Experimenters Handbook 1965 Fall

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FALL EDITION $1.2b
1

6OMIif

e.uu .

ELECTY

ELECTRONIC

EXPERIMENTER'S

HANDBOOK
PROJECTS
GALORE
----SCIENCE FAIR
AUDIO
HOUSEHOLD
AUTOMOTIVE
TEST EQUIPMENT

HI-FI
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HAM RADIO
CB AND TV

PLUS:
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SECTION
"THE
FABULOUS
DIODES"

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1966

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1965 Fall Edition

---

N EW
VHF/UHF
UNITIZED TRANSMITTERS
50 mc -420 mc

FROM
INTERNATIONAL
International's new unitized VHF/UHF transmitters make
it extremely easy to get on the air in the 50-420 mc range
with a solid signal. Start with the basic 50 or 70 mc
driver. For higher frequencies add a multiplier-amplifier.
All units are completely wired. Plug-in cables are used to
interconnect the driver and amplifier.

220 mc

50 or 70 mc

144 mc

DRIVER/TRANSMITTER

MULTIPLIER/AMPLIFIER

MULTIPLIER/AMPLIFIER
two 6360
tubes providing 6 to 8 watts
output on 220 mc. Requires
ADD -57 for driver. Heater
power: 6.3 volts @ 1.64 amps.

The ADA -144 uses two 6360
tubes providing 6 to 10 watts

The AOA-220 uses

(specify

output. Requires AOD-57 for
driver. Heater power: 6.3
volts @ 1.64 amps. Plate

Plate power: 250 vdc @ 50 ma.
$69.50
AOD-57 complete

power: 250 vdc @ 180 ma.
$39.50
AOA-144 complete

Plate: 250 vdc @
AOA-220 complete

RELAY BOX
Four circuit double throw.
Includes coil rectifier for 6.3
vac operation.

FILAMENT
SUPPLY

The AOD-57 completely wired
with one 6360 tube, two
tubes and crystal
12BY7

frequency). Heater
power: 6.3 volts @ 1.2 amps.

ma.
$39.50

150

420 mc

MULTIPLIER/AMPLIFIER
The AOA-420 uses two 6939
tubes providing 4 to 8 watts
output on 420 mc. Requires
ADA -57
plus AOA-144 for
drive. Heater: 6.3 volts @ 1.2
amps. Plate: 220 vdc @ 130
ma.
AOA-420 complete

ARY-4 Relay

complete

$12.50

$69.50

The APD-610 provides 6.3 vac
@ 10 amperes.
$9.50
APD-610 complete

COMPLETE TRANSMITTER
A00-57

6 METERS

50 mc

METERS

144 mc

AOD-57 PLUS AOA-144

220 mc

AOD-51 PLUS AOA-220

420 mc

AOD-57 PLUS AOA-144 PLUS AOA-420

MODULATOR

Box

The AMD-10 is designed as a companion unit to the AOA series of transmitters. Uses 6AN8 speech amplifier
and driver, 1635 modulator. Output: 10
watts. Input: crystal mic. (High Imped.)
Requires 300 vdc 20 ma, no signal, 70
CRYSTAL MFG. CO., INC.
ma peak: 6.3 vac @ 1.05 amps.
OKLA. CITY, OKLA. 73102
$24.50
la NO. LEE
AMD-10 complete
CIRCLE NO, 13 ON READER SERVICE CARD

INTERNATIONAL

Order Direct
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Electronic Experimenter's Handbook

FALL EDITION
1965ELECTRONIC
EXPERIMENTER'S
POPLILA

ELICT.ONICS

HANI7HOCJK

The Fall Edition of the ELEC-

PHILLIP T. HEFFERNAN
Publisher

OLIVER P. FERRELL
Editor

ROBERT CORNELL
Managing Editor

JOHN D. DRUMMOND
Technical Editor

WILLIAM GALBREATH
Art Editor

MARGARET MAGNA
Associate Editor

ANDRE DUZANT
Technical Illustrator

NINA CHIRKO
Editorial Assistant

PATTI MORGAN
Editorial Assistant

LAWRENCE SPORN
Advertising Sales Manager
ARDYS C. MORAN
Advertising Service Manager

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Editorial and Executive Offices (212 ORegon 9-7200)
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M PA
1965 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. Copyright © 1965
by Ziff -Davis Publishing Company. All rights reserved.

1965 Fall Edition

TRONIC EXPERIMENTER'S

HANDBOOK is the tenth in a series
that began in 1957. Due to the increasing popularity of electronics
project building and experimentation, two editions of the EXPERIMENTER'S HANDBOOK are now
being printed every year. In February we publish a Spring Edition, in
October a Fall Edition. As in the
preceding nine editions, this one contains construction projects and feature articles especially selected by
the Editors of POPULAR ELECTRONICS.
We are particularly pleased with,
the projects in this Fall Edition and
direct our readers' attention to the
new chapter category of Science Fair
Projects. It is anticipated that this
chapter will be enlarged in future
issues.
In the center of this Edition you
will find a special 16 -page article by
Louis Garner on solid-state technology as it particularly applies to
diodes. This is a state-of-the-art report and is comparable to feature
articles of a similar nature that appear from time to time in POPULAR
ELECTRONICS. Also in this Edition are several projects that first
saw the light of day in our next -doorneighbor publication, ELECTRONICS WORLD. These articles have
been completely revised for use in
the EXPERIMENTER'S HANDBOOK.
If you have suggestions for future
content, please don't hesitate to write
THE EDITORS
to us.

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FALL EDITION
' 96-Z ELECTRONIC

EXPERIMENTER'S
H AN D B OO K

CONTENTS
1

USEFUL
HOUSEHOLD
PROJECTS

2
AUDIO
STEREO
HI-FI
PROJECTS

3
THE
FABULOUS
DIODES

4
SCIENCE
FAIR
PROJECTS

5
COMMUNICATIONS
SWL
CB
HAM

6
TEST
EQUIPMENT
PROJECTS

7
"CQ

Fish"-Panic Alarm-Pocketable Metronome
Those Lights-Elec-

-For Greater Safety Flash

tronic Candles Dance and Glow-Add D.C. Restoration to TV-Multi-Trol-High Wattage Reducer
-Nonsense Box

39
For Better Sound Build the Bi-Coupler-Stereo
S'Lector-Vibrato Simulator-Hi-Fi Volume Compressor Expander-Hi-Fi Interlock-Shotgun
Sound Snooper

67
The Fabulous Diodes: Zener Diodes-Diode
Switches-Photodiodes-Tunnel Diodes-Capacitor
Diodes-Power Diodes-Surge Suppressors-Thermoelectric Diodes-Special Diodes

87
60 -Cycle Repulsion Coil-Resonance
TC-Li'l TC

Engine-Big

103
Transistorized 6 -Meter Converter-Adjustable
Speech Filter-Companion 6 -Meter TransmitterSoup Up That AM Broadcast Receiver-6 -Meter
7 and 2 Preamp

123
Hybrid Circuit for Transistor Power-SCR Tester
-Field -Effect Transistor Voltmeter-Multiple
Meter Test Set-Multi-Output Zener Voltage Regulator-Best of Tips and Techniques
1965

Fall

Edition

NEW!

CA EXPL

IM NTER!S KITS

BUILD A MODEL RACE CAR
MOTOR SPEED CONTROL
EXCITING SCR CONTROL
CIRCUITS WITH HUNDREDS OF
USEFUL APPLICATIONS

13 OTHER

Here's what you've been waiting for...now, you
can build your own silicon controlled -rectifier
control circuits. Start with RCA's Basic Experimenter's Kit (KD2105). With it, you can build
a model race car speed control, a universal motor speed control, or eight other interesting circuits. Add-on Light Sensor and Heat Sensor
Kits (KD2106 and KD2110) enable you to
build 4 more electronic control circuits for hundreds of useful applications around the house,
hobby shop, and garage.
The 80-page, illustrated RCA Experimenter's
Manual (KM -70) will familiarize you with the
theory and operation of solid-state components
in the kits. At the same time, it will give you
complete detailed information on all 14 circuits
including schematic diagrams, circuit descriptions, and construction details, as well as photographs of the circuits as easy -to -follow assembly

Here is what You Need...
RCA Basic Experimenter's Kit (KD2105) One
Silicon Controlled -Rectifier; Two Transistors; Five
Rectifiers.
RCA Experimenter's Manual (KM -70) 80 Illustrated Pages; 14 Circuits and How to Build Them.
RCA Add-On Light Sensor Kit (KD2106) One
Photocell for light -operated switches.
RCA Add-on Heat Sensor Kit (KD2110) Three
Thermistors, special solder for heat -control circuits.
Plus readily available standard components.

guides.
Here is what you can make...
1. 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
(Torn -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.

r, check with
1f you ,,cant to build one circuit or all
your RCA Distributor where kits and RCA Experimenter's Manual are on display. He'll be glad to
help you select the kit or kits for the solid-state cir.
cuit you have in mind. Do it today!
Available from your RCA semiconductor distributor
1

.
RCA

ELECTRONIC COMPONENTS AND DEVICES, HARRISON,

Ilri

N.J.

The Most Trusted Name in Electronics

CIRCLE NO. 23 ON READER SERVICE CARD

Electronic Experimenter's HSndboo)..

CHAPTER
1

USEFUL,
HOUSEHOLD
PROJECTS

Construction projects to be used around the
house are generally of great interest to readers of
the ELECTRONIC EXPERIMENTER'S HANDBOOK, since such projects can be displayed and
operated by the "non-electronically % inded"
members of the family. They "prove" that the
hobbyist -experimenter is not just fooling around
and wasting his time. The projects in this chapter have been selected to appeal to the entire
family-even though the first project ("CQ Fish"
on page 8) is for the OM himself.
The "Panic Alarm" (page 11) and "Nonsense
Box" (page 36) are wonderful electronic "gags."
Both of these projects appear in the stores at
Christmas time-selling for 5 to 10 times the cost
of building one with brand-new parts. The metronome (page li), safety flasher (page 15), and
"Multi-trol" (page 28) are all handy household
items. And, speaking of Christmas, take a look
at the electronic device to make your tree lights
twinkle (page 17). The d.c. restorer project
(page 22) is one you should consider if you have
a TV set that could use some improvement in
black and white picture reproduction.

8
Bill Billick

"CQ FISH"

11
PANIC ALARM

Roy

Pafenberg, W4WKM

14
POCKETABLE METRONOME

Stella

Sal

15
FOR

GREATER SAFETY FLASH THOSE

LIGHTS

Louis

Cortina

17
ELECTRONIC CANDLES DANCE AND GLOW

Jeff H. Taylor

22
ADD D.C. RESTORATION TO TV

Charles

Cohn

28
MULTI-TROL

Ryder Wilson

31
HIGH WATTAGE REDUCER

Frank A. Parker

36
NONSENSE BOX
1965 Fall Edition

Alan

Danzis
7

"CO FISH"
Fish can't resist this CQ from a
weight belt. You have your pick of
the pack when this electronic lure
broadcasts its call of the deep . . .

By BILL BILLICK

ELECTRONIC FISH LURES have been
used for years by "stick" fishermen.
Such lures depend on the low intelligence level of the fish, and have actually
worked well. While it is dubious that
anybody ever psychoanalyzed a fish, the
great attraction would seem to be that
the noise emanating from the lure sounds
like food. Another theory is that all
fish do not dine in the same fashion,
and what might sound like food to one
would just arouse the curiosity of another. In either case, the fish is lured
to his ultimate destruction
!

Double -Duty Lure.

The fish lure de-

scribed here can be employed with a
fishing rod or by a skin diver. The housing of a pressure -proof skin-diving flashlight permits its use at depths up to 200
feet. To use the lure with a rod, you
lower it into the water after turning it
on and replacing the end -cap. A skin
diver should turn the unit on before entering the water. The flashlight housing
can be attached conveniently to a spear
gun, weight belt, or a line.
The transistor circuit is á simple
Hartley oscillator whose tone or repeElectronic Experimenter's Handbook

Earphone is mounted with
cement on a disc cut from

the perforated

R2
Earpher.e

board.

Switch is mounted on an
aluminum bracket, bracket is attached to board.

Earphone
R2

Looking at frcnt end, earphone which is used as a
small speaker is protected by flashlight glass disc.

1965

Fall

Edition

To turn on. remove waterproof end -cap and press
Sl, which will lock into position. Replace end -cap.

"CO FISH"

Completed unit fits into watertight
flashlight case after works come out.

tition rate is determined by R/C circuit
R1, R2 and Cl. By varying potentiometer R2, you can create any sound from
that of a bee to a grasshopper through
the high -impedance dynamic earphone.
Construction. To build the unit, start
by stripping the skin-diving flashlight
down to its shell. Remove all switches,
springs and hardware. Next, fill all holes
with cement, using epoxy or household
cement. Make sure the rubber gaskets
( included with the original flashlight)
seal all the openings when the basic
flashlight is reassembled. You can test
for leaks by submerging the unit in water and watching for air bubbles.
Cut a perforated mounting board into
two pieces. One piece should be 41/2" x
13/K"; the other is formed into a circle of
about 11/2", or to fit the lens area of
your flashlight. Cement the circle to the
end of the rectangular board as shown
in the illustrations. The bracket for
switch 21 is formed from scrap aluminum.
After you assemble the major components on the board, paying careful attention to the polarity of Q1, C1 and B1,
cement the back of the earphone to the
center of the circular piece.
Testing. When the wiring is completed,
turn the unit on and listen for the tone
at the earphone. Varying the setting of
R2 should change the tone. If the unit
works, coat all wiring with polystyrene
"Q" -dope to minimize corrosion damage.
Now assemble the circuit into the
flashlight housing and, once again, submerge the unit to make sure that it is
watertight. If all is well, watch those
fish sit up and QRZ!
-®to

2N107

MAGNETIC
EARPHONE

Switch Si is a push-on/push-off type, and Rl, R2,
Cl determine frequency varied by potentiometer R2.

PARTS LIST
B1 -1.5 -volt battery (two Eveready

#912's

parallel)
CI -50-µf., 25 -volt miniature electrolytic capacitor

Q1 -2N107

transistor or equivalent
R1 -27,000 -ohm, ,A -watt resistor
R2 -5000 -ohm miniature potentiometer
S1-S.p.s.t. locking push-button switch

T1-Subminiature output transformer; 500 -ohm,

center -tapped primary, 8 -ohm secondary (Lafayette 99-G-6129)
1-Pressure-proof skin-diving flashlight (U.S.
Divers, Voit, Sportsways, or equivalentavailable at most sporting goods stores)
1-Battery holder, two-cell type
1-High-impedance earphone, 7000 -ohm dynamic
(Lafayette 40-G-7801)
Misc.-Knob, transistor socket, switch bracket,
perforated mounting board, wire, solder
Electronic Experimenter's Handbook

COINED during World War II, "push
the panic button" has since become
a colorful and descriptive addition to our
everyday language. The phrase is used
to describe any hastily conceived and
ill-advised command or management reaction to an emergency situation that
sends all hands racing helter-skelter in
a flurry of frantic and ineffectual activ-

ity. In response to the popular appeal
of the idea, dummy panic buttons can be
found strategically located in the offices
of many enlightened business executives.
This article describes the construction
of an electronic panic alarm that will
electrify the deadest office. When activated, the device sounds off with a piercing blast of acoustical energy that combines the most desirable tonal character -

By ROY E. PAFENBERG, 'N4WKM

Guaranteed to start
a panic every time

an adventurous

soul pushes

that button

BUILD

p41e
ALARM

The author mounted his alarm in a sloping
front cabinet, but there is no reason why
other design housings won't work as well.

Perforated board is held to the bottom of the
box with four bolts. The 25 -watt lamp has no
socket; the connections are soldered in place.

As mentioned above, the
layout can be modified to
suit the individual re-

quirements of the builder.
If you want to follow the
author's model, this photograph will spot some
of the more important
components for you. Be
sure that none of the circuitry contacts the metal
chassis. See text for
parts value changes to
alter output tone.

R5 C4

istics of a fire engine siren, a submarine
diving alarm, and a hound with its tail
caught in the screen door.
The panic alarm is activated by a deceptively labeled PUSH TO TEST switch.
A special latching relay circuit is provided to keep the alarm sounding until
the a.c. line cord is disconnected. The
panic-stricken confusion that continues
until someone finally unplugs the power
cord adds greatly to the effectiveness
(?) of the device.
A simple, easily wired circuit is used
in the panic alarm. As shown in the photographs, the circuitry is housed in a
small sloping -panel aluminum cabinet
(Bud AC -1613). The front panel contains a speaker cutout with a red painted
grille and a large matching, attentiongetting red lamp. The PUSH TO TEST
switch is mounted on the top of the
cabinet.
12

I2II

Theory. The heart of the circuit is a
rather unusual dual neon lamp relaxa-

tion oscillator. Because of the relatively
long time constant of capacitor Cl and
resistor R2, the circuit of lamp 11 oscillates at a subaudible rate. This results
in a varying d.c. voltage at the junction
of resistors R1 and R2.
The time constant of capacitor C2 and
resistor R3 is such that the circuit of
lamp 12 oscillates at an audible rate.
Since the voltage for this circuit is obtained at the junction of R1 and R2, the
output frequency of this oscillator is
swept at a rate determined by the frequency of the 11 oscillator. Time constants of both circuits have been chosen
to produce a very distinctive swept -tone
siren effect. Output of the 12 oscillator
is coupled to a conventional audio output
stage through capacitor C3.
A 25 -watt, 117 -volt red -frosted lamp
Electronic Experimenter's Handbook

Dual neon lamp relaxation os-

cillator gives rising and falling siren effect. Amplified
by V1, a 5005, it is LOUD.

PARTS LIST
C1 -0.5-µf., 400 -volt capacitor
C2, C3 -0.001-µf., 600 -volt capacitor
C4 -25-µf., 25 -volt electrolytic capacitor
C5-20-20 µf., 150 -volt electrolytic capacitor
D1-Silicon diode, 750-ma., 400 -volt PIV (Lafayette SP -241 or equivalent)
11, 12-NE-2 neon bulb
-watt, 117 -volt light bulb, red frosting
I3
K1-S.p.d.t. relay, 6 -volt, 335 -ohm coil (Potter
& Brumfield RS5D or equivalent)

-25

R1, R2, R3-1-megohm, %-watt resistor
R4 -470,000 -ohm, 3/2 -watt resistor

(13) is used in the power supply section
of the circuit. This lamp, connected in

series with the 5005 tube heater, serves
the dual function of indicator light and
series-dropping resistor to reduce the
line voltage to the 50 volts required by
the tube heater.
The B + power supply uses diode D1
in a conventional half -wave rectifier circuit. The winding and the normally open
contacts of relay KZ are connected in
series with the B + output. The normally open contacts of the PUSH TO TEST
switch are connected in parallel with
the relay contacts. When this switch is
closed, the charging current of capacitor
C5b causes the relay to operate, and the
current drawn by the 5005 tube holds
the relay closed until power is removed
1965 Fall Edition

R5 -150 -ohm, 1 -watt resistor
R6-22 -ohm, ,A -watt resistor
S1-S.p.s.t. push-button switch, normally open,
momentary contact (Switchcraft FF -1001 or

equivalent)

Ti-Audio output transformer, 2000 -ohm plate
winding to 3.2 -ohm voice coil winding

V1-SOCS tube
Misc.-4" speaker (3.2 -ohm voice coil), cabinet
(Bud Radio AC-1613 used by author), lamp
cord, mounting hardware, perforated circuit
board, solder, wire, etc.

by disconnecting the a.c. line power cord.
Construction. Although the circuit is
noncritical and parts placement can be
varied, the method of construction shown
in the photographs is convenient. If a
different method is used, two precautions must be observed. Since the circuitry is connected directly to the power
line, care must be used to insure that no
portion of the circuit makes connection
to the metal cabinet. Secondly, in the
relay specified for use as Kl, the movable contact is connected directly to the
frame of the relay. Therefore, any method of construction used must provide
an insulated mounting for this compo-

nent.
The speaker is mounted on the panel
(Continued on page 146)
13

POCKETABLE

METRONOME

variable -speed pacer

will be

a boon

for any

tyro instrumentalists

PEOPLE are rhythm -conscious, and if you are learning to type,
play an instrument, dance, exercise, or any of countless other
rhythmical functions, this metronome will mark the beat for you at
a rate of from 80 to 300 clicks per minute. It is small enough to
fit in a pocket, and the earphone stores nicely in the roomy case.
The metronome circuit is a simple relaxation oscillator with a
20-µf. emitter bypass capacitor (C2) to stabilize the circuit. Two
holes in the circuit board are enlarged to accept jack J1 and potentiometer R1. As these components also hold the circuit board to
the plastic case, the jack hole should be enlarged sufficiently to
pass the collar of the jack.
Before permanently wiring the circuit, check the range of clicks.
If they are too slow, decrease the resistance of R2; if they are
too fast, increase R2's value. Potentiometer RZ has a tapered resistance, and both outer terminals should be tried to see which
gives the greater spread of click range.
Metronomes are usually bulky affairs, never thought of as portable. This one is a departure from the norm, with more applications than a normal metronome could shake its pendulum at!
-Sal Stella
Switch SI, on back of Rl, closes when
knob is turned; Rl varies click speed.

PARTS LIST
51- -S.p.s.t. switch (part of
C1 -8-µf., 15 -volt miniature
R1)
electrolytic capacitor
TI-Transistor miniature
C2 -20-µf., 15 -volt miniaoutput transformer (Lature electrolytic capacitor
fayette
99-G-6127
or
11-Miniature phone jack
equivalent)
Q1-2N107 transistor
1
-ohm earphone
R1 -500,000 -ohm miniature
1-Battery connector
potentiometer with switch
1-7/3" x 17/8" circuit board
S1 (Lafayette 32-G-7368
I-Plastic hinged box or
or equivalent)
other housing approx. 1" x
R2- 68,000 -ohm resistor
2"x2A"
BI

-9 -volt battery

-6

Electronic Experimenter's Handbook

It's night. Suddenly a
tire blows. You pull
over to the side, but
another car is coming
up fast from behind...
Photo courtesy National Safety Council

For Greater Safety
Flash Those LlOht5!
IF

YOU'VE ever had to stop your car

on or near the road while driving

night, you know how nerve-wracking
this experience can be. Most of us have
thought at one time or another of buying flares for use in such an emergency,
but how many drivers actually carry
them? The news stories concerning rear end collisions with stalled vehicles point
up the danger involved in not having
some positive means available to alert
other drivers.
Of course, you can pump your brake
pedal to flash your rear lights, but this

By LOUIS F. CORTINA

becomes tiresome very quickly. However,
there is a practically tireless device on
almost all cars which can be used to perform the same job-the flasher which
operates your turn -signal lights. Some
stalled drivers have the presence of mind
to use this device in its normal manner,
that is, to operate the turn signals. The
danger here is that the driver in back
may not realize until too late that the
car is not moving, but standing still.
Two -Light Flasher. The additional wiring needed to make the flasher operate
both rear lights is quite simple. The
SWITCH ON
STEERING COLUMN

Fig. 1. A two -light flashing arrangement requires only the connection of a s.p.s.t. switch
between the flasher and brake -switch leads.

RIGHT
FRONT

RIGHT
REAR

FLASHER

IGNITION
SWITCH
ACCESSORY

FI
I4AMP

TERMINAL

BATTERY

1965 Fall Edition

F2
ISAMP

THIRD TERMINAL
ON SOME FLASHERS
FOR PANEL LIGHT

BRAKE
SWITCH

RIGHT
PANEL

1V
EMERGENCY
SWITCH
ADDED

FLASHER

IGNITION

SWITCH ON
STEERING COLUMN

RIGHT

FONT

RIGHT
REAR

LEFT

FI
REAR
¡'_FRROOON'NTT

LEFT

--'PANNELL

BRAKE
SWITCH

18ATTERY

Fig. 2. Connected as indicated,

3-p.s.t. switch provides four -light front and back flashing.

usual turn -signal switch has six leads;
one from the flasher, one from the brake
switch, and four leads to the various
exterior lights. When the turn signal
switch is in the center-or neutralposition, there is continuity between the
brake -switch lead and the two leads
which go to the rear lights of the car.
If a path is provided from the flasher
lead to the brake -switch lead, the rear
lights will receive power through the
flasher and will blink on and off in the
same manner as the turn -signal lights,
making an attention -getting device.
Figure 1, on page 15, shows a typical
wiring layout and the necessary modification. The switch used is a s.p.s.t. type,
and may be a toggle, rotary, or pushpull device rated to carry 3-5 amperes.
Since most cars normally use two lights
for signaling, one in the front and one
in the back, the flasher will be operating
under its normal load when flashing the
two back lights.
One exception is some General Motors
cars which normally flash two lights on
either side in the back, and one on either
side in the front. If the flasher is connected to the four back lights, it will be
operating with an overload and will run
fast. To overcome this deficiency, one of
the heavy-duty, variable -load flashers,
designed for truck service or for vehicles
towing a trailer, can be substituted for
the original flasher. These variable -load
units, which are manufactured by Ideal
and Tung -Sol, will operate from one to
eight lights of 21 or 32 candle power
while maintaining a constant flashing
16

rate. Replace a 6 -volt flasher having
three terminals with a Type 535 or 2535,
a 12 -volt unit having two terminals with
a Type 536 or 2536, and a 12-volt unit
having three terminals with a Type 550
or 2550.
Most cars made since 1949, as well as
some earlier models, have a flasher socket under the instrument panel on the
driver's side. It is only necessary to remove the original flasher and plug in the
heavy-duty unit. Chrysler products from
1949 to 1954 have the flasher mounted
on the engine side of the firewall. For
those cars which do not use a flasher
socket, remove the leads from the original unit and wire them to the corresponding terminals of the replacement
unit.
Four -Light Flasher. While the simple
hookup illustrated in Fig. 1 can be used
in most states, California requires that
any warning -light setup include "four
or more approved turn -signal lamps .. .
at least two of which must be toward
the front and at least two toward the
rear of the vehicle." Your local motor
vehicle department can tell you the rules
that apply in your area.
The added wiring needed to connect
the flasher to all four light leads is not
very involved. A three -pole, single -throw
switch, either rotary or toggle, will do
the job. An advantage of this method is
that the panel indicator lights, which are
usually paralleled with the corresponding front light on late -model cars, will
also be energized. This keeps you from
(Continued on page 148)
Electronic Experimenter's Handbook

..._

._.

Electronic Candles
Dance and Glow
Ordinary incandescent bulbs become sparkling, flickering holiday
decorations when they're powered by the Electronic Candlelighter
By JEFF H. TAYLOR

THERE'S NOTHING LIKE the warm glow of candlelight for festive occasions. Unfortunately, in modern times, the candle flame
with its rhythmic, yet random, light has been largely replaced by
the more intense, steady brilliance of incandescent bulbs. This article describes a method of reproducing the effect of candlelight, however, using ordinary electric light bulbs. And, unlike the candle,
there's no smoke, melted wax, or fire hazards to contend with. You
simply plug a lamp or string of decorative lights into the "Electronic Candlelighter," sit back, and enjoy the age-old effect of flickering, dancing candlelight.
1965 Pall Edition

The Candlelighter is built into
a 3" x 4" x 5" aluminum box
with a fuse and an output socket mounted on top panel for
one lamp or a string of lights.

Component layout is shown in
the photo below and those on
the opposite page. Note R8
mounted to D4 and SCR1 by its
leads; the exact value of this
resistor depends on the load
wattage, and can be estimated
by using the table on page 19.
Various substitute unijunction
transistors such as the 2N489,
2N490, etc., series can be
used in place of the 2N1670;
some SCR's will replace the
TI40A2, including the 2N1602,
2N1603, T40A3, or TI40A4.
R8

How It Works. The "Electronic Candle lighter" provides a half -cycle sine wave
to the lamp (s) continuously, plus other
random currents during the remaining
half-cycle. These random signals are
generated by three neon -bulb relaxation
oscillators operating at three slightly
different frequencies. The oscillators
beat with each other and the 60-cycle
line frequency to produce a flicker in the
lamp which is plugged into the socket.
The unit has three basic circuits the
neon relaxation oscillators, the driver, and
the power control circuit. The oscillators
are capacitively coupled to the driver
through C4, C5, and C6. These capacitors prevent oscillator interaction.
The neon lamp oscillators are supplied
with a negative charging potential so
that when they fire they produce the
positive -going waveform necessary to
forward -bias unijunction transistor Q1.
The driver circuit consists of the transistor (Q1) to which the oscillators are
coupled. Base 2 of the unijunction is
supplied with positive pulses through
diode D3. The voltage on base 2 has a
peak excursion of about 15 volts. The
oscillator pulses at the emitter of Q1
which are in phase with the half -cycle

,%1

positive pulses on base 2 produce pulses
at base 1 which are coupled to the silicon-controlled rectifier, SCR1. Diode D2
provides d.c. restoration without loading
the signal portion of the oscillator output.
18

C1 -C6 -0.1-µf.,

pacitor

PARTS LIST
200 -volt miniature paper ca-

Dl, D3-1N2071 silicon rectifier (TI)
D2 -1N2070 silicon rectifier (TI)
D4 -1N254 silicon rectifier (TI)
F1

-3

-amp 3AIG fuse in panel -mounting holder
11, 12, 13--''E-2 neon bulb
Q1 -2N2160 unijunction transistor (TI)

R1-5.6-megohm, V, -watt resistor
R2-4.7-megohm, %,-watt resistor
R3-39-megohm, V, -watt resistor

R4 -10,000 -ohm, 10 -watt resistor, ±5%
R5 -390 -ohm, /,-watt resistor
R6 -1000 -ohm, 2 -watt resistor
R7-47 -ohm, yj-watt resistor
R8-Sec text
SCR1-T140Á2 silicon -controlled rectifier (TI)
1-3" x 4" x 5" aluminum box
1-2%" x 2%" piece of light aluminum
1-21/2" x 4" piece of perforated phenolic board
1-Panel-mounting a.c. receptacle
111isc.-Transistor socket, line cord and plug,
press -in solder terminals, wire, solder, hardware, rubber grommet, decals, etc.
Electronic Experimenter's Handbook

Three basic circuits
are used: neon relaxation oscillators,
a driver (Q1), and
power control circuit (D4 and SCR1).

03
1N

2071

R4
10K
ION/

117 VAC

39011

2N2160

I(
BI

IN2070

47R

R6
IK

Tyf.

Bend piece of light aluminum to form heat sink for
D4 and SCR1; make sure they're not shorted to it.
D4

SCRI

LAMP

SOCKET

How to Select Resistor R8
To determine the value of R8, use the table

below. Choose the lamp wattage you want to
use and read across for the approximate resistance value and wattage of the resistor that
will give the best candlelight effect. Although
no resistor is recommended for loads above 100
watts up to the unit's maximum rating of 300
watts, it may be desirable to use one in some
cases, especially with strings of decorative
bulbs. Optimum resistor values will range from
1 to 20 ohms at 20 watts.

Bulb
Wattage

Resistance
(ohms)

71/2

325
250
200
150

125
100
80
50

25
40
50
60
75
100

1965 Fall Edition

Remaining parts are neatly laid out on a phenolic
board which is mounted to box with small brackets.

Power

(watts)
2
5
5

10
10
10

The power control circuit consists of
a conventional rectifier (Di) which continuously provides half -cycle a.c. to a
lamp load up to 300 watts, and the silicon -controlled rectifier (SCR1) which
supplies the "flicker" pulses. A resistor
selected to match the wattage of the
load, R8, is placed between the anode of

the silicon -controlled rectifier and the
load to reduce the magnitude of the
flicker, thereby producing a more realistic candle flame effect.
Building the Unit. As with the "Spook in' Light" (a somewhat similar project
in POPULAR ELECTRONICS, Sept., 1964)
it is imperative that none of the components in the "Electric Candlelighter"
come in contact with the 3" x 4" x 5"
aluminum box used as a cabinet, or the
,

PARTS PROBLEMS?
We can supply parts kits and
circuit boards for:

Adjustable Speech Filter
Bargain Page Amplifier
This Issue-and
Ultrasonic Sniffer Mar. 1963
Ultrasonic Trans. Sept. 1964
RC Receiver Apr. 1965
RC Transmitter June 1965
Others
Send for free catalog listing
these projects and others plus

circuit board type components

DEMCO
Box

16297

San Antonio, Texas 78216
CIRCLE NO. 5 ON READER SERVICE CARD
To Home or Shop...
for business or personal use!

"Messenger" Citizens Radio opens
up the exciting field of personal communications to everyone in any
application. Used by builders, contractors, trucking, delivery services,
garages on-the-job-ideal for sportsmen, hunters, fishermen and campers! Anyone can operate
license
issued on request, Investigate the

"Messenger" line
nation's most
popular, most reliable Citizens Band
equipment!

YOUR OWN

2-WAY RADIO

aluminum heat sink on which SCR1 and
D4 are mounted. Use a 21/2" x 4" piece
of Vectorbord and press -in solder terminals for mounting all of the other
components, following the general layout
shown in the photographs. The semiconductors are all Texas Instruments types,
but equivalent units made by other manufacturers could be employed instead.
Due to the fact that NE -2's tend to be
photosensitive, cover each one with black
plastic tape before wiring them in place.
Transistor Q1 is mounted in a socket
which is force -fitted into a hole drilled
in the Vectorbord; the mounting board
is attached to the front panel of the cabinet with two small angle brackets.
To make the heat sink, simply bend a
21/4" x 21/2" piece of light aluminum to
form a mounting bracket at one end (see
photos). Drill mounting holes in the
heat sink for SCR1 and D4, and mount
them with mica insulating washers. As
an additional safety measure, check with
an ohmmeter to make sure there is no
electrical contact between the diodes and
the heat sink.
To complete the unit, mount the lamp
socket, fuse holder, heat sink and circuit board to the front panel, and install
the line cord through a hole lined with a
rubber grommet.
Operation. Select R8 by referring to
the table on page 19. The resistance
values are not critical; simply select
one close to the recommended value.
Remember to calculate the total wattage
if the unit is to be used with a string of
decorative lights rather than with a single bulb. Check the wiring carefully,
then try the unit out in a dimly lit room.
For a festive or romantic atmosphere,
use electronic candlelight!
-1
-

YEn

Write Today

JOHNSON

E. F. JOHNSON CO.
2521 10th Av. S.W.

Waseca, Minn. 56093

CIRCLE NO. 14 ON READER SERVICE CARD

"And this is Fred's quote, workshop, unquote."
Electronic Experimenter's Handbook

Choose Your Tailor -Made
Course in N.T. S.'PROIECT
METHOD" ELECTRONICS!
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Now! N.T.S. technical schools - offers you GREATER CAREER OPPORTUNITIES
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MASTER COURSE IN ELECTRONICS -TV-RADIO,
PLUS ADVANCED TV & INDUSTRIAL ELECTRONThis course covers everything included in
ICS
Course No. 1 plus Automation and every phase of
the Electronics industry.
3FCC LICENSE
Preparation for this government
license essential for interesting jobs in radar,
radio, television, communications, guided missiles,
many others. Upon completion of this course, if
you do not pass the FCC exam for a 1st Class
Commercial Radiotelephone License your tuition
will be refunded.
RADIO SERVICING (AM -FM -Transistors) Train for
radio sales and service with dealer or distributor.

Work
on the

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computers, data
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or succeed in your own business.

FUTURE!

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STEREO,

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7BASIC ELECTRONICS

Gives you the fundamen-

tals you must know to build on for

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Electronics career. Also offers an excellent background for Salesmen, Purchasing Agents, and
others in Electronics.
ELECTRONICS MATH
Simple, easy -to -follow instructions in the specialized math you need in

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Most courses include Equipment Kits.

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Everything included in
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you for your own sales and service business.

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take classroom training in our
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4000 S. Figueroa St., Los Angeles, California 90037

CIRCLE NO. 35 ON READER SERVICE CARD
1965 Fall Edition

ADD
D.C.

restoration
to TV
BY CHARLES E. COHN

When they cut the costs
they leave out
this important picture circuit
ALTHOUGH the d.c. restorer was regularly used in the earliest TV sets,
it is a neglected feature in today's receivers. The omission is regrettable,
since this circuit makes a valuable contribution to picture fidelity. However,
it is not difficult to add to a set.
The need for d.c. restoration stems
from the manner in which a signal is
generally applied to the picture tube.
To simplify comparison, assume the detector's video polarity is such that a
positive signal (see drawing) corresponds to black information, with smaller voltages corresponding to lighter gray
shades until white is reached with the
smallest voltage.
If this signal is directly coupled from
detector to picture tube, a given voltage
always corresponds to the same shade.
Reproduction of the black -to -white scale
would then always be correct, provided
only that the receiver's brightness control is properly set.
Where Restorer Comes In. While some
TV receivers use d.c. coupling to the picture tube, most sets use RC coupling.
22

The d.c. level of the signal is thus removed through the coupling capacitor,
with the average amplitude of any signal being placed at the same level. This
permits the standard black level to shift,
depending on make-up of the signal at
any given moment.
The drawing illustrates this action
for typical signals. The first line shows
a signal with the blacks and whites
evenly distributed. The average level to
the CRT, without restoration, is where
it should be. The signal in the second
line is mostly black. When capacitor
coupling, however, moves the average
level down toward gray, the scene is reproduced lighter than it should be. Also,
with sync pulses not reaching the black
level, retrace lines become visible. With
a mostly white signal (third line) , the
shift toward gray makes the picture
darker than it should be.
Where neither direct coupling nor a
d.c. restorer exists, the latter can be
added. The circuit senses the sync pulses,
which are always at the same level just
SIGNAL AT PICTURE TUBE
DETECTOR
OUTPUT

WITHOUT
RESTORER

WITH D.C.
RESTORER
BLACK
GRAY

r-,

WHITE
BLACK
GRAY

WHITE

BLACK
GRAY

WHITE

Without d.c. restoration, mostly black pictures tend
to drop and mostly whits scenes tend to rise into
the gray area, reducing the dynamic contrast range.
Electronic Experimenter's Handbook

beyond black, and adjusts CRT bias accordingly to compensate for the shift
produced by capacitive coupling.
The circuit shown here is easy to install in an existing set, can be used
wherever a video signal is applied to the
picture -tube cathode, and the brightness
control is also located there. This arrangement is usual. The circuit requires
the addition of only one tube, two capacitors, and three resistors.
Circuit Operation. With the large
cathode resistance, RI, V 1 is almost cut
off. Positive video signal is applied to its
grid. Without Cl in the cathode, V1
plate current would increase as video bePICTURE TUBE

FINAL
VIDEO
STAGE

Voltage developed across Cl is a function of the
sync pulse amplitude. This voltage is used to bias
the CRT and to maintain relative contrast levels.
1965

Fall

Edition

comes more positive, the cathode voltage
following the grid voltage. However, Cl
charges the cathode voltage to the most
positive part of the signal, the sync
pulses, and holds V1 cut off over the rest
of the cycle. The voltage on Cl is applied to the CRT grid. Thus the CRT
grid -cathode potential is always constant
on a sync pulse.
Between sync pulses, Cl slowly discharges through Rl. The time constant
of this combination is comparable to the
duration of one frame, so that the circuit will not respond to more rapid
changes in average level. However, the
time constants of the coupling circuits
in the video amplifier are sufficient to
hold the black level for one frame.
Installation of the circuit poses no
special problems. For V 1, use that variant of the 6AU6 whose heater characteristics can be most conveniently incorporated in the set's heater circuit. Some
point having no more than 150 volts of
"B-}-" must be found for the plate and
screen supply. Note that C2 is connected
directly to the end of the video -amplifier
plate load resistor closer to the plate
and after any of the peaking coils. This
minimizes the effect of the added stray
capacitance on the high -frequency response of the video amplifier.
The CRT grid is removed from its
existing connection and taken to the
cathode of V1. Many sets have retrace
blanking circuits connected to this grid.
Such blanking should not be necessary
after the revision, with the black level
held where it belongs. However, if
blanking should still be needed, it can be
retained by connecting in the CRT grid
lead a resistance approximately equal
to resistance to ground of the previous
grid circuit and returning the blankingpulse connection to the CRT grid.
23

EXPERIMENTER/HOBBYIST ELECTRONIC COMPONENTS

iry
1

LAMP

117 V

LINE

V -BATTERY

Lamp (1)

sistor
(5),

illuminates photocell
(3) to

(2) which decreases in

resistance causing tran-

conduct, causing reed switch (4) to close, cutting off

turning off lamp (1), causing photocell

(2) to

SCR

increase in resist-

ance, cutting off transistor (3) allowing reed switch (4) to open,

ausing SCR (5) to conduct, turning on lamp (1)

Be the
a
24

first

on your block to build

"Pergetual Motion" Machine or
Electronic Experimenter's

Handbook

...build

any number of useful devices

with these

G -E

Electronic Components

General Electric has a
whole line of components that you can use
in your home workshop. Look for this

display-featuring

G -E

components at new low
prices-at your local
electronic distributor's
(see listings below for
distributor nearest
you). All the G -E components listed below
are furnished complete
with schematic diagrams for building exciting new devices.

GE-X1 Silicon Controlled Rectifier for speed
control for hand tools, blenders, mixers, lamp
dimmers, HO train controls, and automobile
alternator regulators.
GE-X2A Light -Activated Silicon Controlled
Rectifier for photoelectric controls, experimental
ignition system, "Slave" photo -flash circuits, and
miniature lightweight static relays.
GE -X3 Silicon Controlled Rectifier for
battery chargers, electroplating, relay replacement,
or low voltage controls operating from auto or
boat batteries.
GE -X4 Silicon Rectifier for Hi -Lo lamp dimmers,
motor speed controls, battery chargers, and in
conjunction with GE -X1 or GE-X3 for full wave
SCR light dimmers or DC power supplies.
GE-X5 Silicon Controlled Rectifier for simple
remote controls, temperature controls, alarm
systems, and many more.
GE -X6 Photocell for relay controls, automatic
light flashers, remote indicator, and punched card
or tape readouts.
GE -X7 Reed Switch for light flashers, burglar
alarms, liquid -level controls, weight -measuring
devices, temperature limiters, multiple relays, and
many more.

Get EXPERIMENTER/HOBBYIST
Components from these local G -E
Suppliers or write General Electric
Company, Owensboro, Kentucky, for
the name of the source nearest you.

GE -X8 Transistor for light flashers, light target,
triggered light source, oscillators, direct -coupled
amplifiers, and bistable lamp driver circuitry.
GE -X9 Transistor for medium -power amplification and switching with GE -X8 for light flasher,
light target, or triggered light source.
GE -X10 Unijunction Transistor for high precision tachometers, oscillators, timing circuits,
voltage sensing circuits, SCR firing circuits, and
bistable circuits.
GE -X11 Zener Diode for high -precision tachometer for automobile -type ignition systems.
GE -M100 Transistor for citizens band receiver
and control unit (27 mc).
2N107 Transistor for simple audio amplifiers; one,
two, or three-transistor radios; code practice oscillator, and loudspeaker audio amplifiers.
2N170 Transistor for three -transistor and pocket
radios, direct -coupled amplifiers, pre -amplifiers,
and many more.
2N2160 Unijunction Transistor for transistor
metronome, code practice oscillator, timing circuits, voltage sensing circuits, SCR firing circuits,
and bistable circuits.

Plus five brand-new components:
GE -X12 Triac for AC lamp dimming, temperature
controls, motor speed controls, and many more.
GE -X13 Diac-Diode AC switch for triggering
triac and SCR's.

GE -X14 Thyrector Diode for limiting voltage
transient in any circuit for constant, reliable
performance.
GE -X15 Thermistor for monitoring temperature
changes in water -depth temperature fishing guide,
photography liquid bath, fire alarm, house fans, and
many more.

GE-X16 Silicon Controlled Rectifier-Threejunction SCR for all power switch control
applications.
ALABAMA
Radio Distributing Supply. Anniston
Southeastern Radio Pere, Anniston, Cede.

den, Montgomery, Selma
James W. Cl.,Y Co., Birmingham
Forbes Distributing Co., Birmingham,

Decatur. Mobile
Reid Distributing, Birmingham
l S

Eger

oDhan a

Rughe, Electronic
Fones ECodrnics,ey

Jones Electronic.,

lie

Jasper

ice.Moeigomery
Muscle Shoal.

Southern Elccieoaico Corp., Opelika

Powell Electronic Supply. Sheffield
Allen & Jemi.on, Tusmloosa

ALASKA
Communication. Eng. Co.. Anchorage

ARIZONA
Coconino Electronics. Flagstaff
Metcalfe Inc., tas Vegas
Delis Radio & TV Sup., Mena, Phoenix
Arizona Wholesale Sup., Phoenix
Electronic Distributing Co.. Phoenix
R. V. Weatherford, Phoenix
Inland Electronic Sup., Tucson

Turn page for more Distributor listings and coupon for FREE Hobby Manual

EXPERIMENTER/HOBBYIST ELECTRONIC COMPONENTS

ARKANSAS
David

White Radio Sup., Fayetteville,
Harrison, Hot Springs, Little Rock,

Monroe, Pine Bluff
Carlton Bates Co., Fort Smith, Little Rock
Carter Electronic Supply. Fort Smith
Wise Radio Sup., Fort Smith
Martin Wholeale, Jonesboro, Paragould
Lavender Radio TV Sup Memphis
Springdale Radio & TV Sop., Springdale

CALIFORNIA
Kiesub, Anaheim,

Bakersfield, Long
Beach, Oxnard, San Bernardino, Van
Nuys
OrvacElectronics, Anaheim
WRESCO, Anderson, Gehenna, Petaluma, San Carlos, San Francisco
J. C. Arbuckle Wholesale Parts Sup.,
Bakersfield, Fresno
Pacific Electronics, Berkeley, Concord,
Richmond

Andrew. Electronic, Burbank
Electronic City, Burbank
Hagerty Radio Sup., Burbank
Sandy'. Electronic Sup., Canoga Park
Wee Valley Electric Sales. Canoga Park
Wholele Electronic Specialists, Cathedral

City

JSH Electronics, Culver City
Southland TV Sup El Cajon

Kimball & Start, E1 Monte
I. F. A. Electronics, Encino
Imperial Sound Co., Encino
Inland Electronns, Fresno,

We.

odesto

Electronic Sup., Freen
Santa
i-Bell Electronics, Garde na
Loan Electronics, Glendale
R. V. Weatherford, Glendale, San Diego
North Valley Elecerooiee, Granada lulls
Bement Electronics, Harbor City
Hollywood Radio & E
e, Hollywood
Pacific Radio Exchange,e. HollywoodHll
Yak Radio Electric, Hollywood
Marn Distributing, Huntington Park
Hurley Electronics of Inglewood, Inglewood
Inglewood Eleceronics Sup Inglewood
Manley Electronic Sup., Lon ,ter
Scott Radio Sup., Long Beach
Bell Radio Sup., Los Angeles
Clarion Shoji, Los Angeles
Electronic Kite Sup., Los Angeles
Figarte Radio Sup., Los Angelo,.
Hmehkit Electronic Cemcr, Lon Angeles,
San Diego
Henry Roth.. Los Angeles
International Television, Los AngelesK
od,, ff Electronics, Lon .Angeles
Ro
Produces Sales, Los Angeles
Reeve. Electronic, Loa Angeles
Universal Radio, los Angeles
Pacific Teleuoeic Radio sup., ModestoHonig
,

Distributing

North Hollywood,

Sylmar,
Brill Electronics, Oakland
Elmar Electronics, Oakland
Millers Radio & TV Sup., Oakland, Santa
Rosa, Walnut Creek

Panorama Electronim, Pacoima
Elwyn W. Ley, Paramount
Allied Radio, Pasadena
Electronic Comp n
. Pasadena
EmpireElectm Distributors, Pasadena
Bay Electronics, Redondo Beach
Colorvieion Sup., Beene,
Electronic Sup., Riverside. San Bernardino
Mission Hemp Sup., Riverside
Noro.l Electronics, Sacramento
i
cam
Sacramento Elec
iu . Sen FranFortune Eke onic, SSu

cisco
Southland Eleceronea, San Diego
Shanks & Wright. San Diego

Southland Electronic., San Diego
Western Radio & TV Sup.. San Diego
EDISCO, San Francisco, San Raphael
Pacific Electronic Distributing, San FranciscoS

Fra deco Radio Sup

San

Francis,

Millers Electronics, Sa Joee
pic t I.den Cal Eleceronice. Son Jose
Channel Radio, Santa Barbara
Lectronic Kit & Porte Center. San ea Barbara
Mobile Radio, Santa Fe Springn
Lombard. Electronic.. Sana Morio, Ven-

tura

Midway Electronics, Santa danse,
Military Electronic Sup., Seaside
Sunnyvale Electronics, Sunnyvale
Wholesale Electronic Supply, Ventura
COLORADO
Dagg Eke.. Dice Corp.. Boulder
Burstein Applebee of Coln., Denver
Electronic Pars Co., Denver
Hea,bkit Elect. Center, Denver
Radio Specialists Co.. Denver
Welker Radio Co.. L. B., Denver, Grand
Junction, Pueblo, Sterling

CONNECTICUT
Pilgrim Elect. Co. Inc., The, Danbury
Crooner Elect. Inc., Hamden
Signal Center loc., Hartford
Modem Electron Sply Inc.. Kensington
Addy. Electronic Slyly.. New London
Arrow Electronic.. Norwalk
Bond Radio Sup., Waterbury

DELAWARE

Almo Radio, Wilmington

FLORIDA

KANSASNorman

Dell Electronics, TaBahae.ee
Dow Electronics, Sarasota
Goddard. Inc.. Eau Genie, Miami, W.
Palm Beach
Come Electronic, West Palm Beach
East Coast Electronim, Miami
Sou,heaet Electronics, Jeckma ville
Southeastern Wholesale Miami

Thurow Elentronico, Bradenton, Clearwater, Cocoa, Daytona Bch,
ea
Ft.
Lauderdale, Ft.t. Myers, Ft. Pierce,
Gainesville, Ilomestead, Key West,

Jacksonville. Lakeland. Miami. (seal,,
Orlando, Panama City, Pensacola,
Sarasota, St. Petersburg, Tollehes.ee,
Tampa, West Palm Beach
Hammond Electronics, Daytona Beach.
Jacksonville, lakelend,Orlando,Tantpa
Electronic Wholesales, SIciboun,e, Miami

Electronic Equipm t, Miami
Cooper Radio, St. Petersburg
Welch Radio, St. Petersburg
GEORGIA
Southeastern Radio Parte, Albany, Athens,
Atlanta, Gainesville, La Grange, Macon, Rome, Savannah
Electronic Sup.. Atlanta
Wcis
orld Electronics. Atlanta
Augulu Wholesale Electronics, Augusta
Hamilton Electronic Sup., Auguella
Radio Sales & Service, Columbine
Curls Radio Sup., Dalton

HAWAII

American Factors, Ltd., Ilonolulu
Pacific Electronics, Honolulu
Precision Radio, Ltd., Honolulu
'Radio Wholesale & Sup., Honolulu
W. A. Ramsay Co., Honolulu
Comte) Engineering, Honolulu

IDAHO
Simply Co., Boise, Caldwell
Roos, S. II., Inc., Boise
Billmeyen Inc., Pocatello
A -Gen

Electronic Sup.. Coffeyville
Interstate Electronic Sup.. Dodge City.
Hay,, Ilutchinton, Topeka, Wichita
Electronics Sup., Great Bend
Renshaw TV Sup., Kma, City, Mission
Acme Radio Sup., Manhattan, Topeka
KENTUCKY
Crescent Radio Supply, Bowling Green,
Somerset
Chesney
Arol.y Electronic, Corbin
Anle Electronicu, Danville, Louisville
Inc., Lexington
Radio Elect. Equipment Co. Inc., Lexington
P. I. Burks Co., Louisville
Peerless Elect. Equip. Co., Louisville
Universal Electronic Sy., Louisville
Ohio Valley Sound, Owensboro
Warren Radio, Paducah
Electronic Service Sup., Alexandria
Davis Electronic Sup., Baton Rouge
Ralph, of Lafayette, Baton Rouge, Lafayette, Labe Charles, Morgan City, New

Iberia

Epcor, Gretna, New Orleans

Crescent, Electronic Sup.,

Houma, Metairie,

New Orleans
Sterling Electronics, Lafayette
Graybar Electric, lake Charles, Shreve-

port

Charles
TV Wholesale Sup., Monroe, W. Monroe
Radio Parts, New Orleans
Shuler Sup., New Orleans
Walther Be,,..New Orleans
(»clow, Radio Equipment, Opelousas
B&S Elcctronia, Shreveport
Koelemay Sales, Shreveport
W'holeeally Radio Equipment, Lake

MAINE
Radio Supply Co., Inc., Auburn, Bangor,

At
Waterville

MARYLAND
Co., Baltimore
Co., Baltimore

A. R. Spa

York Radio, Bloomington, Champaign,
Decatur, Kankakee, Springfield

Kann -Ellen Eke. Inc., Baltimore

Gary, Maywood, Skokie

Bowman & Company, Chicago
Cooper, Jr., R., Chicago
1. G.

Electronic Dian. Inc, Chicago
Newark Electronics Corp., Chicago
Bud Electronic Sup., Danville
Acro Electronic Dut., East Chicago
Knox Electric Supply Inc., Galabue,
Baptist Electronic Su ,., Jacksonville
lleathkit Electronic Center, Lincolnwood
Wahaeh Electronics, Mt. Carmel
Melvin Electronics, Oak Park
Crescent Electric Supply Co.. Peoria
Klaus Ridio & Electric Co., Peoria
Waihle Electronic, Peoria
Yeomans Dintrìhu,ing Co., Peoria
Joyeroice, Rockford
Melvin Elec,roneo Inc., Rockford
Midwc Associated Distr., Rockford
Bruce Electronics, Springfield

INDIANA
Electronic Supply Co., Redford
Staneifer Radin, Bloomington,
Williams Co., II. A., Bloomington, Columbus, Richmond

llutuh

& Son. Evansville
Ohio Valley Sound, Evansville, Vincennes
Wesco Radio Part,, Evansville
e Inc., Fort Wayne
Brown òlec
Fort Wayne
Pemblee n

Labors.

Protective Electrical Supply, Fort Wayne
Warren Radio Co.. Fort Wayne, Indian-

alio

AlhaÌ Radio, Gary

Lafayette Radio Elect., Mt. Rainier

Alm. Radio, Seli,hury

Standard Elect. Supply Co. Inc., Salisbury
Bayneeville Electromm, Towson

MASSACHUSETTS
Gerber Radio Supply. B,,tun
Lafayette Radio Corp., Boston
O'Donnell Elect. Spey. Co., Bunton
Tre Vec Sply Co., Brockton, Jameio.

Plain, Lowell, Peabody
Ware Radio Supply. Brookto
Electrical Supply Corp., Cambridge
Rona Co., E. A..

Fall River

Alen Eleeronics Inc., Lawrence
Dee Roberts. Lynn
Land Electronic Supply, Lynn
Durrell Electronics, SIcdford, Natick, Sen-

Walthem

Wayne to Ind. Elect., Natick
Industrial Elect. Sply., Inc., Needham
Heights
Cramer Eke. Inc.. Newton
Green Shaw Co. Inc.. Newton
Abbott Electronics Co., North Woburn
Pilgrim Elect. Sply. Corp., Quincy
Cushing Inc., T. F'., Springfield
Bounden Electronic Sply Co., Springfield
Radio M aeneenance Sply., Worcester

MICHIGAN
Purchase Radio Supply, Ann Arbor

Electronic Supply Corp., Battle (:reek
Warren Radio Company, Ileetle Creek,

Ferndale, Grand Rapid,, KalaD.,w,,

Coemopelitan Radio. Gary
Electronic Dot. Inc., Indianapolis
Graham Electronics, Indianapolis
Hoosier Rodio Supply, Indianapolis
Radio Di,tg. Co., Indianapolis
George, Electronic Supplies. Kokomo
Television Radio Diets., Kokomo, Lome.-

Owosso
Benton Electronic Supply, Benton Harbor
Radio Electronic Supply, Cadillac, Detroit,

CrAllecVnics, Lafayette

Ma,ter Elect. Supply Co.. Detroit
Newark Ferguson Elect. Inc.. Detroit
Radio Specialties Co., Detroit, Redford,
Wyandotte
Midway Ekmronic Sy. Co.. Ferndale
Lifney Distributing Co.. Flint
Taylor Elect. Sup1,by, Flint
Elect. Supply of Pontiac, Fort Huron,
Pontiac
TAW Electronic, Inc., Grand Rapids
FltaPatrlck Elm. Supply Co., Holland,

Madison Electronic, Madio.,,
Myers Radio Supply Inc., Marion
Tri-State Electric Co., Slichigen City
Rodefeld, Richmond
Colfax Co., South Bend
erre Haute
C. T. Eninger,
& Aesociateo, Jro,, Valparaiso

Bon

IOWA
Mid -State Distributing Co., Ames, Carroll,
Cedar Rapide Centerville, Creston,
Dee Moines, lows City, Marshalltown,
Mason City, Oskaloosa, Ottumwa,
Spencer, Strawberry Point, Waterloo
Crescent Electric Supply Co., Burlington,
Davenport, Dubuque, Sioux City
Iowa Radio Supply Co., Ceder Rapids
Radio Trade Supply Co., Des Moines Ft.

lltown
Dodge d
York Radio & TV, Ft. Madison
Water, Electronic Supply. Mason City
Moletad Distributing, Sioux City
F,poeworeh Electron cs, Waterloo,.

Grand Rapid.

Strains Dicer. Inc., Cheboygan, Sault Ste.

Marie

Glendale Elect. Supply Co.,

Detroit, Lan-

M uekegon
Fulton Radio Supply Co., Jackman, Lansing
Northwest Radio Supply Inc., Nlarquette
Them Doe,, Co., Saginaw
Radio Part, Co., Saginaw
Deyet om Products Corp., St. Joseph
Lafayette Radio Supply Co., Utica

MINNESOTA

Northwest Radio, Duluth
Stark Electronic Supply Co., Duluth, La
Crosse, Minneapolis, St. Cloud, St.

Paul

MISSISSIPPI
Pat, Electronic, Clarksdale, Tupelo
Columbus Electronics, Columbus
Parham Electrons., Greenwood

Gulfport

Creneene Electronic Sup.,

Ellington Electronic Sup., Jackson
May & Jackson Dietrihu,ors, Jackman
Radio & TV E.nentiah, Laurel
TV Wholesale Sup., Natchez

MISSOURI
Snedekurn Electronic Sup.. Cape Girardeau
York Rodio & TV, Hannibal
Ilco,haw TV Sup., Independence, Kansas

Robertson Electronic., Jefferson City
Wholesale TV S"l' 1,0,. JeRereon City
Four State Radio Sup.. Joplin
Norman Electronic Sup.. Joplin, Springfield
Burstein Appeaser, Kunma, City
Radio & Equipment, Kaas

ManhattanKaman
City

SlcCee Radio, Kansas City
Radeolab, Kansas City
Acme Radio Sup., St. Joseph
Electronic Compu ente for Industry, St.
Loue
Electronic Mart, St. Louis
Hollander & Company, St. Louie
Van Sickle Radio Elecernnici, St. Louie
Olive Electronic Supply. University City

MONTANA
Electronic Supply Co., Billings
t Falls
Electronic D
n Inc.,Great
., G

NEBRASKA
Radio E. uipment. Beatrice, Grand Island.
Norfolk, (Omaha
Central R,deo Sup., Hastings
Scott Electronic Sup.. Lincoln, North

Platte

W'holeeak Rodio Par. Co., Baltimore
Allegheny Electronics Inc., Cumberland
Acuson of Maryland Inc., Glen Burnie
Stoddard Supply Co., Ilageretown

ates,

Electronic Center Inc., Minneapolis
Radio Electric Supply, MDoneapolie
Gopher Electronics, St. Paul
Slvl'W.KEE-LINE Elem. Corp., St. Paul

City

LOUISIANA

ILLINOIS
Ohio Valley Sound, Centralia
Electronic Parts, Champaign
Radio Dutton, Champaign
Allied Radio Corp.. Chicago, Forest Park,

Admiral Diet. Inc., Mlnneapolie
Bonn Co., Lew, Minne,ppoolin, Rochester

Omaha Electronic,, Omaha
Joachim Radio Supply Inc., Scot

Bluff

Tri.State Eleceronece, Scotts Bluff.
NEVADA
Electronic Distributing Co., of Nev., Reno
NEW HAMPSHIRE
American Radio Corp., Dover
NEW JERSEY
Almo Radio, Atlantic City, Camden,

Trenton, Vineland
Kean Elect. Produces Inc., Atlantic City
Gem Electronics, Bayonne, East Brunaick, East Orange, Paramus, Springfield, Totowa
Miid,tatc Radio Supply Co.. Berlin
Joe', Radio
General Radio Sú pl Camden
Eastern Radio Corp., Clifton
Emeco Electronics, Hackensack
Nidixe.,. Ilackennack, Jersey City, Passaic,

Ridgefield, Trenton, Union City

State Elect. Parts Corp., lfanover
Leader Electronic Suppi Ilellnide.
Bay Electronic Doug:Co., New Brun,weck
Lafayette Radio & Elect., Newark, Pa ,

ranee, Plainfield

Asbury Electronice Supply, Ocean Grove
Jersey Electron
Dis l'aterman
'Wilma) Elect. Con
Corp.,., Paterson
Penn Electronic, Pte., Pennsauken, Pkila-

delphia

Allas Elect. Inc., Perth Amboy
Carl B. Williams, Phillipsburg
Leon Television Part, Co., Plainfield
Moyer Electric Supply, Pottsville
Sun Radio & Electronic,
Monmouth Radio Supply, Red Bank
Federated Purchaser, Sbrewebury, Spring-

field
NEW MEXICO

KicrulU, Alamogordo, .Albuquerque
Graybar Electric Co. Inc., Albuquerque

Albuquerque
B,,in Electronic Supply, Farmington
alley Engineering, Loa Alamo,
Yucca Wholesalers Inc.,

Southwestern Elect. Parts, Santa Fe

NEW YORK
Fort Orange Radio, Albany
Havens Electric Co. Inc., Albany
Knickerbocker Appl. Service, Albany
Taylor, Edwin E., Albany
Adirondack Radio Supply, Amsterdam
Gem Electronic., Beedsore, Belleroee,
Bronx, Brooklyn, Farmingdale. Foret
11i11,, Great Neck, Ilickaville, Huntington, Menands, tlount Vernon, New
York, Plainview, St. Jaynes,
y
Stream, West Bronx, Yonkers
Lafayette Radio & Electronic, Bronx,
Brooklyn, Jamaica, New York, Scene
dale, Syosset
Rim Electronics Inc., Bronx
Economy Electronic, Corp.. Brooklyn
Electronic Equip., Brooklyn
Graham Ekctronice Diet., Brooklyn
Rygrade Electronic. Co.. Brooklyn
Loco Electronics, Brooklyn
(luron Elect. Supply Co. Inc., Buffalo

Electronic Experimenter's

Handbook

DISTRIBUTOR LISTINGS -CONTINUED

Manfred Elnrronies. Corona
Electronic Supply Corp:. Elmhurst
Eddy Electronics. Elmira
Arrow Eketronicn, Farmingdale, Mineola,

New York
Emerald Electronics, Floral Park
Allen Electronic. Inc., Flushing, L. I.
Ray Supply Inc.. Glenn Falls, Plat rnburgh
Norman Radio Dine. Inc.. Ja moira, L. I.
Johnmn Radio Co.. Jamestown
Aram Elect. Dist., Kingston
Greylock Electronic Die.,Kingston,Poughkeepsie
Peerless Radio Corp.. Lynbrook
S&P Elm. Inc., Ma.eapegna

.ies. n

Seaway

Certified Elect. Inc., Middletown
Atlas Electronics Corp.- New York
Beko Dina. Inc., New York
Calvert Electronics Inc., New York
Elect. Parts Dibtg. Co., New York
Elect. Tube Sales Inc., New York
Grand Central Radio, New York
Harvey Radio, New York
Metropolitan Supply Co., New York
Midway Radio & TV, New York
Milo Electronics Corp.- New York
Terminal Iludion Elect., New York
Atlas Electronic. Inc.. Plain, iew
Higg'ne & Sheer Elect. Dist., Poughkeepsie
Elect. io,e tg. Corp., Richmond hill
Alfred
Rorp., er
Road
tro ic., Corp., Rockville Centre
Rome dlmmnict Rome
Adirondack Electronic.Inc.. Schenectady
Electric City
Supply. Schenectady
Schenectady Sleet.
Elect.
Schenectady"
R&DLNL Disrg., Staten Inland
Island
God D atg.Ela Corp., SymSy orL.
Syracuse
Gordon&
Robertsbet & O'Brien,roninInc..Ise.Syracuse
Salina Elect. Supply Co. Inc.. Syracuse
Watertown
Watertown
r

Oul

Melville

Thruway

White Plains

Elect.,

White

Pline

NORTH CAROLINA
Frock Radio & Sup.. Asheville
Dixie Radio Sup., Charlotte, Gastonia
World Electronics, Charlotte
Vickers Electronic Sup., Durham
Sourheaotcrn Radio Sup.. Fayetteville.
Greensboro, Hickory, Jacksonville,
Kingston, Raleigh, Salisbury, Wilmington, Wilson
Electronic Wholesaler.. Winston-Salem
Walker -Martin, Charlotte, Raleigh
NORTH DAKOTA
' tol D't
Bristol
rib t
Co., Bismarck, Fargo,
rGrand
GrandFork», Minot
John Iverson Co.. Mandan, Minot

OHIO
Akron Electronics Supply Co., Akron
Main TV Supply Co., Akron
Olson Radio (Company,
Sun Radio, Akron

Akron

Warren Radio, Akron. Lima, Toledo
Serves, Ashland, Delaware, Fremont,

Mansfield, Marion, Alt. Vernon, Sandusk
dusky.
Tiffin, W'

n
Canton Electronics. Cat
Sommer Electric Co.. Canton
Elec.,

Chillicothe. Columbus.

Lancaster. Newark, Zanesville
Holub Dist., Cincinnati, Newport
Higbee -Pet

SOUTH CAROLINA
Dixie Radio Sup., Anderson, Columbia.
Florence, Grenville,
Greenwood.
Spartanburg, Sumter
Wholesale Radio Sup.. Charleston
Southeastern It adio Sup.. Columbia

Seaway Elm.. Cleveland
nos, los., Dayton. Fairborn,
Con n Elec

Ha m il to
Rankin & Mouser Inc.. Dayton
Electronics. Dayton,

Srepco

Middletown, Piqua

Hamilton,

SOUTH DAKOTA

Stotts -Friedman. Davlon
Euclid Radio Part. Corp.. East Cleveland
United Elerironics, East Liverpool
Lima Radio Paris Co., Findlay, Lima,
Van Wert
JAB Electronics, Fremont
Standard Radio. Springfield
DAR Radio Supply, Steubenville
Toledo Radio Specialties. Toledo
Rem Elec
s. Ra
Glen Elect. Supply Corp..
Roan Radio,

Youngstown

Burghard. Radio Supply, Aberdeen, Sioux
Falls, Watertown. Rapid City
F.Imronie Supply Co.- Alitrhell
Ellis Elect°mica, Rapid City
Gourley Dis.g. Co., Sioux Falls

TENNESSEE
Clark Radio Sup.. Bristol, Morristown
I:urle Radio Supply. Chattanooga
Darne Electronic Distributor.. Ghat Iacocca
Warren Radio. Dyersburg, Memphis
Chemriiy Electronics. Johnson City, Kingsport
R
lio Ekr,rir Sup.. Kingsport
}Intolerant Bros., Knoxville
WAS, Distributing Co.. Memphis
Braid Electric, Nashville
(ascent Radio Supply, Nashville
Electra Distributing. Nashville

Youngstown

OKLAHOMA
Trier Rholesale Electronic.. Ardmore. Enid,
Lawton, McAlester, Muskogee, Oklahoma City, Okmulgee, Ponca City,
Tulsa
Noria° Electronics Sup., Bartlesville
Bols Amateur Electronics. Oklahoma City
John ll. Cole, Oklahoma City
Industrial Electronics. Oklahoma City
Grayler Electric, Oklahoma City, Tulsa
Radio. Inc., Oklahoma City, Tultra

TEXAS
KEA Electronic Sup.. Abilene, Midland
Graybar Electric, Abilene, Arlington.
Dalles. Fort Worth, Odessa
Radio Communications Sup.. .Abilene
Allironic Sup., Amarillo
Wyat Texas Electronics, Amarillo. Lubbock, Midland
Beta Electronic, Arlington
(ember Electric, .Austin, Beaumont.
Corpus Christi. San .Antonio

Oil Capitol Electronics. Tulsa
SAS Radio Sup., Tulsa

OREGON
Ace Electronics Inc.. Eugene

United Radio Supply, Eugene, Medford.

Portland

Walker, Vml G., Medford

Margin A.M. Austin
Texas Electronic Sup.. Austin
Wholesale Electronic Sup., Austin
Equipment &
Engineering,
Electronic
Brow run, ills, Corpus Christ i, Harlingen,

Pelle

Radin Supply, North Bend
Round -('p Electronics- Pendleton

Eboroolech Inc./Nemronir, Portland

lohmoi, Co., Lou, Portland

Television A Radin Supply,lorrland
Willamette Radio Supply,

Houston, Victoria

Rio Radio Sup., Brownsville. Harlingen.

PENNSYLVANIA
A. A. Peter., Allentown
Gem Electronics,

Alle,own

Allegheny Electronics lac.. Altoona, Johns-

town

Television Parts Co., Ambridge, Butler,
New Brighton, New Castle
Powell Electronic Sales, Bristol
County Sup dy Co.. C.oamnvlllc
Duncombe Co., J. V. Erie
Radio Distributing, Harrisburg
Barpo Radio Company, Mc Keeepert
Almo Radio, Norristown, Philadelphia
A. C. Radio Sply., Philadelphia
Allied Elm. App. Pain Inc.- Philadelphia
Leetronic Dist n., Philadelphia
Lectronic Res. Labs., Philadelphia
Sidney Wagner Elect. Sply., Philadelphia
Simm Elem., Philadelphia
ph,
Electronic Parts Co..C Pittsburgh
Triangle Electronics Co- Pittsburgh
Trrdingo(:nmp¡,
Pi.t ahnrgh

Cincinnati, Columbus

Myer
Cincinnati
Ne ark -H roger Elect., Cincinnati

McAllen
Stirling Electronic, Beaumont, Bryan,
Lufkin. Houston. San Antonio
Leader Electronic Sup., Corpus Cl ' '
Wick. Radio Equipment, Corpus Christi
All State Electronics, Dallas
Allied Electronics. Dallas

Wort,

r &'l'V Ui.., Reading
Connl(Jrd Distge Scranton

Kesel(

General Radio
Wilkes-Barre
Boron Electron
Wholesale Radio Pane. York

Ft.

Modern Electronics, San Antonio
Olen Radio Sup., San Antonio
Radio &'TV Parus. Sen Anìonio
Sherman Electronic. Sup., San Antonio
McCullock Wholesale TV Sup., Texarkana

RHODE ISLAND
Jabhour Electronic Spy., Pawtucket
W. H. Edwards, Providence

Goer Radio Sup.,

Wichita Falls

UTAH
Ballard Sop by Co., Ogden
Tri State Elect. Supply, Ogden
Alpine Elrcmmie Supply, Provo
Manwill S,q, dy Co.. Sall Lake City
O'I.m,gc.,ns Radio Suppply, Salt Lek.
Rona Inc., S.R., Salt lake City

City

VERMONT
Rutland Elect. Direr., Rutland
Electronic Sply. Inc., White River Junction

VIRGINIA
Certified Electronic, Alexandria
Arlington Elect. Wholesaler, Inc., Arlington
Kann -Eller. Elect. Inc., Charlottesville,

Winchester

Virginia Radio Supply Co., Charlottesville
Cain Elecrooio Inc., Hampton, Norfolk,

Portsmouth

Electronic W holaalers, IorrisonLurg
Electrical Wholesalers Inc., Harrisonburg
World Elect., Norfolk
Electronic Supply Co., Petersburg
Mabee Elect.
IliSupply, Richmond
Meridian Elem., R chmond

WASHINGTON
CAC:

Electronics Co.. Aberdeen, Bremer-

ton. Centralia, Longview, Olympia,
Seattle. Turman

Advanced Electronics, Bellingham
Skagit.A !memo Elect. Supply, Bellingham.

Mt. Vernon

Geiger Radio, W. A., Ellensburg
Pringle Elect. Supply Inc., Everett
Columbia Electric Co.. Kennewick
Radio Supply Co., Seattle

Norrbw a. Electronic,
c
Spokane
SJmkane Elect. Supply. Spokane
Electra -Tech Inc (,Newironic, Vancouver
Yakima u!McBee Radio Co., Yakima

WASHINGTON, D. C.
Fairway Elects. Inc.
Silberne Radio & Elect. Sala
Sun Parts
Bluefield Supply Co., Bluefield
Meyer, Electronics Inc., Bluefield
Mountain Electronics Co., Charleston.

('la ksbor

State Electronics Co.,

Fairmont

Electronic. Supply Inc.. Huntington
Chennity Electronic,, Parkersburg
General Elect. Dietr. Inc., Wheeling

WISCONSIN
Elect.

Expeditors

Iluy, Ablwaukcc

Inc, Appleton,

Gras

Bunhhnd Radio Specialties. Eau Claire
Marri, Radio. Fond du Lac
Northern Radio & TV Co., Green Bay
Thompson Elec
can ,title
Ke,osl,aElec
a, Kenosha
Acme Radio Supply Co.. /Milwaukee
Dykrn Distributors Inc., Milwaukee
Radio Part, Co. Inc., Milwaukee
Badger Electronic Parts Co.. Racine
Koepeell Co., J. J., Sheboygan
Marsh Radio Supply Co.. West Allis

WYOMING
Fleming Supply Inc., Casper
G,rrod Eng. & Supply Inc., Laramie

ELECTRIC

this coupon and take

it to the nearest Authorized

-E

Electronic Components Distributor
listed above and receive a free edition of G.E.'s new HOBBY MANUAL.
General Electric is anxious to provide new components and new ideas
for your home electronic workshop.
You can help us, and earn your free
HOBBY MANUAL, by recommending
three new electronic components
you could use in your experiments.

Edition

Dallas,

Wilkinson Bros., Dulles
Ale Nicol Inc., El Paso
S,u,lao, Supply Co.. Inc.. El Paso
Rural Electronic., Ft. Worth
Electronic Corp. of Texas, Galveston.
Ilomston
Aum,mtrE Distributing,.pooston
Bueecker Electronic Equipment. Houston
Electronic Component Dirnibu.or, Houston
Gilbert Electronics, Houston
Bell Electronics, Killeen, Temple
l'an American Electronic Co.. Laredo
P&L Radio & TV Sup., Lubbock
Diehl Radio A TV Sup.- l'or. Arthur
Gumer Wholesale, San Angelo

GENERAL

1965 Fall

Sup.,

Worth, Sherman, Waco. Wichita Falls

F:lem

FREE! Fill in

Electronic

Wholesale

Electronic Sup., Texas City
Fast Texan Electronic,, Tyler
L&M Salon, Waco

WEST VIRGINIA

Co,n.Suppbv. Dallas
Crabtree. Wholesale Electronics, Dallas
Southwest Radio Sup., Dallas
Trice Wholesale Electronic, Dallas, Ft.

University Elect. Co. Inc.. Sa te College
r
Huston
Dine.Inc,
EIm.,

TV Pane, Canton
Buckeye

Broadway Elec. Supply Co.. Cleveland
Pioncer, Cleveland, Lorain. Sandusky

(3)

NAME
ADDRESS

CITY

STATE

ORIGINALLY designed to
provide automatic cutoff for a commercial dehumidifier, the "Multi-Trol"
has proved so versatile that it has been
adapted to a variety of other applications. Electrical appliances that draw
up to 800 watts can be turned on or off
by a signal as small as 50 microwatts.
Cadmium sulphide photocells, thermistors, humidity sensors, or even a carbon microphone can be used to trigger
the unit as they respond to variations in
light, heat, humidity or sound. When attached to a pair of metal probes in the
ground, the Multi-Trol will serve as a
soil moisture indicator and can be used
to turn on electrically operated valves
WHILE

for automatic watering.

Circuit Design. The circuit was designed to provide maximum sensitivity
and power handling with a minimum of
parts. This is accomplished by using a
very high -gain transistor (Q1) as a
grounded emitter current amplifier to
drive a sensitive relay K1 which in turn
operates power relay K2.
The 2N1379 transistor used had a
measured d.c. current gain of 220 with a
base input of 200 ma. A linear 100,000 ohm potentiometer, R3, in series with
28

Build
the
Multi-Trol
By RYDER WILSON

the base, sensor and supply voltage, controls the sensitivity by limiting the base
current. Resistor R3 may be changed to
1 megohm when the resistance across
the input terminals is less than 50,000
ohms to give a little better control. Examples of such inputs would be low resistance photocells or humidity sensors.
A small silicon diode, D2, protects the
transistor from transients developed
across the coil of relay Kl. Pilot lamp
IZ provides a visual indication that the
power relay K2 has operated, and this
lamp may be replaced by a bell, buzzer,
or any other warning device the builder
desires.
Operating power is obtained from a
Electronic Experimenter's Handbook

Use

it to control almost any device

with nearly any signal

You should have no problems in constructing the
Multi-Trol as layout is

critical. The
"NC" and "NO" designanot at all

tions at relays K1 and
K2 refer to "normally
closed" and "normally
open" terminal points.

PARTS LIST
C1 -100-µf., 15 -volt electrolytic capacitor
C2-5094., 15 -volt electrolytic capacitor

D1-1N536 silicon diode
D2 -1N2069 silicon diode
11 -117 -volt, 3 -watt pilot lamp
J1, J2-Nylon insulated pin jack
J3-A.c. connector, female, recessed chassis
mounting
Kl-S.p.s.t., 550 -ohm, 9.5 -ma. relay (Sigma

11F-550-G/SIL)

small filament transformer, Ti. The
transformer output is rectified by diode
DI and filtered by capacitors Cl and C2.
This gives approximately 8.5 volts at the
collector of Ql.
An appliance plugged into the MultiTrol can be made normally off instead of
on, by reversing the two connections to
the normally open and normally closed
contacts of relay K2.
Construction. The author's unit is built
into a 4" x 5" x 6" utility box, but with
some ingenuity the parts could be fitted
into a smaller enclosure. Parts placement is not at all critical. The dehumidifier probe consists of a pair of No. 10
copper wires mounted in a Bakelite ter1965 Fall Edition

lit-S.p.d.t., 115-volt relay (Potter
field MRS A)
Q1 -2N1379 transistor
R1-4.7 -ohm, 1 -watt resistor
R2 -4700 -ohm, 1 -watt resistor

& Brum-

R3-100,000 -ohm linear potentiometer
R4 -100,000 -ohm, /2 -watt resistor
TI-Filament transformer; primary, 117 volts;
secondary 6.3 volts @ 1 ampere
1-4"x5"x6" aluminum Minibox

minal block. This is then encased in a
small plastic box and sprayed with plastic to make it waterproof. The two leads
from the probe are terminated in pin
plugs to conveniently fit jacks JI and J2.
When the probes are in one inch of
water, the resistance across them is approximately 25,000 ohms. Neither the
spacing nor the length of the probes is
critical; they may be adjusted to suit
the builder's convenience.
Using the Multi-Trol. Plug your dehumidifier into outlet J3 and place the
probe on top of the water bucket so that
the two copper wires will be in approximately one inch of water, at the level
where the dehumidifier is to be cut off.
29

HOW IT WORKS
The appliance to be controlled is plugged into
a.c. connector J3 which supplies its line voltage
through the normally closed contacts of relay K2.
Placing a resistance of about 50,000 ohms, such
as a photocell, thermistor, or other resistive sensor, at the input causes a small current to flow in
the base circuit of transistor Ql. This current is
amplified in the collector circuit which actuates
sensitive relay Kl. This in turn supplies the
power to relay K2. When relay K2 operates, the
a.c. voltage is removed from the load, and applied
to indicator lamp Il.

Start with 10" -long probes, and cut them
to the desired length. Plug the MultiTrol into the nearest wall outlet, and it
is ready to go to work for you.
Other Applications. An inexpensive cadmium sulphide photocell (for example,

Lafayette Radio's Stock No. MS 855)
can be used to convert the Multi-Trol to
a controller for house lamps, photoflood
lamps, or other electrical appliances.
Connect the photocell to input terminals
J1 and J2 and adjust the sensitivity control as required.
As an electronic thermostat, the circuit is just as sensitive and as easy to
use as in the photocell application. Select a thermistor with a resistance of
about 100,000 ohms (such as the Lafayette 51CA1) , plug it into J1 -J2, and set
the sensitivity control to trigger the circuit at the selected temperature.
There are many other possible applications for the Multi-Trol. The average
builder will enjoy discovering them for

-®-

himself.

Loudspeaker Code Practice
ANY RECEIVER can easily be converted to a loudspeaker code practice
oscillator. By feeding a portion of the
output signal to the grid of the first audio stage, a squeal is set up that is heard
in the loudspeaker.
Simply hook a pair of capacitors from
.0001 to .01 µf. at the points designated
"x" in the schematic diagram. Mount a
three -circuit (stereo) phone jack on the
radio set and solder the open ends of the
capacitors to the A and B lugs of the
phone jack. Do NOT connect to the
ground lug of the jack.
Attach a matching plug to your key,
connecting as shown, and plug the key
into the jack to practice code. The volume control on the radio will also serve
as a volume control for code practice.
And you can still use the radio as an
ordinary receiver if you remove the key
plug from the jack.

VOLUME
rVÓ
CONTROL

This modified radio code practice oscillator has plenty of pep, and is more
than sufficient to sound off for a class
full of budding hams.

-Frank

Parker

Customize Your Pilot Lamps
that "ultimate touch," add pilot lamps that can
be read. Cut small discs from celluloid or
plastic, and letter them with such legends as "ON," "OFF," or anything else
that is appropriate. Letter the discs with
decals, press -on letters, or with India
TO GIVE your equipment

ink. Most materials will take the ink if
you lightly sand them first. In many
cases, just one letter or number ("P"
for power, "A" for amplifier, etc.) will
be sufficient. The completed assembly
looks like any pilot lamp-until you turn
it on.
-Tim Callan
Electronic Experimenter's Handbook

1111111111111111111111111111

HIGH WATTAGE REDUCER
Use

low-cost, high -amperage silicon diodes for easy power control

THIS HANDY PROJECT is a by-product
of our space age. Without the impetus to
develop high -amperage, solid-state rectifiers
necessary for the space program, electronics
experimenters would not have been able to
buy "over -runs," surplus or seconds. As it
is, silicon diode rectifiers with 20 -ampere
ratings are being offered for about $3. The
multiple household uses for these devices
have never been fully explored, so here are a few ideas
on how to use them-you'll
probably find many more.
As shown above, you can
extend the life of your home
movie high -intensity lighting
equipment. You can halve
the output of a 1000-1200
watt electric heater (as long
as it does not incorporate a
motorized fan), giving you
SOI
controlled warmth and "reserve" heating power. The
same applies to a soldering
iron (no guns), or perhaps
1965

Fall

Edition

your electric cooker (again, no motor).
You'll find the "Reducer" inexpensive and
easy to build. Best of all, the unit itself
consumes no power-it simply saves it.
Construction is simple, requiring only that
the heat sink be well insulated from the
aluminum box. The author used surplus
ceramic bushings about 3/4" high, threaded
on both ends. A 20 -amp diode will run hot

Mount parts as indicated here;
D2 is wired to insulated tie strip.
31

CI
.01y1.

I000VDC

II
"LOW"

I2
"HIGH"

Diagram shows simplicity of High Wattage Reducer.

PARTS LIST
C1--0.01-µ1., 1000 -volt ceramic disc capacitor
D1 -20 -ampere, 400 PIV silicon diode, stud
mounting
D2 -50 -ma., 2110 PIV silicon diode
11-Neon lamp assembly with built-in resistor,
amber color lens
12--Neon lamp assembly with built-in resistor,
red color lens
Sl-S.p.s.t. switch, heavy-duty (15 -ampere minimum rating)
S01--Chassis-mount a.c. socket
1-3" x 4" x 5" Minibox
1-Heat sink (Carl Cordover HSR-4 or equivalent)
Misc.-Four threaded ceramic bushings to hold
heat sink, heavy-duty a.c. cord, terminal strip,
wire, solder, hardware

in addition to mounting Dl on heat sink,
ventilation holes should be provided to
dissipate heat generated in operation.

in series with appliances that have a rated
power drain of 1400-1500 watts, so the heat
sink is a must-it also makes a convenient

mount for the diode.
Holes for ventilation should be punched
in the aluminum box as in the photos. Two
neon lamps (optional) were incorporated in
the circuit to show operation. When switch
Si is open, D1 and D2 are back-to-back,
and 12 will go out. When switch SI is closed,
both neons go on and the silicon diode is
switched out of the "Reducer" circuit.
-Frank A. Parker

CB Dummy Load
CITIZENS BAND regulations prohibit the
practice of tuning up your transmitter
while putting a "dead" carrier on the air.
The commonly -used light bulb dummy antenna prevents this, but it changes resistance
with brightness.
The dummy load shown at right is easily
made by soldering a bus bar to the center
post of a coax connector and two resistors
between the bus bar and the shell. If your
CB transmitter uses 52 -ohm coax line, make
the load of two 100 -ohm, 2- or 3 -watt resistors. For 72 -ohm line, use two 150 -ohm,
2- or 3 -watt resistors. Be sure that the
resistors are carbon and not wire -wound.
Wire -wound units will introduce inductance
and upset readings.
Tune up with the dummy load using the
internal metering in your CB unit or the
r.f. probe of a VTVM clipped across the
load. A reading of 13-13'/ volts corresponds
to 3.5 watts output with 52 -ohm line.
-Alex F. Burr, 16W2941
32

Electronic Experimenter's Handbook

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CIRCLE NO,.

1965 Fall Edition

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State

Zip

ON READER SERVICE CARD

The most useless thing ever

published,

but your children will think it's great

it's a scin1 tillation counter detecting cosmic messages from outer space. Or, you casually
can mention to friends the fact that it's
OU MIGHT tell your kids

a miniaturized digital computer reading
out answers in binary computations.
Chances are they'll believe every word
you say ; only you will know that this
box is actually "nonsense."
The "Nonsense Box" consists of eight
neon lamp flashing circuits flashing at
various independent time rates, and all
powered by a single 90 -volt battery. The
current drain imposed by this circuit is
around 65 microamperes and the battery
should last well over a year. Of course,
this is one of the advantages (?) of the
Nonsense Box-there is no switch to
turn it off.
How It Works. Each flashing circuit
consists of a neon glow lamp, a 0.5-µf.
200 -volt capacitor and a resistor of one
of four specified values from 4.7 to 8.2
megohms. Take a look at the first flashing circuit (NE1, Cl, and R1). Since
36

By ALAN L. DANZIS

there is no current flowing in the circuit, there is no voltage drop across Rl,
or resistor R9 in series with the battery. This permits NE1 to fire (conduct)
setting up a voltage drop across Rl and
charging Cl. As the charge across Cl
rises, the voltage across the neon bulb
drops, and NE1 is extinguished. Now Cl
slowly discharges through R1 (the old
R/C time constant effect) until sufficient
voltage builds up across the neon bulb
to fire it and cause the whole process to
repeat itself.
Even though the flashing circuits are
doubled up (Cl/R1 and C5/R5 have the
same values) , small capacitor and resistor mismatches insure that no two
flashing circuits have the same time constant. Resistor R9 helps insure the random nature of the firing pattern.
Construction. The Nonsense Box can
be made of either metal or wood. It
Electronic Experimenter's

Handbook

NEB

R8
8.2

MEG.

C8 ALL 0

50f.

200V

The neon lamps can be arranged in any
pattern desired-circle, square, etc.

PARTS LIST B1 -90 -volt "B" battery (Burgess type V60 or
Eveready type 479)
C1 -C8-0.5-µf., 200 -volt paper capacitors (eight
required)
.ß"E1-NE8-NE-51 type neon bulb (eight required)

R5-4.7 megohms
R6-5.6 megohms
R3, R7-6.8 megohms
R4, R8-8.2 megohms
R1,
R2,

All resistors

/-watt

R9-47,000 ohms
8-Neon lamp sockets (Dialco type 810-B with
clear plastic lens)

Misc.-Mounting box, battery retaining clamp,
wire, solder, etc.

should have sufficient space inside to
comfortably hold the neon bulb sockets
and permit the battery to be mounted
rigidly in place. The latter measure is
especially necessary since many people
will try to shake the Nonsense Box to
make it turn off.
Care should be exercised in laying out
the holes for mounting the neon lamps.
The spacing is not critical, but uniformity is desirable. The lamps could be
arranged to make a person's initial, or
1965

Fall

Edition

The interior wiring of
the Nonsense Box can be
as haphazard as you want.
Be sure to clamp the battery in place to prevent

it being shaken loose.

in the square fashion shown in the

photos.
Wiring is noncritical-even the battery polarity may be reversed. It is suggested that one terminal of each of the
eight lamp sockets be wired together.
Solder one end of R9 to this common
connection and leave the other end temporarily free. Now solder one end of
resistors R1 -R8 and capacitors C1 -C8 to
each of the unused lamp socket terminals according to the wiring schematic.
Bring all 16 free leads from these capacitors and resistors to a common bus
bar and solder. The two leads from the
battery connect to the free end of R9
and the common bus bar.
The Nonsense Box should start flashing immediately-and only you will
know that it's all "nonsense."
37

Zip through Scott's new solid state FM stereo tuner
kit in one afternoon
Four to six hours! That's all you need to zip elusive life-size, full-color construction book
through Scott's new LT-112 FM stereo tuner kit. details every step ... makes perfect wiring alStart after lunch-enjoy superb stereo at dinner. most automatic.
Scott solid state circuitry is the key to the
LT -112's superior performance. Costly silicon
transistors give performance unapproached by
any other kit on the market. The LT -112 is kit brother to Scott's best-selling 312 solid state
stereo tuner, of which Audio said, "... one of
the finest tuners anywhere."
Your LT -112 arrives with all critical circuitry
pre -wired, pre -tested, pre -aligned, and mounted
on heavy-duty printed circuit boards. Scott's ex-

You'd never believe a kit so easy to build
could be so packed with features. Built into the
LT -112 is a new Scott invention
the Trimodulation meter, used for a Signal Strength
Indicator, Zero Center Indicator, and Alignment Meter.
See your Scott dealer today, and pick up an
LT -112 tuner kit
$179.95 plus one enjoyable afternoon will net you a lifetime of listening pleasure.

...

SCOTT

For Complete information on Scott's kits & componerrts write: Dept. 521-10. -I. H. Scott, Inc., 111 Powdermill Road, Maynard, Mass.
Export: Scott International, Maynard, Mass. Cable HIFI. Prices slightly higher west of Rockies.
Prices and specifications subject to change without notice.

CIRCLE NO. 27 ON READER SERVICE CARD
38

Electronic Experimenter's

Handbook

CHAPTER
2
AUDIO
STEREO
HI-FI
PROJECTS

If you are one of those electronics experimenters who think that audio/hi-fi/stereo construction
is a thing of the past, you'll be surprised at the
content of this chapter. The kickoff project is a
novel speaker enclosure embracing an unusual
principle called "bi -coupling." Constructed by
well-known enclosure designer, David Weems, the
"Bi-Coupler" (page 40) is a modified labyrinth
using 8" full -range speakers. Builders of the
"Bi -Coupler" will be pleasantly surprised by the
smooth sound and stereo effectiveness. Next project in line is the "Stereo S'Lector" (page .44)
-a convenience for those who like automation in
their FM listening.
The "Vibrato Simulator" and "Volume Expander" are also projects that can be classified as
"unusual." The "Simulator" (page 47) will appeal to budding musicians who have a guitar, and
the "Expander" (page 51) is a device for the
serious audiophile. The latter can be used monophonically as well as in the featured stereo version.
Shutting your hi-fi off with the record player
is not new, but the ideas presented on page 58
sure are. You'll admire the versatility of the
"Hi-Fi Interlock" and the safety features it incorporates. Last but not least is the "Shotgun
Sound Snooper" (page 61). This highly directional microphone has created considerable interest and the designers have completely revised
the story to include answers to many questions
raised by readers of POPULAR ELECTRONICS.

40
FOR

BETTER SOUND BUILD THE BI -COUPLER

David B. Weems

44
Alton

THE STEREO S'LECTOR

Otis, Jr.

47
Fred Ippolito, Jr.

VIBRATO SIMULATOR

51
Roger H. Russell

HI-FI VOLUME COMPRESSOR EXPANDER

58
HI-FI INTERLOCK

Charles

Ulrick

61
SHOTGUN SOUND SNOOPER
James R. Hollinger & John
1965 Pall Edition

Mulligan, K3TIB
39

For Better

und

Great for either stereo or mono listening, this
By DAVID B. WEEMS

HERE is a versatile, labyrinth speaker
11 system that gives you an almost unlimited choice of speakers because
matching them to the enclosure is not
critical. This is a real virtue if you decide to switch to a transistorized stereo
system and want to make a speaker
change. Or, at a later date, you may want
to upgrade your speakers or change simply for the sake of change-you can go
right ahead and do so, and keep the "Bi Coupler" enclosure. The only limitation
is that you will have to stick to 8"
speakers, and, we hope, good ones.
Stereo? One Bi -Coupler can certainly
be used as a complete stereo system. The
sound will be very satisfactory-quite
realistic in fact, since that old "hole
in the middle" is nicely filled. While you
may ultimately want to add another Bi Coupler in the interests of greater channel separation, one will serve until you're
ready to do so.

Electronic

Experimenter's

Handbook

Build the Bi=&nipler
flexible little system features two full -range speakers
Theory. The labyrinth type enclosures
have other virtues but they seem to
have fallen by the wayside, although
some manufacturers used them for
years. The Bi-Coupler is a modified labyrinth with some special features. First,
as you might guess from the name, it is
compartmentalized. The benefits of multiple full-range speakers are well known,
but when more than one such speaker is
mounted in a single compartment, there
is no guarantee that optimum results
will be obtained.
The phase relationship of sound waves
on a single baffle gets pretty confusing
with more than one speaker, particularly
behind the speakers where reflections
play an important role. Instead of mutual
coupling, the result is likely to be mutual cancellation at some frequencies. The

midrib in this enclosure separates the
speakers, insuring that they are in phase
on the rear wave, which produces bass
reinforcement.
Good high frequency dispersion is obtained from the angled baffles, which
also reduce midrange peaks due to reflections from the rear walls. A less obvious advantage to treble reproduction
is contributed by the outside shape of
the enclosure. A cabinet with corner
angles greater than 90° theoretically
reduces diffraction effects which, again,
are a source of phase distortion and can -

The basic parts of the Bi -Coupler are
shown in these photos along with their
dimensions. The two front pieces, above,
are each 121/2" x 331/2"; note spacing
and diameter of speaker cutouts. At
right, above, is the rear partition and
one of the two sides; the diagonal cutouts in the partition create labyrinth
effect. Directly at right is the top, bottom,
and the midrib. All parts (including a
cabinet back if desired) are cut from a
single sheet of 4' x 8' x 1/2" plywood.
1965

Fall

Edition

Diagram of the top of the Bi -Coupler's
enclosure shows how it is assembled. The
front edges of each side, those of the
four cleats, and both edges of the front
baffles are cut to a 78 -degree angle.
Photo at right shows the rear partition, the sides, midrib, and four
long cleats mounted to the bottom.

cellation. Finally, the front of the enclosure approximates the same shape a
sound wave assumes when it is emitted
from a point source, an aid in coupling
the speakers to the air.
Panel vibration should be avoided in
any type of enclosure. In this case, the
specified 1/2" plywood is adequate because an open "pipe" is subject to less
pressure build-up than a "box," and also
because the panels are narrow and well
braced. You may question the advisability of using 1/2" material for the midrib
which is subject to stress produced by
both speakers. Reconsider. The speakers
are mounted symmetrically with regard
to that panel, which means that if they
are connected in phase the change in
pressure from one speaker should exactly cancel the change in pressure
from the other speaker! It's an imperfect world, but that was the plan.
Bi -Coupler Construction. The parts for
the enclosure can be cut from a single
4' x 8' sheet of plywood with enough left
over to make a back if desired. The back
was not needed for the author's version
because the sides fit tightly against the
walls of the room in which it is installed.
By placing the cabinet on its back on a
rug, you can quickly compare the possibilities-complete or backless.
The sides and front pieces of the enclosure are first cut to a width of 121A",
but the front edge of each side is then
42

cut or planed to an angle of 78° as shown
in the illustrations. The 1" x 2" cleats
should also be cut to this angle. If a
power saw is used, set the saw blade at
12°, since 0° gives a cut of 90°. Both
edges of the front baffles are later cut at

the same angle.

Assembling the Cabinet. For a solid job,
use glue, screws, and nails. First, glue
and nail the 1" x 2" cleats to the midrib,
then glue and nail the midrib on a line
down the center of the partition (the
section with the diagonal cutouts) adding screws when it's in position. Glue
and nail the bottom to the partition and
midrib. The 1" x 2" cleats can now be
glued and screwed to the sides; glue
and screw the sides to the bottom and
,

rear partition.
Speaker holes should be cut in each
front baffle and then the angled cuts
made at the baffle edges. It may be necessary to take off a small amount at
each edge to secure a proper fit for these
parts. When fitted, glue and screw the
front baffles in place. Then locate the
speaker mounting bolts, which can temporarily be secured with glue.
The next step is to place the top in
position. By reaching in through the
speaker holes, an outline of the sides,
"fronts," midrib, and partition can be
marked under the top with a pencil. The
short cleats can be glued and screwed
to the underside of the top in the prop Electronic Experimenter's

Handbook

4-I/2

4-V2"

I/2"

B-V2 "

1/2-^1

Diagram above shows placement of top
from edges.
cleats; these are positioned

Nails, glue, and screws are used to
tightly bond the parts of the enclosure together, and eliminate vibration.

BILL OF MATERIALS
4' x 8' x %" plywood sheet:
4-123/2" x 33%" pieces for sides and fronts
Cut from one

1-10" x 33" piece for midrib
1-23" x 33" piece for rear partition
1-11" x 24" piece (less cut-offs) for top
1-15" x 23" piece (less cut-offs) for bottom

Cut from 1" x 2" lumber (actual
material size approx. g" x 1w):
4-33" pieces for front and side cleats
2-10%" pieces for top cleats
2-9" pieces for top cleats
2-4%" pieces for top cleats
1-21" piece for foot (optional)
2-10,A" pieces for foot (optional)

Last step is to
add padding in
cabinet top, and
to sides and rear

of speakers. How
much is mostly a
matter of taste.

Terminals permit the speakers to be connected in series, parallel, or separately.

busc.Four dozen #6

x 1%" screws, 6-d box
nails, glue, eight 3/16" x 1%" bolts for
speakers, grille cloth

er position to receive screws from the
outside of the cabinet.
It is a convenience to have an outside
connection for each speaker post. In the
prototype, this was done by drilling
holes in the rear partition and running
wires from the speaker terminals to
bolts on the back. Thus, the speakers can
be connected in series, parallel, or to
separate circuits as desired without tearing into the cabinet. When the speakers
are mounted, a test should be run to determine how much padding is necessary.
(Continued on page 147)
1965 Fall Edition

THE

s''

No more switch -throwing scramble when a stereo

station comes in! The S'Lector does it for you
By ALTON B. OTIS, JR.

you have a mono FM tuner and an
outboard multiplex adapter, the "Stereo
S'Lector" is for you! In addition to
giving you a visual indication that a
stereocast is coming through, it will
automatically switch the multiplex adapter into the circuit and connect the
adapter's output to the stereo tuner
terminals of the amplifier-a feature
found only in the more expensive commercial FM stereo tuners. The cost of
the parts required to build the S'Lector
is nominal-only about $15.00.
How it Works. The single compactron
tube, V1, is a 6D10 which has three separate triodes in one envelope. The multiplex signal from the tuner is applied to
44

Via, which is a low -gain amplifier with
a high input impedance. From there, it
goes to a variable -mu, high -gain amplifier, V1b. The output of V1b is fed to a
filter consisting of L1 and C5. This
removes all but the 19-kc. components
of the signal.
The 19-kc. signal is rectified by diode
D1 and the resulting d.c. voltage is applied to the grid of relay control Vic.
When no 19-kc. signal is present (as in
a monophonic signal) , the relay remains
pulled in, connecting the normal output
of the tuner to the amplifier. A 19-kc.
signal will apply a negative voltage to
the grid of Vie, which causes the relay
to open, connecting the tuner stereo out Electronic Experimenter's

Handbook

Finish the Stereo S'Lector with a
coat of spray paint and press on letters for jack identification.

put to the amplifier, and simultaneously
turning on the stereo indicator lamp

(I1).

Building the Unit. The Stereo S'Lector
is constructed in a 3" x 4" x 5" aluminum Minibox. Parts layout is not critical,

but the photos show the layout used
satisfactorily by the author.

Coil Li is mounted by means of a
flange provided with the coil. Power
rectifier D2 is mounted on a three -lug
(center ground) terminal strip which is
attached under one of the power transformer mounting screws. A single solder
lug under the other transformer mounting screw serves as a ground for capacitors C6 and C7. Capacitor C5 mounts
directly across the terminals of Li, and
D1 is connected directly between LZ and
R9.
Two of the four poles of relay Kl are
used for switching the output between
the tuner and multiplex adapter. The
other two relay poles can be used to
trigger external indicators (as shown
here) or for other signaling or switching functions.
Tuning Up. Check the unit carefully
for short circuits, and remove all solder
splashes and wire bits. Before installing
the 6D10, plug the unit in; the voltage

VI C2

R4 C3

Indicator lamp jack is connected to miniature plug so
lamp can be mounted at
tuner or amplifier panel.

JI
THROUGH
J7

1965 Fall Edition

RIO

R2 R3 C4

Parts layout is not at all
critical but author's model
is detailed in photo at
left with parts calf -outs.
45

.002,1

I/3 -6D18012
C2

0023f.

33K
DI
INGO

a
a

33K

lyf.

J3
J4

J6
J7

NE -2H

A single compactron tube does the work of three in the Stereo S'Lector circuit.

PARTS LIST
R2 -470 -ohm,
Cl, C2 -0.002-µf., 200 -voll Mylar capacitor
C3, C4, C6 -0.1-µf., 100 -volt Mylar capacitor
C5 -0.01-µf. ceramic disc capacitor
C7 -40-µf., 150 -volt electrolytic capacitor
D1 -1N60 diode (or equivalent)
D2 -50 -ma., 400-PIV silicon rectifier
II-NE-2H neon lamp
11-17-Phono jack (single -hole type)
18-117 -volt accessory outlet
19-Miniature phone jack
K1-4-p.d.t. relay, 5300 -ohm coil, 6.6 -ma. pullin (Lafayette 99-G-6094 or equivalent)
L1-19-kc. oscillator coil (J. W. Miller 1354)
PLI-Miniature phone plug
R1, R5-1.2-megohm, %-watt resistor

across capacitor C7 should read about
200 volts. Install the tube and allow a
short warm-up period. Voltage across C7
should now read about 140-150 volts, d.c.
If it is substantially lower, pull the plug
and inspect the unit again for shorts.
Connect the Stereo S'Lector to the
tuner with jacks, as follows: J1 to multiplex output of tuner; J2 to input of
multiplex adapter; J3 to monophonic output of tuner; J6 and J7 to the stereo
amplifier inputs ; J.4 and J5 to the output of the multiplex adapter.
With the tuner set to a strong stereo
station, adjust the slug in 1,1 for maxi46

5/2

-watt resistor

R3 -4700 -ohm, %-watt resistor
R4 -22,000 -ohm, %-watt resistor
R6 -1000 -ohm, %-watt resistor
R7, R8-33,000 -ohm, /2 -watt resistor
R9 -500,000 -ohm linear taper potentiometer
R10 -56,000 -ohm, V2 -watt resistor
Tl-Power transformer; primary, 117 volts;
secondaries, 125 volts, 15 ma., and 6.3 volts,
0.6 -amps. (Lafayette 33-G-3405, Stancor PS 8415, or equivalent)
VI -6D10 compactron tube
1-3" x 4" x 5" aluminum Minibox
Mise
-pin compactron socket, terminal strips,
wire, solder, line cord, etc.

-l2

mum a.c. voltage across the coil. The
reading may fluctuate at this point, depending on the program material. Starting with the wiper of R9 at the ground
end, advance the wiper toward D1 until
the relay drops out, then about five or
ten degrees more. The unit is now adjusted and ready for use.
The model built by the author has performed very reliably, never confusing
interchannel noise and a stereo broadcast. If you build the S'Lector, you'll
find it a valuable adjunct to your stereo
system, one that you will wonder how
you ever got along without.
Electronic Experimenter's

Handbook

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Low-cost transistorized
circuit is inserted
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amplifier. Player controls

simulator with

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1965 Fall Edition

homemade foot switch

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//////// %/%%/'

THIS article describes the construction of a simple, low-cost, transistorized vibrato simulator which can provide

most musical instrument amplifiers with
a vibrato effect. When used in conjunction with a guitar and amplifier, it
produces a pleasant-sounding amplitude modulated signal, similar to the effect
of varying the volume control on the
guitar.
The vibrato simulator is battery -operated and completely self-contained. No
external power source is required and
no circuit modifications to the amplifier are necessary. Installation of the
simulator consists of plugging it into
the amplifier and plugging the instrument into the simulator. The current
drain on the battery is so low that in
normal use the life of the battery should
approach its shelf life. Construction costs
are small, less than $10, even when all
the parts are purchased. But you will
probably have some of the parts available, reducing the cost even further.
Two controls are provided; one for adjusting the desired intensity and the
other for adjusting the vibrato speed.
A foot switch is also provided so that
the musician can switch the vibrato effect in or out while playing.
47

R2 R4 01 C3 R5 CI C4 RI R6

ûi=;

Underside view of the simulator shows compact, sturdy
construction used by the
author. All connections are
made to the potentiometer
terminals or to one of the
66-terminal tie strips mounted at either end of the box.

R9 C2 R7

the
self-contained
battery, the author wired
the simulator so it would
always be off unless momentary d.p.s.t. switch Si
was closed. The guitarist
With

this switch on
its doorstop mount under
his right or left foot.
slips

DOOR /STOP

About the Circuit. Transistor Q1 is used
in a sub -audio phase -shift oscillator circuit to produce the vibrato speed or
frequency. Transistor Q2 is used in a
voltage -divider network to modulate the
incoming signal. The effectiveness and
efficiency of the vibrato oscillator is remarkable. Using a 15 -volt battery, the
sine -wave output signal at the collector
is 8 volts peak-to -peak, with a current
drain on the battery of only 300 µa.
Common, low-cost transistors can be
used. In testing the circuit, the writer

tried at least ten 2N1265/5 transistors,
with each providing satisfactory results.
Although a 15 -volt battery is used to
provide sufficient output for this application, the circuit will oscillate with
a voltage of 9 to 12 volts.
48

4-COND. CABLE

The oscillator operates at a frequency
of 6 cycles, since this is the most commonly used frequency in commercially
available units and in electronic organs.
Potentiometer R2 provides for an oscillator range of approximately 4 to 14
cycles. Resistor R4 prevents oscillator
cutoff at the maximum clockwise rotation of R2, which is the fastest speed.
Capacitor C4 couples the oscillator
signal to potentiometer R6, which is
used to adjust the vibrato intensity.
Switch S1 is a momentary d.p.s.t. (nor-

mally open) type, used to make and
break both the oscillator and modulator
circuits. It is mounted in a molded plastic door stop and is used as a foot
switch so that the vibrato effect can be
switched in and out.

Electronic Experimenter's Handbook

INPUT
JI

15V.

OUTPUT
RB

SIA

PARTS LIST
B1 -15 -volt battery (Eveready 411 or equivalent)
C1-0.5-4. capacitor-see text
C2-1.5-4. capacitor-see text
C3-5-4. capacitor-see text
C4-0.05-4. ceramic disc capacitor
J1-Phone jack (Switchcraft 1.-11 or equivalent)
P1-Flat-type phone plug (Switchcraft 220 or
equivalent)
QI, Q2-21\1265/5 transistor (Sylvania)
RI -30,000 -ohm 112 -watt resistor
R2 -10,000 -ohm potentiometer (Philmore PC -51
or equivalent)
R3 -3300 -ohm, .A -watt resistor
R4 -3000 -ohm, )/2 -watt resistor
R5 -620,000 -ohm, TA -watt resistor
R6 -500,000 -ohm potentiometer (Philmore PC 54 or equivalent)
R7 -470,000 -ohm. %-watt resistor
RS, R9 -100,000 -ohm, 'A -watt resistor
S1-D.p.s.t. momentary push-button switch (normally open)
1-31/4" x 2%8" x 1) g" chassis (Bud CII-3001A
or equivalent)

-5 -foot,

4 -conductor shielded cable (Belden
8434 or equivalent)
1-Molded plastic door stop-see text
1

The output signal appearing at P1 is
fed to the instrument amplifier and will
vary in amplitude at a rate equal to the
oscillator frequency. Transistor Q2 does
not act exactly as a switch with only a
full "on" or full "off" condition. It
responds to the magnitude of the sine wave signal applied to its base. Therefore, the percent of modulation or
intensity can be adjusted through R6.
The values of R8 and R9 (100,000 ohms)
were chosen to provide up to 50% modu1965

Fall

Edition

SIB

Theory of operation of this
circuit is described in the text
at the bottom of the facing
page. Although the author
plugged his simulator right
into the amplifier, some
builders may find it necessary
to use an extension cable
instead of rigidly mounting
Pl to the aluminum box.

lation. Raising the value of R9 will decrease this percentage while lowering
the value will increase it. Changing the
value of R8 will accomplish the same
thing but in the reverse of the above
conditions.
Construction. The unit was completely
assembled in a 31/4" x 21" x 11/2" Minibox (Bud CU -3001A) with a shielded
cable going to the external foot switch.
Although there is no critical requirement for parts placement, it is advisable
to keep resistors R8 and R9 and the signal wires of JI and PI away from other
components in the simulator. It is also
advisable to use just one or two ground
lugs and make certain that a good mechanical and electrical ground is obtained.
When selecting capacitors Cl and C2,
consider using the Sprague "Hypercon"
ceramic disc type, part numbers HY330 and HY-135 respectively. These are
high -capacitance, low -power-factor miniature ceramic discs. They are also lowpriced. The manufacturer rates them
with a capacitance tolerance of guaranteed minimum value. In checking an
assortment of these capacitors on a
bridge, it was found that the 0.47-µf.
units (HY-330) invariably exceeded 0.5
µf. and the 1-µf. units (HY-135) were
closer to 1.5 µf. When selecting capacitor
C3, consider using a 4-µf. electrolytic
rather than a 5-µf. unit. The low-priced
variety of miniature electrolytics have
,

capacitance tolerances of -20 to +150,
the higher tolerance usually being the
case.
The capacitors listed above were used
in the author's model with excellent results. Of course, if standard -sized components are employed, which normally
have a ± 20% tolerance, the specified
values of 0.5 µf., 1.5 µf., and 5µf. should
be used.
Phone plug P1 is a fiat type with the
plastic case removed. Drill a hole at one
end of the chassis large enough to pass
the plug connectors through. Drill three
additional holes corresponding to the
screw holes on the plug to facilitate
mounting it to the chassis. The three
screws removed with the plastic cover
can be used for this purpose.
Mount the phone jack (J1) on the opposite end of the chassis. The two miniature potentiometers (R2 and R6) are
mounted on the bottom of the chassis.
All electrical components are assembled
using two 6 -terminal strips mounted on
the chassis bottom.
The foot switch is a momentary d.p.s.t.
push-button type mounted in an ordinary molded plastic door stop, which can
be purchased at most hardware stores.
Since the simulator is battery-operated
and does not have a pilot light, a momentary switch was used to eliminate
the possibility of leaving the oscillator
on when the simulator was not in operation. A push -on, push -off type switch
can be employed if desired.
The cable for the foot switch is a
miniature four -conductor shielded type
(Belden 8434). This cable is excellent
for this purpose because it contains two
pairs of wire separately shielded. Using
an unshielded cable, it was noticed that
a small transient pulse caused by the
opening and closing of Si (A) was picked
up through the wires of 21(B) and
transmitted to the amplifier as a click.
If desired, two small -diameter, two -conductor cables (one shielded) can be employed. Use the shielded pair for the
modulator circuit since this will also
help minimize stray hum and pickup.
The author made some attempt to
keep the unit small, which necessitated
the use of miniature parts. These parts
are generally more expensive and less
readily available than standard size
parts. There are, however, many differ50

ent ways in which the simulator can be
built. For example, the entire unit can be
assembled in a chassis fabricated to also
serve as a foot switch (Bud chassis
C-1606 can be used). This would eliminate the need for the shielded cable to
the foot switch and would preclude the
possibility of transient or hum pickup.
The unit can also be assembled in a
chassis which has provisions for mounting it to the amplifier case or chassis.
Another possibility would be to replace the 15 -volt battery with an a.c.operated power supply and assemble the
entire unit in a chassis attached to the
instrument amplifier chassis. In this
case, the simulator could be switched on
and off with the instrument power switch.
The oscillator circuit could be left running, which would eliminate the need
for switch SI(A), and an s.p.s.t. switch
could then be used for S1(B) to make
and break the modulator circuit.
Operation. Once the vibrato simulator
has been assembled, all that remains to
be done is to put it to use. Plug the unit
into the guitar amplifier and the guitar
cable plug into connector J1. Adjust the
guitar and amplifier controls for normal
operation. With the foot switch open,
the guitar operates in the normal manner. Depressing the foot switch couples
the vibrato circuit into the amplifier input. Adjust R2 for the desired vibrato
speed and R6 for the desired intensity.
It is unlikely that trouble will be encountered unless, of course, an error has
been made in wiring. In case of trouble,
carefully re -check the wiring, especially
the terminals of J1 and Pl, since it is
easy to reverse these connections and
thereby ground the input or output of
the unit. The oscillator can be checked
for oscillation by connecting a VTVM
between the collector and ground. A
reading of approximately -3 volts
should be obtained. Also, the pointer of
the meter will be moving at the oscillator rate. Check to see if the circuit
oscillates through the complete rotation
of R2.
It is possible to get a 2N1265/5 transistor with an extremely low gain factor.
Therefore, try another transistor of the
same type if everything else appears
normal. The only other factor that could
cause a problem is the variance in capacitance tolerances of Cl, C2, or C3. -i-Electronic

Experimenter's

Handbook

BUILD A

Hi-Fi
VOLUME

11113

3-1/113

1210742113

213

By ROGER H. RUSSELL
Add dynamic realism to FM stereo and to your tapes and records. Superbly
designed and inexpensive to build, this little unit is alone in its class

NEW GADGETS for the audiophile have not been slow in making
an appearance on dealers' shelves, at least one has been consistently
shoved aside or completely ignored: the volume compressor -expander.
Here, for the first time, is a method of controlling the dynamic range of
your hi-fi system for less than $25.00. And the low cost is not the only
attractive feature. Hirsch -Houck laboratory tests reveal that this volume
compressor -expander is virtually unmatched in its performance, even when
compared to commercial units costing much more.
What exactly is volume compression -expansion? It's as simple as this:
much
The dynamic (loudness) range of live program material is usually
for
example,
wider than a recorder or broadcast transmitter can handle. If,
WHILE

1965

Fall

Edition

Controls at

rear of unit are d.c. balance
pots which are adjusted initially. A cartridge, tuner, or other audio source is connected to inputs; outputs go to amplifier.
Speaker jacks allow unit to sample amplifier
output at speakers and react accordingly.

Controls on front of unit (photo above) are
threshold controls which determine the level
at which expansion or compression takes
place. Panel lamps 11 and 12 glow in proportion to the voltage of the audio tapped from
speakers; switches control power, function.

the gain is set halfway up, the soft

parts will be accompanied by noise ( tape
hiss, hum, etc.) and the loud parts will
be distorted from overdriving the re-

cording or broadcast amplifier. Unfortunately, the solution to this problemturning up the amplifier on soft passages
and turning it down on loud ones-destroys the dynamic range of the original
program material.
Since automatic volume compression is
used to some extent in all commercial
recording and broadcasting, volume expansion offers the audiophile an easy
way to restore dynamic realism to a
broadcast or to a tape or disc recording.
On the other hand, the volume compression of which this unit is capable
will be useful for those who want to
listen to background music or who want
to listen to the hi-fi without disturbing
their neighbors.
How It Works. The idea of using a
lamp and cadmium sulphide photocell in
a feedback circuit is not new, but few
experimenters have had the chance to
try this circuit in their hi-fi systems.
Use of transistor amplifiers-unique
with this unit-allows expansion and
compression at relatively low listening
levels.

Output voltage at the speaker terminals of each stereo channel is used
to drive a transistor amplifier/limiter
which, in turn, controls the intensity of
52

O.0
R1GiT

BALANCE
LEFT

a lamp. The intensity of the lamp causes
the resistance of a cadmium sulphide
photocell to change. The CdS cell is
switched in a voltage divider to either
aid or retard the input voltage to the
amplifier.
Since the input impedance of the
transistor amplifiers is high compared
to the impedance of the speakers, connecting the unit to the speaker terminals
has virtually no effect on speaker performance. With the d.c. balance controls
(R1 and R2) adjusted so the lamps just
go out with no audio at the speakers,
a slight voltage input at the bases of
Q1 and Q2 will fire the transistors and
the lamps will begin to glow. The lamps
will glow brighter as higher voltage is
applied to the point where the transistors begin to saturate. The amplifiers
act as limiters at this point-since a
higher input will not increase outputpreventing the bulbs from burning out.
Photocells PC1 and PC2 are placed
next to lamps Il and 12 respectively,
and vary in resistance from almost infinity when the lamps are dark to a few
hundred ohms when they are brightly
lighted. For volume expansion, the photocells are switched into the part of a
voltage divider circuit in series with
the audio source ( tuner, phono cartridge,
etc.) and the audio amplifier. Resistors
R5 and R7 in the left channel, and R8
and R6 in the right channel, are selected
Electronic

Experimenter's

Handbook

J3
OUT

LEFT

DC BAL

15
RI

LEFT

PCI

2N554

THRESHOLD

LEFT

SPKR

150yf.

50V

loon

J4
OUT
RIGHT

Je
E

THRESHOLD

RIGHT

XPAND

OUT

CDS

#49 -CELL

COMPRESS

RIGHT
SPKR

RIO

6.8K

150yf.

50V

R14

6.811

1/2AMP

R13

6.3 VAC

Ili

5611

VAC

2000pf.

NE51H

+15V

Simple circuit is duplicated for each channel. Basically, it consists of a transistor amplifier that drives a pilot bulb. Photocell for each channel is in a
voltage divider circuit which changes value as the light falling on the cell changes.

PARTS LIST

Cl, C2 -150-µf., 50 -volt electrolytic capacitor

C3 -2000-µf., 15 -volt electrolytic capacitor
D1-200-PIV, 750 -ma. "top hat" silicon diode
-ampere fuse, type 3AG
11, 12, 13, 14-#49 pilot lamp (GE)
15-NE-51H neon bulb
11, 12-Standard open -circuit phone jack (for

F1-/

speaker connections)

13, 14, 15, 16-Phono pin jack (single mounting
hole type)
PC1, PC2-Cadmium sulphide photocell (Lafayette 19 G 2101 or equivalent)
Ql, Q2 -2N554 power transistor (Motorola) or
equivalent
R1, R2 -5000 -ohm, 4 -watt wire -wound potentiometer
R3, R4 -500 -ohm, 4 -watt wire -wound potentiometer
R5, R6 -68,000 -ohm, /-watt, 5% resistor
R7, R8 -82,000 -ohm, /-watt, 5% resistor
R9, R10 -6800 -ohm, /-watt, 5% resistor
R11, R12 -100 -ohm, 1 -watt, 5% resistor
1965 Fall Edition

R13 -56 -ohm, 1 -watt, 10% resistor
R14 -6.8 -ohm, 1 -watt, 10% resistor
R15-22,000 -ohm, /-watt, 10% resistor
-pole, 3 -position rotary switch (LaSl, S2
fayette 99 G 2002 or equivalent)
T1-Filament transformer, 6.3 volts @ 1 ampere
1-Bakelite cabinet (Lafayette 19 G 2002,2'4" x
x 634", or similar)
1-Panel for cabinet above (Lafayette 19 G 3702)
2-Panel lamp assemblies for 11 and 12 (Dialco
930 series less resistor or equivalent)
1-Bayonet-type bulb holder for 15
1-Fuse holder for 3AG fuse
o.d.,
1-Length of polystyrene tubing,
i.d. (Lafayette 13 G 5126 or equivalent)
1--%" polystyrene sheet cut to 134" x 2 %" for
mounting Q1 and Q2
Misc.-Rubber grommets, terminal strips, 6-32
x %" hardware, knobs, wire, shielded cable,
a.c. line cord, small brackets for mounting
Q1 -Q2 mounting board, cement, tape, plastic
lens for 15, etc.

-4

,_;1,
r, ,.
_

Wk%
..

RIG

As shown in the pictorial and
photo, parts layout is very
compact. A larger cabinet or
metal chassis can be used if

desired, allowing loose layout.

R15

R13

12
R9

RIO

RII
TI

RIZ

R6
PCI

PC2
F'I

RI
CI

R2
C2

R7
R6

LEFT SPKR

J3
54

J6 J4

RIGHT SPKR

Electronic Experimenter's Handbook

compression occurs, to a maximum of 15
db. The amplifier now sees the output
as a slowly rising voltage.
The amount of expansion is determined
by the size of resistor R5 with respect to
resistor R7, and the size of R6 with respect to R8. If R5 and R6 are made
larger, more expansion may be obtained ;
if they are made smaller, less expansion
will result. On "compress," smaller valcurve.
In the "expand" position, a small in- ues for resistors R9 and R10 will give
crease in the input causes a large in- more compression; larger values will
crease in output, and this unequal change give less.
Construction. Although a metal chassis
in voltages is where expansion occurs.
Did we get something for nothing? No, can be used for the compressor -expander,
because the output was 6 db less than a Bakelite instrument case was selected
the input to start with (6 db is the for ease of construction-it can be
"line" or insertion loss of the unit), drilled and filed much like wood-and
but the amplifier doesn't know this. On compactness. Place drafting tape on the
"expand," it sees the output only as a front and rear of the case and use a
pencil to locate holes to be drilled. Larger
fast rising voltage.
PC2
are
holes should be filed or reamed as large
PC1
and
For compression,
switched into voltage dividers that now drills can cause chips around the hole
include R9 and R10 as well as R5 and R7 being cut.
Mount the components using lock
and R6 and R8. Here, PC1 and PC2 are
on the inside to prevent slippage
audio
washers
the
across
in
parallel
connected
source in combination with R9 and R10 on the smooth Bakelite. The power tranrespectively. As shown by the "com- sistors do not require a heat sink in
press" curve below, a large increase in this application and are mounted on a
input results in a small increase in piece of clear polystyrene. If transistors
output. This unequal change is where Q1 and Q2 are mounted on a metal

to give the desired amount of expansion
-about 6 db in this case-as the resistance of PC1 and PC2 changes. Voltage relationships for expansion can easily
be seen in the curve below. With the
unit in the "out" position (PC1 and PC2
out of the circuit), any increase in audio
input results in an equal increase in output as shown by the straight-line "out"

ilu

!-'-7/8-'1
f'/A,v

EXPAND

PHOTOCELL
O

5/8"
OUT

*49

PILOT LAMP

POLYSTYRENE
TUBING

TAPE

20
COMPRESS

PARTS

CEMENTED

TOGETHER

Photocell -pilot lamp assemblies-one for each channel-are constructed as detailed here (see text).

-50
INPUT-db

Hirsch -Houck laboratory curve shows 6 db expansion
and a maximum of 15 db compression for P.E. unit.

1965 Fall Edition

chassis, insulation must be used between to the socket prior to pushing over the
them and the chassis.
transistor lugs. This will make it posAssembly of the two photocell -lamp sible to avoid direct soldering to the
units is easy. As shown on page 45, transistor.
cut a 7/8" length of i8"-i.d. polystyrene
Resistors associated with the inputtubing for each. Push a #49 lamp into a output circuit should be accessible as
3/8" grommet and insert the grommet
you may want to experiment with the
and bulb into one end of the tube. Wrap amount of expansion and compression in
1/4" wide tape around each photocell,
the future.
using enough so they will fit smoothly in
As finishing touches, add rubber feet
the ends of the tubes opposite the bulbs. to the cabinet, and label the controls
Cement each assembly in place. Both of with decals.
the assemblies should be painted black
Hookup and Final Adjustments. Connect
so that external light won't affect the the compressor -expander into your stereo
resistance of the photocells. To make system as shown in the drawing below.
sure they are light -tight, measure the The amplifier input impedance should
resistance of the photocell -lamp assem- range between 50,000 ohms and 1 megblies in normal reading light-if it's ohm. The transistor portion of the circuit
less than one megohm, check for leaks. must be connected to the power ampliCaulking compound is a good material fier speaker terminals; be sure to connect
for sealing leaks around the bulbs and the ground of the speaker terminals to
photocells.
the ground of the transistor circuit. The
Wiring the Unit. Two separate groundinput-output circuit can be connected
ing systems are used in the compressor- between the preamp output -power amp
expander to avoid possible hum loops in input, tuner or tape recorder outputthe amplifier to be used with it. The preamp input, or the magnetic cartridge
speaker ground leads and power supply output-preamp input.
ground form one system; the shielded
To use the compressor-expander, turn
leads for the input-output circuit and it on and set the amplifier volume conphotocell section form the other system.
Wiring is straightforward. Use differHIRSCH-HOUCK REPORT
ent colors of wire for leads associated
The 6 db expansion was definitely more pleasing
with the left and right channels to make
than the 8.5 db of a comparable commercial unit.
The compression was more than adequate. Under
checking the circuit easy ; use shielded
conditions of compression or expansion there
wire for the input-output circuit conwas no high -frequency loss. The unit was easy to
nections. Polarity of D1 and Cl, C2 and
install and adjust, and did all that could be exmust
C3
be observed.
pected. Well planned and constructed ..
Care should be taken when soldering
to the lugs of the germanium power trol to zero. Adjust the d.c. balance
transistors, which can be easily dam- controls (R1 and R2 at the rear of the
aged by heat from the soldering iron. case) so the corresponding front panel
Use a heat sink between the solder joint lamps, 11 and 12, just go out. Next, set
and the body of the transistor, or use the front -panel threshold controls, R3
a transistor wafer socket. If a wafer and R4, to maximum clockwise and turn
socket is used, the leads can be soldered up the amplifier volume to a normal
.

Simply connect compressor -expander between audio source and amplifier.
PROGRAM

SOURCE

TUNER, PREAMP,
TAPE RECORDER,
OR MAGNETIC
CARTRIDGE

LEFT

SPEAKER

LEFT 4, 8, OR

RIGHT 4, 8, OR

INPUT

OUTPUT

RIGHT

INPUT
RIGHT

SPEAKER
LEFT

LEFT

STEREO AMPLIFIER

SPEAKER
RIGHT

L
I

RIGHT

SPEAKER

Electronic Experimenters Handbook

OUTPUT
DC

BAL

' INPUT

////J'''3

i
E XPAND

PCI

THRESHOLD

_1L

OUT

aR 49

#49

CÉLLj

COMPRESS

6.85

I/2AMP
117

47R
Iw

VAC

+ C2
II

NE51H

2000y(.
15V

Circuit diagram of the compressor-expander for monophonic use. See text below.

listening level. Expansion or compression
can then be selected.
Optimum setting of the threshold
controls has been found by the author
to vary from one type of program material to another. On the average, they
are set to produce full illumination on
the loud parts and no illumination on the
soft parts.
Special Notes. The compressor-expander
can be used between a magnetic cartridge and preamplifier when no other
connections are possible. If it is necessary to use the compressor-expander
in this fashion, provision must be made
to reduce the possibility of a.c. hum
pickup. This is done by cementing a
piece of kitchen aluminum foil to the
bottom of the Bakelite case underneath
the photocell assembly, The foil is
grounded internally through the flathead screw that holds the assembly in
place. Care must be taken that no other
screws are connected to the aluminum
foil to form a "ground loop."
There are a few stereo amplifiers on
the market that do not have a common
speaker ground connection. These amplifiers are generally transistorized and
present an unusual problem when con1965

Fall

Edition

nected to the compressor-expander. The
amplifier can be permanently damaged if
the stereo channels are coupled together
through the compressor. The only safe
solution to the problem of using amplifiers lacking a common speaker ground
with the compressor-expander is to construct the compressor -expander with
two separate power supplies. In effect,
the builder would assemble two monophonic versions of this circuit and each
channel would have its own ground to
each speaker-thus removing the coupling between the channels through the
common power supply.
The circuit diagram for either a
strictly single channel (monophonic)
version of the compressor-expander or
one of the two identical stereo units for
speaker isolation is shown above. The
only circuit change between this version
and the stereo version on page 55 (except parts numbering) is that R13-the
power supply bleeder-becomes two resistors (R6, R7) to compensate for the
increased supply voltage when the second channel power demands are removed.
Needless to say, whichever version of
the unit you build, It will greatly en-{3hance your listening pleasure.
57

For less than $15 you can

build real convenience

into your hi-fi stereo system

IN THIS

AGE of automation, it's ridiculous to have to throw more than one
switch to accomplish one ultimate function. If, for example, you want to listen
to a record, why should you first have to
turn on the phonograph, then the amplifier? With the "Hi-Fi Interlock," turning
on the phonograph (or the FM tuner or
the tape recorder) also turns on the
amplifier. An auxiliary benefit accrues in
that turning off the primary device also
turns off the secondary, or controlled
device, preventing the possibility of leaving the amplifier on all night to cook up
lots and lots of heat.
How It Works. Diodes D2 and D3 are
connected back-to-back in series with
sockets SO1 through 204, and then
across the a.c. line. A load applied to
these sockets will cause a voltage drop
in the diodes, activating the relay -controlling circuit at Q1, and causing relay
KZ to pull in and apply full 117 -volt a.c.
to socket SO5 where the controlled devices are connected.
When a load is applied at sockets SO/
through 204, diode D2 or D3 will conduct ( one or the other, depending on the
a.c. polarity at the time) providing a
negative base voltage for transistor Ql.
This base is normally held positive by
the bias supply formed by diode D1,
capacitor Cl and resistor Rl. Diode D2
limits the voltage to 0.75 volt. Resistor
R2 is used to limit base current, and capacitor C2 is used as a filter for the
half -wave d.c. that is applied to relay
Kl by transistor Ql.
Mounting the Components. All of the
components are mounted in a small, openend chassis. While parts placement is
not critical, you can obtain a general
idea of the arrangement the author used
by examining the pictorial diagram on
page 60.
Mount the larger components firstthe transformer, relay, and transistor.
Next mount diodes D2 and D3, then the

Build
INTERLOCK

By CHARLES J. ULRICK

Electronic

Experimenter's

Handbook

Devices plugged into

H7VAC

sockets SOl through
SO4 will control voltage at socket SO5.
If your record player doesn't draw sufficient current to

trip

this

circuit,

wire a 7 -watt light
bulb across phono
motor; another solution is to slightly
increase value of Rl.

PARTS LIST
C1, C2 -250-µf., 12 -volt electrolytic capacitor
D1, D4-400-PIV, 750 -ma. silicon rectifier
D2, D3-200-PIV, 12 -amp. silicon rectifier (Allied Radio Stock No. 39 A 926-D or equiva-

lent)
K1--S.p.s.t. relay, 6 volts d.c., 10 -amp. contacts
(Guardian IR -505-A6 or equivalent)
Q1 -2N176 transistor
R1 -2700 -ohm, 2 -watt resistor

standoff terminals. Transistor Q1 and
diodes D2 and D3 should be mounted on
the mica forms supplied as mounting kits
for these components.
Drill two holes in the base of the
open-end chassis in order to mount it on
the larger chassis. Use the small chassis
as a template to locate the mounting
holes in the larger chassis before proceeding with the wiring.
Because transistor Q1 must go on during the negative half-cycles of the a.c.
line, the transformer voltage must also
be negative at that time to turn it on.
To phase the transformer, connect a secondary lead to a primary lead and apply
117 volts a.c. across the primary. Measure the voltage at the open secondary
and primary, and if it is higher than
the 117 volts, untwist the two transformer leads you connected together, and substitute the other secondary lead. Be sure
to remove the primary voltage while
making these tests. When the transformer is properly phased-resulting in
a voltage lower than the line voltagesolder the leads.
1965 Fall Edition

R2 -22 -ohm,

2 -watt resistor
SO1-SO5-Chassis-mounting a.c. receptacle
TI-Filament transformer: primary, 117 volts
a.c.; secondary, 6.3 volts a.c. @ .6 amp
1-2" x 5" x 7" aluminum chassis
1-13/4" x 31" x 5" aluminum open-end chassis
14-122" standoff insulators
Misc.-A.c. line cord and plug, rubber grommet,
assorted wire, hardware, solder, etc.

To insulate diodes D2 and D3, drill
larger holes than are required for the
mounting studs. A pair of mica washers
above and below the hole will keep the
diodes from touching the chassis. Transistor Q1 must also be insulated from
the chassis, and in addition to using
oversize holes for the two terminals, it
will be necessary to insulate the transistor case as well. Toward this end, a
mica sheet is placed under the transistor,
and fiber shoulder washers are used for
the mounting screws. After D2, D3
and Q1 have been mounted, an ohmmeter
should be used to check for continuity to
the chassis. If such continuity is present, additional adjustments in positioning are indicated.
Drilling and Wiring. The larger chassis
also serves as a cabinet for the unit. The
two mounting holes that were marked
are first drilled, and then additional
holes for the line cord and a.c. sockets
are marked off. A hand nibbler is a great
help in cutting the square -cornered holes
for the sockets. Do not mount the
sockets or the small chassis until after
59

SO4

Pictorial diagram helps locate various components
in unit. Only inner chassis
is shown. Outer chassis
also serves as cabinet.

After wiring, subchassis (above, left) is installed in larger chassis and fastened in place.

the unit has been tested and is working
properly.
Following the schematic diagram, carefully wire the small subchassis, twisting
the wires to the sockets before soldering
them into place. Before wiring the line
cord into place, knot it so it will act as
a strain relief.
Be sure to deburr all mounting holes
to guarantee proper fit. This can best
be accomplished by the judicious use of
a
' or 3/4" twist drill, gently rotated
by hand.
1

Using the Interlock. To install the
interlock in a high-fidelity stereo system,
plug the various controlling units into
sockets SO/ through 504. The interlock
is then plugged into a wall outlet and
the unit to be controlled is connected
at S05. If it is necessary to control more
than one unit, a cube-tap can be connected to 205, or more sockets can be
added. Other applications for the interlock will be found in the ham or CB
shack, or wherever remote or automatic
-{3]0power switching is needed.
Electronic Experimenter's

Handbook

Build the
SHOTGUN

SOUND
SNOOPER
Operating on 'organ pipe"

principles, this amazing

ONE WINDY DAY last fall, the authors hustled a skeptical friend out
into a field bordering on a wooded area
to test a homemade long-range tubular
microphone. Waiting until the friend had
crossed the field and disappeared completely, we panned the mike toward the
spot where he had last been seen. At
first only the sounds of birds were heard ;
then, on the last swing, came the sound
of crashing brush and a voice mumbling
"Mary had a little lamb." When we told
him later that we had enjoyed his
nursery rhyme, he looked at us incredulously. At a range of 250 yards, under
adverse wind conditions, we had picked
his voice out of the woods!
The tubular microphone, one of the
less publicized but one of the most spectacular long-range listening devices,
might be described as a bundle of openend tubes designed to pick up and amplify sounds of different frequencies by
virtue of different tube lengths. The
principles involved are familiar: In re -

tubular microphone
amplifies distant sounds
By JAMES R. HOLLINGER and
JOHN E. MULLIGAN, K3TIB

1965 Fall Edition

Thirty-seven tubes ranging from 1" to 36"
make up the author's tubular mike; all
construction details are given in text
and in drawing at right. Completed unit
is mounted on a camera tripod and panned
like a machine gun to find sound source.

sponse to sounds of various frequencies,
the air columns within each tube vibrate and, in doing so, amplify the original sounds.
Applications of the tubular mike,
which has far greater sensitivity, better
frequency response, and superior directional characteristics than parabolic
types, are many. Bird and animal watchers are delighted with the added dimension of sound when it is applied to nature studies. Small boat operators may
find the unit of value as a navigational
aid, especially in fog or conditions of
poor visibility. The tubular mike can
pick up conversations from busy streets,
and under the right conditions, can actually pick up conversation through closed
windows 40 or more yards away.
Design and Construction. As you might
assume, tubes are cut to resonate over
a specific range of frequencies. To calculate tube length, first find wavelength
by dividing the speed of sound (1100
feet per second for practical purposes)
by the frequency. For example, the
wavelength of 256 cycles equals 1100
62

256, or 4.296 feet. Tube length,
however, is half this, or 2.14 feet, since
tubes open at both ends resonate at a
wavelength twice as long as their length.
In designing a tubular mike, it is necessary only to assemble enough tubes to
cover the frequency range of sounds you
want to hear. The exact number of tubes
is not critical, but should be the greatest
number that can be efficiently covered
by the microphone element. The range
of tube lengths may vary too. Some
builders may wish to use tubes longer
than those suggested here for increased
pickup of the lower frequencies. The
graduated lengths should be stepped
evenly from the shortest to the longest
so frequency nulls are avoided.
The "Shotgun Sound Snooper", designed for portability, is built with 37
aluminum tubes, :%" O.D., ranging from
1" to 36" in length, and graduated in
1" steps. The 37th tube is an extra 1"
length added to complete the hexagonal
symmetry of the pickup. The tubes can
be conveniently cut from ten 6' lengths,
using a tubing cutter or fine-tooth hack Electronic Experimenter's Handbook

5/32" DIA. DRILL -6

3/8"

3/8'

HOLES

I-a-- 2"-

1/8'-+1

7-3/4"

71/2.

HORIZONTAL SUPPORT BAR

TOP

5/32"

DIA. DRILL

-4

HOLES

7/8"

GLUE

FRONT SUPPORT BRACKET

FUNNEL ENCLOSURE

5/32' DIA.

DRILL-2 HOLES

1/16H1. CABLE
GROMMET
RUBBER

9/32'
I

2-13/16'=-m-

3%8

M3/8"

ANGLE

5/32"DIA. DRILL -4 HOLES

--MICROPHONE

HOLE

ö
H3/32.-1.<

RIM

GLUE

DIA. DRILL

BRACKET h-1-1/4"
la

Easily worked aluminum is used for fabricating the
pickup. The tubes can be conveniently cut from ten
6' lengths of 3/a" diameter stock, the support brack-

REAR SUPPORT BRACKET

13/8+
I

---

-I/4

e-9/16"

ets from a sheet or strip of 1/32" aluminum. The
horizontal support bar is made from heavier s' c*.
Angle bracket mounts to standard camera tr
I.

BILL OF MATERIALS FOR MICROPHONE

1-56'

length of %"-O.D. aluminum tubing (ten
6' lengths preferable)
1-Crystal microphone cartridge, approx. 21/2"diameter (Lafayette PA -27 or equivalent)
1-Household funnel, 2'5/4" -diameter (or equiv.)
1---3/4"-wide, 's" -thick aluminum stripping for
support brackets, battery bracket (approx. 2'
required)

saw. Dress the edges with a fine file to
remove burrs. Assemble the tubes as
shown in the drawing above, starting
with the 36" length and gluing the 35"
tube to it for the entire length. The

authors used fast -drying rubber base
cement, but epoxy glue can be used for
greater strength. In any case, be sure
the tubes are flush at one end by checking each one against the others as you

glue them in place. Don't worry about
the spaces between the tubes; they simply become air columns.
Cut and drill the front and back support brackets from easily worked 'i3s"1965 Fall Edition

',á" -thick aluminum strip for hori
zontal support bar (approximately 1 % ' lengtl

required)

1-Standard camera tripod

(fast -drying rubber base contact
cement or epoxy glue), 8-32 machine screw,
and nuts, rubber grommet, microphone cable,
solder, etc.

tlüsc.-Glue

thick aluminum as shown in the dr
ings. The brackets are shaped aro
the tubes to form a tight fit ; it will I
if you bend each one at the exact cer
to form a slight V before you shape
Make the horizontal support bar fr
" aluminum as shown, and cut of
piece of aluminum angle to form the
gle bracket.
Cartridge Mounting. The microphl
cartridge enclosure is made from a ?
diameter household funnel, but can be
improvised from sheet metal. The shape
of the enclosure is not important, provided it permits the microphone car 63

HIGH

IMPEDANCE
OUTPUT
INPUT
J;

LOW

IMPEDANCE
OUTPUT

Wire amplifier and other components
as above; T2, S2, J3 are optional.

Battery Mounting
Bracket

RI-SI

AMPLIFIER PARTS LIST

J3-Standard open -circuit
phone jack
R1 -10,000 -ohm miniature potentiometer with s.p.s.t. switch SI
(Lafayette 32-G-7364 or equiv.)
11, J2,

S1-Part

of RI
S2-S.p.d.t. toggle switch
T1-Transistor input transformer;

200,000-ohm primary, 1000 -ohm
secondary (Lafayette 99-G-6034
or equivalent)
T2-Transistor output transformer;
2500 -ohm primary, 11 -ohm secondary (Argonne AR -114 or
equivalent)

1-Lafayette PK-544

5 -transistor

audio amplifier or other high -gain amplifier
1
-volt transistor battery (Burgess 2U6 or
equivalent)
1-Aluminum box, approximately 2 %" x 3" x
5%" (LMB #136 or equivalent)
1-Miniature knob (Lafayette 32-G-2405)
1-18" length of single -conductor shielded microphone cable
1-Set of headphones, high or low impedance
Misc.-4-40 x 54" machine screws and extra
nuts, scrap aluminum, contact cement or epoxy
glue, wire, solder, etc.

-9

tridge to be mounted very close to the
ends of the tubes. Hold the wide end to
the tube cluster and mark the sides to
indicate the corners of the hexagonal
shape. Place the funnel on a smooth,
solid surface, and make dents at each
of the six corners of the hexagon with
a small ball peen hammer. With the flat
head of the hammer, flatten the areas
between the indentations for about 'I" in
from the edge of the funnel. Place it
over the end of the tube cluster and peen
again if necessary. A tight sliding fit is
desirable, but a loose fit can be remedied
with tape.
As shown in the drawing on page 63,
the rubber-rimmed microphone cartridge is mounted in the funnel with
64

PK-544

Follow parts placement indicated (unit is inverted
in this photo) to avoid possible feedback problems.

glue. It is important at this point to
make sure the cartridge will position
as close as possible to the ends of the

tubes without actually touching them
when the enclosure is fitted to the tubes.
The cartridge must be insulated from
the enclosure, either by the rubber rim
which is part of the recommended cartridge, or by some equivalent means.
The space behind the microphone element may be packed with a sound insulating material such as glass wool or
foam plastic to help reduce pickup from
the rear. Before placing the cartridge,
first connect a length of mike cable and
install a rubber grommet in the small
end of the funnel ; apply glue to the rubber rim of the mike cartridge and to the
funnel. Press the cartridge into the funnel, truing it up and clamping it into
position until the glue is dry.
Final Assembly. Place the rear support
bracket over the tube cluster 14" forward
of the flush end and tighten it onto the
(Continued on page 144)
Electronic Experimenter's Handbook

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want an interesting hobby, a well paying
business or a job with a future, you will find
the "Edu-Kit" a worth -while investment.
Many thousands of individuals of all

ages and backgrounds have successfully
used the 'Edu-Kit" in more than 79 countries of the world. The "Edu-Kit" has been
carefully designed. Step by step, so that
you cannot make a mistake. The "Etlu-Kit"
allows you o teach yourself at your own
rate. No instructor
s
is necessary.

PROGRESSIVE TEACHING METHOD
.

The Progressive Radio "Edu-Nit" is the foremost educational radio Kit in the world,
and is universally accepted as the standard in the field of electronics training. The "EduKit" uses the modern educational principle of "Learn by Doing." Therefore you construct.
learn Schematics, study theory, practice trouble shooting-all In a closely integrated Program dsigned to provide an easily-learned, thorough and interesting background In radio.
You begin by examining the various radio parts of the "Edu-Kit." You then learn the
function, theory and wiring of these parts. Then you bulld a simple radio. With this first
set you will enloy listening to regular broadcast stations, learn theory, practice testing
and trouble shooting. Then you build a more advanced radio, learn more advanced theory
and techniques. Gradually, in a progressive manner, and at your own rate, you will
find yourself constructing more advanced multi -tube radio circuits, and doing work like a
professional Radio Technician.
Included in the "Edu-Kit" course are Receiver, Transmitter. Code Oscillator, Signal
Tracer, Square Wave Generator and Signal Infector Circuits. These are not unprofessional
circuits. Constructed by means of prOlesslonal
''breadboard'' experiments, hut genuine radio
Wiring and soldering on metal chassis, plus the new method of radio construction known
as "Printed Circuitry." These circuits Operate on your regular AC or DC house current.

THE

"EDU-KIT"

COMPLETE

hardware. tubing. punched metal chassis, Instruction Manuals, hook-up wire, solder.
selenium rectifiers, coils, volume controls and switches. etc.
In addition. you receive Printed Circuit materials. including Printed Circuit chassis.
special tube sockets, hardware and instructions. You also receive a useful set of tools a
professional electric soldering iron, and a self -powered Dynamic Radio and Electronics
Tester. The ' Edu-Kit" also Includes Code instructions and the Progressive Code Oscillator.
to F.C.G. Radio Amateur License training. You will also receive lessons for
servicing with the Progressive Signal Tracer and the Progressive Signal Injector, a High
1eaddition
Fdelity Guide and a Quiz Bonk. You receive Membership In Radlo-TV Club. Free Consultation Service, Certificate of Merit and Discount Privileges. You receive all parts. tools.
Instructions, etc. Everything is yours to keep.
I

PRINTED CIRCUITRY

At no increase in price, the "Edu-Kit"
now includes Printed Circuitry. You build
a Printed Circuit Signal Injector, a
unique servicing instrument that can detect many Radio and TV troubles. This
revolutionary new technique of radio
construction is now becoming popular
in commercial radio and TV sets.
A Printed Circuit is a special insulated
chassis on which has been deposited a
conducting material which takes the
place of wiring. The various parts are
merely plugged in and soldered to terminals.
Printed Circuitry is the basis of modern Automation Electronics. A knowledge
of this subject is a necessity today for
anyone interested in Electronics.

PLIERS -CUTTERS

VALUABLE DISCOUNT CARD
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CONSULTATION SERVICE
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PRINTED CIRCUITRY

SERVICING LESSONS
You will learn trouble -shooting and
servicing In a progressive manner. You
will practice repairs on the sets that
you construct. You will learn symptoms
and causes of trouble In borne. portable
and car radios. You will learn how to
use the professional Signal Tracer, the
unique Signal Injector and the dynamic
Radio & Electronics Tester. While You
are learning in this practical way, you
will be able to do many a repair lob for
your friends and neighbors, and charge
fees which will far exceed the price of
the "Eau -Kit." Our Consultation Service
will help You with any technical prob-

lems you may have.

FROM OUR MAIL BAG
.1. Stataitls, of 25 Poplar Pl. Waterbury, Conn.. writes: "I have repaired
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will receive all parts

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You

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CIRCLE NO. 22 ON READER SERVICE CARD
1965 Fall Edition

TOOLS

SOLDERING IRON
ELECTRONICS TESTER

J
65

on a

subscription to

POPULAR ELECTRONICS
io=,ohs
mo

300

At the regular subscription rate these same 18
issues would cost all of $6.00! BUT NOT FOR
YOU. Your cost is only $3.00-HALF-PRICE!
Every month POPULAR ELECTRONICS brings you a
wealth of fascinating features aimed especially at
experimenters and do-it-yourselfers like yourself.
(Just glance to the right for a sample!)

You'll enjoy being right on top of the fast-growing
world of electronics with up-to-the-minute new product reports, lab tests, buying guides, and electronics
breakthroughs you want to know about. Plenty of
articles on hi-fi, money-saving test equipment, tape
recorders, electronic games, computers, photo -aids,
short wave receivers, antenna systems, solar powered and transistorized equipment-and much more.

Construction projects galore! Clear -as -crystal diagrams guide you each step of the way through funto -build projects you can put together in just a few
hours...for pennies! Turn friends green with envy by
building a super hi-fi rig they couldn't match in the
stores for hundreds of dollars! Or throw together a
fool -proof photoelectric burglar alarm to protect your
home and loved ones...or a remote control switch
that actually turns lights on and off when you whistle
a bar of your favorite tune!
POPULAR ELECTRONICS is definitely for men like
YOU. Take advantage of this HALF-PRICE OFFER to
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EXCLUSIVE HAM, SW & CB
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Make Your Signal Reports More Accurate
Safety in the Ham Station
Amateur License Fees and ARRL Petitions
Take Advantage of Changing Propagation
Conditions
Operating Another Ham's Station
Calling All SWL DX'ers
DX Awards
English-Language Newscasts to North
America
Radio Marathon Broadcasts Truth
To Cuba

Satellites

on the Air
Short -Wave Broadcast Predictions
Short -Wave Report
North American Alliance of SWL Clubs
Welcome to the SWL Newcomer
Sure Cure for Ham/CB Mobile Noise

Citizens Band Radio
"DSRC," New CB Features
Equipment Buyer's Guide
Transmitters and Transceivers
Station Accessories
Antennas
Microphones
Hand -Held Transceivers
FCC Report
On the Citizens Band
Sure Cure for Ham/CB Mobile Noise
Vibrator Hash, Wipe Out
Build -It -Yourself
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Antenna Adapter, Power Line
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Double -Duty EICO 772
Hula-Hoop-a Ham or CB Antenna
Idento-Minder
Q

-Multiplier, Nuvistor

Screen Modulator, One -Tube

Transmitter Crystal Switch, Plug-in
2 -Meter Simple Superhet

CHAPTER
3
THE
FABULOUS
DIODES
Throughout the past
11 years, the publish-

ers of POPULAR
ELECTRONICS and
the ELECTRONIC
EXPERIMENTER'S
HANDBOOK have
presented numerous
basic articles on such

diverse subjects as
transistors, trans f orm-

ers, automotive electronics, CB, etc. The
article on the following
16 pages is about germanium and silicon
diodes. It is a capsule
summary of the numerous applications of
diodes, how this new
breed of diodes operates, and the strange
names they bear. Your
Editors would appreciate your comments on
articles of this type
and votes on whether
these articles should or
should not appear in

the ELECTRONIC
EXPERIMENTER'S
HANDBOOK in the

future.

1965 Fall Edition

Many electronics
experts agree that the
usefulness and
versatility of the diode

will-within
another three years-exceed
that of the transistor
By LOUIS E. GARNER, Jr.

transistor is only a little over a decade old,
many hobbyists-and especially newcomers to electronics-feel that all semiconductor devices are quite young.
The truth of the matter, however, is that the semiconductor diode is one of the oldest of radio -electronic components, predating even the venerable electron tube as a
widely used device.
A majority of the early radio receivers employed a
crude type of point -contact diode as their detector-essentially, a small piece of galena (a crystalline lead sulphide mineral) to which contact was made with a fine
wire dubbed a "cat's -whisker." Unreliable, of varying sen ince the

sitivity, and time-consuming to adjust, this early semiconductor device was widely used, and often cursed. It
was, in fact, the search for a superior detector that led
to the development of the electron tube.
While the semiconductor diode was eclipsed for a while
by the electron tube and, to some extent, fell into disuse
and was forgotten, the success of the transistor has brought
the device back into its own-but not as the unreliable,
finicky, open-air, and ugly galena crystal. Instead, the
modern diode comes in thousands of types and styles
and is indeed a fabulous creation. Like the phoenix, it
has been reborn, but with more vigor, reliability, and versatility. In addition to its ability to detect radio frequencies, the modern diode-in some of its forms-has acquired
the additional capabilities of amplification and oscillation.
By definition, a diode is a two -electrode device. However, many modern diodes have three and even four terminal connections. While these multi -electrode devices
are still diodes as far as their basic operating characteristics are concerned, the addition of extra electrodes permits the devices to perform some new and, as we shall see
later, rather interesting feats of electronic wizardry.

How Diodes Work
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junction of p- and n -type semiconductor materials. The diode derives most of its
capabilities from its nonlinear, unidirectional electrical
characteristics, i.e., its ability to conduct freely in one direction while acting as a high resistance or open circuit
in the opposite direction.
The p -type material has a surplus of more or less evenly distributed positive -charged "holes." The n -type material has a surplus of evenly distributed, negative -charged
free electrons. Suppose that a battery or other d.c. voltage
source were connected in series with the meter and diode,
so that a positive voltage would be applied to the p -type
material and a negative voltage to the n -type. Under
these conditions, the positive holes would be repelled by
the positive voltage and would migrate towards the junction. At the same time, the free electrons in the n -material
would be repelled and accumulate near the junction.
Thus, a surplus of positive and negative current carriers
would accumulate at the junction, with a certain percentage "spilling over" into the opposite materials. Holes
would migrate into the n -type material, where they would
be absorbed and become neutralized by the surplus free
electrons. At the same time, electrons would enter the
p -type material, neutralizing holes there. New holes and
electrons would be created by the applied d.c. potential
and these, in turn, would migrate towards the junction.
The result, then, would be a heavy flow of current, as indicated on the meter. The diode, under such conditions, is
Diodes are essentially a

Electronic Experimenter's

Handbook

said to be biased in its forward (or conducting) direction.
Let's consider the opposite situation now. With the battery voltage reversed, the positive holes accumulate at
the negative terminal, while the free electrons gather at
the positive terminal. The junction region is depleted of
current carriers and, therefore, there can be no "carryover" through the junction. Under these conditions, current
flow is very low and the diode acts as a high resistance. It
is biased in its reverse (or nonconducting) direction.
Going a step further, let's see what happens when the
supply voltage is increased with the diode reverse-biased.
At this point, we must remember that while there are a
majority of holes in the p -type material there are also
a few free electrons present (these are called, appropriately, minority current carriers). By the same token, there
are a few positive -charged holes in the n -type material.
As the electrical pressure (voltage) is increased, these
minority carriers start to accumulate in the junction area.
Eventually, a certain amount of "carry-over" can take
place, and the diode switches rapidly from a nonconducting to a conducting condition. In a way, we can say that
the junction has "broken down." The diode current increases very suddenly and, unless there is something to
limit current flow (such as a resistor in series with the
battery), the diode will be destroyed. The voltage at which
this reverse breakdown occurs is called the zener voltage.

How They Are Made
Diodes are manufactured using essentially the same tech 2-7 niques that are employed in producing transistors.
Thus, we have point -contact, alloyed -junction, grown -junction, mesa, planar, and epitaxial types. (Refer to "Transistors-Types and Techniques," POPULAR ELECTRONICS,
November, 1962, page 65.) The same types of semiconductor materials are used, including n- and p -doped germanium and silicon. In addition, some diodes are manufactured of intermetallic and metallic compounds, including
copper oxide and sulphides, cadmium sulphide, gallium arsenide, and various selenium compounds.
Physically, small diodes can be mounted in plastic,
glass, metal or ceramic cases, while larger types can be
assembled on flat plates, on cooling fins, or in electron
tube -shaped envelopes. Externally, some may appear to
be resistors or capacitors, others look like tiny buttons
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similar to a mercury cell battery, while still others seem
to be transistors, for they are assembled in similar cases.
Aside from basic electrical specifications and materials
of construction, there are many, many types of diodes.
Some are designed for operation in their zener region ..
still others have a variable
others are light-sensitive
capacitance characteristic. While most are single -junction
devices, there are multilayer, multijunction types. Special
schematic symbols are used to identify these different types.
Where greater voltage or current handling capability is
needed than is available in a single diode, several units
can be connected in series or in parallel. The series connection is used where higher voltages must be handled,
while the parallel connection is used to increase current
carrying ability. A straightforward series or parallel connection can be employed where the individual diodes have
virtually identical characteristics. If the diodes' characteristics are not identical, however, the voltage (or current)
distribution may be such that one or more of the diodes
are destroyed. To avoid this, shunt or series resistors can
be employed to equalize voltages (or currents). Shunt
resistors are used when the diodes are connected in series,
series resistors when the diodes are wired in parallel.
.

PARALLEL
At

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5E.?/ES PROTECTioN

General -Purpose Diodes

ANTENNA

Manufactured of germanium, silicon or selenium, and designed for a broad range of circuit applications, general-purpose diodes are identified by the basic diode schematic symbol. A line represents the cathode, while the
anode is identified by an arrowhead. This symbol derives
from the original point -contact diode, with the arrowhead
indicating the direction of "classical" current flow-just the
opposite of electron flow. The general-purpose types include such popular units as the 1N34 (and 1N34A), 1N38,
1N39, 1N56A, 1N58 and 1N66. In practice, the cathode
lead is generally identified by a color -band, polarity
marking, or similar symbol on the diode's body.
The adjacent diagrams illustrate typical general-purpose diode applications. Almost any general-purpose diode
can be used in these circuits, provided the maximum ratings are not exceeded. Low -voltage types may be used in
the receiver circuit, while a high -voltage type should be
- - - - - - -used in the stroboscope.
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Electronic Experimenter's Handbook

ZENER DIODES
Physically, low-power zener diodes look very much like
general-purpose diodes. In fact, any standard diode can
be used as a zener diode. Commercial zener diodes, however, are especially processed and selected for their performance in the zener region. Some zener diodes are
manufactured primarily for use as voltage regulators and
cu
are so designated. Others are selected for close breakdown
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voltage tolerance and are referred to as reference diodes.
03
Since the zener breakdown, when it occurs, builds up with
the suddenness of an avalanche, zener types are sometimes
called avalanche diodes. Finally, some firms manufacture
i!/wc -,PEG[/LATo,e
special zener types which they identify as Stabistors.
Zener diodes can be series -connected, either to obtain
R/
higher voltage ratings or multiple output voltage. A typical multi -regulator circuit consists of an unregulated
d.c. source, an adjustable current limiting resistor, R1,
and a chain of zener diodes, DI, D2, etc. In operation,
the regulated d.c. voltage available between any pair of
output terminals is equal to the sum of the zener diode
voltage ratings between the two terminals. For example,
C. ,PEGLGATo,2.
if D3 is rated at 3.6 volts and D4 at 6.8 volts, 3.6
volts will be available between terminals C and D, 6.8
volts between D and E, and 10.4 volts between C and E.
Zener diodes can be used as an a.c. line regulator. Two
diodes are connected "back-to-back." One breaks down UNQEGl1(47E
LQaO
4).C.
on positive line peaks which exceed its rated value while
the other breaks down on negative peaks, in both cases
dropping the excessive line voltage across the current

limiting resistor.
A d.c. voltage regulator circuit is similar to that of the
a.c. regulator, except that a single diode is used.
The same principle used in the a.c. regulator can be
applied in a simple square -wave generator or clipper. The
applied a.c. voltage should be from 10 to 20 times the
rated zener breakdown voltage for best action and good,
sharp output square -wave signals. The series resistor is
large enough to protect the diodes from excessive currents.
Used in conjunction with an audio generator, this circuit
will provide square waves for checking audio amplifiers.
A voltage -sensitive relay circuit can be used for remote
control applications. In operation, the application of
a d.c. voltage below either zener diode's breakdown
voltage will have no effect. If the voltage is increased
until, say, D1 's rating is exceeded, relay RLY1 will close,
but relay RLY2 (assuming D2 has a higher rating than
DI) will remain open. If the voltage is then increased still
further, until D2's rating is exceeded, RLY2 will also close.
This circuit is well -suited to applications requiring sequential relay operation with remote voltage control.
Zener diodes can also be employed in meter protection
1965 Fall Edition

D.C. ,QEGUL_,4Tv,e

ziivz 7-/íuE7'EK

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circuits. In the circuit shown here, Rl, R2, R3 and R4
are the multimeter's multiplier resistors and SI is the
range switch. The zener diode, DI, protects the meter
against accidental overload damage. Its rating should
be just slightly greater than the voltage required for a
full-scale meter reading, but below the meter's maximum
rating. Resistor R4 is chosen so that its resistance, combined with the meter resistance, is considerably greater
than the diode's resistance when in a breakdown state.

7-70

DIODE SWITCHES
Adiode switch is analogous to a mechanical switch in
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that it has two states-"off" and "on." When in an
"off" state, it acts like an open circuit; and when "on,"
it conducts heavily. In practice, both standard and zener
diodes may be used as switches by applying a bias voltage
to hold the devices in a nonconducting state, then adding
a control signal voltage of sufficient amplitude to cause
heavy conduction. There are, however, a whole new class
of semiconductor diodes and diode -like devices which are
specifically designed for use as switches. Included in this
class are the bistable diode, dynistor, silicon -controlled
switch, binistor, and double -based diode.
The bistable diode is made up of four alternate layers
of p -and n -type silicon. For this reason, it is also called
a 4 -layer diode. In use, the bistable diode does not conduct and remains "off" when biased in its forward
direction until the applied voltage reaches a predetermined
trigger or "firing" voltage. At this time, the diode switches
rapidly into a heavy conducting state, remaining "on"
until the applied voltage is dropped to a very low value.
When reversed -biased, it behaves very much like a conventional diode, acting as an open circuit until its zener
breakdown voltage is reached. (See diagram below.)
Somewhat similar to the bistable diode, except that its
basic material is germanium and its fourth layer is metallic
rather than n -type semiconductor material, is the dynistor.
The dynistor's forward characteristics are essentially
similar to those of the bistable diode, but the unit does
not block reverse current flow.
The silicon -controlled switch (SCS) is a four -layer
device closely resembling the bistable diode, but with an
electrical connection made to the third layer. A small
"trigger" voltage applied to this electrode, called a gate,
will switch the device from a nonconducting to a conducting state quite rapidly, even though the cathode -anode
voltage is below that normally required to trigger. Several
versions of this device are offered by various manufacturers. In its basic form, the SCS can only be switched "on"
Electronic Experimenter's

Handbook

...

afterwards, it can be returned to its
by a gate signal
stable "off" state only by dropping the anode -cathode
voltage to a low value. Slightly modified forms which can
also be switched off by the application of a reverse bias
to the gate are called Trigistors (Clevite-Shockley) and
Transwitches (Transitron). A germanium version of the
device is called a Dynaquad by its manufacturer
(Tung -Sol).
It is possible, of course, to provide an electrical connection for the second as well as the first, third and fourth
layers in a four -layer device. In this case, we have another
gate electrode and, to differentiate between the two gate
connections, the one nearest the anode is called the anode
gate (GA), while the one nearest the cathode is termed
the cathode gate (Gc).
One manufacturer of the four -layer, four -connection
"diode" suggests that the anode gate connection be used as
an output terminal. The device is then called a binistor,
and new designations are assigned to each of the electrodes.
The anode is called an injector, the anode gate a collector,
the cathode gate a base, and the cathode the emitter.
At right is a generalized characteristics curve applicable
to the whole "family" of four -layer diodes (except for the
dynistor, which conducts when reverse biased). These
devices do not conduct appreciably in either their forward
or reverse direction until either their zener voltage is
exceeded (in reverse bias mode) or their trigger or forward
"breakover" point is reached. Once the breakover voltage
is attained, the devices switch rapidly to a heavily conducting state, acting as low resistances even at low voltages. The effect of a trigger applied to a control gate is
to reduce the anode -cathode voltage point at which break over occurs. In effect, then, these four -layer switches have
three forward states-an "off" state in which they do not
conduct, a transition state during which they exhibit a
negative resistance characteristic, and an "on" state in
which they conduct heavily.
There is yet another diode switch, different in construction from the class of four -layer devices we've just
discussed-the double -based diode, now more popularly
known as the unijunction transistor (or UJT). This
device consists of a bar of n -type germanium or silicon
with ohmic contacts at each end, designated Base 1 (B1)
and Base 2 (B2), and a pn junction slightly off-center.
If B2 is made positive with respect to B1, the emitter -B1
junction behaves like a high value resistor . . . up to a
point. If sufficient voltage is applied to the emitter -B,
junction, the device will switch suddenly from a high
resistance to a low resistance (virtually a short circuit)
state, passing quickly through a negative resistance transition region.
A relaxation oscillator circuit employing a bistable diode
is shown at right. In operation, the voltage applied by
1965

Fall

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the d.c. source (BI) charges the capacitor (Cl) through
series resistors Rl and R2. The bistable diode, Dl,
remains in an "off" or nonconducting state until the
capacitor voltage reaches the diode's trigger voltage, at
which time the diode switches to a low -resistance conducting state and discharges the capacitor through its
internal resistance and R2. Then the action repeats itself.
In general, the battery voltage is considerably greater that
the diode's trigger voltage. Resistor Rl is much larger
than R2. Both Rl, R2, and Cl, are chosen so that their
combined time constant is appropriate to the repetition
rate (frequency) desired.
The flip-flop circuit shown here is similar to those used
extensively in computers. A controlled switch such as a
Trigistor or Transwitch might be used (Q1). In operation,
Ql is normally in a nonconducting or "off" state, and full
battery (B2) voltage appears at its upper terminal. If
a positive pulse is applied to the device's gate through
blocking capacitor Cl, the device switches to a heavily
conducting state, dropping B2's voltage across the load
resistor, R2, and developing a negative output pulse. The
device remains "on" until a negative pulse is applied
through Cl, at which time it reverts to the original "off"
state, developing a positive output pulse. Battery 131
applies a fixed gate bias to the device through RI to
insure stable operation.
A time -delay relay using a unijunction transistor is at
left. The relay closes a specified period of time after Si
is closed, and then remains closed until SI is opened to
"reset" the circuit. A simple RC time constant network
is formed by RI and Cl to furnish the delayed emitter
voltage which "fires" the UJT. Base 2 voltage is furnished
through R2 and, of course, the upper relay contacts. Once
the UJT fires, the relay is pulled in, removing the emitter
and base 2 voltages and applying a "holding" voltage to
the relay coil through R3. The second set of relay contacts is used to actuate an external circuit.

PHOTODIODES
Nearly all semiconductors are sensitive to light. When
light strikes the surface of the material, electrons are

freed from their valence bonds and, in some cases, positive charged holes are created. Under the proper conditions,
enough electrons may be released so that a small voltage
develops. This has led to the development of a large
group of light-sensitive semiconductor diodes-or photodiodes.
Commercial photodiodes may be divided into three
74

Electronic Experimenter's Handbook

broad groups-photoresistive devices, photovoltaic devices,
and light -activated switches.
Photoresistive diodes have a resistance inversely proportional to the amount of light falling on their sensitive
surface-the stronger the light, the lower their resistance.
Any of the standard semiconductor materials, including
germanium, silicon, and selenium, can be used for their
manufacture, but a good many are made with semiconductor compounds such as cadmium sulphide.
Photovoltaic diodes ("sun batteries") generate a d.c.
voltage when light falls on their surface. In general, the
amplitude of the voltage developed is proportional to the
intensity of the light, up to a maximum fixed by the type
of material used in construction, while the amount of
current that can be delivered is proportional to the unit's
exposed sensitive area. Most present-day photovoltaic
diodes use either silicon or selenium as their basic material.
Light -activated switches are similar to four -layer diode
switches, except that they are mounted in a transparent
glass (or partial glass) enclosure to enable light to reach
the junction area. Their operation is similar to that of
diode switches, too, but with the gate trigger signal replaced
by light energy. The Photran, a unique type, has an electrical connection provided for the normal gate terminal,
resulting in a three -electrode light-sensitive device.
The semiconductor laser is a special type of "photodiode"
which emits light. Typically, these units are made of
intermetallic compounds. Such a device may consist of a
small pn junction of gallium arsenide with the front and
back faces cut perfectly parallel to each other perpendicular to the junction plane and highly polished. When
heavy current pulses are passed through the device, intense
coherent light is emitted perpendicular to the polished
surfaces along the pn junction. Typical pulse currents
may run as high as 20,000 amperes per square centimeter.
Electrical -to -light energy diode converters of this type are
nearly 100 per cent efficient. The emitted light, for a
gallium arsenide diode, is in the infrared region.
The standard photographic light meter circuit at right
is basically just a photovoltaic diode connected to a
sensitive microammeter. The meter scale may be calibrated either in terms of foot-candles or in camera
shutter/iris settings.
The automatic light switch consists of a photoresistive
diode connected in series with a sensitive relay and a d.c.
power source. As long as there is sufficient light on the
diode, its resistance is kept low and it passes sufficient
current to hold the relay closed. When darkness falls,
the diode's resistance increases, reducing relay coil current
and allowing the relay to drop out, closing the lamp
contacts.
Another photographic instrument circuit is a remote
slave flash. A light -activated switch is connected in series
1965 Fall Edition

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75

with a current limiting resistor (R1), a power source (B1),
and a power transistor's base -emitter circuit. In operation,
FLA2M
BYLO
light from the main flash triggers the photodiode, causing
it to fire and applying a heavy base current to the
transistor. The transistor, in turn, conducts heavily,
firing the flash bulb. The power switch, SI, must be open
before a new bulb can be inserted.
A lock -in relay uses a Photran with its gate biased by
eawxromeans
of Rl. In operation, the relay remains open until
uecvs'
light strikes the Photran's sensitive surface. When this
happens, the Photran switches to a conducting state,
closing the relay. The relay then remains closed until
the power circuit is interrupted (by opening Si). This
general type of circuit might be used as an automatic
switch for, say, a darkroom, or in alarm applications.

SLAVE FLAsN

TUNNEL DIODES

VOLTAGE

Sometimes called the Esaki diode in honor of its Japanese
inventor, the tunnel diode is an extremely versatile
device. It is capable of being used as a detector, amplifier,
or oscillator, is extremely efficient and, in some types, is
useful at frequencies up to 10,000 megacycles or more.
Manufactured from standard semiconductor materials
such as germanium as well as from intermetallic compounds such as gallium arsenide, the tunnel diode is
basically a pn junction, but with the junction depletion
region made very thin. The result is that the device is
essentially in a "reverse breakdown" condition even when
a small forward bias is applied. As the bias is increased,
there is an increase in current, up to a point. As the
reverse breakdown condition is neutralized, the diode's
current decreases with increasing voltage until a valley
point is reached-afterwards, the tunnel diode behaves
much like a conventional diode. A decrease in current
with increasing voltage is the basic characteristic of a
negative resistance (as distinguished from a "positive"
resistance, in which current increases as applied voltage
is increased). It is this characteristic (negative resistance)
which makes the tunnel diode useful as an oscillator.
In a conventional semiconductor device, the current
carriers move rather slowly, diffusing through the
crystalline structure of the material. In a tunnel diode,
the current carriers (electrons, for example) traverse the
junction area at what appears to be the speed of light.
In effect, when an electron enters the junction, another
suddenly appears at the other side, much as if there were
a "tunnel" through the junction area (hence the device's

name).
76

Electronic Experimenter's Handbook

A practical FM wireless microphone based upon a circuit suggested by GE, is shown below. The resistors are
all half -watt units, while C3 and C4 are electrolytic capacitors, C2 a small ceramic disc unit, and Cl a tiny air
variable capacitor. Coil LI consists of six turns of No. 16
wire, air -spaced /8" in diameter. The antenna is a 43/4"
length of No. 14 wire, and the microphone is a Shure
Brothers No. 42G or equivalent.
The tunnel diode serves as an oscillator in conjunction
with tuned circuit Ll-C1, with its d.c. operating voltage
supplied by voltage divider R1 -R2. The audio signal obtained from the microphone is amplified and superimposed
on the d.c. voltage through coupling capacitor C3. This
varies the tunnel diode's instantaneous supply voltage in
accordance with the audio signal, frequency -modulating
,M,r
the r.f. signal developed by this device.
/,W93

PM LU/RELE55

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CAPACITOR DIODES
application of reverse bias to a junction diode will
cause the junction area to be depleted of current carriers (electrons and holes) and thus act as a high resistance, insulator or dielectric. There is still an electrical
capacitance between the p and n areas, however. This
characteristic of the semiconductor diode has led to the
development and production of a variety of voltage -variable semiconductor capacitors. These devices are identified
by a variety of names, including varactor (for variable
reactor), Semicap and Varicap.
The operation of a varactor is easily understood. If a
semiconductor diode junction is reverse -biased, the central
junction area is depleted and acts as an insulator (dielectric). There is always an interelectrode capacity between
the p and n areas. As the reverse bias is increased, the depletion layer expands, reducing the interelectrode capacity.
Conversely, as the reverse bias is decreased, the depletion
layer shrinks, increasing capacity. Maximum capacity is
obtained when the device is operated at zero bias.
Commercial varactors can be made of germanium or
silicon and are generally specified in terms of maximum
working voltage, capacitance (at a specific voltage), and
typical "Q." The latter characteristic indicates the "quality" of the device and is obtained by dividing its reactance

I/jT.qy4Ms4

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1965

Fall

Edition

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(in ohms) by its equivalent series resistance (in ohms).
5 to 100 or more.
In practice, varactors are used for electrical tuning in
circuits such as the basic frequency doubler shown on page
77 or the FM wireless microphone at left.
A Q may range from less than

/ci

¡,(iZRELESS

miCROP/fONE

POWER DIODES
Power diodes are basically similar to small signal diodes.
They are manufactured of the same materials, have
similar characteristics, and, in general, are produced using
the same construction techniques. The chief differences between power and small signal diodes, then, lies in their
physical size and actual specifications. Power diodes have

larger junction areas in order to pass heavier currents and,
in some types, have thicker junctions to permit them to
handle high voltages without breakdown. At the same
time, the larger junctions mean greater interelectrode capacities and hence limited high frequency capabilities.
As do their smaller cousins, power diodes conduct
heavily when biased in the forward direction and block
current flow when biased in their reverse direction. Their
forward and reverse resistances are likely to be lower than
small signal types with, of course, correspondingly higher
forward and "leakage" currents. Power diodes are rated
and specified in the same general terms as are applied to
small signal types-typically, maximum forward current,
nominal reverse current, nominal reverse voltage, and peak
inverse voltage (PIV).

Rectifier Diodes
primarily for use in a.c.-to-d.c. power supplies,
power rectifiers can be manufactured of selenium,
germanium, or silicon. A few types are made using copper
oxide, copper sulphide, and various magnesium compounds,
but these have been largely supplanted by the former
types. Since they are intended primarily for power supply
use, some types may be specified in terms of maximum
a.c. input voltage, output d.c. volts and current rather
than in the more general terms mentioned above.
In a half -wave rectifier using a single diode, the PIV
is twice the output d.c. voltage or 2.83 times the a.c. input
voltage with a capacitive input filter under "no load" conditions; the nominal d.c. output is 1.41 times the r.m.s.
(a.c.) input voltage. The ripple frequency (which must be
Designed

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78

Electronic Experimenter's

Handbook

removed by the filter circuit used) is equal to the line frequency.
The full -wave rectifier requires a center -tapped source
(such as the transformer secondary) and uses two diodes.
Under the conditions described above, the PIV is twice
the output d.c. voltage or 2.83 times the r.m.s. (a.c.) input
voltage, while the nominal d.c. output is 1.41 times the
a.c. voltage from half the secondary winding. The ripple
frequency, in this case, is twice the line frequency.
A center -tapped source is not required for the full -wave
bridge rectifier, but four diodes are used. Here, the PIV
is equal to the d.c. output voltage and is 1.41 times the
r.m.s. (a.c.) voltage supplied by the transformer's secondary winding.
The voltage doubler supplies an output d.c. voltage
which is twice the peak input voltage-or 2.83 times the
r.m.s. (a.c.) input voltage. The PIV is equal to the d.c.
output. In operation, diode Dl conducts on one half -cycle,
charging Cl to the peak supply voltage. On the next half cycle, D2 conducts, charging C2 to the peak supply voltage.
The two capacitors (Cl and C2) are discharged in series
through the filter to the load.

F.1/LL -/vsj

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I-OL-TOGE DOUBLER

Silicon Controlled Rectifiers
The silicon controlled rectifier, or SCR as it is commonly
called, is a "big brother" version of the silicon controlled switch (SCS). It is a four -layer semiconductor de-

vice with an "all or nothing" characteristic. When forward biased, it does not conduct until its breakover voltage is
reached unless it is triggered by a control signal applied
to its gate electrode; afterwards, it conducts heavily and
will continue to conduct until its anode -cathode voltage is
dropped to a low value. When reverse-biased, the SCR
blocks current flow until its zener voltage is exceeded and
junction breakdown occurs.
Most SCR's have the gate connection made to the third
layer of the four pn layers making up the device. Those
SCR's with a cathode gate are identified by the schematic
symbol shown at left below while a few types are equipped
with an anode gate (at right below) and are identified by
a slightly different symbol.

.!V

TERM/N4I_

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1965 Fall Edition

ANODE

c,A7NuoE

Commercial SCR's are sold in sizes with current ratings
1 ampere to well over a hundred amperes, and
with voltage ratings up to 500 volts or more. While standard SCR's can be turned "on" by the application of a
trigger signal to their gate-and "off" only by dropping or
reversing the anode -cathode voltage, there are several new
types which can be turned "off" by the application of a
,eEMoTf C4Vri(ìCU_
reverse bias trigger to their gate.
A remote control SCR circuit is shown at the left. In this
circuit the gate is biased just below its firing point by
voltage divider R1 and R2. Diode D1 is included for
temperature compensation. A radio signal from a nearby
transmitter, picked up by antenna coil Ll, "fires" the SCR,
actuating the Load, which might be, as an example, a
7vC
motor in a toy.
This timer circuit is designed for operation on a standard
a.c. line. When the control switch, SI, is turned to its
"TIME" position, Cl is charged through DI, Rl and R2.
T/MER
When sufficient voltage is built up across this capacitor,
the SCR is triggered, supplying power to the load device.
Potentiometer R2 sets the time delay, which is a function
of the R1/R2/C1 time constant. The circuit is reset by
turning SI to the "RESET" position, which discharges the
capacitor and applies a reverse voltage to the gate. The
SCR, of course, stops conducting on alternate half -cycles.
Although a polarized capacitor is shown for Cl, this
normally would be a large -value metalized paper unit.
You can use an SCR to rectify line voltage and power a
d.c. motor-while furnishing control over motor current in
M0722Q SPEED CYWrR12L
this motor speed control circuit. The motor speed adjustment control is R2, while the zener diode, D1, stabilizes
the gate voltage. The point at which the SCR "fires" on
alternate a.c. half -cycles is determined by its gate voltage.
If R2 is set for maximum voltage, the SCR conducts over
virtually an entire half -cycle, supplying maximum power
to the motor's field and armature windings. If R2 is set for
minimum voltage, the SCR conducts only during the last
half of each alternate half -cycle, or for a quarter -cycle,
supplying minimum power to the motor.
of less than

S Coe

nrr

see

SCR

SURGE SUPPRESSORS
Electrical circuits, whether operated on a.c. or d.c. voltages,
are often plagued by transient voltage peaks or surges,
either externally or internally generated. Silicon and
germanium semiconductor devices are especially sensitive
to surge voltages, and a high -voltage transient or "spike"
can destroy a semiconductor junction. Manufacturers have
introduced special semiconductor devices to guard against
and suppress transients. Most of these devices are made
80

Electronic Experimenter's

Handbook

up by connecting a suitable pair of selenium zener diodes
back-to-back and are identified by a variety of trade
names, depending on the manufacturer, including Voltrap,
Thyrector, Klip-Sel, and Silgard.
Typical surge protector applications are illustrated here.
A single unit is used in one circuit to protect the a.c. voltage supplied to a load by a transformer. A pair of units
are frequently used in a full -wave rectifier to protect the
rectifier diodes against transients. Circuit operation is
similar in both cases. Under normal conditions, the surge
suppressors act as open circuits, since one or the other of
the two diode elements making up the device is always
reverse -biased. If a transient voltage spike or surge occurs
which exceeds the device's rating, the unit goes into zener
breakdown, shorting out the surge.

SURGE PROTECT/ON

FLL

4'4E Su

&E PROTECT/OÁ'

THERMOELECTRIC
DIODES
the classical
the thermo-

Although not a "diode" in
sense,
electric diode is a thermocouple -type device with a
variety of applications. It consists of p- and n -type semiconductors bonded together by copper or similar high conductivity metal. Straps are connected to the opposite
ends of the semiconductor bars for electrical connections
and the two ends of the bars are thermally insulated.
If the connection straps are attached to an insulated heat
sink and heat is applied to the sides of the semiconductors
which are bonded together, the electrons and positive holes
in the n -type and p -type semiconductors, respectively,

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undergo thermal diffusion from the high- to the low temperature side, developing a potential difference. This
voltage can be used as an effective power source for a
standard electrical load as long as a temperature difference
is maintained between the two sides of the device. Thus,
the unit becomes a heat -to -electrical energy converter.
The output voltage supplied by a single element is relatively small, and commercial thermoelectric generators
generally are made up of a number of elements in a series parallel arrangement to obtain usable voltages at fairly
1965 Foil Edition

high currents. The 3M Type 18A thermoelectric generator
is a typical unit: it can supply up to 15 watts -3.5 volts
at 4.3 amperes-while consuming 0.15 lb. of propane fuel
per hour.
Essentially the same type of thermoelectric diode can
be used in a different manner. If power is applied to the
device by an external d.c. source, with the negative terminal
of the power supply connected to the p -type semiconductor
and the positive terminal connected to the n -type material,
the top plate becomes cool and the lower connectors warm.
In effect, the device absorbs heat at one end and releases
it at the other and becomes a type of electronic heat pump.
Commercial thermoelectric heat -pumps of this general
type are used in the manufacture of motorless refrigerator
and air-conditioning units and as "spot coolers" for high power transistors, diodes, SCR's, and similar semiconductor devices. One firm identifies its line of thermoelectric
cooling elements as Frigistors.

SPECIAL DIODES
While

oUrPUT
P/EZoELECTRIC D/ODE

the diodes described on the preceding pages con-

stitute the overwhelming majority of commercially
available semiconductor diodes, there are a number of
important special-purpose units. Most are experimental,
but are expected to be useful in the very near future.
The piezoelectric diode is one that is currently under
development. It consists of a pn junction to which a mechanical pressure contact is made. The junction's resistance
(and hence its effective output) is proportional to the
mechanical pressure exerted. Undoubtedly, piezoelectric
diodes will have potential applications in microphones,
hi-fi phono cartridges, and vibration pickups.

THE FUTURE
we have seen, the semiconductor diode is one of the
most versatile of simple electronic components. It has,
today, more applications than the proverbial dog has fleas.
If past performance is any criteria, we can expect many
new applications in the future-and many new types of
semiconductor diodes. Of the various experimental types
now being tested, the semiconductor laser, the tunnel diode
(and its first cousin, the "camel" diode), and the thermoelectric "diode" hold the greatest promise for startling
future developments. But even the best of prophets can be
wrong. A completely new type of semiconductor diode may
even now be in the development stages in our nation's
research laboratories!
As

Electronic Experimenter's Handbook

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1965 Fall Edition

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Electronic Experimenter's Handbook

CHAPTER
4
SCIENCE
FAIR

PROJECTS

Each year tens of thousands of high school and
junior college students enter "Science Fair" contests. Originated to encourage more interest in
science at school levels, the "Science Fair" has
gradually become a highly competitive event with
prizes worth hundreds and even thousands of dollars. Electronics has always played a prominent

role in "Science Fairs"-partially because of the
space-age interest, and partially because of the
visual effects that electronics projects offer to the
public.
For this portion of the Fall 1965 ELECTRONIC EXPERIMENTER'S HANDBOOK, the Editors have selected three "Science Fair" projects
that are sure winners. In each story all of the

necessary construction details are presented to
make the project operative, but only a minimum
of background theory is included. This presentation is in keeping with the philosophy of "Science
Fairs" in that the student must analyze the subject matter and then demonstrate his findings.
The "Repulsion Coil" project on page 88 demonstrates the principle of resonance using 60 -cycle
house current. Two visual effects offered by this
project are a reciprocal resonant engine and a
magnetic gun. The "Big TC" Tesla Coil (page
93) has been a "Science Fair" winner since its
original appearance in the July 1964 issue of
POPULAR ELECTRONICS. This article has
been brought up to date and, as can be seen in our
cover photo, the spark output greatly increased.
Extra safety precautions have been incorporated
in the revised circuit. A small Tesla coil using
commonly available TV components is shown on
page 99. This "Li'l TC" can be used to demonstrate brush discharges from high -frequency,
high -voltage power supplies, or even to spin a
near-weightless aluminum vane.

88
A 60 -CYCLE REPULSION

COIL-RESONANCE ENGINE

Walter

Ford

93
BIG TC

Charles Caringella, W6NJV

99
LI'L TC
1965

Fall

Edition

Edwin N. Kaufman
87

A 60 -CYCLE
REPULSION COIL
RESONANCE
ENGINE
By WALTER B. FORD

Startle your friends with
this dynamic. demonstration
of loir -frequency resonance
and other dramatic a.c.
effcris. This Science Fair
pro jeet Yorks on ordinary
60 -cycle house eurrent

NEARLY EVERY electronics experimenter is familiar with the process
of adjusting a circuit to resonate at a
specific radio frequency-you do this
every time you tune in your favorite
radio or TV station. Much more mysterious and surprising, however, are resonant circuits operating at the low 60 cycle frequency of our home lighting
circuits. The repulsion coil-resonant
engine described here reveals some of
the secrets of this fascinating phase of
electronics and provides a unit that can
be used for a number of exciting experiments.
The values and dimensions given here
are from the author's working model,
and while they may be varied somewhat,
changes of any kind are not recom-

Electronic

Experimenter's

Handbook

Constructed on a black lacquer wooden base, the
resonant -coil engine is an impressive -looking unit.

mended unless the experimenter understands what effect the changes will have
on the operation of the unit. If, for example, capacitors of lower value are
used, the stroke of the engine piston will
change. This will mean that there will
have to be a proportionate change in the
length of the flywheel crank.
Making the Coil. The inductive part of
the series -resonant LC circuit used in
the unit is in coil Li. Begin by making
up a coil form as shown in Fig. 1 (page
90) Although plain wood discs may be
used for the ends, plywood, fiber, or Mi carta is preferred, since there is less
chance of breakage if the coil is accidentally dropped. The center tubing can
be Micarta, Bakelite, or fiber, or can be
made by drilling a .3á " hole lengthwise in
a piece of 3/ ' dowel rod. Whichever material is used, make sure the inside surface is smooth, sanding if necessary, so
the engine piston will travel freely.
Complete the coil form by drilling
holes in the end discs that make a snug
fit around the center tubing, and gluing

the ends and tubing together with epoxy
glue. This step is important because there
will be considerable pressure against
the ends when the wire is in place on the
coil. Drill 146" holes through one end of
the coil form for the coil leads as indicated in Fig. 1. Drill and tap two holes
for 6-32 machine screws in the same end
of the form to hold the completed coil
to its base (if wood is used, wood screws
can be used and the threaded holes will
not be needed). Wind the coil form with
21/2 pounds of 24 -gauge magnet wire.
While it is not necessary to wind the coil
perfectly, like thread on a spool, it
should not be allowed to pile up at any
one point.
Constructing the Cores. Uncoil enough
16- or 18-gauge soft iron wire to make
the engine core, grip one end in a vise,
grasp the opposite end with a pair of
pliers, and pull until you can feel the
This will
wire stretch somewhat.
straighten the wire. Cut the wire into
434 lengths and make forms to hold
the bundle in cylinder form from pieces
of thin -wall metal or plastic tubing.
Holes (/16") drilled in small pieces of
wood or cardboard can also serve the
purpose. Since the forms must be cut
away after the core is glued, keep their
outside dimensions down to a minimum.
Bundle the 43'," wires together and
insert them in the forms. Press the end
of a screw eye into the center of one
end of the core, and cut off the ends of
the wires forced out of the core at the
opposite end. Withdraw the screw eyeit will be fastened permanently later.
Apply epoxy glue to the areas of the
core not covered by the forms holding
the core wires and allow the glue to set.
The type of epoxy glue that will set with
artificial heat is preferred for this, since

1965

Fall

Edition

Straighten the iron wire for the cores by stretching it as explained in text. Then cut and bundle
the wires into cylindrical form as shown in Fig. 2.

\SECURE ENDS

TO TUBING
WITH EPDXY GLUE

--{
I

I/2'

1/2"

I/2"

DRILL AND TAP FOR 6-32 SCREW

TO SECURE COIL TO BASE

Coil form may be made of fiber, plywood or Micarta. End plates must
be strong and firmly glued to center.
4

Both cores are made of #16- or
#18 -gauge soft iron wire. Straighten
the wire as shown in the photograph
on the bottom of the facing page.

3/4"

9i
SCREW EYE

SOLDERED TO CORE

(MAKE SECOND 9/16"DIA X 12"CORE
FOR REPULSION COIL EXPERIMENTS)

This arm couples the flywheel to the
core, which acts as the piston. Prototype was cut from brass stock.

3
4

5/8"
5/8'

1/2

3/IB'DIA""

Several small parts must be fabricated
to connect the arm to the flywheel.
At right, below, are two possible ways
of constructing the engine crankshaft.

5
THREAD WITH

i -20

The flywheel weighs about 15 ounces.
The author used aluminum, but plastic or brass would serve as well.
War surplus stores or machine shops
may have such flywheels for sale.

DIE

IIIIIIIIIIIIII--_
SHAFT-.1
3" BRASS

1/4"

LIDIA

DRILL AND TAP
ENO FOR

6-32

SCREW

I/B"

ak 28 DRILL

I-5/8"

1-5/16"

+-I/8'ROUND

ROD

1/4

gQ20 GA.

SHEET
BRASS

6
90

ADJUSTABLE TEMPORARY
CRANKSHAFT

Electronic Experimenter's Handbook

I-1/16"

I-1

/Ifi'-.

FLYWHEEL BEARING

I/2"ROUND BRASS ROD
WITH I/4"HOLE DRILLED
THROUGH CENTER

2-1/16

-1/8'

9/16"

1-41
2

'-.1 9/I6
1/8"

The size of the stand necessary to hold
the flywheel for experiments will depend on the length of the shaft (Fig. 3)
and diameter of the flywheel (Fig. 6).

BILL OF MATERIALS
f., 600 -volt non -electrolytic capacitor

C2 -2-µf., 600 -volt non -electrolytic capacitor

C3 -10-µf., 600 -volt non -electrolytic capacitor
J1, 12, J3, J4-Insulated pin jack

L1-See text
R1 -10,000 -ohm, 10 -watt resistor
S1-D.p.d.t. (center-off) 10 -amp
(motor start type)

1965 Fall Edition

carta, or wood

toggle switch

8" -thick

discs of fiber, Mi-

1-"-i.d., 4%" -long

piece of fiber or Micarta
tubing, or wood dowel
1" -thick flywheel; aluminum,
brass or plastic-see text
Misc.-Brass rods for crankshaft and connecting rod, wood for bracket and base of engine,
brass bearing, wood screws, machine screws
and nuts, wire, solder, a.c. line cord, epoxy
glue, etc.
1

spool of 24 -gauge magnet wire, cotton- or enamel -covered
-lb. spool, 16- or 18-gauge soft iron wire

-1

2 -33/4a' -diameter,

-3%" -diameter,

small coil connected to a flashlight bulb illustrates transformer action of mutual inductance.
A

Permissible changes in certain component values
are discussed in text. However, do not eliminate
discharge function of the d.p.d.t. toggle switch.

This is how the various pieces for the resonant
engine shown in detail on page 90 are assembled.

drying time is shortened and because
surplus glue may be more easily pared
off. After the glue has set, remove the
forms and apply epoxy to the uncovered core areas. When this second application is dry, remove any rough spots
on the core with a coarse file. Solder a
screw eye in the hole that was made in
the end of the core. The finished core
should look like Fig. 2, on page 90.
For the repulsion coil experiments,
make another core following exactly the
same procedure outlined, but using 12"
iron wires and omitting the screw eye.
Parts for the Engine. The connecting
rod (Fig. 3, page 90) is made with 3hu"
brass tubing soldered into pieces of 1/4" square brass, the ends of which have
been drilled and shaped as shown. This
92

construction was used to "dress up" the
prototype, and need not be duplicated
exactly. A rod made from a single solid
piece of brass will work as well.
The engine crankshaft is shown in
two forms in Fig. 4. If you want to experiment with different values of capacitors, or longer or shorter piston travel
with a corresponding change in speed,
build the slotted version so you can adjust its length. The two parts are held
together with a small machine screw
and nut. Since this is made of lighter
material, it is not recommended for permanent use. If all the values and measurements given for the engine are followed, make a solid crankshaft exactly
like that shown.
The engine flywheel is made of brass
or aluminum, and is 1" thick and 31/2" in
diameter. It is supported by a 1/4" brass
shaft 3" long (see Figs. 5 and 6, page
(Continued on page 141)
Electronic Experimenter's

Handbook

BIG

IC
A quarter of a million volts? All

takes is a transformer, a capacitor,
a spark gap, and Tesla's famous coil
By CHARLES CARINGELLA, W6NJV
TESLA COILS have

fascinated experimenters
ever since the early 1900's when Nikola
Tesla first experimented with giant coils that
produced lightning -like discharges which
would span his laboratory-the work of millions of volts of electricity. The Tesla coil
described here is smaller than some of Tesla's
designs, but it's capable of putting out almost a quarter of a million volts! Brilliant
corona discharges as long as a foot or more
provide a spectacular display of its intense
electrical field, and neon and fluorescent
lamps can be excited as far as five feet away.
Intended both as a dynamic demonstrator
of electrical principles and as a crowd -attracting science fair project, "Big TC" can be
put together for about $30. However, if a used
transformer from a neon sign shop can be secured reasonably, the cost will be even less
i

WARNING: The voltages used in
this project are highly dangerous.

Inexperienced persons should seek
aid from an instructor or other
expert before building it.

COVER STORY
1965

Fall

Edition

BIG TC

Spark gap generates r.f. energy to excite coil. It
consists of two copper rods mounted on standoffs.
DISCHARGE
ELECTRODE

The secondary of a neon sign transformer is usually grounded internally to the
metal case. Connect bottom of Tesla coil
secondary to case and to a good external
ground, such as a water pipe. This precaution will keep danger of a short circuit in transformer at a bare minimum.
SPARK
GAP
T

Ito

VAC

GLASS -PLATE
CAPACITOR

Mount Ll-L2 in center of base, Tl and Cl at edges.
A bigger base and greater component spacing will
permit greater voltage output with less arcing.
GOOD EARTH GROUND
(SUCH AS WATERPIPE)

As shown in the schematic diagram
above, Ti steps the household line voltage up to 12,000 volts. The transformer
is the type commonly used to operate
neon signs. A high -voltage glass -plate
capacitor, Cl, is connected directly
across the high -voltage secondary winding of Ti. The capacitor serves as an
energy storage device, charging up to
Ti's secondary voltage and then discharging in response to the 60 -cycle
a.c. voltage.
Discharging of Cl is through the
spark gap into coil Li. Each time the
spark gap "fires," a high current flows
through Ll. The larger capacitor Cl is
made, the larger will be the current

through Li. Discharges across the spark
gap produce extremely jagged pulses of
power which are very rich in r.f. harmonics. The energy-due to the values
94

of the components used-is greatest in
roughly the 100-kc. region.
Windings L1 and L2 form a air -core
step-up transformer, with LI the primary and L2 the high -voltage secondary. The voltage at L2 will be 75,000
to 250,000 volts depending on the size
of Cl.
Design and Layout. The prototype of
"Big TC" was built on a plywood base
measuring 3/4" x 22" x 22", although a
larger base would be desirable for high voltage units to prevent arcing between
L2 and Ti and Cl. Mount L2 in the center of the base and T1 and Cl as close
to the edges as possible ; if you plan
to operate the unit at voltages exceeding 100,000 volts, make the base 3' x 3'
for even greater separation between
components.
Power transformer T1 is the only
Electronic Experimenter's Handbook

Constructed for classroom demonstration, the
author's unit was mounted on mahogany veneer
plywood which was sanded and covered with five
coats of plastic varnish. Other finishing touches
were wood tape veneer around the edges, and
nylon casters to make the unit easy to move.

-3/4"-r
DIA.

DISCHARGE
ELECTRODE
FEED THRU

INSULATOR
4 1/2'

3/8°

WOOD OR PHENOLIC END COVER,

FASTEN WITH TWO
NYLON SCREWS

*8-32

34-1/211

381

WINDING

LENGTH

1/2" DIA
PLASTIC ROD-( (B PIECES)

I/8" PLASTIC SHEET
I/2"

DIA LEGS -WOOD,
OR PHENOLIC
ROD (3 PIECES

PLASTIC,

FEED-THRU
INSULATOR

r-END

WOOD OR PHENOLIC

3/4"

2-1/2"

I-5/8'

-I/4" NYLON CASTOR

(ONE PER CORNER)

COVER, FASTEN
WITH TWO a0í8-32
3/81. NYLON SCREWS

\3/811 X I-1/211BOLT
2211 X

Form for Li with center cut out to
take base of L2 is shown above.
Polystyrene was used, but wood or
cardboard can be substituted. The
critical dimension is the outside diameter; less than 9" will result in
arcing between coils Ll and L2.

22"

SQUARE BASE
3/32" BRASS

The various dimensions of the prototype coil
are indicated in the drawing; none is particularly critical. Note that space has been
left at each end of coil, and that stand-off
insulators are used to bring out the ends.
Nylon screws or glue must be used to fasten
top end cover to avoid arcing. After winding

COPPER ROD
BINDING POSTS

I/4"PLASTIC
ROD HANDLES

STAND-OFF

INSULATORS

coil, cover with many coats of acrylic plastic
spray. Spray form first if cardboard is used.
Details on spark gap are shown at right.
1965 Fall Edition

BIG

Leads are soldered directly to capacitor
plates. Note use of stand-off insulators.
19"

14" X14"

METAL
ELECTRODE
(EACH SIDE
OF GLASS)

(9'

LWOOD FRAME

-I/4

T
+
+
I

WINDOW GLASS

r3,4.
Glue metal plates to
glass, leaving a generous margin of glass
on all sides (see

text). Epoxy glue,
STAND-OFF
INSULATOR
(TWO EACH)
WOOD OR PHENOLIC

SUPPORT BRACKET
(TWO EACH)

1-1/2'

8-3/4"

contact cement, or
any other glue which
will form a tight bond
can be used. The
wood frame protects
the glass and makes
mounting it possible.

high -cost component. A neon -sign unit
rated at 12,000 volts a.c. at 30 ma.,
it sells for about $40 new, but used
transformers are constantly being salvaged by sign shops, and can be picked
up for $10 to $20. It is also possible
to find neon signs in junk yards, in
which case you can probably buy the
transformer for practically nothing.
The author used a GE unit, No. 51G473,
known technically as a "luminous tube
transformer." Measuring 91/2" x 6" x 4",
it has 2" feedthrough insulators at
either end connecting to the high -voltage winding.
Primary coil L1 and all connecting
leads must be made with high -voltage
wire, preferably supported away from
the base on 1" ceramic standoff insulators. Test prod wire such as Belden
Type 8899 is ideal-it has flexible rubber insulation with a puncture voltage
rating of 20,000 volts.
Winding the Coil. For the big coil
(L2) a phenolic coil form* measuring
43/4" in outside diameter and 38" in
length was used. Alternately, cardboard,
wood or other insulating materials can
be substituted. You can improve these
latter types of coil forms by spraying
on at least six coats of acrylic plastic
spray before winding the wire on them.
The winding itself is done with No.
26 Formvar-insulated wire-two 1 -lb.
spools (splice them together and keep
the solder joint as small as possible)
will give you a 2000 -turn, tightly spaced
coil covering 341/2" of the coil form.
There should be extra space between
the ends of the winding and the ends of
the form-see the drawing on page 95.
The lower end of the coil is terminated at a 1" feedthrough insulator installed in the side of the form, the top
end of the coil at a 41/2" feedthrough
mounted to the top end of the form.
Make the end covers of wood or phenolic
discs cut to the inside diameter of the
coil form, and mount them in place with

"Tubing can be found in metropolitan areas at
surplus houses and establishments which sell plastics (sheets, rods, etc.). Clear acrylic tubing (48"
long, 41/2" O.D.) can be ordered from Industrial
Plastics Supply Co., 324 Canal St., New York,
N. Y. 10013, for $13.85 including shipping charges
and postage; address your order to the attention
of Mr. Charles Roth.
Electronic Experimenter's

Handbook

This Mark Il version of "Big
TC" used a second outboard
capacitor-increasing the capacity across the primary by
0.0014 uf. Estimated output
of the Mark ll model was about
130,000 volts. See page 96.

nylon screws (metal screws at the top
end would produce corona discharges
which could burn the coil form). Alternatively, the top coil cover can be
cemented in place with epoxy cement if
a sturdy coil form is used. The coil is
attached to the base with a 3/e" bolt.
Winding the coil is not nearly as
difficult as it appears-the author completed the task in about two hours.
Spray the entire winding with acrylic
plastic for added insulation, moisture
protection, and to keep the windings in
place. You can't overdo this step-the
author used the contents of an entire
aerosol spray can on the prototype, applying one thin layer at a time and
letting it dry before adding another.
Building the Primary. As shown on
page 93, the form for LI was made with
polystyrene rods and sheeting. While
the plastic has excellent insulating
qualities and looks attractive, wood or
even cardboard can be substituted. If
plastic is used, it can be strongly
"welded" together with acetone. Regardless of the material used, the form
should have an outside diameter of at
least 9" to avoid arc -over between LI
and L2. The coil itself (L1) consists
of 20 turns of heavy test prod wire.
Spark Gap. The spark gap is simply
two ordinary binding posts mounted on
stand-off insulators. In turn, these are
mounted on a phenolic base measuring
3/g" x 21/4" x 6". The electrodes are
brass and copper rods with a gap on
the order of 1" between them. This
distance will vary slightly, depending
on the size of capacitor Cl.
Fabricating the Capacitor. The capacitor consists of two 14" x 14" sheets of
1965

Fall

Edition

tin cemented to a 181/2" -square piece
of window glass. Although aluminum
foil can be used for the capacitor plates,
tin was obtained from a sheet metal
shop for this purpose so that connecting leads could be soldered directly to
it. If you use aluminum foil, a fairly
good connection can be had by making
leads of 1/2" -wide aluminum foil strips
and taping them down to the electrodes.
Glass is an excellent dielectric material for this application since it has
an extremely high puncture voltage and
a high dielectric constant. As you will
note in the drawing on page 94, a border of glass is left around the capacitor
plates-this should be at least 11/2"
wide. The calculated capacity of Cl is
approximately 0.0027 µf.
Testing and Operation. Caution! Adjustments to the Tesla coil, and specifically to the spark gap, should be made
only when the unit is off. Although the
output voltage of the Tesla coil may be
on the order of 150,000 volts, the current capacity is only hundreds of microamps. This current can inflict a
nasty shock and r.f. burns, however.
Use EXTREME CAUTION around
the neon sign transformer. It delivers
12,000 volts at 30 ma., and this voltage
could be lethal under certain conditions.
97

Again, be sure the plug is out when you
make adjustments.
To adjust the spark gap, first open
it to about 11/2"; it will not fire at this
point. Gradually move the electrodes
together-unplugging the unit each
time you adjust the gap-until the point
is reached where the gap "fires."
The author's original version of "Big
TC" produced an output voltage of about
100,000 volts with the single plate glass
capacitor described above. To increase
the output of "Big TC," it is only necessary to increase the capacity across the
primary by adding one or more plate
glass capacitors in parallel with Cl.
With two capacitors (both the same size
as detailed on page 94) the author's prototype produced over 150,000 volts output; and with three capacitors in parallel, the output exceeded 200,000 volts.
However, at such high voltage there was
a tendency for insulation breakdown between coil L2 and capacitor Cl. This
breakdown could have been overcome by
making the mounting base larger and
increasing the spacing between components.
,

The author's Mark II version of "Big
TC" compromised by adding a second
capacitor with half the plate area of Cl.
Except for size, this new capacitor was
fabricated in exactly the same way and
had a measured capacitance of 0.0014 µf.
The new capacitor was attached to the
base board with a 6" x 9" piece of
thick phenolic board. Four retaining
screws held the board to the underside
of the base board and four more screws
affixed the phenolic to the wooden frame
of the outboard capacitor. With this
second capacitor (see cover photograph) ,
the voltage output was estimated to be
in the neighborhood of 130,000 volts.
The output of your Tesla coil can be
estimated by drawing an arc to a me-

tallic object attached to a long wooden
handle. Slowly increase the distance
between the object and the discharge
terminal until the arcing stops : a 6"
arc represents 100,000 volts, a 14" arc
about 200,000 volts, and a 21" arc some
300,000 volts. More amazing than figures, however, are the brilliant, spectacular phenomena exhibited by high voltage, high -frequency electricity. -MI-

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CIRCLE NO. 30 ON READER SERVICE CARD
Electronic Experimenter's Handbook

you have read the preceding article on
"Big TC," you will have learned that a
Tesla coil is simply a radio -frequency step-up
transformer carried to extreme limits. While
a coil that can generate 150,000-200,000 volts
is exciting and very dramatic, many of the
same visual effects can be demonstrated on a
smaller scale with "Li'l TC." In fact, "Li'l
TC" is much safer, easier to build, and less
expensive.
The only item many experimenters will have
to buy in order to build "Li'l TC" is the r.f.
coil. This coil is manufactured by the J. W.
Miller Co. for use in generating the high voltages required in large -screen TV receivers.
It is an item that is not stocked by many
parts stores, although most of them can obtain it for you within 48 hours. If you have
trouble finding the coil, it can be ordered from
Allied Radio Corp., 100 N. Western Ave., Chicago 80, Ill., as their stock number 61G102 at
a price of $8.82 plus postage. An experienced
project builder may not find it necessary to
buy one of these coils, but may be able to

A potent

"little brother" to "Big

TC," this

Tesla coil version is inexpensive, easy to

build, and it can put out 30,000 volts!

By EDWIN N. KAUFMAN

Tuning capacitor C3 is
attached to the h.v. coil
with two bus -bar leads
so that it will be suspended in mid-air away
from the coil and metal
chassis. Use an insulated
alignment tool to rotate
the setscrew adjustment.

Most of the parts are
grouped around the base
of tube V2. Leads to the
h.v. coil pass through
grommeted holes to the

terminal connections on

the Miller coil

form.

construct "Li'l TC" using a high -voltage by the manufacturer. However, noticetransformer from a large -screen old- ably improved effects were obtained by
style TV receiver.
the author by substituting a 6L6. A 6V6
Construction. The mechanical layout or another equivalent power pentode
is not critical, and the design shown in would do in a pinch.
the photographs need not be followed
Capacitor C3 is used to tune the priexactly. It is convenient to place the r.f. mary of the h.v. coil. For convenience,
coil off in one corner of the chassis two bus -bar leads about 1" in length
and to drop the connecting leads to V2 were soldered to the capacitor and used
through grommeted holes in the chassis to support it in mid-air. The remaining
deck. The high -voltage output lead of components are scattered around below
the coil is shortened and a sewing needle the chassis deck.
soldered to the end to show "point disFiring Up Li'1 TC. When used in a TV
charge" effects.
receiver, the high voltage generated by
The power supply is of conventional this coil/oscillator arrangement is rectidesign and the B -plus applied to the fied and filtered. It is then considerably
plate of V2 can range from 250 to 500 more dangerous than the unfiltered r.f.
volts. However, 250 - 350 volts is more generated by Li'l TC. Nevertheless, Li'l
than ample for an output of between TC should be treated with respect, for
12,000 and 15,000 volts. The output will the voltage can puncture the skin of a
also vary according to the type of tube finger, although high -frequency voltages
used at V2. When you open the coil box, usually tend to flow relatively harmlessyou will see that a 6Y6 is recommended ly along the skin's surface.
too

Electronic Experimenter's Handbook

SEWING

NEEDLE

The numbered terminals shown in this wiring diagram
pertain to the Miller 4526 coil. A separate instruction
sheet accompanying the coil identifies the positions.

H.V.

WIRE

VANE
(SEE TEXT)

250-350 VDC

PARTS LIST
C1 -8.0-µf., 450 -volt electrolytic capacitor
C2 -0.1-µf., 600-volt molded capacitor
C3-360-1000 pf. trimmer capacitor
-pf., 1.6 -kv. ceramic capacitor-see text
C4
CS -0.004 -uf., 600 -volt mica capacitor

-82

R1 -47,000 -ohm, /-watt resistor
RFC1-30-mh., 100-ma. r.f. choke (J. W. Miller
692 or equivalent)
Sl-S.p.s.t. toggle switch
Tl-Power transformer: primary, 117 volts a.c.;

After double-checking your wiring,
turn on the a.c. power and permit the
two tubes to warm up. Take an insulated
screwdriver-something like a long alignment tool-and adjust C3 for a brush
discharge from the needle point. If you
do not have enough range in C3 to tune
through the maximum discharge, change
the value of C4-add more capacitance
at C4 if the plates of C3 are tightly
meshed; use less if C3's are too loose.
You can set C3 for maximum discharge
by listening to the sound of the brush
effect-tune for a clean high-pitched hiss
and not a sputtering sound.
The brush discharge from Li'l TC will
be about 1" in height and can be seen
best in a dimly lighted room. Actually, a
brush corona will appear at any sharp
edge on the output lead, so be careful to
round out the soldered connections between the eye of the needle and the
shortened h.v. lead.
1965 Fall Edition

secondaries, 500 volts, CT, 5 volts at 2 amperes, and 6.3 volts at 2.5 amperes (Thordarson 24R09Ú or equivalent)
V1 -5Y3 tube
V2 -6L6 tube-see text

1-High-voltage coil (J. W. Miller 4526-see
text)

1-Metal

chassis (Premier ACH -404 or equiva-

lent)

Misc.-Tube sockets, wire, solder, etc.

Ionic Propulsion Vane. Probably the
most impressive demonstration of a Tesla
coil is the ionic propulsion vane. You
can make one for Li'l TC by cutting out
the general pattern shown in the diagram above.
Make the over-all length of the vane
about 1" to 11/2". Cut the vane from
aluminum foil and puncture the center so
that the vane is balanced. Use one of
your wife's extra beads as a bearing by
slipping it on the upright needle. Then
drop the vane over the needle so that it
rests on the bead and can rotate freely.
Put a piece of cork or rubber on the tip
of the needle to stop the vane from picking up so much speed that it spins right
off the needle.
The photograph on the first page of
this article is a two -second time exposure (slightly enlarged) showing what
the brush corona discharge and rotating
vane should look like.

-101

COMPLETE BUYER'S GUIDE

STEREO HI-FI

DIRECTORY

How to go about selecting the best hi-fi equipment
in
your price range (avoiding all the nerve-racking guesswork,
to say nothing of the costly disap.. ointnlents), .in
a nutshell.
,

The "meat" in this nutshell is guaranteed to whet
the appetite
of every audiophile and music lover who plans to
buy hi-fi
equipment during the next twelve months.
In over 172 fact -and -photo -filled pages,
the new 1966
STEREO/HI-FI DIRECTORY gives you all the vital
statistics on
amplifiers, changers and turntables, cartridges, tonearms
and
accessories, receivers, tuners, tape machines,
speakers and
cabinets-on every hi-fi component being manufactured
today!

With this authoritative guidebook, you can compare
similar
items, feature-for-feature, dollar -for-dollar, before
you buy!
You'll avoid making even one costly mistake by
making sure,
in advance, that you get the best value for your
money, on anything and everything you buy!

bRECTCR/T 1966

First Time Ever Offered!
A DELUXE, GOLD -EMBOSSED

LEATHERFLEX-BOUND EDITION

... just $3.00 postpaid

This deluxe edition is a permanent, handsomely-bound collector's item that belongs in
your hi-fi library) Check appropriate
box on
coupon.

102

The 1966 STEREO/HI-FI DIRECTORY will
help you select the
finest equipment in your price range, so
that you can derive
greater pleasure than ever from your records
and tapes. Now,
(to ask a redundant question) where else
can you get

of "satisfaction insurance" fora mere $1.25?

this kind

---FILL IN, DETACH & MAIL COUPON TODAY!--ZIFF-DAVIS SERVICE DIV., Dept. SD
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--I

Electronic Experimenter's Handbook

CHAPTER
5
COMMUNICATIONS
SWL
CB
HAM

Projects included in this chapter of the ELECTRONIC EXPERIMENTER'S HANDBOOK are
aimed at the 6 -meter ham with a Technician Class
license. In case you are not already aware of it,
Technician Class hams can operate in the 50 -mc.
band and above. The license requires passing the
regular theory examination but only a 5-wpm
code sending and receiving ability. It is issued
for a 5 -year period-unlike the Novice license
(1 year)-and can be renewed.
A companion unit to the 6 -meter receiver
(ELECTRONIC EXPERIMENTER'S HANDBOOK, 1964 Edition) is the 6 -meter transmitter
on page 111. If you want to improve receiver
sensitivity, the small outboard r.f. preamplifier
(page 121) may be your cup of tea. Also intended
for the Technician (or General Class ham) is the
solid-state converter (page 104). This converter
has extraordinary sensitivity and can be broad banded to cover 1.5 megacycles.
Two valuable projects round off this chapter:
a speech filter with fully adjustable controls
(page 107), and some excellent ideas on how t'o
pep up AM receiver sensitivity (page 116).

104
TRANSISTORIZED 6 -METER CONVERTER

Roy C. Hejhall, K7QWR

107
AN ADJUSTABLE SPEECH

Daniel Meyer

FILTER

111
THE COMPANION 6 -METER TRANSMITTER

Charles Green, W3IKH

116
SOUP UP THAT AM BROADCAST RECEIVER

Bauer, Jr., W6FP0

121
THE 6 METER 7 AND 2 PREAMP
1965 Fall Edition

Joseph Tartas, W2YKT
103

TRANSISTORIZED

6 -MEIER
CONVERTER
By ROY C. HEJHALL, K7QWR

Build a
sensitive converter
using inexpensive
mesa transistors
GOOD PERFORMANCE can be obtained on six meters with a transis-

torized converter that uses inexpensive
transistors and is easy to construct. The
converter described in this article incorporates three Motorola 2N963 pnp mesa
transistors which can be purchased for
about the same price as a set of tubes for
a vacuum -tube converter. The total parts
cost (including the transistors and the
43 -mc. crystal) is under $20 if all new
components are employed. Sensitivity of
the unit is about 1 microvolt for a 10-db
signal-to-noise ratio.
The Circuit. The converter consists of
an r.f. amplifier, a mixer, and an oscillator. The r.f. amplifier stage is a neutralized common -emitter circuit. The
mixer is also common -emitter, and base
injection of the oscillator signal is used
for simplicity. The crystal oscillator is
a Colpitts type using a third -overtone
crystal to generate the required 43 -me.
oscillator signal directly. The intermediate frequency is 7 to 11 mc., which allows
a 40 -meter receiver with bandspread to
be employed for the low end of six meters. Input impedance of the converter is
50 ohms.

Power requirements are 9 volts d.c. at
about 8 ma. Either a power supply or a
9 -volt transistor radio battery can be
used to power the converter. The power
supply leads are filtered to reduce spurious responses.
Construction. The converter was constructed on a copper chassis, which was
104

cut and formed as shown in the photos,
so that the completed converter could
be enclosed in a gray LMB 51/4' x 3"
x 21/g" chassis box. Copper was selected
for the chassis only for ease in soldering
components directly to it; an aluminum
chassis could have been used with equal
success.
Each end of the chassis was slotted for
BNC coaxial connectors; the connectors
serve as input and output signal jacks
and also clamp the chassis to the box.
Care must be given to vertical placement
of the chassis in the box, since the crystal above and coil forms below the chassis leave little clearance when the box is
assembled. Two banana jacks were
mounted in the box for power supply
leads.
The usual precautions in VHF wiring,
such as short leads and minimum chassis
current paths, should be observed. The
photograph of the bottom of the chassis
can be used as a guide for layout. It is
suggested that the general layout of
the r.f. stage, including the shield between base and collector, be followed.
Minor changes will be insignificant, but
a radically different layout might affect
neutralization.
There are no special precautions to be
taken in the construction of the mixer
and oscillator stages. The r.f. stage
shield should also function to shield local
oscillator signals from the r.f. stage input.
The coils are wound on 1/4" -diameter
coil forms. The oscillator coil is slug tuned ; the other coils have no slugs.
Another version of the converter has
been built by the author using no coil
forms in the r.f. stage input and output
Electronic Experimenter's Handbook

2N963
R.F. AMP

2N963
MIXER

The 3 -db bandwidth of this con-

verter is approximately 1600 kc.
Alignment should be set up on
about 50.5 mc. to put the most
sensitive part of the bandwidth
in the low end of the 6-meter
band. Good results can still
be obtained up around 51.5 mc.

circuits, since the #20 wire used is rigid
enough to support itself.
Building the converter on such a small
chassis did cause some crowding of components, and a slightly larger chassis and
box could be used, particularly if you
want to power the converter with an
internal battery.
Alignment and Testing. Before attempting alignment, a check for correct d.c.
operating conditions should be made.
About the simplest check is to measure
total current drain; it shoud be about
8 ma.

The first step in the alignment procedure is to tune the r.f. input and output circuits and the mixer output circuit
to approximate resonance, using a grid dip meter. This can be done with the
power to the converter off. Couple the
grid -dip meter to LI and tune C2 for
resonance at 50 mc. In the same manner, couple to L2 and tune C6 for resonance at 50 mc. Then couple to LS and
tune C11 for resonance at 7 mc. In each

case, a definite dip should be obtained if
the circuits are operating properly.
The next step is to adjust the oscillator coil (L4) slug. Set the slug about
mid -range in the coil. Connect an r.f.
signal generator to the converter input
jack and connect the converter output to
the antenna terminals of any receiver
which will tune to 7 mc. Then connect
a 9 -volt d.c. power source to the converter. Apply a 50 -mc. modulated signal
to the converter and locate the signal
with the receiver tuned to 7 mc. If the
oscillator is detuned too far, it may not
oscillate; so if the signal cannot be
located at first, continue to search for it
while slowly moving the oscillator slug.
Once the signal is located, adjust the slug
for maximum audio output in the re-

ceiver.
Now, with the 50 -mc. signal still applied to the converter input, tune C2, C6,
and CIZ for maximum signal output.
If the converter is constructed in a
box, placing the cover on the box has a

of copper is
bent to form a sub chassis and mounted
as shown. Power for
the converter goes
through the tip jacks
right-hand
the
on
side of the box. If
you have not already
noticed, the converter is upside down

A piece

1965

this

Fall

illustration.

Edition

105

C12

This under -chassis view of the
converter shows the location of
the major components. A shield
extends across the socket
of transistor Ql to prevent
coupling between Ll and L2.
The crystal socket is just visible below Q3. Output jack J2
is unlabeled, but is located
at the right of the chassis.

slight effect on alignment. Therefore,
holes should be drilled in the box to allow
the final peaking of C2, C6, and C11 to
be done with the box assembled.
If no grid -dip meter is available, it is
possible to skip the first alignment step by
tuning C2, C6, and C11 all about midrange, and using a strong signal from

PARTS LIST
C1 -0.003-µf, disc ceramic capacitor
C2, C6-5-80 pf. mica compression or ceramic

trimmer capacitor
C3, C7 -0.1-µf. disc ceramic capacitor
C4 -0.01-µf, disc ceramic capacitor
C5 -18 -pf. mica capacitor
C8 -0.001-µf. disc ceramic capacitor
C9
-pf. mica capacitor
C10-0.05-µf. ceramic capacitor
CI1-25-280 pf. mica compression or ceramic
trimmer capacitor
C12, C13, C16, C17, C18-0.02-1.4. ceramic
capacitor
C14 -12 -pf. mica capacitor
C15 -82 -pf. mica capacitor
11, 12-BNC coax connector
L1-5 turns of #20 enamel -covered wire,
diameter, close -wound; tapped I turn and 2
turns from cold end (0.15 µh.)
L2-8 turns of #20 enamel-covered wire, r/4"diameter, close-wound, tapped 2 turns and 4%
turns from cold end (0.19 µh.)
L3-26 turns of #28 enamel -covered wire, '//"diameter, close -wound, center-tapped (2.3 µh.)
L4-10 turns of #26 enamel-covered wire, %"diameter, close -wound, slug -tuned (0.55 to

-5

0.85 µh.)
QI, Q2, Q3 -2N963 transistor

R1-5100 ohms
R2-8200 ohms
R3-1200 ohms
R4-11,000 ohms
R5-10,000 ohms
R6-2000 ohms
R7-12,000 ohms
R8-2200 ohms
R9-470 ohms
R10-1000 ohms
RFC1-18-µh. r.f.

all resistors
watt

choke

Xtal-43-mc. third -overtone crystal

the signal generator until the signal is
located with the receiver. Once the signal has been located, the remainder of
the alignment is carried out as described.
If no signal generator is available,
tuning C2, C6, and C11 to approximate
resonance with a grid -dip meter should
be done first, as before. Then the converter input is connected to a 6 -meter
antenna and the remainder of the alignment procedure performed as previously
described, except that on-the -air signals
are used in place of the signal generator.
Aligment can be performed at any frequency in the 6 -meter band where maximum sensitivity is desired. The 3 -db
bandwidth of the converter is 1.6 mc.,
and if the alignment is done at 50.5 mc.,
the converter will provide optimum performance from 50.0 to 51.5 mc.
Once proper alignment has been completed, it probably will never have to
be done again, since transistor characteristics normally do not change with age
and the life expectancy of the transistors
is greater than that of the person constructing the converter. Also, the circuit
operates at room temperature, so there
is no heat present to harm the other
components.
Some spurious responses may be encountered from strong TV or FM broadcast stations mixing with oscillator harmonics. The best cure for this is to place
a trap for the offending station or a
6 -meter low-pass filter ahead of the converter.
The author wishes to express his
thanks to Frank Davis, K7VKH, for his
valuable assistance throughout this project.

106

Electronic Experimenter's Handbook

FILTER OUT

-10

FUL L

F I LT E R

AC TION

20
N

m
ó-30

-50

30 40 50

100

150 200

N 500 700

1.5K

4K 5K

10K

15K

20K

30K 40K50K

FREQUENCY -CPS

An Adjustable Speech Filter
Cut out noise and increase intelligibility with this
all-purpose amateur, CB, hi-fi, and recording filter
By DANIEL MEYER
WOULD YOU LIKE to have a speech
filter to use with your CB receiver
that could be adjusted to give the best

reception for various signals and noise
conditions? A filter that can also be
used with your transmitter to get more
modulation in the 300 to 3000 cycle
range where it will do the most good?
A versatile unit which can also be used
with your hi-fi system to clear up the
noise on old recordings or weak FM signals? If so, here is a simple three transistor circuit that will do these jobs
and more.
Two feedback -type filters are used to
produce the high and low frequency attenuation. The circuit has zero unity
gain and may therefore be used at any
point in a system that has a signal level
of one volt or less. In addition, the
amount of high or low freeuency filter 1965 Fall Edition

ing may be adjusted and either filter
may be switched out of the circuit to
give a flat response.
How It Works. Transistor Q1 is an
emitter follower which gives the filter a
high input impedance and also provides
a low impedance driving source for transistor Q2. Capacitor C2 and resistor R3
form a feedback loop around transistor
Q1 that reduces the loading effect of the
bias resistors R1 and R2 on the input of
the filter.
Transistor Q2, with its associated resistors and capacitors, acts as a variable,
high-pass, active filter. Potentiometer R5
varies the cutoff frequency of the filter
from approximately 100 to 400 cycles.
In the "out" position of R5, switch Si
closes and shorts out the filter.

Transistor Q3, with its associated
components, is a variable, low-pass, ac 107

R3 R2

R4 C3

R12

RI4

C7
CI

mieubbser

Re Q2

Re RIO

Q3 RI3

Refer to the schematic diagram
on the facing page to locate
the components in photo above.

Potentiometers, switches and
jacks are wired before the
board is installed in cabinet.

tive filter. Potentiometer R11 is used
to vary the cutoff frequency of the filter
from approximately 3000 to 6000 cycles.
In the "out" position of R11, the normally closed pole of switch S2 opens and
breaks the signal connection to R11,
while the normally open pole of the
switch closes and shunts the signal
around the filter.
The input impedance of the filter is
about 50,000 ohms and the output impedance on the order of 1000 ohms. The
circuit draws 6 ma. at 12 volts d.c. or
3 ma. at 6 volts d.c.
Constructing the Filter. The filter is
built on a printed -circuit board to simplify construction and make for compactness. Install the parts on the board
in the positions indicated, and solder to
108

the etched copper pattern on the reverse
side of the board. Use rosin core solder
throughout, and use an iron rated at
less than 50 watts. Solder the connections as quickly as possible to avoid
prolonged heating of the laminate.
Next, drill the holes for the connectors
and the controls. Mark the hole positions with a punch, then use a x,4(3" drill
to make pilot holes. Now drill out the
connector holes to 1/4" and the control
mounting holes to %". Place a block of
wood under the metal during the drilling
operation.
Cut the shafts of potentiometers R5
and R11 to a length of %" from the
mounting bushing. Mount R5, R11, J1
and J2 on the case. Use lock washers
between the controls and the case to
Electronic Experimenter's Handbook

_4.
O6

TO
12

47K

VDC
01

2NI380

18--M.NvVJv

RI
5K
J

RIO
4TO11

15011

5K
IC1r)
+

R7
22K

if92

a7K

2.2K

R9
2.2K

R14

.002yf.

2.2K

PARTS LIST

-1-µf.,

Cl,

6 -volt electrolytic
C2, C7
C4 -0.25-µJ., 75-volt capacitor
C5
75 -volt capacitor
C6 -0.002-µj., 75-volt capacitor

capacitor

C3,

-0.05-µf.,

11,

12-Phono jack

Ql, Q2,

Q3 -2N1380 transistor

R3-10,000 ohms

All 'A -watt
fixed resistors

prevent slipping while using the unit.
Now wire the controls (low -frequency
filter R5, high -frequency filter R11, and
jacks J1 and J2) . Follow the schematic
diagram and photographs. The wires
from these controls are connected to the
coded points on the board corresponding
to similar points on the schematic. Fasten the board to the brackets, and mount
the entire assembly in the case.
Testing. Before applying voltage to
the filter, check carefully for shorts or
incorrect connections. Now connect the
points marked plus and minus to a 6 -to 12 volt battery or power supply. Note
that the positive lead is grounded and
common to both the input and the output.

Do not attempt to connect the filter
in an automotive electrical system if the
car has a negative ground. If the filter
has to be used with a mobile system,
strap a 6 -volt dry cell to the rear of the
filter box for a power supply. This will
also help keep ignition noise out of the
filter and eliminate any possibility of
short-circuiting the electrical system.
1965 Fall Edition

potentiometer with d.p.d.t.

switch, log taper (Centralab B-12 with KR -3

switch)
Sl,

S2-D.p.d.t. switch mounted

on rear of RS,

R11

R1, R2-47,000 ohms
R4, R9, R14-2200 ohms
R6, R7-22,000 ohms
R8, R13-150 ohms
R10-470 ohms
R12-5600 ohms

R5, R11 -5000 -ohm

4-Mounting brackets (Cambridge Thermionic
Corp. 1963 or equivalent)
1-2%"x234"x4" aluminum case (Bud CU -2103
or equivalent)
1-Circuit board (the author used an etched -circuit board (No. 101) which is available with
three transistor sockets for $1.25 from Demco,
Box 16041, San Antonio, Texas 78216)

The input and output connections may
be made to the filter at any point in the
circuit having a signal level of less than
one volt. The best place to connect into
a receiver would be at the volume con-

trol. Simply disconnect the wire from
the center terminal (wiper) of the volume control and connect the input of the
filter to this terminal. The wire is then
connected to the filter output.
On a transmitter, the filter can be
used with a crystal microphone, but volume will be reduced due to the loading
effect of the 50,000 -ohm input impedance of the filter on the high-impedance
crystal. In a hi-fi system, the filter can
be installed between the preamplifier
and the power amplifier units.
Using the Filter. Turn the control knobs
to the position that will clear up the
maximum amount of noise without affecting the intelligibility of the speech
or distorting the music any more than
necessary. For communications work,
especially under noisy conditions, you
will find that the narrower bandpass settings are the most desirable. If condi109

tions on the band improve, you may
want to set the filter for a wider response, but let the noise on the band
dictate this. Should noise conditions
clear up completely, or if you want an
absolutely flat response, you can easily
switch the filter completely out of the
circuit by rotating the controls fully
counterclockwise until the switches engage. The response will now be an essentially flat
1 db from 10 to 50,000
cycles. The filter itself has less than one
per cent total harmonic distortion in its
bandpass for any given setting of the
controls.
The device can also be used for many
special effects in tape recording, where
it functions almost in an opposite manner to a reverberation unit or echo
chamber. You can usually connect the
filter into the tape recorder's recording
preamplifier right at the record level
controls. (Naturally, for stereo effects
you will require two filters.) With the
filter in the circuit, and the controls rotated clockwise, you will notice a marked

NOW

- BUILD

2 EASY STEPS

decrease of high and low frequencies.
Since all the high-fidelity manufacturers
are trying to open up the frequency response, you may well wonder how such
a filter can be considered beneficial.
Speech recorded through the filter will
easily simulate telephone conversations,
or communications radio reception. Other applications are certain to suggest
themselves upon experimentation.
In a mobile installation, you will find
this filter an ideal adjunct to your electronic equipment, be it broadcast, Citizens Band or amateur radio. Static noise
is largely a high frequency function, and
as you can sharply attenuate high frequencies with this filter, you can reduce
static.
If you follow the diagrams, photographs and instructions, you will have
no trouble putting the filter together and
getting it to work properly. After you
have used it for a while to silence static,
or break through local noise with your
transmitter, you'll probably find it indispensable.

ANY CIRCUIT IN ONLY

WITH

VEROBOARD KIT

MODEL

BK -6

NO MORE ETCHING, WIRES
OR TERMINALS!

Now
for the first time you
can build circuits for ANY electronic project faster, easier and

more economically than ever
before and achieve real professional results.
Veroboard* is the newest,
most advanced method of cirSTEP NO. 1
STEP NO. 2
cuit construction yet developed
with Veroboard you design
Layout components on the back (plain)
Break the circuit where required by
your component layout directly side of the Veroboard across the copper
breaking the copper strips with the Vero
spot -face cutter provided in your kit. The
on the board and solder... strips inserting leads into appropriate
holes. You have now connected your comcutter is a precision, hardened steel tool
that's all there is to it!
ponents as required using the copper
which has a pilot pin that fits into any
This all -new Veroboard kit strips as your interconnectors. Leads may
hole, and two cutting edges. Simply turn
be
soldered
directly
to
the
strips
using
a
the cutter several times and the copper
contains 6 Univerlight,
printed
circuit
type
Careful
iron.
strip in the area of the chosen hole will
sal wiring boards
soldering will enable you to remove combe removed. Your circuit is now complete.
and spot face cutter
ponents and replace them if required.
NYS residents add 2% sales tax.
with instructions for
I
use.
TO: VERO ELECTRONICS INC.
Order your kit to48 ALLEN BLVD., FARMINGDALE, N. Y.
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AVAILABLE FROM LEADING DISTRIBUTORS OR DIRECTLY FROM
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*Patented
110

PLEASE SEND VERO BK-6 KIT.
ORDER) FOR $5.95.

AM ENCLOSING CHECK (OR MONEY

NAMF
ADDRESS

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CIRCLE NO. 31 ON READER SERVICE CARD
Electronic Experimenter's

Handbook

Just tiro tubes and a power supply gire you a 6 -meter
phone transmitter that's hard to beat for simplicity
By CHARLES GREEN, W3IKH
The pentode section
WANT TO KNOW how you can put a

high -quality 6 -watt, 6 -meter phone
signal on the air at a rock -bottom price?
It's easy-just build this beautifully simple three -tube (counting the rectifier)
"Companion Transmitter." Although this
attractive little rig was designed to complement the "Simple Superhet for 6"
which appeared in the April, 1963, issue
of POPULAR ELECTRONICS and the 1964

the 6CX8

(Vib) in the r.f. section is both a doubler
and final amplifier this type of circuit
was chosen as it does not require neu;

tralization. The plate circuit pi -network
matches the r.f. output to an antenna of
50 to 72 ohms impedance.
As shown in the schematic on page
113, a second 6CX8 does duty as a speech
amplifier-modulator. The mike input signal from J is amplified by Va and fed
ELECTRONIC EXPERIMENTER'S HANDBOOK,
C15 to the grid of V2b. The
through
receivit can be used with any 6 -meter
amplified by V2b which
is
further
signal
ing setup.
r.f.
output by means of
the
modulates
the
Designed for easy construction,
Companion Transmitter incorporates two the inductance of T1 which is common to
6CX8's, combination triode -pentodes the plate circuits of both V1b and V2b.
(Vib and V2b have internally connected Only the primary winding of Ti isbyused.
Metering of the final is provided M1,
suppressor grids) ordinarily used in TV
receivers. In the r.f. section, the triode connected to measure either grid or
portion of one 6CX8 (Via) functions as plate current using switch S1. Rotary
a crystal overtone oscillator using stand- switch S2 is a d.p.d.t. type which
ard FT -243 8-9 mc. crystals to produce switches the antenna and receiver and
transmitter B -plus supplies when going
an output in the 25 -mc. region.
r

1965

Fall

Edition

111

from receive to transmit. A 6X4 rectifier (V3) and the RC filter circuits of
C18 and R13, R14, R15 deliver the required B -plus voltages to the transmitter circuits.
Layout and Construction. To simplify
construction, the bulk of the transmitter
is built on a 41/2" x 8" piece of aluminum. As shown in the photographs
and pictorial diagram, this piece of aluminum is mounted 2" from the bottom
of a 41/2" x 6" x 8" utility box with aluminum angle stock. It will pay you to
follow the layout shown as closely as
possible, as lead length and component
placement are relatively critical at 6
meters. Grouping the components on
the chassis before you cut the mounting
holes will help you determine the best
layout.
Antenna tuning capacitor C11 is
mounted on the top of the chassis shelf

with two 3/8" spacers to clear its Bakelite end plates. Bend up the unused lugs.
Mount a single-lug terminal strip under
one of the mounting screws of the filter
capacitor (C18) on the chassis top to
connect C9 and L2 to the plate lead from
V1b. Drill a hole for this lead, and position it so it does not touch the chassis.
Position C9 annd L2 at least 1/2" away
from V1's envelope, and make their
leads as short as possible. The shielded
wire to meter switch S1 should be positioned against the front panel, away
from pi -network coil L3.
The leads going from J1, J2, J3, and
from the junction of C11 -L3 to transmit
switch S2 should be positioned over the
top of the back of meter M1 and taped
together. All of the leads except that
going from J3 are made of RG -58/U
coaxial cable. The secondary leads of
T1 are not used, and should be cut short

Layout is shown in pictorial below. For approximate spacing, see right photo on page 114.

112

Electronic Experimenter's Handbook

.001pí

V B

V'A

I/2-6CX8

I/2-6CXB

47.f

CII

4pf.
PLATE

TUNING

RECEIVE.-

365pí.

ANT.
TUNING

RECEIVER
ANT.

TRANSMIT

S2A

J2
2

-.005p3)

GRID

PLATE

CURRENT

ANT.

5.6K

pf.

T.00Ipf.

C3
.00S f.

J3
RECEIVER
STANDBY

S28

I0011
MI

C2 2

.005pf.

.005pf.
V2B

I/2-6CX8
J4

C12

(ja.

RII

RIO

220K

As shown in schematic, one
6CX8 comprises the r.f.

section of the transmitter,
while the other is used as
a speech amplifier -modulator. Receiver standby jack

optional

MEG.

c187, --

20yí.

-extra.

614

313

6BK

33K

+
CIBB

20p

450V

12011 +

J05pf.

CUM

CIBC

POWER

20pf.
450V

117

V3
HTR

HTR
C19

VAC

5
VI

OOSyf.
C21

T05pf.

and taped. In completing the Companion Transmitter, make sure the
meter switch is labeled correctly: "G"
for grid drive and "P" for plate current.
Drill a %" hole in the top of the box for
adjusting grid drive coil LI, and cut a
row or two of holes in the back of the
box cover for ventilation.
Testing and Adjustment. Insert the
tubes in their sockets and a good active
crystal in the front panel crystal socket.
Place the cover on the transmitter, in1965 Fall Edition

stall a 52 -ohm dummy load at jack J2
and let the unit warm up for a minute
or two. Set switch Si to measure grid
current, and insert a plastic alignment
screwdriver through the access hole in
the cover onto the adjustment slug of
coil Li.
Depress transmit switch S2 and adjust
the grid current to 2 ma. This adjustment should be made as quickly as possible to prevent damage to the tube. If
the grid current adjustment cannot be
113

PARTS LIST

Cl, C4 -47 -pf., 600-volt ceramic tubular capacitor

C2, C3, C5, C8, C12, C15, C19, C20, C21, C220.005-µ5., 1000-volt ceramic disc capacitor
C6, C7, C9 -0.001-µf., 1000-volt ceramic disc

capacitor

C10 -14 -pf. miniature variable capacitor (E. F.
Johnson Type 160-107 or equivalent)
C11 -365 -pf. variable capacitor (Lafayette
32-G-1103 or equivalent)
C13, C14 -330 -pf., 1000 -volt ceramic tubular or
mica capacitor
C16 -10-µf., 25-volt electrolytic capacitor
C17 -0.01-µf., 1000 -volt ceramic disc capacitor
C18-Four-section electrolytic capacitor, 20 µf.,
450 volts per section
F1
-amp type 3AG fuse in panel -mounting fuse
holder
11, 12-Chassis-mounting coax receptacle (Am phenol 83-1R or equivalent)
13-Phono pin jack, single -hole mounting
J4-Microphone connector, male, chassis -mounting (Amphenol 75-PC1M or equivalent)
L1-3.3-µh. to 4.1-µh., miniature adjustable r.f.
coil (J. W. Miller Part No. 20A336RBI)
L2-7-µh. r.f. choke (Ohmite Z-50 or equivalent)
L3-6 turns of B&W "Miniductor" Type 3010
with 3" leads (coil size fi" x
" dia.)
M1
-ma. d.c. panel -meter
R1 -10,000 -ohm, Vs -watt resistor
R2 -5600 -ohm, 2 -watt resistor
R3, R5 -12,000 -ohm, 1 -watt resistor

-1

-5

made, change the crystal for a more active one. Set the transmit switch to
standby position and move the meter
switch to indicate plate current. Rotate
the antenna tuning control to the maximum counterclockwise position (full capacity) and depress the transmit switch.
Tune the plate for maximum current dip,
then adjust the antenna and plate controls alternately until the current is 22
ma. The last adjustment should be made
with the plate tuning control. At this
point, the transmitter is fully loaded.

GRID DRIVE
ACCESS HOLE (LI)

R4 -1000 -ohm, Vs -watt resistor
R6 -10 -ohm, Vs -watt resistor
R7-100 -ohm, %-watt resistor
R8, R11-1-megohm, Vs -watt resistor
R9-2700 -ohm, 'A -watt resistor
R10-220,000 -ohm, Vs -watt resistor
R12 -560 -ohm, 1 -watt resistor
R13 -33,000 -ohm, 1 -watt resistor
R14-68,000 -ohm, 1 -watt resistor
R15 -120 -ohm, 1 -watt resistor
SI-D.p.d.t. slide switch
S2-D.p.d.t. rotary switch, non -shorting (Mallory Type 32227)
S3-S.p.s.t. toggle switch
TZ-Audio output transformer; primary, 10,000 ohms, secondary 4 ohms (Stancor A-3879
or equivalent)
T2-Power transformer; primary, 117 volts;
secondaries, 460 volts CT @ 50 ma., 6.3
volts @ 2.5 amp (Thordarson 24R11 -U)
V1, V2-6CX8 vacuum tube
V3 -6X4 vacuum tube
X1
-+-mc. transmitting crystal
1--4%" x 6" x 8" aluminum utility box (LMB

-8.

146 or equivalent)
x 8" aluminum

1-4%"
2
1

plate
-9 -pin miniature tube socket
-7 -pin miniature tube socket

for chassis shelf

1-Xtal

socket for FT -243 crystal holders
Misc.-Aluminum angle stock, terminal strips,
RG -58/U cable, shielded audio cable, hookup

wire, hardware, solder lugs, grommets, etc.

Check the grid current again, and re1,1 if necessary for a 2 -ma. reading.
These tune-up procedures should also be
used for on -the -air operation with an
antenna connected in place of the dummy load.
Your receiver can be used to check
modulation with a high -output crystal
mike connected to J4. The radiation
from the dummy load should be sufficient for this test. In the interests of
economy and simplicity, the speech amplifier -modulator of the Companion

set

*I %4"

1/4"

3/4'

11/2"

2 1/4

J4
The d mensions above show approximate component spacing.
114

Electronic Experimenter's Handbook

CII

R6 R7

CIB

C22

Top of rig looks like
this, with M1 mounted
at center of front panel and 1/2" from top,
Si and C10 directly
below it. Switch S2,
hidden behind T2, is
mounted in middle of
panel and about 11/4"
in from side; C11 is
similarly mounted on

the opposite side.

Transmitter was limited to a single tube.
For this reason, a high -output mike
must be used for a good percentage of
modulation. Strongly recommended is
the Astatic Model 150 recorder mike
which has an output of -44 db. It is
readily available and sells for under
$4.00.
"Simple Superhet" Conversion. If you

plan to use the "Simple Superhet for 6"
as the station receiver, a few simple
modifications will give you improved reception and single -switch operation.
A remote control jack and standby
switch (J3 and S2 in the drawing below)
are installed on the side of the receiver

RII

cabinet. The ground lead of the receiver
transformer is then connected as shown.
This arrangement permits transmitter
switch S2 to control the receiver. More
B -plus for the receiver can be obtained
by replacing the selenium rectifier (see
the April, 1963, issue) with a 400 -Ply,
450 -ma. silicon unit.
The most -used portion of the 6 -meter
band, 50-51 mc., can be made to cover
more of the receiver dial by connecting
a 10 -pf., 600 -volt ceramic tubular capacitor between the stators of Cl and C2.
Readjust the bandset capacitor C2 and
calibrate the receiver as described in the
original article.

CI9B

TRANSMITTER

RECEIVER

TO XMITTER J3

STANDBY
REMOTE
CONTROL

S2
REC.-STDBY.

Receiver is modified as shown at left to permit single
switch operation of station. Connections between
the units are for antenna and power switching.
1965 Fall Edition

115

SOUP
UP
THAT
AM BROADCAST

RE('EIVER
By F. J. BAUER, Jr.,

W6FPO

Want to improve the sensitivity of your small rereirer?
Here are several ideas that really work
IF

BROADCAST BAND DX'ing is your
cup of tea, you are aware of the
shortcomings of the "All-American 5"
and the built-in loop antenna. As the
loop is not just a signal catcher but also
a part of the first tuned circuit of the
receiver, you can't tamper with it with-

out altering receiver alignment.
Simple Coupler. Will a coupler and
long-wire antenna improve your reception ? They certainly will, and here's a
quick-and -dirty test to prove the point.
String up a good antenna, the longer
(at least 50 to 100 feet) and higher the
better. Connect one end of this wire to
a four- or five -turn coil of wire that you
wind around your hand. The other end
of the coil goes to a good water -pipe
ground (see Fig. 1, on page 120) . Now
tune in a weak station and bring the
coil of wire closer to the loop antenna
on the receiver. See ? The signal
strength increases, and the weak station
comes in strong. The next step is to
build something more permament.
116

Better Coupler.

better antenna

coupler tunes the antenna to the frequency of the station you want to hear.
It consists of an adjustable ferrite coil
with a series capacitor that can be
switched in or out of the circuit (Fig.
2) With the capacitor in the circuit,
the upper half of the broadcast band is
covered, and with the capacitor out of
the circuit, the lower half is covered.
You can adjust the ferrite coil to obtain
optimum results.
Still Better. A more elaborate, more
flexible coupler will work with any antenna length (Fig. 3) . The author utilized parts available in the junk box,
using coil L2 for maximum coupling to
the receiver. This coil was salvaged
from an old receiver as was capacitor
Cl, made by paralleling the three sections of an old tuning capacitor.
Adjusting the Couplers. The first thing
to do is determine the amount of "coupling" that will best suit your own
(Continued on page 120)
.

Electronic Experimenter's Handbook

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CL -215

CIRCLE NO.. 10 ON READER SERVICE CARD
119

Looking at the backs
of the two couplers
diagrammed in Figs.
2 and 3, it's obvious
that there isn't any
complex wiring to be
done. Use point-topoint wiring throughout, build panels of
Masonite,woodscrap.

ANT.

Fig. 1. Simple coupler
consists of four or

five turns of wire
connected to
LI

long
(50'100') antenna
and good ground. To
use, place coil near
receiver's antenna.
a

Fig. 2. Better coupler
has s.p.d.t. switch to

insert or remove 100

pf. capacitor Cl.
Ferrite antenna coil
Ll fine-tunes antenna.

lirl-

system. ("Coupling" refers to the placement of your antenna coupler with relation to your receiver antenna coil.)
There are two ways to do this. If you
have a VTVM, connect it to the a.v.c.
bus in your receiver. Now move the
coupler closer to your antenna coil as
you observe the meter. The voltage will
increase-to a point-and then start
to fall off. The best location for the
coupler is where it was at that highest
voltage point.
A simpler way to achieve maximum
coupling efficiency is to place the antenna wire near a fluorescent fixture
and couple for maximum noise in the
receiver loudspeaker. In either case, do
not increase the coupling beyond the optimum point, for over -coupling serves
only to introduce interference with no
increase in gain.
Using the Couplers. To use the coupler
shown in Fig. 2, first select the switch
position (capacitor Cl-a 100 -pf. unit
in this coupler-in or out) that corresponds with the frequency you want
to hear, and then adjust the slug in 1.1
140

Fig. 3. This coupler
is more flexible. A

double -pole, 3 -position switch selects
portion of band to be
heard, .001-0. capa-

citor Cl fine-tunes.

for best reception. Coil L1 in Figs. 2
and 3 is an Olson Radio No. L-75.
To use the coupler shown in Fig. 3,
tune in a station near 540 ke., with the
plates of capacitor Cl (.001 µf.) fully
meshed, and adjust the slug in coil L1
for maximum volume. Then you can
use switch S1 to rough-tune the coupler,
and capacitor Cl to fine-tune. The
switch positions and frequency ranges
are as follows
Frequency
Switch Position
:

kc.
740-1200 kc.
1100-1650 kc.
improve any
will
An outdoor antenna
1
2
3

540- 870

(center tap)

"All-American 5." An antenna coupler
will permit you to use an outdoor an-[]tenna with your receiver.
Electronic Experimenter's

Handbook

THE

LAND
.1

METER

PR EAMP

high -gain, low -

noise transistor
p eain p

for

for just ti7 and
2 hours of labor

By JOSEPH TARTAS,

IF YOU work

W2YKT

meters and can use

more r.f. gain on receive along with a
reduction in signal-to-noise ratio (and
who can't ?) , the "6 Meter 7 and 2 Pre amp" is for you. Heart of this little
one -evening project is a new low -noise
germanium transistor, the 2N2188, made
by Texas Instruments. At 50 mc., the
preamp has a measured 6 db noise figure,
which represents a maximum sensitivity
(the smallest signal it can receive) of
about 1.5 µv. Inserted between the antenna and receiver input, it can boost
signal level by at least 12 to 15 db.
Other advantages of the preamp are
that it is compact and self-powered-at
a battery drain of 4 ma., the battery
should last for nearly its shelf life. Although the unit was designed for 50 -ohm
input and output, it will work well at
impedances up to 300 ohms without
much deterioration in performance. Lastly, the total cost is only about $7.00.
The 6 -meter preamp is housed in a
1965

Fall

Edition

small 1%" x

21/2" x 23/4' Minibox, and
straight-line, minimum length leads are
employed. Carefully follow the layout
as shown in the photos. Drill holes in
the box for mounting r.f. connectors
J1 and J2 (use the type you presently
employ for convenience), the on -off
switch S1, the transistor socket, and the
output coil form (L1 and L2).
The Coils. Wind input coil L3 with
#14 wire; consisting of five turns with
an i.d. of 3', it should have an approximate length of '/2". Support it by soldering the center turn directly to the center
conductor of the input r.f. connector.
The grounded end is connected to a lug
held to the chassis with a screw and
bolt. The same lug also serves as a
ground for the 47 -pf. capacitor (C1)
and resistors R2 and R3.
The output coil is wound with the
three -turn secondary (L2) at the cold
121

TO FIT
CONNECTOR
T

2N2'8S

5/B"

.001Ní.

C3
001 f.

.00

RFC -1
1

5.6yh.

R3
IK

47p f.

I«581
5/8"

(ty1

TO FIT

1/2"
1/d

Follow "straight-line" layout shown here.
Leads must be kept short for good results.
Advanced experimenters might try an Amperex 2N2495 for less noise at lower cost.

BATTERY RETAINER

re:s LI,L2

DIMENSIONS SHOWN
FOR CU -3000A MINIBOX

R3 C3

PARTS LIST

-9

B1
-volt transistor battery
C1-47 -pf. ceramic disc capacitor
C2, C3, C5 -0.001-µf. ceramic disc capacitor
C4-18 -pf. ceramic disc capacitor

JI, J2-R.f. connector
Ll, L2-8 turns and 3 turns, respectively, of
#24 wire wound on Cambridge Thermionic
slug -tuned coil form PLST/2C4L/P
L3-5 turns of #14 wire, i.d. %", length

Q1 -2N2188

C4
SOCKET,

1/2"

transistor (Texas Instruments)
RFC -1
R1 -3900 -ohm, 1 -watt resistor
R2, R3 -1000 -ohm, 1 -watt resistor
RFC -1-5.6-µh. miniature r.f. choke (J. W. Miller 9330-18 or similar)

Si-S.p.s.t.

slide switch
Minibox (Bud CU -3000A)
or equivalent)
or equivalent)

1-1 "x2%"x23"

1-Transistor socket (Elco 3304
1-Battery clip (Cinch -Jones 5D

end of the primary (the end of the coil
form closest to the box top). The primary (L1) has eight turns. Wind the
coils in the same direction, connecting
the top leads to Q1's collector and to J2,
respectively. Both are wound on the
slug -tuned, .2"-o.d. (coil winding area)
coil form given in the Parts List. As
specified, this form comes with terminals and slug designed for VHF applications. It is available from suppliers in
large cities, or from most parts suppliers on special order. Another source
is Newark Electronics Corp., 223 West
Madison St., Chicago 6, Ill.
122

Tuning the Preamp. To peak the pre amp, simply insert the transistor in
the socket-after checking first to make
sure battery polarity is correct-and
tune the output coil for maximum noise
or signal level in the middle of the band.
If necessary, the input coil can also be
peaked by squeezing the turns together
or gently pulling them apart. Since the
bandwidth of the preamp is about 2.5

mc., adjustment is not critical. For best

results, you may want to peak the unit
in the middle of the portion of the 6 meter amateur band most used in your
-i®own area.
Electronic Experimenter's Handbook

CHAPTER
6
TEST
EQUIPMENT
PROJECTS

Because of the commercial availability of test
equipment-either in kit form or prewired-projects for the home constructor must be instruments
he can't buy. This is the philosophy used in selecting projects for the Fall Edition of the 1965
ELECTRONIC EXPERIMENTER'S HANDBOOK.

The "Field -Effect Transistor Voltmeter" (page
first-if not the very firstconstruction project to take advantage of the unusual characteristics of the field-effect transistor.
This device is simple to build and calibrate, and
has an input resistance comparable to that of a
VTVM. The "SCR Tester" (page 126) is a companion piece to the "Automatic Diode Checker"
(in the 1963 Edition of the ELECTRONIC EXPERIMENTER'S HANDBOOK). It could also be
labeled "automatic"' since it checks operating
characteristics of the gate as well as checking
for opens and shorts.
This chapter is rounded off with several short
items and some of the best "Tips and Techniques"
from past issues of POPULAR ELECTRONICS.
127) is one of the

124
HYBRID CIRCUIT FOR TRANSISTOR POWER

Roy E. Pafenberg

126
SCR

TESTER

Hopkins

127
FIELD-EFFECT TRANSISTOR VOLTMETER

Jeff

Taylor

131
MULTIPLE METER TEST SET

Roy

Pafenberg

132
MULTI -OUTPUT ZENER VOLTAGE REGULATOR

Harold Reed

133
BEST OF TIPS AND TECHNIQUES
1965

Fall

Edition

123

Hybrid Circuit for
IOVDC

TO"x

i60yf.
i5 V OC

> +1OVDC

Schematic for zener diode version is shown above.
Current increases through diode as load current
goes up. Diode can safely handle one ampere.

Good heat sink is prime requirement of zener reg ulator above. No insulation is required between
diode, bracket. Capacitor connects to standoff.

Put that high -voltage bench

AN A.C.-OPERATED power supply furnishing a range of commonly used
voltages is a "must" for experimental
electronics work. These "bench supplies" range from very elaborate commercial units to those built on open
chassis from junk box parts. Most such
supplies were designed for use with vacuum tube circuits, but with the popularity of transistors on the upswing,

supply to work powering
your transistor pro jectsa simple addition gives you
a handy low -voltage tap

By ROY E. PAFENBERG, W4WKM

they have limited application.
One answer to this problem can be
found in the assemblies shown here.
Either of the units will convert a conventional B -plus supply to furnish suit-

Typical supply is shown in schematic (right). Attach regulator
at "X." Disconnect tap, connect
to low -voltage regulator input,
and then ground the regulator.
124

Electronic Experimenter's Handbook

Tra n sistor Power

Schematic diagram of 2D21 regulator. Higher voltages can be obtained by adding additional tubes, but
increase voltage rating of Cl appropriately as well.

Tube regulator is assembled on bracket of bent -up
aluminum sheet scrap. This mounts under supply
chassis. Capacitor Cl is not shown in photograph.

able low -voltage outputs for transistor
work. A peculiarity of this conversion
is that the current that may be drawn
from the low -voltage tap is limited to a
value somewhat less than the combined

a cold -cathode, gas -filled 2D21 thyratron. As the voltage drop of a gas tube
is fairly independent of current variation, a well -regulated voltage is developed. The 2D21 is inexpensive, which
adds to the appeal of this version.
Building the Regulators. Construction
details are shown for assemblies de-

bleeder-high-voltage output current.

This is no drawback with tube or tube and -transistor equipment, however, and
another bleeder can always be added to
the high -voltage end of the supply if you
need more current while using the low voltage tap exclusively.
How It Works. If you insert a resistor
in series with the transformer center -tap
in a conventional power supply, a voltage (determined by the current in the
circuit) will be developed across the resistor. This is how negative bias voltages have been obtained for years. When
you insert a zener diode in series with
the center tap, the rectified voltage
across it causes the diode to conduct, and
the voltage drop remains constant over
a wide range of bleeder and external
load current of the B -plus output. While
the voltage of the diode is subtracted
from the output, it is negligible when
considered as a percentage of the output.
The second version of this circuit uses
1965

Fall

Edition

signed for installation under the chassis
of the supply. In the diode version, 3/4 inch aluminum angle stock is used to
mount diode D1 and capacitor Cl. A
standoff insulator is used for one end of
the capacitor. No insulation is required
for the diode stud, as in the usual
grounded bias supply. The aluminum
provides a good heat sink for the diode,
which is an International Rectifier 10 watt, 10 -volt unit. You can substitute
at will, but do not exceed the diode cur-

rent ratings.
In the 2D21 version, bend up a small
bracket from scrap aluminum for the

tube socket. You can, if you wish, increase the voltage output of the 2D21
circuit by adding additional tubes in
series, but be sure to increase the working voltage rating of the capacitor if
you make such a change.
125

SCR TESTER
By T. E. HOPKINS

There's no easy way of testing an SCR
but this handy gadget solves the problem
INCREASING commercial and domestic use of silicon controlled rectifiers
(SCR's) in such popular devices as light
dimmers, for power tool speed control,
etc., has created a need for a simple,
quick, and reliable method of checking
the condition of those suspected of being
faulty.
An SCR is a four -layer semiconductor
device with two main conducting termi-

nals and a gate terminal. It contains
junctions that are intended to block all
current in a reverse direction, block current flow in the forward direction under
normal or ungated conditions, and allow
forward current flow when the gate is
energized or triggered. Thus, it is possible for an SCR to break down in either
the forward or reverse direction or both.
It is also possible for the gate connection
to become either shorted or open. Therefore, it is not possible to determine the
condition of an SCR by simple ohmmeter
tests as may be done with a rectifier or
even, to some extent, with a transistor.
The device described in this article
will test both forward and reverse breakdown and gate operation. Transformer
T1 provides a 25 -volt, r.m.s. source of
a.c. to the circuit. This voltage is alternately applied in the forward and reverse directions across the anode -cathode
connections of the SCR. If initial breakdown is present in either direction, current will flow in that particular direction
and the current will be detected by either
the "Forward" or "Reverse" lamps.
(Continued on page 139)

All of the components can be
readily fitted into a convenient
aluminum box. The wire from
switch Si to center binding post
J3 ("Gate") may not seem visible,
but it's really there. Numerous
inexpensive 24-25 transformers
are available as substitutes for
the filament transformer called
out in Parts List on page 139.
SI
126

II
Electronic Experimenter's Handbook

ADVANCED EXPERIMENTER'S CORNER

FIELD-EFFECT

Extraordinarily high

TRANSISTOR

input impedance,
portability and accuracy,
with a single transistor

VOLTMETER
By JEFF H. TAYLOR,

THE field-effect transistor has steadily
gained in popularity due to its ability
to act like a vacuum tube. With increased popularity, the price of such
transistors has fallen and is now within
the budget range of most experimenters.
The 2N2498 is currently being sold for
$12.75, and the new 2N3330 for $10.82.
The transistor voltmeter described in
this article is similar in many respects to
1965

Fall

Edition

Texas Instruments, Inc.

a VTVM, but uses, instead of a vacuum
tube, a single unipolar field-effect transistor-the 2N2498.
The unipolar transistor-unlike its bipolar brothers-exhibits extremely high
input impedance and some of the other
characteristics that might be attributed
to a vacuum tube, specifically a pentode.
Because of these characteristics, a voltmeter can be designed with a single
127

transistor and a bare minimum of parts.

As the specifications on the next page
show, the field-effect transistor voltmeter is small, lightweight, and has a
battery life equal to the shelf life of the
mercury cells used to power it.
Technically, the voltmeter uses a fieldeffect transistor in a source -follower
configuration (similar in many respects
to the familiar cathode -follower arrangement used with vacuum tubes) . The voltage gain of the final circuit is less than
unity, and varies with changes of the

small -signal common -source forward
transfer admittance and other circuit
impedances.

Circuit Theory. The basic voltmeter circuit is shown in the small diagram in
the upper right-hand corner of the next
page. To analyze it, assume that a zerb
potential is established between points
A and B and that current will flow
through the transistor and resistor R8.
This places point C negative with respect to point B. Combination resistors
R3 and Rb can be adjusted to provide a
potential at point D equal to the potential at point C. The meter will now indicate zero. If a negative potential is
applied to the input (A -B) , the current
through the transistor and resistor R8.
will increase and point C will become
more negative-causing a meter reading
proportional to the potential difference
between points A and B.
S2

The input resistance of this circuit
can be extraordinarily high since it is
determined by the gate -to -channel leakage of the field-effect transistor. ("Channel" refers to the conducting path between the "source" and the "drain.")
Obviously, this circuit will not work in
actual practice since the open gate would
permit static potentials at point A to
cause the meter needle to wander. A
practical version of this basic circuit is
shown in the large schematic diagram
and construction photograph.
A Practical Circuit. Through a rather
modest arrangement of switches and resistors, a single field-effect transistor
voltmeter can be built possessing the
detailed specifications outlined at the
bottom of page 129. The input impedance
of this voltmeter is determined by the
series combination of resistors RI
through R9. To provide protection from
transient overload or stray a.c. voltage
injection, the filter consisting of Cl and
R10 has been introduced. Diode D1 has
been wired across the meter so that the
movement current can be limited to
about 11/2 times the full-scale deflection
value. Although this circuit was designed
using the 2N2498 field-effect transistor,
the 2N3330 will perform equally well,
and so will the 2N2497, 2N2499, 2N3329
and 2N2500.
Since the over-all accuracy of the
(Continued on page 140)
al

RIO

RII

The voltmeter is mounted in a black Bakelite
meter box available at

most radio supply

houses. The circuit components are mounted on
a piece of perforated
phenolic board which is
attached to the back of

meter M1 with nuts on
the meter input terminals. Although layout is
not critical, care should
be taken to insure that
leakage paths do not develop in input circuit.

R8
R7

Ea'

R4
R3
R2

R14

R12

128

R13

R15

Electronic Experimenter's Handbook

(PROBE)

RED

RI
2 MEG.

R6
IOOK

800K
50

The theoretical circuit
at right demonstrates

the operation of the
practical circuit below
(see text for details).

80K

R4
MEG.

100

R3
8 MEG.

1.0

500
Rb
10K

1000

MEG.

S2C

*RI

S2A

10K

2N2498

BLK

R14

YANN

DRAIN

RIO
MEG.

Soya.

RI2

GATE

SOURCE

4.7K

IN456

R15
IK

81-1N456

4.2V

T I

*SELECT

FOR METER ZERO

S2 SHOWN IN POSITION I (OFF COND TION)
POSITION 2 +

S2B

POSITION 3

PARTS LIST
B1 -4.2 -volt mercury battery (Mallory TR233
or equivalent)
C1 -0.02-µf., 200 -volt capacitor
Dl -1N456 silicon diode

M1-0-50 microampere meter (Simpson Model
29 or equivalent)
QI -2N2498 field-effect transistor (Texas Instruments)

R1-2-megohm (or 1.8- or 2.2-megohm), %watt resistor,

10%1

R2-10 megohms
R3-8.0 megohms
R4-1.0 megohm

-watt resistors, 1%
(Aerovox CPX-1 or equiv.)
1

R5-800,000 ohms
R6-100,000 ohms
R7-80,000 ohms
R8, R9-10,000 ohms

%-watt resistors, 1%
(Aerovox CPSX% or
equiv.)

R10-1.0-megohm, %-watt resistor, 10%
R11 -4700 -ohm,

,A -watt resistor, 10%
R12--5000-ohm potentiometer with lock

R13-1000-

to 5000 -ohm resistor-see text
R14 -1000 -ohm potentiometer
R15 -1000 -ohm, ,A -watt resistor, 10%
S1
-pole, 8 -position rotary switch (Centralab
PA -1001 or equivalent)
S2
-pole, 3 -position rotary switch (Centralab
PA -1007 or equivalent)
1-Battery holder (Keystone #173 or equiva-

-1
-3

lent)

2-Banana jacks, one red, one black
1-Black plastic multimeter case (approx.
6 13/16" x 5 9/32" x 2 5/16") or similar
Misc.-Set of test leads with banana plugs, knob
for zero control, perforated phenolic board

SPECIFICATIONS
Accuracy Determined by meter movement
used. Accuracy of instrument shown is within ±2% of full scale.
Battery Life Essentially shelf life.
Input Impedance 22 megohms on any range
(including 2-megohm probe).
Power Consumption Approximately 5 mw.

1965 Fall Edition

Power Supply 4.3 -volt mercury battery.
Voltage Range 0.5 volt to 1000 volts. Eight
ranges selected with front panel switch.
Full-scale readings of: 0.5, 1.0, 5.0, 10, 50,
100, 500, and 1000 volts.
Warm -Up Time Zero.
Weight Approximately 21/4 lb. with battery.

129

Inn/Stem) Review

MODEL 211

TEST RECORD
STEREO
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Realizing this, HiFi/STEREO REVIEW decided to produce
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Stereo Checks That Can Be
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a direct check of eighteen
Frequency response
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the most sensitive tests ever
Pickup tracking
available to the amateur for checking cartridge,
stylus, and tone arm.

foolproof tests that help you
and rumble
evaluate the actual audible levels of rumble and
hum in your system.

./V`Hum

jFlutter-a test to
flutter

check whether your turntable's

is low, moderate, or high.

two white -noise signals that
Channel balance
Jallow you to match your system's stereo channels
characteristics.
for level and tonal
Separation-an ingenious means of checking the
stereo separation at seven different parts of the
musical spectrum-from mid -bass to high treble.

ALSO:

Stereo Spread
Speaker Phasing
Channel Identification

PLUS SUPER FIDELITY MUSIC!
The non -test side of this record consists of music
recorded directly on the master disc, without go
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130

UNIQUE FEATURES OF HiFi/STEREO REVIEW'S
MODEL 211 STEREO TEST RECORD
Warble tones to minimize the distorting effects of room
acoustics when making frequency-response checks.
White -noise signals to allow the stereo channels to be
matched in level and in tonal characteristics.
Four specially designed tests to check distortion in stereo

cartridges.
Open-air recording of moving snare drums to minimize
reverberation when checking stereo spread.

All Tests Can Be Made By Ear
HiFi/STEREO REVIEW's Model 211 Stereo Test Record will give you
immediate answers to all of the questions you have about your stereo
system. It's the most complete test record of its kind-contains the
widest range of check -points ever included on one test disc! And you
need no expensive test equipment. All checks can be made by ear!
Note to professionals: The Model 211 can be used as a highly efficient design and measurement tool. Recorded levels, frequencies, etc.
affording accurate
have been controlled to very close tolerances
numerical evaluation when used with test instruments.

DON'T MISS OUT-ORDER NOW
The Model 211 Stereo Test Record is a disc that has set the new
standard for stereo test recording. There is an overwhelming demand
for this record and orders will be filled by POPULAR ELECTRONICS
promptly upon receipt. At the low price of $4.98, this is a
value you won't want to miss. Make sure you fill in and mail the
coupon together with your check ($4.98 per record) today.

FILL IN AND MAIL TQQA-YJ
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Popular Electronics-Dept. SD
One Park Ave., New York 16, N.Y.

test records at $4.98 each. My check
Please send me
is enclosed. I understand that
(or money order) for $
you will pay the postage. (Orders from outside the U.S.A. add 50c
to partially defray postage and handling costs.)
Name

(Please Print)

Address

City

Zone

State

Sorry-No charges or C.O.D. orders!

Electronic Experimenter's

EEH65

Handbook

MULTIPLE
METER
TEST
SET
CONNECT A VOLTMETER across the power supply and prepare
to meter the input to the amplifier. Adjust the value of the Q2
bias resistor for a base to emitter voltage of -0.1 volt, making sure
that the collector current does not exceed 12 ma." At about this point,
you curse the writer of the instructions as a bloated plutocrat-he
and all his test equipment vs. your lonely VOM.
Anyone who constructs electronics equipment as a hobby is well
aware of the measurement problems involved. Voltage readings are
not too difficult to take, but measurement of current at a number of
points in the circuit is a different matter. Invariably the circuit must
be opened, a meter inserted, a reading taken, the circuit closed up and
the meter moved to the next point.
The compact little instrument shown here is a convenient answer
to the problem of how to make several simultaneous measurements.
Its cost is surprisingly low since use is made of imported metersthe author obtained his from Lafayette Radio via mail order. Besides
a 0-15 volt d.c. meter, the cabinet holds one 0-50 µa. (d.c.) one
0-i ma., one 0-5 ma., one 0-50 ma., and one 0-100 ma. meter. The
cabinet is a Premier ASPC-1202 with a sloping front.
-Roy E. Pafenbery
,

Mount the six meters in

logical

pattern so that the scales in-

crease from left to right and top
to bottom. Bring the meter leads
out to insulated terminals or binding posts on the top ledge of the
cabinet. Use color -coded terminals
so that red indicates the plus meter lead and black the minus lead.

1965 Fall Edition

131

MULTI -OUTPUT
ZENER VOLTAGE
REGULATOR
By HAROLD REED
6

THIS simple voltage regulator will provide regulated outputs at most commonly used values for semiconductor circuits-nominally 3, 6, 9 and 15 volts. By

using a special switching arrangement,
only two low-cost zener diodes and three
resistors are required. Any suitable d.c.
source adjusted to 17 volts can be used
for the input.
If a d.c. supply is not on hand, the
constructor can build an a.c. rectifier
especially for the regulator. Good regulation is obtained even with a simple
half-wave diode supply.
How It Works. The schematic shows
that the two zener diodes (DI and D2,
6.2- and 9.1 -volt units respectively) are
switched into four different circuit configurations.
With the switch in the first position,
both diodes are used. The regulated output is the difference potential of the
diodes, which is 2.9 volts. The second
switch step provides a 6.2 -volt regulated
output. Here, only Dl is used. On the
third switch step, only D2 is used and a
9.1 -volt regulated output is available.
In the fourth position, the two diodes
are connected in series, giving a 15.3 volt regulated output.
The zener diodes are rated at 400
milliwatts. These diodes are also available with ratings from 250 milliwatts
up to 10 watts at various voltages. Thus,
a regulator of this type can be constructed to handle considerably larger
currents and with many different combinations of regulated outputs.
The device is housed in a 4" x 21/4" x 21/4"
aluminum box with identifying decals on
the front panel. Parts placement and
internal wiring are not critical. If a
slightly larger box is used, a completely
self-contained unit can be made by incorporating a power supply using germanium or silicon diodes.
132

Multiple outputs are available from this
regulator. Note that the 2.9 -volt
circuit has a separate negative terminal.
small

Testing the Unit. The regulator was
tested with one of the simplest types of
power supplies consisting of a half -wave
rectifier and a capacitor -resistor filter.
With a regulated output of 6.2 volts,
starting with zero load current, the output remained steady as the load current
was increased. When the load current
reached 24 ma., the output dropped 0.3
volt. The 9.1 -volt output held steady
from zero load current up to 20 ma., when
it also went down only 0.3 volt. Output
from the 15.3 -volt terminal dropped 0.5
volt between zero and 22 ma. load current. Likewise, the 2.9-volt output held
steady and went down only 0.2 volt when
the load current reached 10 ma.
In these tests, zero load current represented no load at all connected across
the output terminals.
-[0]
Electronic Experimenter's Handbook

TIPS & TECHNIQUES
TETRACHLORIDE
TAPPING TIP

If you use oil as a lubricant when tapping
holes in metal, you may find that after a
short time the oil gums, binds the tap, and
the tap breaks
off. To prevent this sort
of tragedy, try

using carbon

tetrachloride

as a tap lubricant. Because
of its high rate
of evaporation,

dispenser. However, make sure that the
room is well-ventilated while you're using
the carbon tet.
-Robert K. Dye
CLOCK RADIO
SERVES

TV TIMER

A few slight modifications to your clock

radio will enable it to turn your TV set on
automatically at a definite time. Add an
outlet to your radio and wire it according
BREAK
TO
RADIO

CIRCUIT

II? VAC

S.P. D.

CIRCUITS

SWITCH

neither gum-

ming nor binding will occur,
and you'll have
a cleaner job.
The carbon tet
can be stored in an old medicine dropper
bottle which will also serve as a convenient

HERE

CLOCK

ADDED

OUTLET

RADIO

to the diagram. The s.p.d.t. switch can be
mounted near the outlet. Locate the wire
from the clock switch to the radio circuits
and wire the added components as shown.
When the TV set is plugged into the new

HOW TO

IMPROVE YOUR
TWO-WAY RADIO!
The right communications microphone may
double the talk power of even the finest trans-

mitters! Learn how unwanted noise can
be

eliminated-reliability improvedintelligibility increased by proper
microphone selection.
Write for our helpful
free booklet today!

ELECTRO -VOICE, INC., Dept. 1052EH

Buchanan, Michigan 49107

E -V booklet on choosing communications
microphones. I am Interested in the following areas of two-way
radio:
Aviation
Amateur
CB
Business.

Please send the tree

NAME
COMPANY
ADDRESS
SETTING NEW STANDARS

SVUNG

CIRCLE NO.
1965 Fall Edtion

7 ON

CITY

STATE

READER SERVICE CARD
133

mumummummalio

SELLING YOUR

i TRANSCEIVER?

`p,

BUYING THAT

AMPLIFIER?

11Z-

outlet, it will be controlled by the clock
mechanism if the switch is in the TV position. If the clock radio is equipped with
a "sleep switch," you can use this to shut
the set off automatically.
-Fred Blechman, K6UGT
SUBSTITUTING
RECTIFIER TUBES

Be wary about replacing a rectifier tube
such as a 5U4 with a 5DJ4 or similar tube.
While at first glance the tube pin numbers
and specifications may seem similar, many

manufacturers utilize unused socket terminals as convenient tie points for components
5DJ4

5U4

PINS 1,3,5, AND 7
MAY BE USED AS

TIE POINTS

that may not even be a part of the rectifier
circuit. The 5DJ4 has internal connections
to tube pins that are not normally used in
the 5U4. For example, if your set has a
5U4 rectifier socket with pin 5 as a ground,
you'll have real trouble substituting a
5DJ4!
-Carleton A. Phillips

The 400,000 Live Wires who buy POPULAR
ELECTRONICS each month will make it
worth your while to place a classified ad
at the low personal rate of only 55¢ a word.
This, the largest readership in its field
in the world, offers the perfect market for

NEAT LAYOUT FOR
PRINTED -CIRCUIT BOARDS

making contacts. It's possible a great
many of these readers are practically
neighbors of yours, yet it is only through
the medium of our classified columns
that your mutual needs may be met.
Take advantage of our special personal
rate of 55¢ a word (including name and
address)
NO MINIMUM REQUIRED
a saving of 35¢ a word from
our commercial rate of 90¢

small investment is sure to bring
large results. Write your ad today and
mail it with your payment, to:
A

.I
,
al as mill

Hal Cymes
Classified Advertising Manager
POPULAR ELECTRONICS

One Park Ave.. New York, N.

10016

JANUARY ISSUE CLOSES NOV. 1ST

134

You'll find it easier to keep components on
a printed -circuit board aligned and neatly
arranged if you try this simple tip. Instead
of laying out the board with penciled guide
lines ( they tend to erase
themselves while you
work) , place a piece of
perforated board over
the copper laminated
board, and spray with
acrylic paint from a
height of at least two
feet. This will give you
a grid of small dots on
the circuit board to use
as component centers
and guides for the cop-

per runs. After laying
out the resist tapes,
quickly slosh the board
with lacquer thinner to
remove the paint; if
you work fast, the tapes will not be affected.
If you use the resistive ink method, the dots
can be removed with an ordinary ink
-Donald E. Lancaster
eraser.
Electronic Experimenter's

Handbook

You've got to SEE it to BELIEVE it!

HANDY HOLDER
FOR HARDWARE

If you attach a large and small rubber suction cup back to back, the result is a handy
stick -on hard-

dry transfer

ware holder.

Fill the hole
in the larger
cup with epoxy
cement, and insert the screw

MARKING KITS

tor

ELECTRONIC EQUIPMENT

lug of the

smaller. The
hardware holder can then be
attached to TV
cabinets, tool
box lids or other supports, and used for
small parts, nuts, bolts or washers.
-John A. Comstock
STORING
ADAPTER

SOCKETS

To keep your
adapter sockets handy and
safe, there's no
better place to

put them than
in your tube
pin straighteners. The adapter socket pins
will be protected, and the sockets themselves will be ready for use at all times.

-Clyde

C. Cook

AEROSOL "WILDCATS"
TO AVOID MESSY ACCIDENTS
CAP

Don't discard the protective cap on the next
can of aerosol tuner cleaner you buy-it can
keep the contents of the can from being accidentally released, particularly when
the can is carried from job
to job. As slipping the cover
on and off and
attaching and

detaching the
extender for

each job would
be a nuisance,
you can neatly
trim out the top of the plastic cover with a
small knife. Then drill or punch a hole
on the side of the cap for the spray extender tube. When the can is empty, the
modified cap can be transferred to a new
-Elmer C. Carlson
can.
1965 Fall Edition

you all the necessary
elements for completely marking electronic equipment,
drawings, prototypes, schematics, etc. in a fast new easyto -use form.
Words, letters, numerals, switch patterns, arcs, etc. are
printed on a special transparent carrier film. Rubbing over
one of these elements with a ballpoint pen releases it from
the carrier film and adheres it to your working surface.
"Instant Lettering" words and patterns transfer to almost
any surface including glass, plastic, metal... even crackled
finished metal. Now you can quickly mark all panels, even
especially calibrated two-color meter dials, tap switches,
panel nomenclatures, pilot light jewels, sub -assemblies, circuit boards, etc. Reproduction quality "Instant Lettering"
transfers are clean and sharp, leave no background haze or
film, make prototypes look like finished production equipment
and give all equipment and drawings a professional look.

"Instant Lettering" marking kits bring

TITLES FOR ELECTRONIC EQUIPMENT
This set contains hundreds of preprinted titles researched to
give you up to 95% of all electronic marking. For labeling,

marking, titling all electronic control panels, drawings, prototypes, etc.
$4.95
WHITE
No. 959
$4.95
BLACK
No. 958

TERMINAL & CHASSIS MARKING KIT

Contains all the necessary letters, letter combinations and
numerals for marking chassis, printed circuit and terminal
boards, rotating components, etc.
$4.95
WHITE
No. 967
BLACK
$4.95
No. 966

METER & DIAL MARKING KIT

Arcs, dial patterns, lines, wedges, graduation lines, switch
symbols, alphabets and numerals in black, white and red for
marking standard and special rotary tap switches, potentiometers and prototype and especially calibrated meter dials.
Colors provide contrast on scales and switches simplifying
usage of complex instruments.
$4.95
METER & DIAL MARKING KIT
968

No.

WRITE FOR FREE SAMPLE AND COMPLETE DETAILS

THE
63

DATA K
71st St.

Dept. 634

CORPORATION
Guttenberg, N. J.

CIRCLE NO. 4 ON READER SERVICE CARD

135

"FILM"

If you missed it ...

boxes. An easy
way to keep
them in order
is to slip their

SPRING

Small parts, such as resistors, capacitors
and diodes, often become tangled and hard
to locate when

they are stored
haphazardly in

Is THE
19ßrRo=

1965

EXPERIMEN,...-TER

STORAGE
FOR SMALL PARTS

EDITION

leads through

the perfora-

ELECTRONIC

EXPERIMENTER'S

tions of 35 -mm. film strips as shown. The
film strips, together with the components,
can then be neatly filed or tacked to a
convenient shelf for easy access.

-Art

HANDBOOK

Blaske

SNAP -TYPE CLOTHESPIN
MAKES BANANA PLUG ADAPTER

SEND FOR.

There's probably a bunch of banana -plug to -pin-jack adapters in your home-in the
family clothespin bag. To make an adapter,
take the spring off a snap -type clothespin
and cut the arms of the spring as shown
here. The straight end of the spring can

IT RIGHT
NOW!
be soldered to a printed -circuit board, giving you a banana jack, or you can insert
the end in a pin jack and use leads terminated in banana plugs.
-R. D. Holen

ALSO AVAILABLE:
Limited Quantities of the
1962, 1963 and 1964 editionspriced at just $1.00 each!

QUICK

ZIFF-DAVIS SERVICE DIVISION
Dept. EEH
589 Broadway, New York, N. Y. 10012

YES!
want to receive copies of the editions of
ELECTRONIC EXPERIMENTER'S HANDBOOKS
checked below:
I

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1964

1963

1962

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*add 15c per copy for postage and handling. Add 25c per
copy outside U.S.A.
name

please print

city

136

FOR

EXPERIMENTS

When you need some multiple of
d.c.
for an experimental hookup, the9 volts
quickest
way to get it is to
plug two or more
9 -volt transistor
batteries together,

as shown. Make
the output connection to the two terminals left exposed
on the directly con-

nected dry cell

address

---PAYMENT MUST

SERIES CONNECTION

OF DRY CELLS

EEH-65

state

zip code

BE ENCLOSED WITH ORDER.

---

bank. Incidentally,
you can use con -

nectors taken from discarded cells for the
wire ends to make connection and dis connection easy.
-Patrick Snyder
Electronic Experimenter's Handbook

DEGAUSS

YOUR

TAPE RECORDER

HEADS

When your tape recorder begins to sound
"muddy," it's a good indication that the
heads are in need of degaussing (or demagnetizing). There are commercial degaussers
available, but it's easy to make one. Saw
a 1/a" slot in a
1/2" flat iron
washer and

wind six or

eight turns of
#14 or #16
insulated wire
on the washer.

Connect the
wire ends to
your soldering
gun (after you
remove the soldering element), and you'll be able to de-

gauss both the heads and guides. The tool
can also be used to erase small sections of
recorded tapes, such as unwanted switch
-R. K. Dye
pops, or words.
RUBBER FEET

FROM

SUCTION

CUPS

You can make some

dandy rubber feet

for your instru-

ments from simple
suction cups. Rubber cement will
hold them in place,
or, if you like, a
small hole can be
drilled in each suction cup and a bolt
used to attach it to the cabinet. The suction cups are resilient and provide good
-John A. Comstock
shock protection.
LIGHT FLASHER MAKES
LOW -HEAT SOLDERING GUN

Ever need a particularly low heat for soldering miniature or transistor circuits ? If
you connect your

soldering gun
through an ordinary Christmas

tree light flasher,
it will cycle the
gun on and off,
keeping the heat at
a low but usable
level. You can get
a 100 -watt flasher from your local hardware
or electrical appliance store. Just plug the
flasher unit into the bench outlet, and the
soldering gun into the flasher.
-John Lias Wilson

Get Your First Class Commercial

F.C.C. LICENSE
and earn your

A.S.E.E. DEGREE
Grantham School of Electronics can
prepare you quickly for a career in
electronics. In 4 months you can prepare for employment as a communications technician, or in 8 months as a
television technician, or in 18 months
as a highly -trained electronics technician holding an Associate in Science
in Electronics Engineering Degree.
The Grantham degree curriculum is
laid out in such a manner that the
first semester (first 4 months) prepares you for a first class FCC license
and for technical employment in communications, and that the first two
semesters prepare you for employment as a television technician in a
TV -service shop or in a TV -broadcast
station. Therefore, you may choose to
discontinue Grantham training at the
end of either the first or second semester and still enjoy a productive
career in electronics. Also, if you wish
to continue and earn the degree, your
ability to work in electronics after
the first semester may enable you to
"pay your way" through t_e rest of
the course.
Those who continue for the degree
must take the final two semesters at
the Hollywood Division of the School.
These final semesters include a lot of
applied math, as well as some physics,
technical drawing, English, etc.
Daytime or evening class schedules
are available. Also, FCC license preparation is available by correspondence. Get complete details by telephoning or writing any one of the
Divisions of the School listed below.
Ask for Catalog 5X.
Grantham School of Electronics
1505 N. Western Av., Hollywood, Cal. 90027
(Phone: HO 9-7878)
408 Marion Street, Seattle, Wash. 98104

(Phone: MA

2-7227)

3123 Gillham Road, Kansas City, Mo. 64109
(Phone: JE 1-6320)
818-18th St., NW, Washington, D.C. 20006
(Phone: 298-7460)

137
1965

Fall

Edition

GIANT CR SALE!!

Hallmark Transceiver (Model 1250)
Midland Walkie Talkie (Model 13-105)

CAMERA TRIPOD

SPECIAL SALE

Ross Walkie Talkie (11 transistor)
Ross 6 Transistor AM RADIO
2 Station Transistor INTERCOM

PAIR $ 7.99

BUILDER'S SPECIALS

Capacitor Substitution Box (600 WVDC)
Resistor Substitution Box
Test Oscillator-transistorized (Sig
Gen)
Volume Controls (10 ass'td)
Timing Motors -110V (5 ass'td)
Solder Gun -100W with spotlight

$ 2.39
$ 3.59

SALE
SALE
SALE
SALE
SALE
SALE

$16.95
99¢
$ 1.99
$ 2.49

TERRIFIC SALE PRICES ON HY-GAIN
CB TOPPER ANTENNAS!
TLWR Roof mount Omni -Topper (reg
$11.97) SPECIAL $ 9.88
TTMP AM -CB Duo -Topper (reg $14.95)
SPECIAL $12.19
TLWT Telescoping Topper Whip (reg $7.20)
SPECIAL $ 5.88
TLWM 50" Topper
Chr. Body Mount (reg
$8.95)
SPECIAL $ 7.20
TRC Roof mount Omni -Topper
(reg $14.95) SPECIAL $12.15
TMC All purp. Topper
Body Mount (reg
$12.95)
SPECIAL $10.50
TLW 50" Top -loaded Whip (reg $6.96)
SPECIAL $ 5.40
CB -3 3 element Beam Antenna (reg
$19.95) SPECIAL $17.95

Command CB Crystals (.002%)
SpeciFS-60f

EACH $ 1.79

Model, Channel), 12
SWR Bridge & Field Str. Meter

at EACH

SALE $ 9.89
Mobile Noise Suppressor Kit (15 pc) .SALE $
4.99
Headset with Mike for CB
SALE $ 4.88
Trumpet Horn Speaker (5"round-paging)
SALE $ 7.49
SEND FOR GROVE BARGAIN FLYER-MAILED
SN -3

PINCH-HITS AS MIKE STAND

SALE $99.99
EACH $13.50
2 for $25.88
SALE $29.95
SALE $ 3.99

FREE!

Send check or money

order, include postage, excess re
funded. Minimum order
service charge
under $1 0.00. 50 7 deposit$5.00-50f
on COD's.
GROVE ELECTRONIC SUPPLY COMPANY
4107 W. Belmont Ave.
Chicago, III. 60641
CIRCLE NO. 9 ON READER SERVICE CARD

A floor stand for
a microphone is
not often listed as

standard

equipment for a home
tape recordist. For
easy recording of
noise -free tapes,
however, it is almost a necessity.
If you own a camera tripod, you can
attach your microphone to the tripod's swivel head with a simple clamp or
bracket, and derive all the benefits of a
good mike stand.
-Glen F. Stillwell
EASY WAY TO MOUNT
PHONO JACK ON P -C BOARD

Here's how to mount a phono jack at right
angles to a printed circuit board with
minimum of fuss. You'll need a crimp -ona
closed -eye -terminal for a 1/4" stud and a
Cinch -Jones Y-142 adapter (available for

about three
distributor)

cents from any
.

Cut the terminal just at the
ferrule so you
have a 1/g " tab

projecting

GIANT NEW CATALOG
Ì'

from the original eye. Flatten the Y adapter. Now mount the terminal
and adapter near the edge of the board facing each other and about 7/16" apart. Insert
the phono jack, tighten the nut, and solder
the connections. The resulting mount is compact, neat, and rugged.
-Don Lancaster
PLASTIC CASES HOLD
METERS OR SPEAKERS

Discarded plastic TV booster or antenna
rotor control cases of the type shown in the

photo make excellent
mounts for meters or
for a miniature speaker. Strip the parts and
chassis from the case,
and, if you're lucky,
the meter or speaker
will fit in the hole left
by the dial without
further modifications.
If necessary, enlarge

1OO's OF BIG P ' GES
CRAMMED WITH SAVINGS

BURSTEIN-APPLEBEE CO.

Dept. EX, 1012 McGee, Kansas City,Mo.
L.
Rush me FREE 1966 B -A Catalog.
Name

64106

the mounting hole

Address

State

City

I
I Please be sure to

!FREE

show your Zip No

CIRCLE NO. 3 ON READER SERVICE CARD

with a hacksaw blade, and drill holes for
mounting screws around the perimeter.
-Carleton A. Phillips
138

Electronic Experimenter's Handbook

CATHODE
J2

ANOJIDE

SCR Tester
(Continued from page 124)

GATE\y'/J3
SI

03
R2
REVERSE

Thus, lighting of the "Forward" lamp
as soon as the SCR is connected into the
circuit indicates failure of the forward
blocking junction. Lighting of the "Reverse" lamp at any time indicates breakdown of the reverse blocking junction.
If neither lamp lights when the SCR is
connected into the circuit, the "Test"
push button is operated, applying a
source voltage to the gate.
The "Forward" lamp should light under these circumstances if the SCR is
good. If this lamp does not light when
the button is depressed, the gate is either
open or shorted.
This tester applies about 35 peak volts
to the SCR anode so that higher voltage
capabilities of the unit are not indicated.
With very small SCR's, heat sinking
may be necessary.
The device can also be used to test
ordinary rectifiers by connecting them

YOUR NEW
COPY IS

WAITING

FORWARD

PARTS LIST
200 -volt capacitor
DI, D2, D3 -100 -volt, 1.6 -amp. silicon rectifier
C1 -0.05-µf.,

(1X1218)
indicator lamp (Dialco 81410-112-green-or equivalent)
12-#47 indicator lamp (Dialco 81410-111red-or equivalent)
11, 12, J3-Binding post (Johnson 111-101,
111-102, 111-103, or equivalent)
R1 -100 -ohm, 1 -watt resistor
R2 -50 -ohm, 10 -watt resistor
R3, R4, -75 -ohm, 5 -watt resistor
SI-Normally open push-button switch 1 amp.
TI-Filament transformer, 25.2 volts @
secondary (Stancor P-6469 or equivalent)

I1-#47

across the "Anode" and "Cathode" terminal posts. With the rectifier properly
connected, a good one will light the
"Forward" indicator lamp, an open one
will keep both lamps off, and a shorted
one will make both lamps come on. -i[-

FREE! For fun and pride in assembly, for long
years of pleasure and performance, for new adventures in creative electronics mail the coupon
below and get Conar's brand new catalog of
quality do-it-yourself and assembled kits and
equipment. Read about items from TV set kits
from VTVM's to scopes
to transistor radios
.. from tube testers to tools. And every item
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no -loopholes, money -back guarantee! See for
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CIRCLE NO. 19 ON READER SERVICE CARD
1965 Fall Edition

139

Transistor Voltmeter
(Continued from page 129)

voltmeter is largely determined by the
input resistor string, resistors R2 through
R9 should be stable and preferably have
an accuracy of -±1.0%. Of course, if you
have access to a bridge, standard ±5%
resistors can be measured and very close
values selected on this basis.
Resistor R13 must be selected so that
potentiometer R14 will adjust near its
center position to set meter M1 to a zero
deflection. The value of R13 may vary
from 1000 to 5000 ohms, but once set it
will need no further adjustment.

Construction and Calibration. The voltmeter can be built on a single piece of
phenolic board and attached to the back
of meter MI through the meter input
terminals. Except for the resistor in the
probe, all of the resistors can be mounted
to the board with Vector terminals and
soldered in place. The layout should
approximate that in the photo to eliminate the possibility of leakage paths in
the input part of the circuit.
The final accuracy of the voltmeter
depends on the values of resistors R2
through R9 as well as a calibrating voltage source. Ideally, a digital voltmeter
of known accuracy and a variable d.c.
voltage source should be used. However,
initial calibration with several 1.34 -volt
mercury batteries may be used to set
the 0-5 volt scale. Full-scale sensitivity
is adjusted by varying potentiometer
R12 and locking it into position once
satisfactory calibration has been estab-

lished.

Solder resistor R1 to pin of probe and slip it inside red handle. Probes need not be reversed to reverse polarity; this is accomplished through S2.

smek

"One at

VERNIER DIALS

-9 to 1 and

Combination 36 to
MODEL
NUMBER

TURNS
RATIO

$ 8.25
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9 to

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6
6

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tot&6to1

*Dial allows fast tuning at a
the 36 to 1 ratio over any

J. W.

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PRICE

9 to

36
36

& 6 to

NO. OF
SCALES

D-6
MD -7"
M D-8*

6 to 1 ratio with
6 -division portion

$15.00
$15.00
fine tuning at
of the scale.

MILLER COMPANY

59.17 So. Main Street

140

M D-5
M

scum,'

time, Mister!"

CIRCLE NO. 16 ON READER SERVICE CARD

Los Angeles, California 90003
Electronic Experimenter's

Handbook

Thinking of college and

Resonance Engine

(Continued from page 92)

space age career in

electronics ?
90). Although the weight of the flywheel should not be too critical, some
experimenting may be in order. The
author's was made of aluminum and
weighed about 15 ounces. Drill and tap
one end of the flywheel shaft for a 6-32
machine screw and thread the opposite
end with a 1"-20 die.

The flywheel shaft bearing-a 11/2"
brass rod 1/2" in diameter with a 1/4" hole
drilled through the center-is mounted
in the bracket shown in Fig. 7 and in
the assembly drawing. The bracket is
made with a stiffening buttress so that
it will stand up under the vibration of
the engine. In the author's unit, the
bracket was mounted to the coil platform
by tapping three small pieces of brass
rod and cementing them into holes
drilled into the bottom of the bracket.
Wing bolts thread into the holes from
the bottom of the coil platform, making
it easy to disassemble the engine for
other experiments. In any case, drill a
1/2" hole in the bracket at the height
shown in Fig. 7, and cement the bearing
in it with epoxy glue.
Mounting Stand. Make a double -deck
stand as shown in the photos and secure
the capacitors, Cl, C2, C3, to the lower

section. Mount the d.p.d.t. toggle switch,
Si, and four pin jacks, J1, J2, J3, J4,
on the upper deck of the stand in front
of the coil position. Drill holes in the
upper deck for coil leads, coil mounting
screws, bracket mounting screws, and
for the engine piston. The piston hole
should be large enough to provide ample
clearance.
Mount all of the parts on the stand
as shown in the assembly view on page
92. Solder the end of the flywheel shaft
to the end of the crankshaft where the
two join together. To hold the long 12"
core in place for repulsion coil experiments, drill and tap the top disc for a
setscrew that extends from the outer rim
into the center hole.
Connect the parts as shown in the
schematic diagram on page 92. You will
note that the diagram shows a "discharge" position for 21. This is a safety
1965 Fall Edition

141

Send for this booklet on
ENGINEERING TECHNOLOGY
AND ENGINEERING
Learn how you can prepare for a dynamic
career as an electrical or mechanical engineering technician or engineer in such
exciting, growing fields as avionics, missiles, reliability control, fluid mechanics,
data processing, metallurgy, microelectronics, and advanced aerospace research.
MSOE offers residence study programs
leading to these degrees in engineering
technology and engineering:
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4 years
Also get facts about scholarships and financial aids, job placement and other
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just mail the coupon
no obligation.

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Milwaukee, Wisconsin 53201
Please send the "Your Career" booklet.
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n Electrical fields
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ZIP
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CIRCLE NO. 17 ON READER SERVICE CARD

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Receiving Tube Specifications and Substitutions
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Transistor Specifications and Substitution Handbook lists over 5,000 American and foreign types,
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Experimenters Handbook 1965 Fall

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