic electronics
could after a comprehensive three-year well ?' That's a far cry from the old incourse in industrial electronics or ad- sistence on pedigree -Where did you go
to school ?'"
vanced communications systems.
Correspondence school graduates have
One vital factor in job hunting is frehigh- ranking positions in busiachieved
it
puts
quently overlooked. CIE's Allen
this way : "For CIE and other well - ness and industry, too. The national
trained students," he says, "job place- service manager of a large mail order
they store is a veteran of home study, as are
ment is not much of a problem
but many radio and TV station chief engiobvious,
will face realities. It seems
many young men from rural areas or neers, manufacturers, and company exsmall towns expect to find suitable em- ecutives. In fact, some educators think
ployment at home. They may find it, but that men and women with enough drive,
they should be prepared to go to the job ambition, and self -discipline to complete
correspondence courses are likely to be a
-the job will seldom come to them. A notch
above average. Recently, just on
his
in
works
seldom
college graduate
home town. The same is true of a high- a hunch, ICS sent questionaires to several thousand company presidents
ly-skilled professional."
Can home -study graduates compete for around the country, asking how many
jobs with those who get their training in were former ICS students. About half
resident schools? "What we're really answered. And of those, an astonishing
talking about here," says John Sivatko seven percent were, indeed, ICS alumni.
of ICS, "is what does the employer think. If all former correspondence students
If an industry is unfamiliar with the had been counted, the number would
quality of home -study training, there have been higher.
may be some prejudice against it. The
How about pay?
competence of the students is not that
It's impossible to give precise figures
different; the attitude of the employer
too much variation according to
there's
is the pertinent factor."
W. A. Robinson of DeVry makes an- geographical area, amount of training,
other point. "The resident student has branch of industry -even the state of
the advantage of meeting recruiters from business. But here are some samples
various industries who come to the that will give you an idea of the range.
school to interview. The home -study The U. S. Department of Labor's Occustudent, however, must go to the em- pational Outlook Quarterly shows avployer for his interview. Where home - erage technicians' salaries in private instudy programs compare closely with dustry starting in the vicinity of $4900
resident programs, employment will a year. Also, ICS reports that its gradprobably depend on how effectively the uates average $80 -$110 a week.
The range, however, can be far wider.
student presents himself to a prospec"Some of our recent graduates are well
tive employer."
In the past, some employers who hired over the $10,000 -a -year level already,"
resident-school graduates regularly were says Allen of CIE. "At the other exhesitant about putting home-study grads treme we have men who, because they
on the payroll. To some extent, the sit- are not willing to relocate or enjoy a
uation still exists. "It is only fair to certain type of electronics work, are
say that correspondence education does making as low as $2 per hour."
Don't overlook the possibility of worknot yet receive the recognition it should
as adequate preparation for initial em- ing for the federal government. Elecployment in the field," says CREI Execu- tronics technicians from GS3 to GS9
tive Vice President L. M. Upchurch. But earn from $4005 to $9425. You may want
the situation is changing-rapidly. "I'm to apply for a civil service rating at the

-if

;

ELECTRONIC EXPERIMENTER'S HANDBOOK

long ago and asked each one how much
money
any -he had made repairing
radios and TV sets in his spare time before he finished his course. Among them,
the 500 students had picked up more
than $100,000 while studying. That's an
average of better than $200 each-more
than the total cost of the course.

-if

O0
®om
o

Can I qualify for enrollment?
You can for most home -study courses
if you can read and write and really
want to get into electronics. The only
additional requirements come from
schools that offer advanced courses.
For example, CREI expects students
to have a high -school diploma and a job
or prior experience in electronics. The
whole course, in fact, is designed for the
working technician who wants to increase his skill and his pay check, not

for the beginner.
Several other schools have similar requirements, virtually all for advanced
courses. It wouldn't do you much good
to take a course in servomechanism
theory if you weren't yet on speaking
terms with Ohm's law.
How can
Illustrations
by John Hanna

end of your schooling to see if you can
qualify.
There's virtually no limit to what you
can make. Start your own business and

your ultimate earnings are determined
only by the sweat you're willing to put
into it and your ability as a businessman. You can advance rapidly working
for others, too. Listen to Charles J.
Roesle of Washington, D. C.:
"Six years ago I was at the end of any
advancement at $5500 per year. But
after completing a National Radio Institute course I passed a Civil Service
exam for an Electronics Production Engineer at $7000 per year. In May, 1961,
I was promoted to Guided Missile Project
Officer at $9000 per year. Recently, I
was promoted to Guided Missile Supervisor, with a salary of $11,500 per year."
Incidentally, while you're dreaming of
future riches, you can begin making
your home -study course pay its own way.
Peter Cooke of Coyne surveyed the
school's 500 most recent graduates not
1966 Fall Edition

pick the right school for me?

It isn't easy. There are hundreds of

schools across the country offering thousands of courses. Prices, estimated time
to completion, and many other factors
vary widely. But the job, while difficult,
isn't impossible. Here's advice from the
experts on how to proceed.
Says William B. Callahan, president of
Chicago's Commercial Trades Institute:
"Look for the schools offering courses in
the field you want to study. Compare
tuition prices, look for accreditation,
state licensing, and a good Better Business Bureau record." Adds J. F. Thompson of NRI: "Compare prices, faculty,
and reputation. If you're still in doubt,
Where can

get more information?

For more information on who offers which course and on accreditation, write to the National Home
Study Council, 1601 Eighteenth St.,
N. W., Washington, D. C. 20009, and
ask for the Directory of Accredited
Private Home Study Schools. It's
free.

Should kits be included in a home -study course?
can be made either construction in conjunction with corcase
A good
way. "At best," says M. E. Hough- respondence study, we know that
ton of DeVry Technical Institute, "a many of our students would find the
kit is a laboratory, a teaching device use of kits impractical because of
that's carefully built into the rest of military restrictions, travel, space
the course. Our students don't just limitations, and so on," says L. M.
assemble a kit. Eventually they Upchurch, Jr. "Further, since our
understand exactly why the kit is students are already employed in
electronics, their daily work frebuilt as it is."
Another point in favor: The kits quently gives them the advantages
to be constructed in many courses they might otherwise get from workare multimeters, signal generators, ing with kits."
One guideline, then, might be this:
scopes, and other useful test instruments. If you're planning to go into If you're a beginner with no elecservicing, these instruments can tronics experience and no prospect
of having a chance to work with
form the basis of your equipment.
Some schools, such as Coyne Elec- equipment during your course, you'll
tronics Institute, feel that kits aren't probably do well to select a course
necessary. A kit's primary purpose, with kits. If you will be working
the school maintains, is to familiarize with equipment, or if you're already
the student with actual electronic a practicing technician taking adhardware. "But most of our stu- vanced courses, then kits are far
dents begin to repair radios and TV less important, and in many cases
sets almost immediately," says Peter may not be needed at all.
And, of course, there's one other
Cooke of Coyne. "So they don't
important aspect: Courses without
need kits."
Capitol Radio Engineering Insti- kits, all other things being equal, are
tute offers another reason for the certainly far cheaper than those
non -kit course. "While we recognize with kits. Some schools offer courses
the value of properly integrated kit either way.

write one or more graduates." Many
schools will supply lists of graduates.
David Lockmiller of the NHSC offers
this thought: "First, the school should
be accredited by a nationally-recognized
accrediting agency. There may be one
or two good schools that are not accredited, but it is difficult to evaluate
these schools. Look for such things as
proof of performance, price, length of
the course. Examine a sample lesson,
check the employment features. No one
of these criteria is conclusive, but they
will help you to reach a final decision."
When you're making comparisons,
don't overlook some of the special or
bonus features a school might offer.
Some of these "extras" may not be of
value to you, but check to see what's
being featured by the school in addition
to the regular curriculum. Here are
some examples -by no means complete:
Consultation service. If you have a
problem on the job -say in the design of
88

a circuit or repairing a particularly
knotty trouble -some schools will have
a whack at helping you solve it.
Schematic service. One school maintains a file of more than a million schematics-from old Atwater-Kent radios
of more than three decades ago to the
latest color TV sets. For a small fee,
the school will copy any schematic and
send it to you -an invaluable aid in
troubleshooting.
Course tailoring. Some schools fit the
course precisely to your needs. If you already have some background in math or
electronics, you can get a series of tests
from some schools to see where you
stand. Then you start at the right place
and don't waste time repeating material
you are already familiar with.
Special devices. A midwest school
supplies a projector and training films.
Another school sends a transistor trainer
special board that allows you to rig
experimental circuits rapidly. Some

-a

ELECTRONIC EXPERIMENTER'S HANDBOOK

courses often take from 18 months to
two years. Despite this rather formidable assignment, we frequently have
completion percentages for individual
companies as high as 90 to 95 percent
sometimes 100 percent. These men are
highly motivated because the company
provides funds and often company time
for training, and is certainly in a position to influence the student's future
employment. On the other hand, we
sometimes encounter completion rates as
low as 10 to 15 percent for students enrolling individually for these same
courses. Self- discipline simply does not
produce the same results as discipline
administered by an employer. In some
courses that run up to three years, we
experience similar results from our
group enrollments, but an even lower
completion rate for individual students."
Despite these gloomy statistics, you'll
have a lot going for you. "Any reputable
school will do all it can to help the student finish the training he has selected,"
says DeVry's W. A. Robinson. "Most
schools keep a steady flow of inspirational and motivational material in the mail,
particularly to students who lag. In fact,
most schools bend 'Over backwards offering extra help to those they feel need
it. In the final decision, however, it is
the student himself who makes the decision to complete his training."
"The difference between a completer
and a non -completer," adds R. Parma of
National Tech, "is the degree to which
he allows himself to procrastinate. Procrastination is the student's worst enemy, but the fault does not always lie
with the student. Home study competes
with the family, sports, TV, etc. But
whether or not a student completes his
course depends on how he rationalizes
the importance of his time and career."
Just who can benefit from home study?
"Anyone who is interested in improving himself," says Robinson of DeVry.
"Anyone who will bend his mind and
back to the task," adds Hal Kelly of the
National Home Study Council.
"The question should be," says John
Sivatko of ICS, " `Who can benefit from
study ?' Home study is just a technique. If you can benefit from any kind
of learning, you can benefit from home
study."

schools offer programmed lessons; others
supply slide rules and other devices to
help you learn. No one feature should
determine which course you select, of
course, but consider them along with all

other factors.

What does it take to complete
home -study course successfully?
No reputable school will tell you it's
easy. But it can be challenging, interesta

ing, rewarding. The completion average
for home -study students is higher than
the national college average. The dropout rate in colleges is high in some
cases going up to a peak of 80cí' but
one out of every three students completes his home -study course.
Why do so many fall by the wayside?
"The two most important reasons," says
G. O. Allen of CIE. "are motivation of
the student and length of the course involved. For example, we conduct many
courses for industrial concerns. These
1966

Fall

Edition

There's no doubt that the country
needs more trained people. "Our economic progress today is being hampered
by an increasing shortage of skilled men
and women," says NRI's Thompson. "At
a time when four million people are jobless, newspapers are crammed with ads
for workers who can connect an electronic circuit, program a computer, service aircraft and missile equipment -or
even qualify for training in hundreds of
new skills that were unheard of 20 years
ago. To put it another way, there would
be virtually no unemployment if today's
four million jobless obtained the skills
to match business and industry's needs."
Correspondence education could play
an increasingly important role in training men and women for tomorrow's evermore- demanding jobs. In fact, the whole
notion got some pretty high -level en-

dorsement recently, as President JohnShould

son voiced this opinion: "Home -study
courses are an important link in the
ever-lengthening chain of educational

services our nation provides for its
citizens. They represent an important
resource in our society's commitment to
provide unlimited opportunities for every
American to reach his highest potential."
"We need correspondence education in
this country now more than at any time
in our past," says G. O. Allen of CIE,
who is also the recently-elected president of the National Home Study Council. "We have a tremendous shortage
of classroom facilities and qualified
teachers, and this shortage is bound to
get worse. Correspondence education
can easily help fill the gap."
Maybe it can fill a gap in your life, too,
and start you on a rewarding career in
the important and fascinating field of
electronics.

study at home or go to

If you're looking for controversy,
this is the question to ask. Of
course, if you have a job and a
family and can't simply take off and
go to a residence school, your choice
is easy. You'll study by mail.
But what if you do have a choice?
There's no doubt that home study
has important advantages. Among
them You can study in your spare
time, at odd hours, or while traveling. You don't have to leave home
or lose income. You can study at
your own pace. You don't miss
classes; they wait for you if you're
sick or busy. You can move from
one city to another without missing
a beat. And home study is certainly far less expensive than residence
training. You'll probably spend less
for an entire electronics course
lasting two years or more by mail
than for one semester in college.
But would you learn more in a
regular classroom? Actually, the
evidence shows it's the other way
around. One study by the dean of
the College of Education of the
University of Michigan showed that
correspondence students did slightly
better on exams than others who
:

residence school?

learned the same material in the
classroom. Several other studies
showed similar results. "You learn
by doing, not by copying someone
else," says Richard S. Frazer, president of Christy Trades School. "You
learn more thoroughly because you
do it all yourself."
Then should you study by mail in
preference to residence school? "If a
home -study student is willing to put
forth some effort toward self -improvement, we feel it is comparable
to the best resident -school training
to be found," says J. F. Thompson
of National Radio Institute. "It depends on the individual," says John
Sivatko of International Correspondence Schools. "Some people can get
more out of a home -study course
than they can in residence, and vice
versa." G. O. Allen of Cleveland
Institute of Electronics agrees.
"Much depends on the person," he
says, "his goals and motivation, his
geographical location, his time
availability, the nature of the subject to be learned, etc. I will state,
however, that other things being
equal, I do believe the student who
learns through a good home -study
ELECTRONIC EXPERIMENTER'S HANDBOOK

program not only learns better, but
retains it longer."
But C. L. Foster of Central Technical Institute says "We recommend resident school training if it
is at all possible. If resident school
is not practical, we recommend
home -study courses because we believe that worthwhile education can
be obtained through home study."
And W. A. Robinson of DeVry Technical Institute brings up another
point: "Some types of training are
offered at a more advanced level in
our resident school than through
home -study programs. In such cases,
we could not provide equivalent
home -study training."
Finally, L. M. Upchurch, Jr., of
Capitol Radio Engineering Institute sums up his feeling. "We do
not know of any authoritative comparative study of correspondence
as opposed to classroom -learning
that has indicated any significant
superiority of class attendance. Several studies, on the other hand, have
shown slightly better results from
home study.
"Comparing correspondence and
classroom study of technical subjects is difficult in one respect:
:

1966

Fall

Edition

laboratory work. Because CREI
students are, as a condition of enrollment, employed in the field of
electronics, we know that to a considerable extent their practical experience gained on the job is a
satisfactory substitute for supervised laboratory work. This is not
invariably true, however.
"In any case, we would not ordinarily recommend correspondence
study to a prospective student with
the qualifications, the means, and
the opportunity to attend a good
residence school in the same field.
(Nevertheless, there are some students for whom home study would
be the better choice.) Neither would
we claim that the average correspondence student completing our
course is as well prepared as the
average graduate of a comparable
program in residence.
"The value of home study," Mr.
Upchurch concludes, "is not as a
competitor of residence school instruction, but as a valid educational
method for individuals who want
and need further education, but
whose circumstances are such as to
make class attendance undesirable
or impossible."
91

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One Park Avenue, New York, N.Y. 10016

albums at $3 98 each. My
is enclosed. I
check (or money order) for $
understand that you will pay the postage. (Add 75g to
partially defray postage costs outside U.S.A.)
CHECK ONE: MONO
STEREO
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Name
DON'T MISS OUT ON THIS OUTSTANDING OFFER.
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Code_
EEH.66

ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER
4
AUDIO

STEREO
HI-FI
PROJECTS

Six months ago, when the introduction to this chapter in
the Spring 1966 Edition of the ELECTRONICS EXPERIMENTER'S HANDBOOK was being written, the Editors
discovered that Dave Weems had had speaker enclosure
projects in the six preceding issues. With one more project in the Spring Edition, and two different designs in
this Fall Edition, Dave has certainly carved a niche for
himself and ranks
our estimation -as the number one
designer and writer on build -it- yourself hi -fi speaker enclosures. A tip of our hat to Dave!
Besides enclosures, the Editors selected for publication in this edition of EEH the "Hi -Fi à Go -Go" color organ circuit developed by Don Lancaster. At first glance,

-in

this circuit might appear to compete with our cover photo
project, but the two construction projects are quite dissimilar. The "à Go -Go" lamps are high -wattage bulbs, as
compared to the low- intensity but very attractive Christmas lights of the Wortman project on page 21.

94
TOTEM POLES FOR STEREO

99
HI -FI À

GO -GO

LAMPS

105
THE "CINDERELLA"

David B. Weems
Don Lancaster

David

Weems

109
SOLID -STATE 6 -WATT AMPLIFIER FOR 10 BUCKS
Charles

Fenoglio

112
UNIQUE 99¢ SPEAKER ENCLOSURE
1966 Fall Edition

John N. Ayres

stereo speaker systems are simply two mono speakers connected to
a stereo amplifier. Any good system,
when duplicated, can be expected to perform well in stereo. But good stereo presents unique requirements.
The first requirement is that the system be able to provide perspective, or
give direction to the sound of individual
voices or instruments. Some of the
early stereo recordings seemed engineered for this purpose alone, with the
result that we got a "ping -pong" effect.
It was probably exaggerated effects such
as this one that caused some audiophiles
to condemn stereo hi-fi as inferior to
mono hi -fi. Regardless of the misuse of
directionality, however, without it there
would be little reason for stereo recording and reproduction.
There are a number of factors which
influence the ability to locate sound
sources, such as the difference between
sound intensity, waveform, and arrival
time at each ear. Another factor, and
one which influences the others, is the
ratio of arrival times of direct to reflected sound. If this ratio is made very
high, the sound source can be easily
located. In an extreme case, the pingpong effect is the result, with the music
coming from two widely spaced "holes
in the wall."
A second important requirement for
good stereo sound is an apparent enlargement of the source. One way to accomplish this is to simply enlarge the source
itself, i.e., use a large multiple speaker
system. Another way is to utilize reflected sound ( reverberation) to augment
the direct sound from the speakers.
Properly utilized, reverberation can give
the effect of a sound source even larger
than the room itself.
Other requirements for stereo include
the suitability of room acoustics, of
course, as well as the usual high -fidelity
characteristics of wide and smooth frequency response, low distortion, good
transient response, and wide dynamic
range.
MOST

TOTEM
POLES
FOR

STEREO
Sixteen"
one better with a
column speaker system
and a separate
bass speaker enclosure

Go the "Sweet

By DAVID B. WEEMS

Control of Reflections. It would appear,
in looking back over the above requirements, that there is a conflict. For directionality, we need a high ratio of

direct sound to reflected sound, but for
enlargement, we need a mixture of re94

ELECTRONIC

EXPERIMENTER'S HANDBOOK

fleeted sound with the direct sound. The
trick, then, is to control the reflections.
One way of controlling reflections is to
limit the dispersion of sound to one
plane, either horizontal or vertical. The
choice of which to use is an easy one
since horizontal dispersion gives good
distribution of sound over the listening
area, whereas vertical distribution does
little except bounce the sound waves off
the floor and ceiling. If we can limit
dispersion in the vertical plane and increase it in the horizontal plane, we can
achieve two benefits; more efficient use
of sound energy and an opportunity to
control the ratio of direct sound to reflected sound simply by positioning the

speakers properly.
Excellent horizontal dispersion of
sound can be obtained from a vertical
line source. A single loudspeaker acts
like a point source, radiating sound in
the form of a spherical wave. which
spreads out in all directions at once. The
sound wave propagated from a line
source, however, travels outward in a
cylindrical pattern. If we use several
speakers to produce the sound and mount
them in a straight line, we can approximate a line source. By making the line
a vertical one, we can concentrate the
sound into horizontal dispersion and conserve some of the energy that a point
source squirts out in the vertical direction. Reflections from ceilings and floors
are minimized.
A vertical column, of course, is not a
new idea in sound reproduction; column
speakers have been known and appreciated for years by the manufacturers of
public address systems and by the sound
engineers who install them. Perhaps one
reason for the acceptance of column
speakers by public address people was
the fact that their p.a. systems had to
be used in such impossible acoustic environments as half-empty gymnasiums
with their hard reflective surfaces.
"Sweet Sixteen" Concept. The benefits
of using multiple small speakers for low
distortion are well argued by the popularity of such systems as the "Sweet

Sixteen" (POPULAR ELECTRONICS, January and April, 1961) Critics of these
multiple speaker systems insist that they
produce no measurable low frequency
bass or extreme highs. However, pro.

1966 Fall Edition

as a square. This results in identical
distances between identical speakers,
which causes certain points in their frequency range to be boosted or cut, and
peaks or valleys appear in the response
curve. These variations are measurable
and have contributed to the criticism of
the whole idea of multiple speakers.
An obvious answer to this deficiency
is to use the Sweet Sixteen concept where
it is strongest and to eliminate its weaknesses. The prescription for changing
the Sweet Sixteen into something really
great is to install a crossover network,
add woofers and tweeters, and string the
mid -range speakers to create a line
source of sound.

For awhile, when the "totem poles" were being developed, the workshop looked like a hi -fi supply house.
The single woofer gave way to separate woofers.

ponents go right on building Sweet Sixteens, indicating that there are benefits
that can't be measured. One reason, perhaps, is the apparent enlargement of the
sound source. Those who have heard a
multiple system usually admit that the
speaker arrangement does have something to offer.
One deficiency multiple speaker systems have is that the speakers must be
mounted in a concentrated pattern, such
20"
18

1/2"

2"
-

/2"

i+3/4"

PORT

Speaker Selection. If you already have
a Sweet Sixteen system that you want
to update, you can split the speakers
into two groups of eight each. Ten speakers were used in the system shown here
to obtain an 8 -ohm impedance, but omitting one pair would not appreciably affect
performance.
Either 4- or 5 -inch speakers can be
used with the design shown. If you are
buying new speakers, choose them by
magnet weight rather than size. Avoid
consideration of arbitrary phrases such
as "heavy duty," "heavy magnet," etc.
Magnet weight should be about 1 ounce
or more. Actually, magnet weight by itself is not a foolproof way of determining
magnet size. Look for the gauss rating
-the larger it is, the better.

2 "P281

3- /2"

3/4X3/4"
CLEAT

6 -1/4'

"X2'
(3/4X1-1/2 ")
1

29'

23-

CLEATS

/2'

6-I/4"

I-1/2"

Electro -Voice speakThe author attached poles to his
column speakers so
the systems could be
rotated and aimed at
the audience. Sound
radiation from column
speakers is mostly
horizontal with little
ers.

zz"

3/4,

These drawings show
all the necessary woodworking details. A Bill
of Materials is given
on page 98. Width and
depth of the ports in
the combined bass
speaker enclosure are
somewhat critical as
ports are cut for the

3/4'X3/4'
DUCTS

I.-

CLEAT

I-1/2" 1

vertical dispersion.

NI-I/2"F00T
INSIDE VIEW
RIGHT SIDE
COVER REMOVED

ELECTRONIC EXPERIMENTER'S HANDBOOK

The small speakers can all be of a
single brand and model, but a slight improvement will be gained by using two
different brands. If you do, pair off the
unlike speakers and connect them in
parallel, then connect these pairs in
series. Ten speakers, each having a 3.2ohm voice coil, provide a final impedance
of 8 ohms when wired in this manner.
There are small foreign -made speakers
available with 8 -ohm voice coils. If you
want to use some of these, you'll need
a different wiring arrangement. To obtain an impedance of 8 ohms, you can
parallel three speakers in one set, and
wire three sets in series for a total of
nine speakers to handle the mid -range
instead of ten. For a 16 -ohm hookup,
use eight 8 -ohm speakers-four parallel
pairs in series. Don't try to use speakers
of mixed impedance ratings in the same
system unless you are sure you can design a circuit that will provide equal
power to each speaker. You might end

7-I/2'

33
4"

SPKRS.

22"

27"

up with one or two speakers doing all
the work.
While you can substitute other woofers
with good results, the Electro -Voice
SP8B specified in the Bill of Materials
is highly recommended. It was the final
choice over the other 8 -inch woofers that
were tested for this particular application. Of course, you can use separate
woofer systems, or other quality brands
of woofers in the manufacturer's enclosures, if you don't mind having two
woofer cabinets plus two columns in your
living room. The compelling reason to
put the two 8 -inch woofers in a single
enclosure is to keep the cabinet population within acceptable limits. You also
gain the advantage of mutual coupling
between the two woofers with improved
low- frequency performance.
There is an alternative, though, particularly if you have an amplifier that
will tolerate mixing of the two stereo
channels (some transistor amplifiers
won't) . The alternative is to use one
woofer for both channels, but the woofer
should have either a dual voice coil or
an added mixer transformer to which
the bass from each channel is fed. For
the latter method, a possible choice is
the Electro -Voice XT -1 transformer with
an E -V SP12B either in the manufacturer's enclosure or in "Mr. Thuras' Magic Box" ( Spring, 1966, ELECTRONIC ExPERIMENTER'S HANDBOOK) .

3/8"

TWEETER
CONTROL
TWEETER

MIDRANGE
CONTROL.

3/8"
60"
61

-1/2'

IS 3-1/2" FOR 4' SPKRS.
4 "FOR 5' SPKRS.
TWEETER HOLE IS 2- 15/16"

DAMETER OF SPEAKER HOLES

1966 Fall Edition

It is also possible to substitute other
tweeters for the University T-202 specified, but you must check for similar
wide -angle dispersion characteristics
first. (Note that the totem pole control
of dispersion angle is essentially for midrange sound.) The T -202 has its own
built -in filter network and is hooked
directly across the output of the amplifier. If you substitute a tweeter without a high -pass filter or with a filter
operating at a different crossover frequency (other than 3000 cycles), then
you'll have to change the wiring or the
crossover network to obtain the required
crossover frequency.
Some of you may note that the wiring
of the crossover network is unusual and
somewhat different than any shown in
University's instruction book. The
changes were made necessary by the use
of a 16-ohm woofer and a tweeter with a
high -pass filter set at a frequency not
97

AMPLIFIER

16f10
TWEETER

8n0

CONTROL

-0-

0-0

3 4

>-O 0 0

MID RANGE

CONTROL

0 0 0 0

o 0 0
5

L PAD

N-28

N-2A

TWEETER

6 7

In wiring a "totem pole," this diagram must be followed.
Be sure to phase the mid -range speakers so that all of
the cones move in the same direction at the same time.

4 4
MID RANGE

covered by the manual. As used here,
the University N -2A acts as a frequencydividing network operating at 350 cycles,
and the N -2B serves as a low -pass filter
at 3000 cycles.
BILL OF MATERIALS
Speakers and Accessories
Electro -Voice SP8B 8 -inch woofers

2T -202 tweeters
2- University
20-4" or 5" mid -range speakers
crossover networks
2- University NN-2A
-2B crossover networks
2- University AP-8
controls for mid -range
2- University

liK

WOOFER

speakers
Lumber for Two Columns
x 60" pieces of 3" fir plywood (for
2
speaker panels)
4-4" x 60" pieces of 3" fir plywood (for sides)
4-4" x
pieces of 34" fir plywood (for tops
and bottoms)
2-71/2" x 611/2" pieces of %" fir plywood (for
backs -optional)
Lumber for Woofer Enclosure
1 -18 1/2" x 231/2" piece of 34" fir plywood (for
speaker panel)
1 -181/2" x 271/2" piece of fir plywood (for

-6"

7/"

back)

2 -161/2" x

281/2" pieces of 34" fir plywood

(for sides)

1 -161/2."

x 181/2" piece of

bottom)

fir plywood (for

piece of Y4" fir plywood (for
x 181/2" pieces of 34" fir plywood

-161/2" x 20"

-6"

top)
(for

duct panels)
-1/"
x 22" pieces of 3" pine (for cleats on
speaker panel)
2 -1 /" x 26" pieces of 3" pine (for back
cleats)
-1 /" x 181/2" pieces of 3" pine (for back
cleats)
2

4 -3/4" x 141/2" pieces of

%" pine (for corner

cleats)

Miscellaneous

screws (for small
-#8 x /" sheet metal
and crossover networks)
84-#8 x PA" wood screws (for woofer enclo104

speakers

sure)

-Tool

or "gripper" clips (to fit lamp poles,
if used)
plastic veneer, glue, finishing nails,
cloth,
Grille
fiberglass
2

inside of an unfinished bass reflex cabinet
shows the two University N -2A crossovers attached
to the front panel. See the wiring diagram above.

A peek

Construction. The speaker enclosures,
both the woofer box and the columns,
are constructed from 3/4 -inch plywood.
The columns are quite simple in design,
and should cause no difficulty, but you
should wait until you decide whether you
need a back or not before putting on the
plastic veneer covering (see Speaker
Placement section of this article)
(Continued on page 145)
.

ELECTRONIC EXPERIMENTER'S HANDBOOK

1114x À GO -GO LAMPS

Add a new
dimension to your hi-fi
... in color
By DON LANCASTER

WHY BE SATISFIED with just listen-

ing to hi -fi programs when for a
sawbuck you can have the added enjoyment of seeing what you're hearing, and
intriguing all your friends. A pair of
ten dollar bills will get you two sets of
audio controlled lights to let your stereo
system really brighten up the place. For
those who want something different, it's
quite a conversation piece.
With the A Go -Go circuit, the brightness of one or more incandescent lamps
is controlled by an audio signal. Its
full -range proportional control is capable of bringing the lights from full darkness to full brilliance; the louder the
sound, the brighter the lamps. You can
use it to control up to 200 watts of light,
and with modification and a few dollars
more, up to 2000 watts. The unit is
about the size of two ice cubes.
How It Works. Sounds fed into J1 are
stepped up by Tl, rectified by D1 and
filtered by C2 only to become a control
voltage for trigger diode D3. (See Fig.
1.) It takes 30 volts to make D3 conduct. The time required to build up 30
volts on C3 depends upon the amplitude
of the sound and the values of C3 and
R2. The louder the sound, the quicker
the voltage buildup the larger the re;

1966

Fall

Edition

sistor or capacitor, the longer it takes
to build up the voltage.
When D3 fires, it triggers the SCR
into conduction only if the SCR anode
also has a positive voltage on it. Once
the SCR fires, it continues to conduct
until the anode voltage drops down to
about 0. This happens each time the
line voltage waveform goes through
zero. The SCR will remain off until another pulse is applied to its gate. The
sooner the gate pulse occurs when anode
voltage is present determines the amount

Fig. 1. Ratio of "on time' to "off time" of SCRI
changes in step with music levels, and brightens or
darkens different colored bulbs plugged into SOI.

11/4°
ALL HOLES

#60 DILL
OR

3/64'DIA

I-3/4

FOIL SIDE
Fig. 2. Printed circuit board is shown actual size to
help you make your own. However, almost any suitable chassis or breadboard arrangement can be used.

PARTS LIST

C1- 0.02 -s/., 200 -volt Mylar capacitor
C2-0.05 -µf., 200 -volt Mylar capacitor
C3- 0.1 -14., 200 -volt Mylar capacitor
C4- 0.005-µf., 600 -volt disc capacitor
DI, D2, D4- 1N4003 diode
D3- Trigger diode (Texas Instruments TI -42

optimize the circuit to prevent premature turn -on of the SCR and allow more
accurate proportional control by discharging C3 before a new "on" cycle
begins.
As the audio is used for bias only,
little audio power is consumed. The
A Go -Go has high sensitivity and very
little volume is needed to drive it.
Construction. Start construction by
laying out and etching the printed circuit board shown in Fig. 2. Drill holes
and mount components as shown in Fig.
3. Watch the polarity -one wrong connection can destroy the semiconductors.
After you've finished the wiring, connect an a.c. socket and plug to the board
and test the A Go -Go with a 25 -watt bulb.
The bulb should glow slightly with no
audio. A fairly low level audio signal
should drive the lamp to full brilliance.
If this test checks out okay, test the
board using the lamps and audio source
(Continued on page 104)

equivalent)
jack
33,000 -ohm, /2-watt resistor
R2-39,000 -ohm, ,4 -watt resistor
R3-200,000 -ohm, % -watt resistor
SCR1- 2N3528 silicon-controlled rectifier
S01-Chassis-mounted a.c. socket (Amphenol
61 -F or equivalent)
to
T1- Output transformer, 4 ohms primary-203
10,000 ohms secondary (Thordarson TR
or equivalent)
Full -wave bridge rectifier module, 1.5 amp.,
200 volts (Motorola MDA942 -3)

/1 -Phono

RI-

11-Chassis -mounting
or equivalent)

NOTE'
FOIL PATTERN
IS ON BACK SIDE

a.c. plug (Amphenol 61 -M

-Case (Millen 74400 or equivalent)
1 -2" square of 1/16" single -sided circuit board
Misc.- Silicon potting compound, hookup wire,
1

solder, pop rivets or screws

of time during each half -wave that current can flow through the lamps plugged

into 201.
Neither the eye nor the lamps can follow the 120 -cycle unfiltered pulsating
voltage out of the rectifier module, but
the lamps do respond in a proportional
manner. The brilliance of the lamps is a
function of the ratio of "on" time to
"off" time; or the louder the music, the
brighter the lights.
Capacitor Cl serves as a filter to prevent the switching transients in the
A Go -Go from getting back into the
power line and causing AM -type radio
interference. The other components
100

Mount the jack and socke s in the case
before connecting them to the circuit. if space is
not a factor you can add more features. See text.
Fig. 3.

ELECTRONIC EXPERIMENTER'S HANDBOOK

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1966 Fall Edition

103

you plan to have in the permanent installation.
For best appearance and greatest sensitivity, the display lamps should barely
light with no audio input. A different
background level can be obtained by
changing the value of R2; increasing its
value will decrease the background light
level. You might also experiment with
C2 -use too small a value, and you'll
have a choppy response; too large, and
the response will become mushy.
The components are mounted inside a
modified Millen octal base and shield.
Cut the shield to about 134 long (see
Fig. 4), and drill or punch a 1`'f ;4"
keyed or r;32" round hole in the top
for the socket. Drill a '744" hole in
one side of the shield for the audio

jack. Screws or rivets can be used to
fasten the two parts of the case.
Once you've wired the board, socket,
and audio jack, you can pot the circuit
in silicon rubber. To do this, turn the
A Go -Go upside down and place small
bits of tape over the inside openings of
J1 and 21. Then pour in about half an
inch of rubber and let it set. The printed
circuit board is then positioned in place
and another half inch of rubber added.
Complete the assembly by connecting
the plug.
Modifications. The A Go -Go operates
on 117 -volt, 60 -cycle lines and utilizes
incandescent lamps only. For the unmodified unit, you can use a total of 200

watts maximum, but for cooler operation and longer life, 100 watts or less is

advisable.
If you plan to use a bigger package
than the modified Millen shield, you might
adá a 250 -ohm potentiometer in the input
circuit as a sensitivity control, and replace R2 with a 250,000 -ohm potentiometer to serve as a variable background
control. A selector switch with several
capacitors (0.02 µf., 0.05 µf. and 0.1
µf.) to replace C2 will give you control
over lamp response.
More power is a snap, but it will cost
extra and you'll definitely need a bigger
(Continued on page 114)

Fig. 4. Octal base shield houses all components.
If desired, silicon rubber can be poured into the
case to keep the printed circuit board in place.

104

ELECTRONIC EXPERIMENTER'S HANDBOOK

Build The
ßß

By DAVID B. WEEMS

Half-cubic foot sealed enclosure costs under $10
IF

YOU'RE thinking of putting down

$30 or more for one of those depart-

ment store "no name" speakers in a box,
wait. Here is a little hi -fi speaker system that can save you money and will
probably sound better. At least you will
know what went into the box! And you
won't find a similarly well- constructed
enclosure with a good -quality small
speaker system on the market for anything like this price. If your idea of
what $10 will buy in speaker systems is
based on what was available just a few
years ago, the Cinderella system will
amaze you.
The secret of the Cinderella is in the
design and construction of its XS -5052
woofer. This woofer's distinctive qualities are noticeable in two ways. The
first is the obvious visual differences between it and a normal 6 -inch speaker.
Second, and more important, there is a
distinct aural difference, which can be
made apparent by a frequency test run.
1966 Fall Edition

Test Results. I set one of these woofers on my workbench and hooked it up
for the usual bass resonance frequency
test, starting downward from 200 cycles.
Although most 6 -inch speakers resonate
at about 120 to 150 cycles, a few "hi -fi"
6- inchers have a bass resonance of
around 70 cycles, and, frankly, that is
where I expected this woofer to fall.
Low resonance is the crucial characteristic for woofers to be used in small
sealed enclosures; the restricted air volume in such systems will raise the point
of resonance.
My eyes were glued to the oscilloscope
screen as the audio generator dial passed
70 cycles, then 60. Not until 48 -49 cycles
did the voltage across the speaker reach
a peak, indicating resonance. A remarkably low frequency for a $4 speaker.
The remainder of the system consists
of a small cone tweeter with its selfcontained capacitor which acts as a high pass filter, and an enclosure that occupies
105

1/2"

18'

{"-1

10 -1/4'

L
5 -3/8"

6-3/8_H

4 -1/4

ALL MATERIAL
3/4' THICKNESS

"A" SIZE ENCLOSURE
FOR ONE WOOFER-TWEETER

I/2

PAIR

IÌ"

18"

1-9-1/2-.1

2 -1/2"

3-1/2"

3/4"
CLEATS

a'v2
2 -1/2'

ALL MATERIAL

3/4'T HIC KNESS

"B" SIZE ENCLOSURE
FOR DUAL WOOFER TWEETER COMBINATION

Six -inch woofer costs only $3.95 but has surprising
low end response. Tweeter is not sold separately.

Most builders may be satisfied with single woofer tweeter combination, but dual system sounds better.

BILL OF MATERIALS
-A" System-Total cost, $10

1- Woofer -tweeter

combination (Stock No. XSTS-63, McGee Radio Co., 1901 lIeGee St..
Kansas City 8, Mo.; woofer available separately as XS -5052 for $3.95)
2 -91/2" x 16" pieces of %" fir plywood for front
and back
1 -71/22" x 171/2" piece of 3/" clear pine for top
(1 x 8)
1
x 16" piece of %" clear pine for bottom

-7/)"

(1x8)

-71/2"

x 101/4" pieces of

(1 x 8)

-34"

x 91/22" pieces of

for back)

%" clear pine for .sides

pine (side cleats

-1"
x 141/2" pieces of ."
bottom cleats for back)

pine (top and

-#8 x 11/4" wood screws for back
-#6 x 1/2" sheet metal screws for speakers
1--1" x 24" s 30" sheet of fiberglass
[Misc. -#6 finishing nails (% lb.), caulking ma12
8

terial, glue, and grille cloth
"B" System -Total cost, $18
Woofer- tweeter combinations (Stock No. XSTS-63, McGee Radio)
2-12" x 18" pieces of %" fir plywood for front
and back

-11" x 191/2" pieces of 1" fir plywood for top
and bottom
2-11" x 12" pieces of 3/4" fir plywood for sides
2

2 -1/4" x

back)

2 -1/4

12" pieces of 1/4" pine (side cleats for

x 161/2" pieces of 3.4" pine (top and bot-

tom cleats for back)

-#8 x 11/4" wood screws for back
-#6 x %" sheet metal screws for
mounting
-1" x 24" s 60" skeet of fiberglass

14
16

The Cinderella enclosure is caulked and sealed, requiring use of sturdy front, top, back, and side
panels. The author was satisfied with 3/4 -inch pine.
106

Misc.-#6

speaker

finishing nails (1/2 lb.), caulking ma-

terial, glue, and grille cloth

ELECTRONIC EXPERIMENTER'S HANDBOOK

That leaves 37 cents to squander on
grille cloth and trim. You can use screen
molding for trim (as I did-15 cents for
a cabinet) and decorator burlap will
serve as grille cloth at 49 cents a yard
(17 cents) . If anyone mentions finishing the wood, you will find that 5 cents is
still available. and that is just about the
amount of shoe polish I used to stain
and "oil finish" the model shown. For
very little more, you can use a veneer
plastic, such as Contact. Or choose a
hardwood if you want fine cabinetry.
The sound can be improved by putting
two sets of the woofer -tweeter combination ($12.95) in one "B" size cabinet
(see page 52) at a cost of about $18.
Used in multiples, these little speakers
sound even better. There is more solidarity in the bass and somewhat smoother
sound throughout the whole spectrum.
Also, the impedance curve tends to flatten out when two woofers are hooked in
parallel.
Nail side to bottom and front of the enclosure.
In buying material, note that the
Good fit and a liberal use of glue are important.
:'í" x 712" pine shown in the drawing is.
only ''í sq. ft. of shelf space. The sys- of course, what lumber yards sell as
tem is called the Cinderella because. "1 x 8 ". When you have cut all parts
while it bears no apparent pedigree, it to the specifications shown, set them up
does show inborn quality. For example, as in the finished enclosure. At this time
even in the small enclosure, the system you can trim any'of them that do not fit
resonance is a little over 70 cycles. The satisfactorily. One of the economies in
transient response is surprisingly good this system, in time as well as money, is
for a low -cost system. As in all small the avoidance of many cleats which
sealed enclosure systems, efficiency is would require the use of extra screws.
lower than in a large system, but a 7- nails, and glue. The nailing system
watt amplifier supplied all the sound shown in the diagram is quite adequate
you would want in a very large but very for such a small enclosure, but a good
live room. The Cinderella is rated at fit is necessary.
12 watts.
Construction. Begin construction by
Budgeting Your Money. The enclosure nailing the bottom to the front, using
is sturdy, contains sufficient damping plenty of glue between these two parts.
material, and is thoroughly sealed. Any Next, nail one end to the bottom and
one of these features may be missing front. Continue with the other end, and
from a department store box. For the finally nail down the top to the sides
skeptic, here is a rundown of how to and front.
The cleats for the back can now be
budget your money to build the Cinattached, using glue and nails as with
derella "A" system for only $10.
the exterior parts; but if you use the
$6.90
Speakers
same kind of nails, they must be cut
.55
Plywood for front and back
just
short enough so they will not pene.75
Pine for top, bottom and sides
the outer surface of the sides and
trate
.26
Screws
A somewhat easier method is to
top.
.25
Glue
use a different nail, such as sheet rock
Fiberglass
.66
nails which have a large head and are
.20
Caulking material
.06
Nails
the correct length.
The joints should be caulked even
Total
$9.63
1966

Foil

Edition

107

Front view of an experimental "B" system built by
the author to test front and side panel vibration.
This enclosure was built using cleats and screws,
unlike the plans on page 106. Fir plywood was also
used and the enclosure covered with a plastic veneer. It was determined that gluing and nailing of
the panels would be adequate if care was exercised
in fitting the panels together. A grille cloth was
later installed to protect the speakers. Wiring of the
"B" speaker arrangement is shown below. Try the
8 -ohm tap instead of the 4-ohm output of your
amplifier if the bass response seems a little thin.

A SYSTEM

TWEETER

though they seem to be thoroughly sealed
by glue. The caulking material can be
purchased in a cylinder for use with a
gun, or in a squeeze tube. Most building
supply stores have guns to loan, but
some rent them. Force the caulking material along the joint and wipe away excess with a rag so it won't flow onto
the speakers.
The speakers are mounted and wired
as shown in the diagram. The back
should be drilled to allow speaker connections to pass through. The wires can
be brought out through a small hole
which is later filled with caulking material or sawdust and glue, but a better
method is to use small bolts as connectors through the back.
Padding is extremely important in a
small sealed enclosure. Tests indicated
that the Cinderella's resonance could be
lowered 10 cycles or more and the bass
range greatly extended by the use of
proper padding. The whole interior of
the model shown is lined with a 1 -inch
layer of fiberglass. You can get fiberglass from most electronics stores; a
common size measures 1" x 24" x 60 ",
enough for two cabinets. Cut the fiberglass to fit all interior surfaces, except
the front baffle, and secure it in place
with tacks or glue. Then fold the remainder of your sheet of fiberglass so
that it will fit into the enclosure loosely.
This should fill the enclosure.
Now fasten the back in place with the
screws specified, hook the Cinderella up
to your amplifier, and try on the "glass
slipper." That, naturally, is a suitable
wide range program source. When you
do, you'll be glad you didn't settle for
a pig in a poke.
- 30

RED
DOT
TO BA
AMPLIFIER TAP

rÌ

SYSTEM

AMPLIFIER TAP

Be sure to follow this wiring diagram to keep the
speakers in phase. Once the enclosure is sealed,
you may find it fairly difficult to change the wires.
108

After filling cavity behind speakers with padding,
cleats should be caulked and back -nailed into place.
The usual household caulk works out just right.
ELECTRONIC EXPERIMENTER'S HANDBOOK

By CHARLES E. FENOGLIO

SOLID -STATE

6 -WATT AMPLIFIER
FOR 10 BUCKS
All -purpose push -pull audio amplifier operates on wide range of
input voltage and output impedance without bias adjustments
I F YOU would like to have a quality,
I low -cost amplifier for a hi -fi or public

address system -one you can use at
home or in your car, and can convert
into a speech amplifier, modulator, or
high -power intercom -then try your
hand at this transistorized "Six -Watter."
You can build it in less than two hours,
at a cost of about $10.00. All components can be mounted on a printed circuit board, and construction is easy.
Several novel circuit features make
it possible to use few parts, eliminate
transformers, and achieve high efficiency. A unique d.c. bias stabilizing network eliminates the bias adjustments
normally found on this type of amplifier and permits operation with a wide
range of supply voltages without modification.
The excellent low- frequency response
of the Six -Watter is due in part to the
absence of transformers and the use of
high -value coupling capacitors as well as
direct coupling. High -efficiency Class B
operation makes it ideal for use wherever
battery life is an important consideration. Power consumption from a 12 -volt
battery under no- signal conditions is less

than

1966

Fall

watt.

While the amplifier can work on any
Edition

supply voltage ranging from 3 to 15
volts, the higher the voltage source, the
greater the audio power output you can
get. An input signal of less than 0.2
volt is sufficient to drive the Six -Watter
to full output. This is more than adequate gain for most tuners, and crystal
or ceramic phono cartridges.
How It Works. Audio input is coupled
to the base of transistor QI through capacitor Cl. The amplified signal at Qi's
collector is direct-coupled to the base of
Q2. Here again, the signal is amplified
and directly coupled to Q3 and Q4.
Transistors Q3 and Q4 work in opposite
directions; while one is conducting more,
the other is conducting less -their output signals are 180° out of phase with
each other. This type of circuit makes it
possible to drive a push -pull output stage
without the aid of a transformer.
The signals from Q3 and Q4 are directly coupled to Q5 and Q6 respectively.
Transistors Q5 and Q6 operate as Class
B power amplifiers. Balanced operation
requires that the product of the current
gain of Q3 and Q5 be equal to that of
Q4 and Q6.
The filter network, C2 and R4, prevents audio voltage variations at point
109

2AMP

3 TO
RI

39K

15V

2N554

2N 305

03
291304

OI
C
3

INPUT
CI

109f.

47(1

47n

IN2069

29554

10009 f.

04
291305
C2

I009f.
SPKR

3.2R

680(1

39K

L
VOLUME CONTROL
100K

TUNER

gMPLIFIER
INPUT

(SEE TEXT)

Fig. 1. The audio amplifier uses a novel six-transistor circuit requiring

neither transformers nor bias adjustments. It operates with supply
voltages of between 3 and 15 volts. An input signal of 0.2 volt is sufficient to drive it to full output. Volume control can be added if desired.

PARTS LIST

C1- 10 -µf., 10-volt electrolytic capacitor
C2- 100 -sf., 10 -volt electrolytic capacitor
C3- 1000 -µf., 15 -volt electrolytic capacitor
D1- 1N2069 (or any 750 -ma. silicon diode)
F1- 2-ampere fuse
Q1-2N1694 transistor (or 2N167, or 2N2925)
Q2, Q4 -2N 1305 transistor
Q3-2N1304 transistor
Q5, Q6 -2N554 or 2N2148 transistor
R1, R2- 39,000 -ohrn, -watt resistor
R3, R4, R5- 1000 -ohm, 1/2-watt resistor
R6-680-ohm, -watt resistor
R7, R8- 47-ohnz,' -watt resistor

fizz

1- Printed circuit board, available from Hazleton

Scientific Co., Box 163, Hazel Park, Mich.
48030 for $2.85 postpaid with all holes drilled
and for $1.95 postpaid uudrilled
2 -1%" x 21/2" x 1/16" heat sinks, copper or aluminum

from reaching Q1's emitter.
This results in a high degree of d.c. stability without affecting the a.c. gain of
the amplifier.
Any speaker impedance ranging from
1.6 to 16 ohms can be used. Because
power output is a function of speaker
impedance, and source voltage, stick to
a 3.2-ohm speaker and a 12 -volt source,
if possible.
A in Fig. 1

Construction. You can make your own
circuit board, or purchase one for $2.85
110

Y.:,

64R8)-0

0-(DI1)-0

0{R5)-0

-1 R4

o-{R7

}-o

0-( R2 Ye

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Experimenters Handbook 1966 Fall

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