Experimenters Handbook 1966 Fall

BUILD FROM COMPLETE PLANS

Panic Alarm- CD Ignition System

Smoke Detector-99c Speaker B

TV Tube Tester - Electronic St

and dozens more

ELECTRONICS TRAINING

Home Study vs Resident Schools +

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1967

CATALOG NO.

670

FIVE BETTER ELECTRONICALLY WITH LAFAYETTE

1967

OUI 45th VIII

,at SIS

Live Belles Effect, ,C.I /' Wrth

LAFAYET

RADIO ELECTRONICS

Over 500 Pages

ERE

OT r:: S' ' ;: ......, ,...

\ U..,

...Kï a,,, . _ ,...

'

TV Tubes and Parts

Electronic Parts

Test Equipment

C.B. 2 -Way Radio

Tools

Ham Gear

Stereo Hi -Fi

Tape Recorders

Walkie- Talkies

Auto Accessories

Featuring Everything in Electronics for

HOME INDUSTRY LABORATORY

from the "World's Hi -Fi & Electronics Center"

LAFAYETTE'S

MAIL ORDER &

LONG ISLAND

SALES CENTER

LAFAYETTE Radio ELECTRONICS

Dept. EHJ -6, P.O. Box 10

Syosset, L. , N.Y. 11791

Send me the Free 1967 Lafayette Catalog 670

....... - - - - - - - = r

Dept. EHJ -6

Name

Address ________ ..... - ______________

City State

Zip 1

(Please Give Your Zip Code No.)

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111 Jericho Turnpike

Syosset, L. I., New York 11791

OTHER LOCATIONS

NEW YORK NEW JERSEY MASSACHUSETTS

Bronx Newark Boston

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Jamaica Plainfield Saugus

Manhattan

Scarsdale

Syosset WASHINGTON, D.C. CONNECTICUT

(Area) Hamden

PENNSYLVANIA Falls Church, Va. W. Hartr ^r

Pittsburgh Mt. Rainier, Md.

CIRCLE NO. 18 ON READER SERVICá CARD

MN

Introducing EICO's New "Cortina Series "!

Today's electro- technology makes possible near -perfect

stereo at moderate manufacturing cost: that's the de-

sign concept behind the new EICO "Cortina" all solid -

state stereo components. All are 100% professional,

conveniently compact (31/2"H, 12 "W, 8 "D), in an

esthetically striking "low silhouette." Yes, you can pay

more for high quality stereo. But now there's no need

to. The refinements will be marginal and probably

inaudible. Each is $89.95 kit, $119.95 wired.

Model 3070 All- Silicon Solid -State 70 -Watt Stereo

Amplifier: Distortionless, natural sound with unre-

stricted bass and perfect transient response (no inter -

stage or output transformers); complete input, filter

and control facilities; failure -proof rugged all- silicon

transistor circuitry.

Model 3200 Solid -State FM /MPX Automatic Stereo

Tuner. Driftless, noiseless performance; 2.40 for 30db

quieting; RF, IF, MX are pre -wired and pre -tuned on

printed circuit boards - you wire only non -critical power

supply.

7 New Ways to make Electronics more Fun!

Save up to 50 % with EICO Kits and Wired Equipment.

You hear all the ar l P r

t'., NEW F-

4 -Band Short Ware L

plus ham operators, ship-to-shore, aircraft,

Coast Guard, and the full AM band. 550KC to

30MC in four bands. Selective, sensitive super -

het, modern printed circuit board construction.

Easy, -fast pinpoint tuning: illuminated slide -

rule dials, logging scale; "S" meter, electrical

bandspread tuning, variable BF0 for CW and

SSS reception, automatic noise limiter. 4"

speaker. Headphone jack. Kit $49.95, Wired

$69.95.

d, r

"the best ham

transceu"r by for 196e" - Radio TV Experi-

menter Magazine. 200 watts PEP on 80, 40 and

20 meters. Receiver offset tuning, built -in VOX,

high level dynamic AEC, silicon solid -state YFO.

Unequaled performance, features and appear-

ance. Sensationally priced at $199.95 kit,

$299.95 wired,

f._"

Model 460 Wideband Direct -Coupled

5" Oscilloscope. DC-4.5mc for color

and 85W TV service and lab use. Push -

pull DC vertical amp., bal. or unbal.

input. Automatic sync limiter and amp,

$99.95 kit, $139.50 wired.

NEW ctOO 623 S oiic -State

Engine Analyzer

Now you can tune -up, trouble-

shoot and test your own car or

boat.

Keep your car or boat engine in

tip -top shape with this completely

portable, self- contained, self -

powered universal engine ana-

lyzer. Completely tests your total

ignition /electrical system. The

first time you use it - just to tune

for peak performance - it'll have

paid for itself- (No tune -up

charges, better gas consumption,

longer wear) 7 instruments in

one, the EICO 888 does all these

for 6V and 12V systems; 4, 6 &

8 cylinder engines.

The EICO 888 comes complete

with a comprehensive Tune -up

and Trouble- shooting Manual in-

cluding RPM and Dwell angle for

over 40 models of American and

Foreign cars. The Model 888 is

an outstanding value at $44.95

kit, $59.95 wired.

r- FREE 1967 CATALOG

CRAFT New EICOCRAFT easy -

to-build solidstate elec-

tronic TruRitsr. great

for beginners and

sophisticates alike. As

professional as the

standard EICO line -

only the complexity Is

reduced to make kit -

building faster, easier,

lower cost. Features:

pre -drilled copper -

plated etched printed

circuit boards; finest parts; step -by -step in-

structions; no technical experience needed -

just soldering iron and pliers. Choose from: Fire

Alarm; Intercom; Burglar Alarm; Light Flasher;

"Mystifier "; Siren; Code Oscillator; Metronome;

Tremolo; Audio Power Amplifier; AC Power Sup-

ply. From $2.50 per kit.

15. -r PUNCH ,r new EICO ' Sentinel -

Pro" 23- channel Dual Conversion 5 -wait CB

Transceiver. New advanced Big -Reach "Range

Plus" circuitry lengthens "talk- power" reach.

Automatic noise limiter super- sensitizes for weak

signals. "Finger Tip" antenna loading and trans-

mitter tuning controls. 23 crystal -controlled

transmit and receive channels - all crystals

supplied. Rear -illuminated S /RF meter. Tran-

sistorized 12VDC and I17VAC dual power supply.

Wired only, $169.95. Positive- Negative Ground/

Mobile Marine Modification kit (optional 55.95).

EICO Electronic Instrument Co., Inc.

131 -01 39th Ave., Flushing. N. Y. 11352

Send me FREE catalog describing the. full EICO line of

200 best buys, and name of nearest dealer- I'm inter

ested in:

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CIRCLE NO. 7 ON READER SERVICE CARD

Model 232 Peak -to -Peak VTVM. A must

for color or B &W TV and industrial

use. 7 non -skip ranges on all 4 func.

tions. With exclusive Unl- Probe.®

$29.95 kit, $49.95 wired.

1966 Fall Edition 1

NO SPECIAL TOOLS REQUIRED

LIGHT UP THE NIGHT

With RCA's EXPERIMENTER'S KIT

Build Your Own Light -Operated Switch

for Dozens of Applications Around the House

Just let your imagination soar -and you'll trigger your

own application ideas for any of the 14 control circuits

you can build with only three RCA Experimenter's Kits.

For instance, you can build a light- operated switch for a

garage light, a yard or path light, or even an advertising

sign that can be activated with lights from an approach-

ing automobile! You can also build a model race car

speed control, an electronic heat control and other inter-

esting circuits with hundreds of applications. All these

circuits with easy -to- follow directions are described in

the RCA Experimenter's Manual, KM -70, available from

your RCA Semiconductor Distributor.

HERE IS WHAT YOU NEED...

RCA Basic Experimenter's Kit (KD2105). Containing

one silicon controlled- rectifier; two transistors; five

rectifiers.

RCA Experimenter's Manual (KM -70). 80 pages pro-

fusely illustrated; 14 circuits -how they operate and

how to build them.

RCA Add -On Light Sensor Kit (KD2106). Containing one

photocell for light- operated circuits.

RCA Add -On Heat Sensor Kit (KD2110). Containing

three thermistors for different temperature ranges;

special solder for heat control circuits.

Readily available passive components and hardware.

2

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 Rail-

road Speed Control. 7. Light- Operated Switch (Turn -On).

8. Light- Operated Switch (Turn -Off). 9. Electronic Heat

Control (Turn -On). 10. Electronic Heat Control (Turn -Off).

11. Overload Switch, 12. Electronic Synchronous Switch.

13. Universal Motor Speed Control, 14. Lamp Dimmer.

d..

! tSflJS1N11kII

easuu

roi

If you want to build one circuit or all 14, check with your

RCA Distributor where kits and RCA Experimenter's Man

ual are on display. He'll be glad to help you select the

kit or kits for the solid -state circuit you have in mind.

Do it today!

AVAILABLE FROM YOUR RCA SEMICONDUCTOR DISTRIBUTOR

RCA Electronic Components and Devices. Harrison, N.J.

The Most Trusted Name in Electronics

CIRCLE NO. 22 ON READER SERVICE CARD

ELECTRONIC EXPERIMENTER'S HANDBOOK

l 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 KALAWSKY

Editorial Assistant

PATTI MORGAN

Editorial Assistant

LAWRENCE SPORN

Advertising Soles Manager

ARDYS C. MORAN

Advertising Service Manager

ZIFF -DAVIS PUBLISHING COMPANY

Editorial, Circulation, and Executive Offices

One Park Avenue, New York, New York 10016

212 679 -7200

Eastern Advertising Manager, RICHARD J. HALPERN

Midwestern Office

307 North Michigan Avenue, Chicago, Illinois 60601

312 726 -0892

Midwestern Advertising Manager, JAMES WEAKLEY

Western Office

9025 Wilshire Boulevard, Beverly Hills, California 90211

213 CRestview 4 -0265; BRadshaw 2 -1161

Western Advertising Manager, BUD DEAN

Japan: James Yogi

c/o Sekihara

1, Sakamachi, Shinluku -ku

Tokyo, Japan

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

William Ziff, President

W. Bradford Briggs, Executive Vice President

Hershel B. Sarbin, Vice President and General Manager

Philip Sine, Financial Vice President

Walter S. Mills, Jr., Vice President, Circulation

Stanley R. Greenfield, Vice President, Marketing

Phillip T. Heffernan, Vice President

Frank Pomerantz, Vice President, Creative Services

Arthur W. Butzow, Vice President, Production

Edward D. Muhlfeld, Vice President

Member Audit Bureau

of Circulations

1966 ELECTRONIC EXPERIMENTER'S HANDBOOK, Fall

Edition, published by the Ziff -Davis Publishing Com-

pany, 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.

FALL EDITION

EL

19660

R6N6ELECTRONIC

POPULAR

EXPERIMENTER'S

IN VIEW OF THE PRESSING DEMAND

FOR TRAINED ELECTRONICS TECHNI-

CIANS, A SPECIAL TWO -PART STORY

HAS BEEN ADDED TO THIS EDITION

-THE TWELFTH -OF THE ELECTRONIC

EXPERIMENTER'S HANDBOOK. THE UN-

DISGUISED PURPOSE OF THIS PARTIC-

ULAR STORY IS TO ENCOURAGE MORE

ELECTRONICS HOBBYISTS TO SERIOUS-

LY CONSIDER A FULL -FLEDGED CAREER

IN THIS EXPANDING FIELD. THE STORY

DISCUSSES HOME -STUDY TRAINING VS.

ATTENDING A RESIDENT ELECTRONICS

TRAINING INSTITUTE. I URGE YOU TO

READ THIS IMPORTANT STORY. FUR-

THERMORE, THERE IS A FOLLOW -UP

STORY BY THE SAME AUTHOR IN THE

OCTOBER, 1966, ISSUE OF POPULAR

ELECTRONICS. THIS LATTER STORY IS

AN ANALYSIS OF JOB OPPORTUNITIES

FOR HOME -STUDY AND RESIDENT

SCHOOL GRADUATES. IF YOU ARE IN-

TERESTED IN ESTABLISHING A WELL -

PAYING TECHNICIAN'S CAREER IN ELEC-

TRONICS, THESE ARTICLES WILL TELL

YOU HOW MUCH TIME AND MONEY

YOU CAN EXPECT TO SPEND AND WHAT

YOUR EARNING POTENTIAL WILL BE

AFTER GRADUATION.

AS ALWAYS, THE EDITORIAL STAFF

OF THE ELECTRONIC EXPERIMENTER'S

HANDBOOK WILL APPRECIATE YOUR

COMMENTS AND SUGGESTIONS FOR THE

NEXT EDITION. OLIVER P. FERRELL

EDITOR

1966 Fall Edition 3

INTERNATIONAL

CRYSTALS

the first

choice

of the

Radio

Amateur

THE AMATEUR WHO SELECTS INTERNATIONAL CRYSTALS FOR HIS

COMMUNICATION GEAR PROBABLY KNOWS THESE IMPORTANT FACTS:

Every amateur crystal is manufactured by

the same skilled craftsmen who make Inter-

national commercial crystals.

International crystals are the product of a

continuing research and development pro-

gram.

International crystals are designed and man-

ufactured to operate under all types of field

conditions . . . fixed or mobile.

International crystals are used in all major

makes of commercial two -way radio equip-

ment.

International customers include broadcast

stations, airlines, military services, Civil Air

Patrol, taxicabs.

International crystals and electronic com-

ponents are used in the United States mis-

sile and space research program.

All International crystals are guaranteed

against defective materials and workman-

ship for an unlimited time when used in

equipment for which they were specifically

made.

Whether you're an amateur building your first transmitter or an engineer with special

crystal requirements, you can look to International for precision frequency control.

KEEPING YOU ON FREQUENCY IS OUR BUSINESS!

INTERNATIONAL

CRYSTAL MFG. CO., INC.

Write today for a FREE CATALOG of International

precision made crystals and quality electronic equipment.

International Crystal Mfg. Co., Inc.

18 North Lee

Oklahoma City, Oklahoma 73102

NAME

ADDRESS

1E3 NO. LEE OKLA_ I ITV, OKLA 71'02 CITY STATE ZIP

CIRCLE NO. 11 ON READER SERVICE CARD

4 ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER

1

USEFUL

PROJECTS

2

AUTOMOTIVE

ELECTRONICS

3

ELECTRONICS

SCHOOLS

4

AUDIO

STEREO

HI -FI

PROJECTS

5

COMMUNI-

CATIONS

SWL

CB

HAM

TIPS

AND

TECHNIQUES

ELECTRONICS

MARKETPLACE

7

TV PICTURE TUBE TESTER AND REJUVENATOR -

LUMEMIN STEALS THE SHOW- FAIL -SAFE TRANSISTOR

POWER SUPPLY -CHRISTMAS LIGHTS TWINKLE TO

MUSIC -SMOKE ALARM FOR YOUR HOME- SUPER-

SENS -FREEZE MOTION WITH SOUND -LET THE SUN

POWER YOUR PORTABLE- SUPER -X PULSE POWER

PACK FOR HO RAILROADING -LI'L DUSKER: THE LIGHT

WATCHMAN -SOLID -STATE SLOT CAR SPEED CONTROL

-ELECTROLOCK -DON'T PANIC ... PUSH THE BUTTON

63

A UNIVERSAL CD IGNITION SYSTEM -PROTECT YOUR

CAR'S ELECTRICAL SYSTEM -HEADLIGHTS -ON ALARM

-AUTO VOLTMETER SHOWS YOU'LL GO

75

OPERATION ACTIVATE: PART 1- GETTING YOUR TRAIN-

ING IN RESIDENT SCHOOLS; PART 2 -HOME -STUDY

TRAINING

93

TOTEM POLES FOR STEREO -HI -FI A GO -GO LAMPS -

"CINDERELLA" -SOLID -STATE 6 -WATT AMPLIFIER FOR

10 BUCKS -UNIQUE 99¢ SPEAKER ENCLOSURE

115

CAMPER'S SPECIAL -SUPER SELECTIVITY FOR YOUR

RECEIVER -"WATCHDOG" MOBILE MONITOR -DUAL-

SENSITIVITY FIELD STRENGTH /ABSORPTION METER

Copyright i[ 1966 by Ziff-Davis Publishing Company.

129

151

5

3 more

features

-all new

Here is RCA's new WR -50B RF Signal

Generator -wired or kit. It looks just

like the old WR -50A, but the resem-

blanceends there. It has all the features

you liked in the older model...plus 3

new ones you'll find in red below:

Wide frequency range from 85kHz to

40MHz in 6 overlapping ranges plus

harmonics for higher frequencies

Built -in crystal calibrating oscillator

circuit with front panel crystal socket

Internal 400 Hz audio oscillator

NEW -Sweep output at 10.7 MIL with

return trace blanking for sweep align-

ment of FM receivers

NEW -Sweep output at 455 kHz with

return trace blanking for sweep align-

ment of new transistorized AM radios

Individual inductance and capacitance

adjustments for each range

Modulation level control

Two -step RF attenuator switch plus a

continuously -variable attenuator control

NE,1V- additional switch for further

attenuation of crystal oscillator Output

The Optional Distributor Resale Price

is only $65.00. Kit Form, $45.00, includes

pre -assembled range switch with pre -

aligned coils and trimmers. See the RCA

WR -50B at your authorized RCA Test

Equipment Distributor.

RCA ELECTRONIC COMPONENTS AND DEVICES, HARRISON, N.J.

The Most Trusted Name in Electronics

CIRCLE NO. 23 ON READER SERVICE CARD

K

CHAPTER

1

USEFUL

HOUSEHOLD

PROJECTS

1966 Fall Edition

It is not unlikely that the arbitrary definition of "House-

hold" projects has been stretched out of shape in this edi-

tion of the ELECTRONIC EXPERIMENTER'S HANDBOOK.

However, the common denominator in selecting these

projects is still valid -they are all things that might be

seen around the electronically -oriented household. The

projects have been mixed so that there is something here

for father or brother in his workshop, a couple of pre -teen

projects, at least two that should delight your mother,

and a couple that are just plain general -purpose units.

Our cover photo shows the very popular version of the

hi -fi color organ designed and constructed by Leon Wort -

man ( "Christmas Lights Twinkle to Music "). Unlike the

lights for many other color organs, these are not some-

thing you buy extra -they're the lights on your Christmas

tree. If you're looking for something novel and attractive,

we urge you to give this particular project consideration.

8

TV PICTURE TUBE TESTER AND REJUVENATOR Jeff H. Taylor

14

LUMEMIN STEALS THE SHOW Louis E. Garner, Jr.

18

FAIL -SAFE TRANSISTOR POWER SUPPLY

Edward Nawracaj and Fred Forman

21

CHRISTMAS LIGHTS TWINKLE TO MUSIC

25

SMOKE ALARM FOR YOUR HOME

Leon A. Wortman

H. St. Laurent

Louis E. Garner, Jr.

Roy E. Pafenberg

Homer L. Davidson

29

SUPER -SENS

39

FREEZE MOTION WITH SOUND

43

LET THE SUN POWER YOUR PORTABLE

45

SUPER -X PULSE POWER PACK FOR HO RAILROADING

Woodrow Pope

51 LI'L DUSKER -THE LIGHT WATCHMAN Don Lancaster

55 SOLID -STATE SLOT CAR SPEED CONTROL James Fishbeck

Murray E. Coultes

58

ELECTROLOCK

60 DON'T PANIC ... PUSH THE BUTTON Bruno M. Larsen

7

DOES YOUR TV set "smear" when

you try to turn up the brightness to

a comfortable viewing level ? Do the

whites seem to become silvery? Is your

picture so dim that you have to pull the

shades or wait for nightfall to watch a

program? Does it take a long time for

the brightness level to come up? Is it

impossible to vary the brightness level?

Does the picture tube seem to go on and

off? If the answer is yes to any or all

of these questions, you probably have a

"sick" picture tube.

While there are many different types

of tests performed by the picture tube

manufacturer, three types are usually

made in the field: open -short, emission,

and grid control tests. You can make

all of these tests reliably and quickly,

and also "rejuvenate" a "tired" picture

tube with this easy -to -build TV Picture

Tube Tester and Rejuvenator. The parts

are inexpensive and readily available.

HOW IT WORKS

Opens and Shorts. The open -short test

is shown in the simplified diagram in

Fig. 1. In this test a.c. voltage is ap-

plied to the cathode, and to each element

in the tube, one at a time, through a

neon lamp. Each of the elements acts

like an anode with respect to the cathode,

as in an ordinary diode. Since half the

a.c. voltage waveform is passed by the

diode so formed, only one half of the

neon lamp will glow.

Should the element be shorted to the

cathode, current will flow in both direc-

8

BUILD A

TV PICTURE TUBE

tions and both halves of the lamp will

glow. Should the element be open, no

current will flow and the lamp will not

glow. In the heater -cathode check, however,

the lamp will not glow even on one

side when conditions are normal. The

inside of the cathode cylinder is not

coated with the activated emitting ma-

terial and very little current will flow.

A shorted condition will be indicated as

in the other tests ... both halves of the

neon lamp will glow.

Emission. The emission check is shown

in the simplified diagram in Fig. 2. The

control grid is tied to the cathode and

an a.c. voltage is applied to G2 through

a d.c. ammeter and series resistor. The

amount of current that flows (during

each positive half cycle) is a relative

indication of the electron emission

capability of the cathode.

Grid Control. The grid control test is

similar to the emission test except that

instead of having a zero grid bias as

used in the emission test, a negative

voltage is applied to the control grid as

shown in Fig. 3. As the control grid

voltage is made more negative, less G2

current flows. When the control grid

(G,) voltage is made sufficiently nega-

tive, no current will flow and the tube

will be cut off.

The amount of negative voltage re-

quired to achieve cutoff indicates the

relative contrast range of the picture

ELECTRONIC EXPERIMENTER'S HANDBOOK

6

It's easier to plug in

a tester than it is

to change a picture tube

By JEFF H. TAYLOR

TESTER AND REJUVENATOR

SIMPLIFIED CIRCUITS

Fig. 1. Neon lamp indicator shows leakage, shorts,

and opens between each element and the cathode.

G2 l

Fig. 2. Meter reads relative emission. Tests made

at 1- minute intervals show warm -up characteristics.

Fig. 3. Grid control is determined by the amount of

negative voltage needed on G1 to obtain cutoff.

T

Fig. 4. Momentary application of a high d.c. poten-

tial across the cathode and G1 can boost emission.

tube. A tube that will cut off with a

small voltage will produce a more con -

trasty picture than one that requires a

larger voltage. In a 3 -gun color tube, it

is possible to determine if all the guns

will cut off at the same potential, or the

degree of imbalance, if any.

Rejuvenation. The cathode of a picture

tube is a small metal cylinder with an

external coating of emitting material.

The heater is essentially a coiled wire

and is placed inside the cathode cylin-

der. As the picture tube is used, the

outermost activated material on the

cathode becomes deactivated and its

ability to emit is reduced accordingly.

The process of rejuvenating the picture

tube removes some of the deactivated

coating from the cathode and allows the

unused material beneath this "scab" to

once again emit a good electron beam.

This is accomplished by causing a heavy

current to flow from the cathode to G1--

by placing a relatively high potential

across the control grid and the cathode,

for a very short period of time, as shown

in Fig. 4.

If the tube is very weak, sufficient

current may not flow to rejuvenate the

cathode. Increase the filament voltage

one step and try again. When the

REJUVENATE button is depressed, you

may see sparks fly inside the picture

tube in the vicinity of the cathode. This

is caused by the "dead" material being

"stripped" off the cathode.

In a 3 -gun color CRT, each gun in

1966 Fall Edition 9

SI

117 VAC HTR

GRIDI

GRID2

S3 EMISSION

CUT -OFF

REJUVENATE

Fig. 5. When testing tubes, fol-

low the sequence shown on S3,

starting with HTR. Do not reju-

venate unless you have to. The

first three positions help 12

"look" for opens, leakage, and

shorts, and should be used

when the tube is cold and again

when the tube is hot. Push -to-

rejuvenate switch S4 is used

only when S3 is in the rejuve-

nate position. Wiring of the fila-

ment circuit is shown in Fig 7.

54

S3A

536

DI D2

NIN2071

mIN2071

R3

I MEG.

R2

/ 6.8K NE48

10K a MI

0- 5O0ya

03

IN2071 R4

68K

C2

.5°f.

7

S3C

CI

.I

S3D , Vf

T

-J

6.3V

RS

1.2R

R6

1.5f1

V

B

G2

PARTS LIST

1000 -volt paper capacitor (two 0?-

µf., 600 -volt capacitors in series or two 0.05-

µf., 1600 -volt capacitors in parallel)

C2- 0.5 -µf., 600 -volt paper capacitor

D1, D2, D3-1N2071 silicon rectifier

F1-11/2-ampere fuse

11- .VE -51 neon lamp

12- .VE -48 neon lamp

M1 -0 -500 microampere meter (Simpson ,Model

27 or equivalent)

RI- 10,000 -ohm, % -watt resistor

R2- 6800 -ohm, % -watt resistor

R3- 1000 -ohm. V2-watt resistor

R4- 68,000 -ohm, % -watt resistor

R5 -1? -ohm, 2 -watt resistor

R6 -1.5 -ohm, 2 -watt resistor

R7- 100,000 -ohm potentiometer

S1- S.p.s.t. toggle switch

S2 -4 -pole, 9- position rotary switch (Centralab

P.4 2013 or equivalent)

S3-4 -pole. 6- position rotary switch (Centralab

P.1 2011 or equivalent)

S4- Normally -open push- button switch (Grayhill

23 -1 or equivalent)

TI -Power transformer: primary, 117 volts; sec-

ondaries, 470 volts CT 3 40 ma.; 5 volts

2 amp.; and 6.3 volts CT n 2 amp. ( Stautor

PC 8401 or equivalent)

1- Cabinet (Bud WA 1540 or equivalent)

1 -2" x 5" x 7" chassis

Misc. -CRT sockets and adapters, fuse holder,

line cord, knobs, etc.

10

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

larity. Most of the components are panel- mounted.

ELECTRONIC EXPERIMENTER'S HANDBOOK

6.3v

turn can be treated in this manner. Ap-

propriate adapters and switching ar-

rangements to accommodate multi -gun

tubes, or any tube having a different

base or basing arrangement, can be

added to the tester. If you are careful,

and if you don't have an appropriate

socket, you can use clip leads or patch

cords to make connections to the CRT

pins.

CONSTRUCTION

Any convenient layout of parts can be

used in building the tester /rejuvenator.

The wiring is straightforward, except

for the filament wiring. The phase of

POSITION

I

VOLTAGE

1.3

2 1.85

3 2.25(600mo.)

4 2.61(450mo.)

5 3.15

6 5

7 6.3

8 8.15

9 11.3

Fig. 7. Windings are made to aid or oppose each

other to obtain six more filament voltage levels.

1966 Fall Edition

the transformer's filament windings

must be determined before the filament

switch can be wired.

To determine the phase, first tape the

leads from the high -voltage secondary

winding to avoid accidental contact, and

do the following:

(1) Connect one of the 6.3 -volt leads

(not the C.T.) to one of the 5 -volt leads.

(2) Connect the primary to 117 volts.

(Be sure that the other transformer

leads are not touching each other.)

(3) If an a.c. voltmeter is available,

measure the voltage between the two un-

connected (not the C.T.) filament leads.

If this voltage measures about 11 or 12

volts, label the 6.3 -volt lead to which

the meter is attached "A "; label the 5-

volt lead to which the meter is attached

"G"; label the other 6.3 -volt lead "C ",

and the other 5 -volt lead "F ". If the

meter voltage measures 1 or 2 volts,

label the 6.3 -volt lead to which the meter

is attached "A "; label the 5 -volt lead to

which the meter is attached "F"; label

the other 6.3 -volt lead "C ", and the

other 5 -volt lead "G ".

In the absence of a voltmeter, a 12-

volt panel lamp can be used as a voltage

indicator. The bulb will glow brightly

when the winding phase produces 11

volts, and will glow almost impercepti-

bly-if at all -when the winding phase

produces 1 volt.

Wiring is considerably easier if the

switches are wired before installation.

The neon lamp is supported by its

terminals.

Fig. 8. Observe polarity of D3 or you'll put a posi-

tive voltage on G1 and possibly ruin your meter.

11

Fig. 9. Test cable can be fed through the panel,

or plugged into a front -mounted octal socket. Pic-

ture tube socket adapters can be added as needed.

The on -off switch, panel lamp, and

grid -bias potentiometer are mounted

through the front panel and the chas-

sis, and serve to hold the panel and

chassis together. The filament and func-

tion switch are mounted on the front

panel and are held securely in place

with lock washers.

OPERATING INSTRUCTIONS

Open and Short Tests

(1) Select proper filament voltage.

(2) Connect the socket to the CRT.

(3) Turn the power switch to ON and

allow approximately 30 seconds for the

tube to warm up. Look at the neck of

the tube to see if the heater is glowing.

If it is not, the problem may be a loose

connection in the picture tube base.

Often this condition can be corrected

by resoldering with solder containing

noncorrosive flux.

(4) Turn the selector switch to HTR.

If the heater is not shorted to the

cathode, the neon lamp (12) in the cen-

ter of the tester will not glow. If it is

shorted, both sides of the lamp will

glow. (5) Turn the selector switch to GRID

1. If grid 1 is not shorted to the cathode,

one side of the neon bulb will glow. If it

is shorted, both sides of the lamp will

glow. If it is open, or if cathode emis-

sion is extremely low, the lamp will not

glow. (6) Turn the selector switch to GRID

2. If grid 2 is normal, one side of the

neon lamp will glow. If this grid is

shorted to the cathode, both sides of the

lamp will glow. If grid 2 is open, or if

cathode emission is too low, the lamp

will not glow.

Emission Test

(7) Turn the selector switch to

EMISSION. The meter should indicate

approximately 300 microamperes or

more for a good tube; however, a tube

that conducts 100 microamperes or

more will probably produce an accepta-

ble picture. (Some of the newer type

picture tubes designed to use higher G2

voltages may indicate "weak" when

they actually are not.)

Grid Control Test

(8) Turn the selector to CUT -OFF.

With the GRID CONTROL knob turned

fully counterclockwise, the meter should

indicate the same value as it did on the

emission check. Now advance the con-

trol clockwise until the meter registers

no current (or an extremely small cur-

rent). If the potentiometer has not ad-

vanced beyond the vertical mark, the

tube cutoff characteristic is acceptable.

In most cases, the tube will cut off well

below this mark.

Rejuvenation

(9) If the emission check indicated a

weak tube, turn the selector switch to

REJ. Depress the REJUVENATE but-

ton for approximately 1/2 second and re-

lease, then turn the SELECTOR switch

to EMISSION. If the tube now appears

normal, remove the tester. If the tube

still appears weak, increase the filament

voltage to the next higher voltage and

rejuvenate again. Reduce the filament

voltage to its normal value, wait about

a minute, and retest. If it does not now

appear usable, increase the filament

voltage one step higher and rejuvenate

again. If this all -out try doesn't help,

check emission with a higher than nor-

mal filament voltage. If this works, but

rejuvenation doesn't, install a picture

tube brightener. -

12 ELECTRONIC EXPERIMENTER'S HANDBOOK

DORY TECH NOT ONLY TRAINS

YOU . , . BUT HELPS YOU GET

STARTED AT NO EXTRA COST IN

THE PIG -MONEY FILL, OF

HOME LABORATORY EQUIPMENT

- YOURS TO KEEP!

ELECT©JJCSs

VPREPARE AT HOME

Whether you want to prepare for a good -paying new

job or for advancement in Electronics with your present employer,

DeVry Tech offers specialized educational programs designed to

meet your needs. You set up your own HOME LABORATORY

and work over 300 construction and test procedures to develop

on- the -job type skills. You build a quality Transistorized Meter,

a 5 -inch Oscilloscope and a special Design Console. DeVry also

includes modern "programmed" texts, instructive motion pic-

tures, Consultation Service. Effective? Yes!

l.

VRESIDENT SCHOOL

If you prefer you may get all of your training in DeVry's

U.S. or Canadian resident schools under the close guidance

of friendly, experienced instructors. You work with a wide variety

of commercial equipment similar to that actually used in in-

dustry as you prepare in our laboratories for a technician's job

in Communications, Microwaves, Radio -Television, Automation,

Radar, Computers, or other branch of Electronics. DeVry even

provides part-time job placement service to those who wish to

earn extra money while attending day or evening classes.

VPLACEMENT SERVICE

Meet W. E. Bartz, who has helped thousands of DeVry

men toward exciting, profitable careers in Electronics. When YOU

complete your program, he will help you too. As Placement

Manager in touch with business and industry across the nation,

Bartz knows the employer demand for DeVry- trained men. He

has cooperated in placing our graduates with thousands of

firms!

Men 18 -45, start preparing NOW for this vast opportunity field.

Soon you should be ready for DeVry's valuable employment help!

vanced

ducation or

Previous Technical

Experience Needed

to Get Started

ur ambition and desire to suc

are more important! DeVry

ides you every step of the way

ward success.

EVRY TECHNICA

141 Belmont Avenue

1966 Fall Edition

Free

Send coupon

for these two

factual book-

lets NOW!

L INSTITU

Chicago, Illinois 60

DeVRY TECHNICAL INSTITUTE

4141 Belmont Avenue, Chicago, Ill., 60641 Dept. EEH -2 -W

Please give me your two free booklets. "Pocket Guide to Real

Earnings," and "Electronics in Space Travel "; also include details

on how to prepare for a career in Electronics. I am interested in

the following opportunity fields (check one or more):

Space 8 Missile Electronics Communications

Television and Radio Computers

Microwaves Broadcasting

Radar Industrial Electronics

Automation Electronics Electronic Control

Name- Age

Address Apt Zip

City State Code

Check here if you are under 16 years of age.

HOME STUDY AND RESIDENT SCHOOL TRAINING

2103 AVAILABLE IN CANADA

CIRCLE NO. 6 ON READER SERVICE CARD

13

THE CURTAIN RISES and the spot-

light falls on the slender girlish figure

of the performer as she strolls graceful-

ly towards the center of the stage. She

stops behind a thin narrow box perched

atop a microphone stand and turns to

face the audience. Like a symphony con-

ductor, she raises her hands ... and on

the downbeat rich musical tones, chang-

ing in pitch and intensity with each wave

of the hand, fill the auditorium. She

plays marches, polkas, and operatic

themes without once ever touching the

music box.

Magic ? No. "Lumemin" is the word.

Using a pair of sensitive photocell "eyes,"

the Lumemin "sees" our performer as

she moves her hands up and down, caus-

ing varying amounts of light and sha-

dows to fall on its "eyes." In operation,

one photocell controls loudness while the

other controls the musical tones which

are rich in harmonics and sound some-

what like conventional brass, woodwind,

and string instruments.

The UJTO Circuit. The heart of the

Lumemin is a versatile UJTO (Unijunc-

tion Transistor Oscillator) module (Fig.

1), driven by a power supply and its

photoconducting circuit. The UJTO pro-

r

L J

a

F

Fig. 1. Modified sawtooth signal across points B

and E is fed to an external amplifier and speaker.

14 ELECTRONIC EXPERIMENTER'S HANDBOOK

LUMEMIN

STEALS

THE

SHOW

This easy -to -build

musical instrument

reads your hands

like a Gypsy

By LOUIS E. GARNER, JR.

AC

Fig. 2. Diagram of power supply and timing network

shows wiring connections to UJTO plug -in module.

1966 fall Edition

duces square -wave pulses as well as a

modified sawtooth signal rich in har-

monics. The latter is fed to an external

audio amplifier and speaker.

Referring to Fig. 1, an a.c. input ap-

plied across D and E is rectified by diode

Da and smoothed out by Ra and a 500 -

pf. capacitor (Ca) in the power supply

circuit. Zener diode Db limits any volt-

age surges from the power supply to

maintain a constant potential at the

unijunction transistor (UJT) base elec-

trodes through Rc and Rd.

Without emitter bias, the UJT is in a

nonconducting (high- resistance) state.

Capacitor Ca charges up through Rb and

a resistor in the power supply circuit

that appears effectively across A and B.

As Ca begins to charge, the emitter volt-

age increases gradually until its point of

conduction is reached. At this time, the

UJT is triggered and switches from its

nonconducting to a conducting state.

As the UJT conducts, Ca discharges

rapidly through the UJT and Rd, de-

veloping a positive -going pulse at B1

across Rd, and a negative -going pulse at

B2 across Rc. At the same time, a modi-

fied sawtooth waveform appears between

terminals B and E. With Ca discharged,

the UJT reverts to its high- resistance

(nonconducting) state and the entire

cycle is repeated.

The frequency (or repetition rate) of

the circuit is dependent on the RC time

constant of the components in the UJT

emitter circuit. Basically, this boils down

to the values of Ca, Rb, and the external

resistance between A and B, as men-

tioned earlier. The output appears across

points B and E.

The Other Components. Now, let's look

at the rest of the Lumemin's circuit

(Fig. 2) . The major components are an

isolating transformer (T1) and photo-

cells PC1 and PC2. Photocell PC1 is part

of the UJTO's timing network. It is

shunted by R1, and this shunt combina-

tion is in series with R2. Therefore, PC1

serves as the external frequency control

resistor. As PC1's resistance changes

with different light intensities, corre-

sponding changes take place in the

UJTO's frequency. Thus, the instru-

ment's tone is controlled essentially by

PC1. Recall from Fig. 1 that a modified

15

Fig. 3. Rear view of box used by author

shows attractive slide cover design finished

in gray aluminum. However, the builder

can select practically any size or shape

enclosure consistent with good appearance.

3/4"

T

TOP

Fig. 4. If you use the enclosure specified,

lay out the chassis and drill holes as shown.

17"

5 1/2"

5 /e"

DIA

I-1/4"

- TOP

I-I/2" ~ +-IJ8" 13DÌÁ'

3/4" \1/6 "014(4)

MOUNTING HOLES

I I I I/2,

I

1/2"

I-1/2"

3/32" I

DI4 I-1/2'

3/4"

13/32"

DIA

3/16 "DIA 7 /16"

}O

-4

_ 1/2"

3 /IG' I DIA

DIA

7/16" cf 3/4

T

o

2 -1/2"

2 -1/2'

-1.13/4"1-.1

sawtooth signal appears between termi-

nals B and E. It can be seen from Fig.

2 that this signal appears across R3 and

PC2 which are in series. The signal

across PC2 is coupled through C2 to

output jack JI which feeds an audio am-

plifier. Operation of PC2 is such that its

resistance decreases with the intensity

of the light shining on it. Therefore,

the amplitude of the output signal is

directly proportional to PC2's instan-

taneous resistance, and thus inversely

proportional to the light falling on the

device. Accordingly, maximum volume

is obtained with reduced lighting, while

a strong light produces little or no out-

put. Although the UJTO can be powered

PCI C2 CI PC2

directly by the a.c. line, isolation trans-

former Ti is used to insure greater safe-

ty and shock -free operation. Terminals

C and F on the UJTO's circuit board

(Fig. 1) are not used in this application.

Construction. Although the model shown

in Fig. 3 has been designed around an

attractive slide cover gray aluminum

box, and all layout and construction de-

tails are centered around this design,

the instrument can be housed in prac-

tically any type of enclosure, including

a wooden cabinet or plastic box.

Remove the cover and drill the holes

in the box following the layout and hole

dimensions given in Fig. 4. Mount J1,

Si, T1, PC1 and PC2 on the chassis as

STANDOFFS (4)

RUBBER FEET

16

JI UJTO PLUG -IN MODULE SI TI

Fig. 5. Electrical components are

first mounted on the perforated

phenolic board which is then

mounted on the chassis with four

standoff spacers. Orientation

must be as shown in diagram.

ELECTRONIC EXPERIMENTER'S HANDBOOK

t

TOP

TO PCI -0 PCI

501

TO PC2

6 -3/1.

SOT TOM

TO Ti

TO PCI

2.v6

SOI

Fig. 6. Phenolic board showing components mounted

on one side (top) and wiring details on other side.

PARTS LIST

C1- 500 -12f., 15 -volt electrolytic capacitor

C2 -2- o /., 200 -volt paper capacitor

11 -Open circuit phone jack

PC1, PC2 -CdS photocell (GE Type X6)

R1- 10,000 -ohm, % -watt resistor -see text

R2- 1000 -ohm, A -watt resistor -see text

R3- 470,000 -ohm, % -watt resistor -see text

S1- S.p.s.t. toggle switch

S01- Cinch -lanes bifurcated -contact edge con-

nector, Series 250, Type 50 -6A -20 (Newark

Electronics Stock No. 29F952 or Allied Elec-

tronics Stock No. 40 H 319)

T1 -115 -volt isolation transformer (Lafayette

Stock No. 33 G 7502)

CITO- Unijnnnction transistor oscillator module

(MS Type 5100 -4A- available for $5 from

Midland Standard, 161 E. Chicago St., Elgin,

Ill. 60120)

1 -3%" x 2%" x 17" slide cover utility box

(LD1B No. 19)

1 -6%" x 2 'A" perforated phenolic board

Mise. -Line cord and plug, rubber feet (4),

standoff spacers (4), push -in terminals, rubber

grommets (3), machine screws, nuts, wire,

solder, etc.

1966 Fall Edition

Fig. 7. When install-

ing the UJTO module

in the Cinch -Jones

connector (SO1),

make sure it is posi-

tioned with foil side

of the board facing

the chassis rim as

shown in Fig. 5, or

circuit will not work.

shown in Fig. 5. The photocells are

mounted in tight- fitting rubber grom-

mets, and the rubber feet can be put on

at this time. Use No. 6 self- tapping

screws, or if you prefer, machine screws

with nuts and flat washers. Transformer

T1 can be mounted with the same size

hardware. Then put the chassis aside,

temporarily.

You can now begin to assemble the

electronic components on the phenolic

board as shown in Fig. 6. On one side

of the board, mount the Cinch -Jones

socket (201) , and capacitors Cl and

C2, as shown in the top view. Wire the

other side of the board as shown in the

lower view. Refer to Fig. 2 for detailed

wiring information.

The only thing left for you to do is

to plug the UJTO module (Fig. 7) into

socket SO1 (Fig. 6) , and mount the elec-

tronic component board on the chassis

using four standoff spacers ( Fig. 5) .

Be sure to insert the module with the

foil side facing the chassis rim. Then

complete the interconnection wiring.

As a final touch, you can use decals

to label the controls and thus give the

instrument a commercially built appear-

ance. After the decals are put on, they

should be protected with two or three

coats of clear lacquer or acrylic plastic.

Using the Instrument. For personal

use or individual practice, a pair of

high- impedance magnetic or crystal

headphones can be plugged into J1. For

parties, or audience entertainment, you

will need a suitable audio amplifier/

loudspeaker system such as a guitar am-

plifier, a public address system, or a

standard hi -fi system. Simply connect

a suitable cable between J1 and the am-

plifier's high- impedance microphone jack.

The Lumemin should be placed in an

area where a moderately strong light

will fall on its photocells. The light

source can be an overhead lamp or a

sharply focused spotlight, as you prefer.

Since no warm -up is required (except

for the reproduction equipment used),

the moment you turn the instrument on

you can play individual notes by using

your hands to cast appropriate shadows

on the photocells. The lowest frequency

note is obtained when the tone photocell

(PC1) is in complete darkness, and the

(Continued on page 138)

17

BUILD A

FAIL-SAFE TRANSISTOR

POWER SUPPLY

By EDWARD NAWRACAJ and FRED FORMAN

It halts runaway transistors ... eliminates batteries .. .

restores itself instantly ... and dead shorts can't kill it

BY COMBINING a transistorized series -

regulated power supply with a light -

dependent resistor (LDR1) , it is possible

to obtain a fail -safe power supply that

is regulated, short -proof, and self- restor-

ing. There are no fuses to replace or cir-

cuit breakers to reset. Even a dead short

across the load line cannot damage this

power supply.

Before you say, "So what ?" ... keep

in mind that short -circuited, series -regu-

lated power supplies generally cause the

base -emitter junction of the series tran-

sistor to rupture, and end further use of

the supply until the transistor is re-

placed. This does not happen with the

fail -safe supply.

The components selected enable this

18

supply to provide you with a 9 -volt out-

put at 0 to 100 milliamperes. It is ideal

for transistor projects, radios and other

9 -volt battery- operated devices whose

current requirements do not exceed 100

ma. In addition to the fail -safe feature, the

supply tends to protect the devices being

powered. Suppose you had a defect

which could cause a runaway condition

in one of your transistor projects . . .

chances are that with a battery supply

your transistors would draw destructive

currents. With the fail -safe supply,

maximum current is 100 ma. And, of

course, a big advantage is that the pow-

er supply serves as a battery eliminator:

it works off the 117 -volt line.

ELECTRONIC EXPERIMENTER'S HANDBOOK

An overload brightens 11

and darkens 12. You see I1

and LDR1 "sees" 12. If you

don't remove the overload,

the LDR biases Ql to cut

down the output current.

Removal of overload dark-

ens 12 and output volt-

age jumps back to normal. I I7 VAC

TI

DI 1N4001

12V

RI

11

R2

loon SR

02 IN3020A

An overload indicator quickly alerts

you to operating conditions. Here's what

happens. Under normal load conditions

the indicator light Il, protruding through

the top of the cabinet, is off and the out-

put voltage is correct. Under excessive

load conditions, IZ glows and the output

voltage is down sharply. When you re-

move the excess load, 11 will stop glow-

ing and the output voltage will come up

to normal almost instantly.

How It Works. Diode D1 rectifies, and

Cl filters the 12 -volt a.c. output from Ti.

The main current path can be traced

from the bottom of the secondary wind-

ing of T1 through the parallel path of

TO NEGATIVE POWER

OUTPUT LEAD FROM SECONDARY TI

RI 02 CI AO DI

TO R2 I2 LORI OI

POSITIVE INSIDE

POWER HEATSINK

OUTPUT LEAD

Press -fit 12 into a grommet and position the assem-

bly close to and "facing" LDR1. A wire loop holds

the grommet in place. Observe polarity of diodes.

1966 Fall Edition

12 and the load, through the emitter -

collector circuit of Q1 through R2,

through the parallel paths of Il and

LDR1, through DI, and finally back to

T1. A small secondary current path

through R1 and zener diode D2, which is

dependent upon the total effective re-

sistance of all the other components and

the load, establishes and varies QI's base

bias, which in turn varies Q1's dynamic

resistance, the main current flow, the

respective voltage drops across the vari-

ous components in the circuit, and the

load. Output voltage variations due to

larger or smaller loads are compensated

for by these changes in bias, so long as

PARTS LIST

C1- 1000 -11f., 25 -volt elcetrelrlir capacit,u

D1- 50 -PlV, 300 -ma. diode 1.A 2482, 13`40!)1,

or 1.V2610)

D2 -10 -volt, 1 -watt, 10% :c,er diode

(1N3020A)

11 -18 -volt miniature lamp (Sylvania 18ES or

equivalent)

12 -10 -volt miniature lamp (Sylvania 10ES or

equivalent)

LDR1- Light- dependent resistor, 100 footca,dle-

100 ohms, (Sigma 4116 or equivalent, 1 -watt,

300 -volt r.m.s. rating) -

QI- 2,697, 2.V1420, or 23'1613 transistor

R1- 100 -ohm, % -watt resistor

R2- 15 -ohm, 2 -watt resistor

Sl- S.p.s.t. slide switch

T1- Filament transformer: primary, 117 volts;

secondary, 12 volts, 1 amp. or greater ( Stancor

P8130 or equivalent)

1 -4" x 23" x 2" aluminum box

1 -1 %" x 2%" perforated circuit board

11isc.- Transistor heat sink for TO -5 transistor

housing (Thermalloy 2211 or equivalent),

grommets (3), right -angle brackets (2), color

cap for 11, line cord, output leads, wire, screws,

etc.

19

the load does not demand more than the

maximum 100 ma. of current.

Excessive loads reduce Q1's forward

bias to a very low value and sharply lim-

it the amount of main current flow. The

resulting drop in voltage across the load

extinguishes 12. The loss of light on

LDR1 increases its resistance and fur-

ther limits the main current flow. The

voltage drop across LDR1 is now suffi-

cient to light Il and alert you to the

overloaded condition.

When the excessive load is removed,

current flow through 12 will increase

sufficiently to once again illuminate

LDR1, reduce LDR1's resistance, and in-

crease Q1's forward bias. This servo -like

action has a regenerative characteristic

and quickly responds to almost instan-

taneous load variations.

Construction. Prepare a 2" x 2 3'i" x

4" aluminum box as shown and install

the three grommets, switch, transformer

and 11. Preassemble all the other com-

ponents on a 134" x 21/2" perforated

phenolic or other suitable circuit board.

Transistor QI should be enclosed in its

heat sink before you mount it on the

board.

Pressure -fit 12 into a grommet and

position it close to and "facing" the

sensitive side of LDR1. Stand the grom-

met upright on the board and tie it into

place with a small length of bare wire.

Now attach two small right -angle

brackets to the edge of the board as

shown. Because some of the negative

leads are connected to one bracket and

some to the other, this circuit is corn-

Preassemble the circuit board and install after Sl,

Il, and Tl (in that order) are mounted. Connect all

leads and check the circuit before closing box.

20

3/d'01A

2-3i4"

7/8"

1/2" 3/8 "DIA

1/8"

DIA

o

- -- 7/e " 7/8

I-v2"

1/2 "DIA

2 -3/"

Drill holes in the outer portion of the aluminum

box as shown. The size of the rectangular opening

can be modified to accommodate any s.p.s.t. switch.

pleted when the board is fastened to the

box. Therefore, you should avoid con-

tact between the box and the positive

lead or the load.

Install the subassembly in the box,

and hook up the transformer, line cord,

and output leads. Double -check to see

that all wire and components are prop-

erly arranged so that there are no un-

wanted short circuits.

You can now plug in the unit and

check its operation. Touch the output

leads together and watch the action. Do

the same with the leads apart. If you

followed instructions, the action will be

as described. -C-

ELECTRONIC EXPERIMENTER'S HANDBOOK

COVER STORY

Add a new dimension to your holiday

lighting -just use any radio

or record player and the "Rhythmicon"

HERE'S a little project we have dubbed

111. the "Rhythmicon," for with it you

can make your Christmas lights twin-

kle in time to the music from your radio,

phonograph, hi -fi or p.a. amplifier. The

possibilities the Rhythmicon offers are

endless : Use it to control tree lights,

floodlights, spotlights, or conventional

electric bulbs- indoors or out.

Simply connect the two clip leads from

the Rhythmicon to the loudspeaker

leads of the sound source, and play

carols or other seasonal material

through it. The lights plugged into the

socket on the box will automatically fol-

ICnristmas

fights

bu inhk

to Ilitusic

By LEON A. WORTMAN

1966 Fall Edition 21

low the sounds, going from off to full on,

getting instantly brighter and dimmer

as the music gets louder and softer; go-

ing off completely when the music stops.

The music plays, and the lights dance

automatically.

Construction. Basically, the Rhythmi-

con makes use of the ability of a silicon

controlled rectifier to act as a "rheo-

stat," controlling large amounts of cur-

rent in a circuit in response to pulses

applied to its "gate" electrode. Uni-

junction transistor Q2, in combination

with Q1, acts as a pulse generator to

turn SCR1 on. The pulse frequency

(and, consequently, the brightness of

the lamps controlled by SCR1) depends

on the amplitude of the audio signal ap-

plied to TI (see "How It Works," page

24). A 3" x 4" x 5" Minibox holds all of

the circuitry and components for the

Rhythmicon. The SCR and the four sili-

con rectifier diodes must be mounted on

a heat sink. First, fabricate the heat

sink from a piece of 1,46" aluminum, cut-

ting it to 212" x 334 ". A 'I" flange is

bent along the 331" dimension for mount-

ing the heat sink, and five holes are

drilled in it for mounting SCR1 and

D2 -D5. The holes must be large enough

for complete clearance of the mounting

studs.

Referring to the photos on page 23,

mount D2 and D3 directly in the two

center holes without insulating wash-

Christmas

!Tgbts

twinkle

to Music

ers. A solder lug is placed under the

mounting nut of D2 to connect the cath-

odes of D2 and D3 directly to the lamp

socket, S01. Diodes D4 and D5 (as well

as SCR1) must be electrically insulated

from the heat sink with mica washers on

either side. Between the mica washers

and the bodies of these three semicon-

ductors, use solder lugs as shown in the

upper photo on page 23. Use heavy metal

washers between the outer mica washers

and the mounting nuts. When SCR1 and

D4 and D5 are mounted, check with an

ohmmeter to insure that their cases are

not shorted to the heat sink.

The heat sink must be electrically iso-

lated from the Minibox. In the author's

unit, 6 -32 holes for machine screws were

drilled and tapped into opposite sides

of a 3' +" x 1/2" x 1/2" bar of Bakelite. The

heat sink was mounted on the Bakelite

through holes in the 1/1" flange made pre-

viously, and the Bakelite was then se-

cured to the inside of the Minibox in

the same way. Polystyrene or any simi-

lar insulating material can also be used

for this, or the heat sink can be mounted

with machine screws using extruded

shoulder washers to insulate it.

As shown in the top photo, most of

the remaining components are mounted

to a 21/4" x 32" piece of perforated cir-

cuit board (with the exception of S01,

Fl, Tl, S1, and Rl, which are mounted

at the ends of the box) . "Flea clips"

are inserted into the perforated board

at suitable points to provide rigid termi-

nals for connecting the transistors and

other components. The perforated cir-

cuit board is mounted to the box with

several machine screws and 1/" stand-

22 ELECTRONIC EXPERIMENTER'S HANDBOOK

%x5Xsg5SxZ1s:5AWAIiislZVZx5XWME3t;3x3t5Slagxagxfi.4x*A5a5A5:43WA 5,-sSx:4stgxZ;Astgx::FAVS

SOI SCRI R6 03 D2 D5 D4 Aluminum heat sink is mounted

to one side of box on a Bake-

lite strip; PC board is mounted

on 1 /2" spacers. Only rear of

S01-the socket for lights -is

seen. Heat sink and components

should not contact metal box.

CI DI C2 R2 R3 QI C3 Q2

offs to provide clearance for the tips of

the "flea clips" which protrude through

the board.

Before mounting the circuit board and

heat sink, drill holes in the Minibox for

the remaining components. At one end

of the box, mount SOI, F1, and Tl; at

this same end, drill holes for the a.c.

line cord and audio clip leads (these

can also be made with a.c. lamp cord) ,

and line them with rubber grommets.

Drill holes for Si and R1 in the opposite

end of the box.

Final Wiring. Because some of the com-

ponents of the Rhythmicon are at the

potential of the a.c. line, it is essential

that no part of the circuit makes elec-

trical contact with the Minibox. The one

exception to this is the audio lead which

is connected to the bottom end of R1;

connect this lug of RI to the box by

placing a solder lug on the control shaft.

Also, connect the ground terminal of Cl

directly to the box (rather than to the

lower terminal of R1) using a lug under

one of the nuts holding the perforated

circuit board.

Transformer Ti, a universal push -pull-

plates -to- voice -coil audio output type,

is used to couple the audio source to the

Rhythmicon. It is connected so the

secondary or voice coil side becomes the

input. Connect the center lug of R1

1966 Fall Edition

Studs at left (below) are D4-

D5. Mount with mica washers

on both sides of heat sink; use

same method for SCR1 seen at

right. At center are D2 -D3; no

washers are needed for them.

and the positive terminal of Cl to the

transformer terminals that give the

highest impedance -with the unit used

by the author, terminals 1 and 6. Con-

nect the push -pull plate side as shown

in the schematic; the center tap is not

used and can be cut short.

Since transistors QI and Q2 are sol-

dered into the circuit, be sure to use

alligator clips or other heat sinks to

avoid heat damage. Observe similar pre-

cautions with the diodes and SCR1. Com-

ponent values are not critical, and may

vary plus or minus 10(, ; it is desirable

to select a resistor for R6 that is with-

in 5% of 3000 ohms, however.

Operation. It takes less than half a

watt of audio at 4 ohms impedance to

operate the Rhythmicon, and even a

transistor radio can be used to demon-

23

`.9.FSFA^.a5*c5^'9.45a9.%X547Z:eti9Eix..:M.45:55 .S'53T.e..`9.4SZ:Fíae}t"9.4FvF65.. .7"gMU9Fr.^ i5?.'i^'C>.:

(pm

I T1 FI

VAC

CLIPS TO

SOUND'

SOURCEI

SI

14

R2

4.7K R3 R4

3.3K 33011

01

R6 3K

02

2N2160

D61 G

Z4XL20

BI

C3

.0475f. RS

390

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

PARTS

C1 -100 µf., 50 -volt electrolytic capacitor

C2 -20 µf., 25 -volt electrolytic capacitor

C3 -.047 µf., 200 -volt paper capacitor

D1 -1N34A germanium diode

D2 -D5- Silicon diode rectifier (GE -X4 or Lafayette

Stock No. 19G4208 or equivalent)

D6 -20 -volt, 1 -watt zener diode (GEZ4XL20 or

equivalent)

F1- 5- ampere, 125 -volt "slow- blow" fuse and fuse -

holder (Littlefuse Type 3AG or equivalent)

Ql-GE-X9 pup transistor

Q2- 2N2160 unijunctioz transistor (GE)

R1 -10 -ohm, 5 -watt wire -wound potentiometer

R2 -4700 -ohm, Y,-watt resistor

R3- 3300 -ohm, % -watt resistor

R4- 330 -ohm, V2-watt resistor

strate its functioning. No modification

is required at the audio source ; simply

connect the clip leads to the amplifier

speaker terminals, or to the voice coil

leads of a speaker. Any impedance be-

tween 4 and 16 ohms will do, with 8

ohms as optimum.

Potentiometer RI is the sensitivity or

light amplitude control for the Rhythmi-

con. After setting the audio amplifier

for the best listening level, adjust R1

to the point where the lights follow

variations in sound volume; turn it too

high and the lights will stay on with

little variation, going off when the sound

stops.

Lovely lighting effects can be created

by connecting up to four 100 -watt Par -

38 lamps (available in red, blue, and

green) at the base of the Christmas

tree, or as part of an outdoor display.

Plugging in strings of conventional tree

lights further enhances the effect. The

24

LIST

RS- 39 -olum, % -watt resistor

R6- 3000 -o/zm, 5 -watt wire -wound resistor 10%

or better

S1- S.p.s.t. toggle switch

SCR1- Silicon controlled rectifier (GE -X1 or

equivalent)

S01-Panel-mounting a.c. socket

TI- Universal push -pull output transformer (La-

fayette 33G7503 or equivalent -see text)

I -3" x 4" x 5" Minibox

Misc. -Sheet of 1/26" aluminum for heat sink; per-

forated circuit board; flea clips; Bakelite bar for

mounting heat sink; mica washers for mounting

SCR1, D4 and D5; solder lugs; 6 -32 hardware; %"

spacers; alligator clips; line cord; grommets; wire;

solder. etc.

4.7- ampere rating of SCR1 gives a total

of 450 watts of power handling capabil-

ity- that's a lot of dancing, twinkling,

decorative light! -®-

HOW IT WORKS

Audio is applied to Tl, and rectified and filtered

by Dl -C2; the resulting polarized voltage appear-

ing across R2 biases Ql, following audio ampli-

tude variations. Unijunction Q2, C3, R4, and R5

comprise a pulse generator. The frequency of the

pulses depends on the d.c. potential applied to

Q2's emitter by Ql. The greater the audio ampli-

tude, the higher the pulse rate. Resistor R6 and

zener diode D6 form a voltage divider across the

output of the bridge rectifier (D2 -D5), and pro-

vide stable, low potentials for Q1 -Q2. The SCR

begins conducting when a pulse is applied to its

gate: current flows until the pulsating d.c. deliv-

ered by D2 -D5 reaches zero. At that point, an-

other pulse from Q2 is required to again start

conduction. The greater the pulse rate, the higher

the average current through SCR1 and the lights

connected to S01.

ELECTRONIC EXPERIMENTER'S HANDBOOK

Where there's smoke,

there's fire ;

where there's fire,

it may be too late;

this detector

"sees" the smoke

and warns you

A

S KE

LA

F R

OLTIt E

SMOKE can cause as much as, or more,

loss of life and property damage than

fire. In many instances, smoke is present

long before a fire is actually detected.

Homes and business establishments are

often equipped with either simple or

elaborate fire alarms, but relatively few

By H. ST. LAURENT

of them have any provision for smoke

detection. Early warning of the presence

of smoke can give you enough time to

either put out a fire and minimize dam-

age, cr- escape.

Fortunately, most smoke is lighter

than air, and rises. It will accumulate

1966 Foil Edition 25

In the presence of

smoke, light reflect-

ed from lamp 11

reaches the photo-

cell (PC1). Action of

PC1 fires VI., energizes

the relay, and sounds

the alarm. Sensitivity

can be adjusted to

allow for heavy cigar

and pipe smokers.

TI

LENS

R3

IO MEG.

PCI

R2 R4

47K 39011

CI

C2

5yf.

00Ipf. 37

KI

HORN

EXTERNAL

ALARM

on the ceiling and build down. A room

almost filled with smoke may have an

area close to the floor that will allow a

safe crawl space for escape. By the same

token, if a smoke alarm were located

near the ceiling, it would sound an alert

long before a dangerous concentration of

smoke accumulated. Here's a smoke de-

tector you can construct complete with

a built -in alarm for about $10.00.

How It Works. A light source consisting

of a lamp, lens, and shield aims a narrow

beam of light about 1 inch in front of,

and at a right angle to, the "line -of-

2 1/8 "- -

13/16

3/8 W16"

I

9/16"

3/16 "DIA 1/2" DIA

I

IJ2°

{ -,

--.I 5/8" f- SIDE

BOTTOM 1/2

r y 1 /2 "DIA

T/I6

---1_

LENS

REAR

Light- source barrel is made from a block of wood.

Size of lens opening can be varied to accommodate

your lens. Use a cardboard tube as an extension.

26

sight" of a cadmium sulphide photocell.

The cell is recessed in a lighttight cyl-

inder and does not "see" enough of the

light to trigger the alarm under normal

conditions.

When smoke enters the chamber, it

interferes with the light beam and causes

the light to be reflected in many direc-

tions. Some of these reflections strike

the photocell. Under the influence of

light, the resistance of the photocell de-

creases and causes a higher voltage to

appear across R3 and on the starter elec-

trode (pin 4 of V 1) . When the starter

STOCK 'PIA. " 'BTOCK.

d

3f

"AROM "TOP

Photocell is mounted at right angles to the sharply

focused light. Paint inside of the wooden smoke

chamber flat black to minimize light reflections.

ELECTRONIC EXPERIMENTER'S HANDBOOK

a.

electrode voltage reaches the firing point

(approximately 50 volts) , the tube con-

ducts, energizes the relay, and activates

the alarm. The alarm will shut off when

the smoke has cleared the chamber in

the smoke detector.

Potentiometer R3 serves as a sensitiv-

ity control and is usually adjusted to

require a fairly large volume of smoke to

trip the alarm in order to prevent a false

alarm, which could be caused by a num-

ber of people smoking in a confined area.

Transformer Ti provides 6.3 volts to the

lamp (11) and to the horn; RI is a cur-

rent limiter, and tends to protect and

increase the life of II; R2 serves as a

makeup resistor and prevents the re-

sistance divider network across the 117 -

volt line from drawing too much current

in the event that R3 is inadvertently ad-

justed too close to minimum resistance ;

capacitors Cl, C2 and resistor R4 are

VL R2 R3 To KI¡aLINE CI

/-

R4 C2 To UNE To K1 II

Remove unused tube pins and use a drop of ce-

ment to hold the tube in place. Lamp 11 is inside the

barrel. A cardboard tube holds the photocell (PC1).

uncritical circuit stabilizing components.

Construction. The smoke chamber is

made of wood stock lattice strips or other

suitable 1/}" x 13/4" lçlmber and 1 /8"

Masonite or other tempered board. The

lens and photocell holders are made of a

heavy manila paper and glued in place.

If necessary, you can modify the diam-

eter of the holders and the openings in

1966 Fall Edition

the lens block to allow the lens and

photocell to fit properly. The distance

between the lens and the lamp will vary

in accordance with the focal length of

the lens, and should be adjusted to give

the sharpest beam of light possible.

Attach the lamp socket to the lens

block with a small 1" wood screw. A

green or red plastic window can be placed

over the front opening of the lens block

to cut down some of the glare from the

lamp. This light from the front opening

only serves as a pilot to let you know

that the lamp and power are on. Cover

the smoke chamber and other internal

surfaces with a flat black paint to mini-

mize stray reflections.

The cabinet is made of standard 21/2"

x %" pine panel stock. A slot cut about

1/2" from the edge of the panel stock,

and about ',is" deep holds a metal grille

in place when the sides are assembled,

PARTS LIST

C1- 0.001 -14, ceramic capacitor

C2 -4- or 5 -nf., 50 -volt electrolytic capacitor

11 -Pilot lamp (GE 12 or equivalent)

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

(Guardian E -3772 or equivalent)

PC1- Cadmium sulphide cell (Clairex Cl -504 or

equivalent)

R1 -10 -ohm, % -watt resistor

R2- 47,000 -ohm, 1,A-watt resistor

R3- 10- megohnz potentiometer, linear taper

R4 -390 -ohm, Y2-watt resistor

T1 -117 -volt to 6.3 -volt, 1- ampere filament

transformer

V1 -5823 glow tube

1 -Horn (imported type used on bicycles)

1 -14 -nun. x 34 -mm. focal- length lens (any dou-

ble convex lens that fits is suitable)

1 -Lamp socket (Dialco 19 -07 or equivalent)

Misc. -Tube pin sockets (3) removed from mini-

ature socket, wood, 4" x 8" ¡octal grid, quick -

setting glue, wood screws, etc.

The electronic components including the smoke

chamber complete (not wired), machined cabinet

parts, grille, base and cover, hardware, line

cord, wire, etc., are available for $15 postpaid in

the U.S.A. from Lectromek Co., 166 Wendell Rd.,

Warwick, Rhode Island 02888. No C.O.D. Price

list for individual parts available,

and dresses up the appearance of the

cabinet. An alternate method is to rabbet

the top edge of the four sides so that

the grille can be set flush, then topped

off with 1 /2" half -round molding. All

cabinet and smoke chamber parts are

glued in place, with the exception of the

back cover which has a %" hole near

the top, center, to accommodate a hook

27

The smoke chamber should be as

lighttight as possible to keep

the detector immune to outside

light. The plastic window lets

you see if the lamp and power

supply are in working order.

or other wall hanger for holding the fin-

ished smoke alarm. Complete all wiring

and mounting of parts before you screw

down the back cover.

When the back cover is secured, slip

the unit into the cabinet. It should fit

snugly. Two 6 x 3/4" half -round head

wood screws on each side of the cabinet

will hold the alarm in the cabinet.

Installation and Adjustment. Installa-

tion is simple -you just hang the unit in

an upright position, as high as you can

on a wall of the area to be protected,

and plug the line cord into the nearest

117 -volt a.c. outlet. Be sure smoke cham-

ber inside cabinet is pointing up.

Before adjusting the unit, set the

Completed unit is mounted vertically, as close to

the ceiling as possible. Rising smoke enters smoke

chamber through metal grille to set off the alarm.

28

sensitivity control in the minimum posi-

tion (counterclockwise) to keep the

alarm off, and allow about five minutes

of warm -up time for the detector to

stabilize itself. Then all you have to do

is rotate the sensitivity control until the

alarm sounds, and back off slowly until

the alarm stops. That's all there is to it.

You can check this setting by blowing

some smoke through the lower half of

the metal grid and waiting for the smoke

to reach the chamber : if all is well, the

alarm will go on.

Sometimes line voltage variations will

modify the sensitivity characteristic

after you have set the sensitivity con-

trol. So, from time to time, blow some

smoke into the unit to see that it is

working. If the unit tends to "false

alarm" because of a normally smoky

room condition, or because of upward

line voltage variations, densensitize the

detector a bit by a slight counterclock-

wise adjustment of the control.

Another way to adjust the detector is

to use a Variac and step up the line

voltage to 125 volts, then slowly rotate

the control until the alarm just sounds

off. With the control in this position, the

alarm should function properly over a

line voltage range of 105 to 120 volts.

If, for some reason, line voltages in ex-

cess of 125 volts are regularly encoun-

tered, the Variac voltage should be

adjusted accordingly. -®

ELECTRONIC EXPERIMENTER'S HANDBOOK

By LOUIS E. GARNER, JR. SUPER -SENS

Versatile electronic relay provides unlimited control functions

DO YOU need a burglar alarm, a fire

alarm, an automatic fan control, an

automatic light switch, a liquid level

control, an automatic dehumidifier con-

trol, a photoelectric counter, a radio re-

mote control, a lawn sprinkler control,

an automatic door opener, a time delay

relay, an electronic latching relay, or a

sound -actuated relay ?

Would you like to amaze your friends

and neighbors, gain the respect of your

teachers or co- workers, assemble a

Science Fair project that is different,

or build a basic control that can be

used in hundreds of applications ?

If you can answer yes to any of these

questions, you'll enjoy building and

using ' Super -Sens, an easy -to -wire, in-

expensive electronic relay so sensitive

that it can be tripped by a pencil line

drawn on a piece of paper.

Electronic relays are not new. They

have been designed and manufactured

for years. You can purchase a variety

of types at prices ranging from $20 to

$50 or more, or you can build Super -

Sens for less than $10.00.

One popular "supersensitive" electron-

ic relay offered by a leading laboratory

supply house requires a signal current

1966 Fall Edition

of 50 microamperes at a little under 10

volts. Super -Sens, in contrast, will trip

with a miniscule control current of

about 0.2 µa. at approximately 1 volt.

Using its built -in bias circuitry, the de-

vice can trip with as much as 50

megohms between its input terminals.

Super -Sens can be actuated by many

input devices: photocells, humidity

detectors, microswitches, thermostats,

magnetic contacts, pressure switches,

thermistors, and almost any high or low

resistance type of sensor or probe, as

well as the comparatively low level sig-

nals obtained from a carbon microphone

or a simple radio receiver.

Super -Sens, in turn, can be used to

actuate almost any type of electrically

operated equipment: lamps, solenoid

valves, buzzers, bells, power relays, fan

motors, pumps, door openers, heating

systems, etc.

HOW IT WORKS

Super -Sens is essentially a two -tran-

sistor, high -gain, direct -coupled d.c.

amplifier driving a standard sensitive -

type electromagnetic relay. See Fig. 1.

Transistors Q1 and Q2 are connected in

a modified Darlington circuit. (A Dar-

29

N

ARM

f-r---®N.O.

B 10K

R2

Fig. 1. As little as 0.2 µa. at 1 volt is enough to

trigger relay; up to 50 megohms can be sensed.

lington circuit is a circuit having two or

more transistors connected in such a

manner as to have a single input, a

common load and a current gain which

is the product of the current gain of

each transistor.)

Series resistor RI tends to limit base

current to prevent accidental damage to

the transistors by excessively strong in-

put signals. Unbypassed emitter resis-

tor R3 stabilizes circuit operation, and

provides a degree of temperature com-

pensation. Sensitivity control R4 and

current limiting resistor R2 are parts of

a bias and control circuit to permit the

use of external resistive -type and switch -

type sensors. Circuit power is supplied

by BI and is turned on and off with

s.p.s.t. switch S1.

When a signal or bias voltage of prop-

er polarity (base positive with re-

spect to emitter) is applied to the base

emitter circuits of QI and Q2, the tran-

sistors conduct and energize Kl. Bias

voltage can be taken from the internal

R2, R4, B1 circuit (B terminal) or it

can be derived from an external circuit.

There are essentially three basic types

of input circuit control devices that

Super -Sens will cater to: those that

look like a voltage source, those that

look like a resistor, and those that look

like a switch. The voltage source de-

vices are hooked up to I and G.

The resistor control types are given

special consideration: high- resistance

devices are connected across terminals

I and B (in series with the internal

G

SUPER -

SENS

® B

G

SENSOR

D.C. VOLTAGE

OUTPUT

SENSOR

HIGH

RESISTANCE

SENSOR

LOW

RESISTANCE

G

SUPER-

SENS

B

SUPER-

SENS

B

Fig. 2. Any one of three basic types of sensors can be used: those that look like a voltage such as a

photovoltaic cell, etc.; those that look like high or low resistors; and those that act like a switch.

N. C

ARM

N. O.

SUPER-

SENS

LOAD

111111i

EXT. POWER SOURCE

N.C.®

ARM

N.O.

SUPER -

SENS

-D

N

ARM

N.O.

SUPER-

SENS

LOAD A

LOAD B

TO EXT.

POWER SOURCE

EXT. POWER SOURCE

Fig. 3. Controlled external load circuit can utilize almost any source of power. If power require-

ments exceed the relay contact's rating, a power relay can be added. One or two loads can be switched.

30 ELECTRONIC EXPERIMENTER'S HANDBOOK

Fig. 4. Etched circuit

board construction pro-

vides a mounting base for

all the components, in-

cluding the relay. Conven-

tional chassis -type con-

struction is also quite

suitable. If you want to

make your own printed

circuit board, you can use

these actual size photos

as guides. All components

are mounted on one side

of the board (top). The

foil side (bottom) must

be clean to prevent leak-

age between conductors.

bias circuit) and low- resistance types

are placed between terminals I and G

with a jumper from terminals I and B,

as shown in Fig. 2. Actually, the re-

sistive devices are made to function like

a voltage source, since terminal B has

sufficient voltage of proper polarity to

forward -bias the transistors.

Switch -type devices can be connected

between points I and B, and R4 adjusted

to provide just enough voltage to pull

in the circuit when the switch is closed.

Conversely, these switches can also be

made to drop out the circuit. A jumper

between I and B, and R4 adjusted to pull

in the circuit, will keep the circuit on

until a switch across I and G causes the

circuit to drop out when it is closed.

The relay can be hooked up to provide

either a normally open, or normally

closed control circuit, or both, as shown

in Fig. 3.

CONSTRUCTION

Since the basic unit is the same for

all applications, let's put the thing to-

gether, and then we'll consider some of

the many applications. All components

are standard and readily available

through most electronics supply houses.

1966 Fall Edition

PARTS LIST

BI -6 -12 volt battery

KI -Relay (1AICO GS -100 or equivalent)

Q1, Q2 -T1416 transistor

R1- 1000 -ohm, % -watt resistor

R2- 10,000 -ohm, % -watt resistor

R3 -47 -ohm, % -watt resistor

R4- 1- megohm potentiometer, linear -taper

SI- S.p.s.t. toggle or slide switch

1- Etched circuit board*

1- Cabinet (Minibox 2102)

Misc.-Small knob, screws, nuts, hardware, wire,

solder, etc.

*A pre- etched circuit board on an epoxy -glass

base is available from DE\ICO, Box 16041, San

Antonio, Texas 78216 for $2.00. This firm can

also supply: a "basic" kit (board, relay, tran-

sistors) for $7.50; a complete kit for $9.50; and

a pre -etched moisture sensor for $1.50.

If you etch your own board, follow

the actual size layout shown in Fig. 4.

Wiring is not critical, but special pre-

cautions should be taken. First, be sure

there is ample separation between the

I, B, and G terminals. Second, use an

epoxy -glass rather than a paper -base

phenolic copper -clad base board, (mois-

ture absorption in the latter material

may cause erratic operation) . Third, be

sure to remove all of the unused copper

during the etching process, for an al-

31

CII

L 1

C13

FOIL I

SUPER - SENS N.C.

ARM &-

BATT N.O. ®

+ i

Fig. 5. Fire alarm circuit has fusible links Fl to F4, and thermostatic contacts Ti, T2. Door and

window contacts C1 to C3 and foil patterns make up burglar alarm. Place sensors in strategic locations.

most invisible, microscopically thin layer

of copper can provide sufficient conduc-

tion to actuate the relay.

To avoid accidental mechanical

damage, mount the relay last. Heat -

sink the transistor leads with a pair of

long -nose pliers to prevent heat damage

when soldering. The Sensitivity control

can be mounted on either side of board.

The completed board can be mounted

in a small Minibox as a self- contained

instrument, or in another piece of equip-

ment, depending on the device's ultimate

use. Mount the board on spacers to pro-

vide air space between the board and

the cabinet. Power supply B1 can be

built in or externally connected.

A number of component changes can

be made to meet individual needs. Gen-

eral Electric GE -10 transistors will

serve as direct replacements for the

specified TI units. A Sigma 4F- 1000 /S-

SIL relay can be used in place of the

JAICO type, although a new layout and

larger circuit board would be required.

If maximum sensitivity is needed at all

times, omit R.ç and connect R2 directly

to the Si, K1 junction.

A variety of power supplies can be

employed. The total current drain when

the relay is closed is only a few milli-

amperes, permitting the use of small

transistor -type batteries.

As might be expected, the instru-

ment's ultimate sensitivity depends on

supply voltage, component tolerance,

and the gain of the transistors. With

the components specified in the Parts

List, the current sensitivity (for relay

closure) will vary between 0.15 and

0.45 pa., using a 9 -volt power supply.

(Continued on page 36)

Fig. 6. An RC network can be added to make a time-delay relay. Circuits (A) and (B) stay on for a

desired time after the switch is opened. "Turn on" is delayed in circuit (C) when the switch is closed.

32 ELECTRONIC EXPERIMENTER'S HANDBOOK

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1966 Fall Edition 35

If higher gain transistors are used, the

overall sensitivity may be as great as

0.1 (or less) µa., while lower gain units

may provide a sensitivity of 0.75 µa.

APPLICATIONS

Burglar and Fire Alarm. An easily in-

stalled alarm system, suitable for a

home or place of business, is shown in

Fig. 5. It offers fire alarm protection

during the day, and both fire and bur-

glar alarm protection at night.

A break in any part of the external

series circuit will trigger the alarm.

A "push -to- test" switch (S3) , when de-

pressed, will sound the alarm if the relay

circuit is in working order.

Fire protection is afforded by fusible

links Fl to F¢ and by thermostatic con-

tacts T1 and T2 placed on ceilings in

strategic locations. Door and window

contacts Cl to CS, together with the foil

patterns, provide burglar protection.

Any combination of switches, contacts,

or links can be used, so long as the cir-

cuit forms a closed loop and the total

resistance of the loop isn't great enough

to prevent an adequate amount of volt-

age from terminal B to be applied to

terminal I. The sensitivity control can

be adjusted to compensate for loop re-

sistance and battery conditions.

Switch S2 skips the door and window

detectors during the day, and Si, which

can be lock -protected, serves as a master

on /off control. If switching S2 from

night to day or day to night causes a

momentary but undesirable alarm, con-

nect the Night side of the switch to the

switch's center arm. In this mode of

operation, Super -Sens is on all the time,

the relay is energized, and the normally

closed contacts are held open.

Occasionally, a latch or alarm -hold

type of operation is desirable . . . that

is, once the alarm is triggered, it sounds

continuously even after a break in the

loop is restored. In this type of operation,

the alarm can be reset only at the main

panel, which could be located inside a

locked cabinet. To build in the latch fea-

ture, connect a 1- megohm, 1/2 -watt re-

sistor in series with terminal I and S2.

Adjust the Sensitivity control until the

relay just pulls in (silencing the alarm),

then back off slightly. Use the test

switch and control alternately, and ad-

just until the desired action is achieved.

36

Time Delay Relays. Controls which can

switch a circuit "ON" or "OFF" for pre-

set or adjustable periods of time are used

extensively in experimental work, pho-

tography, laboratory tests, chemical

processing and manufacturing. Super -

Sens can be used in such applications by

adding a relatively simple "time delay"

accessory. Typical circuit arrangements

are shown in Fig. 6.

A 20- megohm resistor connected in se-

ries with a 0.25 -4 capacitor in Fig.

6 (A) sets up a time delay on the order

of 3 to 9 seconds, depending on the set-

ting of the Sensitivity control. A mo-

mentary normally open contact switch

connected across the capacitor allows the

circuit to conduct when the switch is

pressed and released. The relay closes

and remains closed until Cl is charged

up and stops drawing current.

The circuit in Fig. 6 (B) permits a

wider range of control. When SI is de-

SHORT LENGTH

OF CO -AX

CLAMP

TANK

(A)

INSULATED

BUSHING \ SUPER -

SENS

77

METAL TANK

(B)

Fig. 7. Levels of low- and high -conductive liquids

can be monitored by easily made probes.

ELECTRONIC EXPERIMENTER'S HANDBOOK

_J SUPER -SENS __J

MOISTURE MOISTURE

SENSOR (A) SENSOR (B)

-®I

®G

SUPER -SENS

B

Fig. 8. These circuits can be used to control humidifiers and lawn sprinklers. Just a drop of rain

on the sensor will release the relay in circuit (A). Circuit (B) can detect slightest trace of moisture.

pressed and released, Cl is charged by

the bias supply and then discharges

slowly through the instrument's input

circuit, holding the relay closed until Cl

loses most of its charge. The time delay

varies with R1's setting, and ranges from

about 25 seconds with RI set at 0 re-

sistance to as much as 1 minute and 45

seconds when RI is set at 1 megohm. The

timing range can be changed if you use

different values for Cl and R1. The

larger the time constant (R1 x Cl) , the

longer the time delay.

In Fig. 6 (C) , a delay in "turn on"

time takes place after the slide switch

is thrown. When S1 is switched to the

"ON" position, the relay does not close

until the current through R1 and Cl falls

off enough to reduce the voltage drop

across R1.

Liquid Level Control. Farmers, chemical

engineers, food processors, electroplat-

ers, beverage manufacturers, industrial

plant operators and others need to check

or maintain liquid levels in large tanks

or vats from time to time. Super -Sens

can do an excellent job in such applica-

tions when used with suitable sensor

probes. Typical techniques are shown in

Fig. 7.

A short length of rigid coaxial cable

can be used as a simple liquid sensor

probe if clamped to the side of a tank.

If the cable's shield is connected to the

instrument's B terminal and the center

conductor to the I terminal, the relay

will close when the liquid reaches the

exposed lower end of the cable. Connec-

tions are as shown in Fig. 7 (A) .

If a metal tank is used, the sensor

probe may be a short length of conductor

mounted in an insulated, liquid -tight

bushing at an appropriate point on the

side of the tank, as illustrated in Fig.

1966 Fall Edition

7 (B) . If the liquid is highly conductive,

connections can be made to the I and G

terminals, with a jumper between the I

and B terminals. With these connections,

the Sensitivity control is adjusted until

the relay just closes. The relay will open

when the liquid level reaches the probe.

Other types of probes can be used, of

course, including insulated metal strips

cemented inside the tank or short paral-

lel metal rods mounted on an insulating

block and attached to the tank. Regard-

less of the probe used or the type of

liquid handled, Super -Sens can control

pumps or solenoid valves, or activate re-

mote signaling devices.

Rain Alarm. A standard moisture sen-

sor plate will make Super -Sens serve as a

rain alarm. The sensor plate leads are

connected as shown in Fig. 8 (A) and

operate in the same way as the level con-

trol in Fig. 7 (B). Just a drop or two of

rain on the sensor plate is enough to

cause the relay to open.

Humidity Control. A modification of

the "rain alarm" circuit is shown in Fig.

8 (B) . Here, the moisture sensor plate

is connected and operated in the same

manner as the circuit shown in Fig. 7

(A). With this arrangement, Super -

Sens' high sensitivity will respond to the

slightest trace of moisture and close the

relay. It can detect the small amount of

moisture condensed from a person's

breath and can be used, among other ap-

plications, for controlling a dehumidifier.

Lawn Sprinkler Control. If the moisture

sensor plate used in the "rain alarm"

and "humidity control" circuits is re-

placed by a pair of semi -insulated spike -

type probes driven into the ground, Su-

per -Sens will serve as an automatic lawn

sprinkler control. Its output terminals

(ARM and either N.O. or N.C. contacts)

37

are connected to switch an appropriate

solenoid valve in the automatic sprinkler

system.

Either the low- resistance connections

or high- resistance connections can be

used, depending on soil conductivity,

electrode (probe) spacing, and desired

soil moisture content. In any case, the

instrument's Sensitivity control can be

finely adjusted to achieve the desired

operating characteristics.

Acoustic Relays. Add an easily -built,

low -cost accessory, and Super -Sens be-

comes a sound -operated relay. Three

types of circuits are shown in Fig. 9.

In Fig. 9 (A), a low- impedance single -

button carbon microphone (Shure R10),

a 6 -volt battery, an 8 -ohm to 500 -ohm

output transformer (Argonne AR -164),

a 1N34A general -purpose diode, and a

2 -4, 15 -volt electrolytic capacitor apply

a positive -going signal to energize the

relay.

A single- transistor amplifier, in Fig.

9 (B) , enables the use of a high- imped-

ance (Philmore M -55) , or a low- imped-

ance carbon microphone. A 1- megohm

resistor (R1) is used with high- imped-

ance microphones and a 47,000 -ohm re-

sistor for low impedance types. The Sen-

sitivity control is adjusted until the relay

closes and is then backed off slightly.

Thereafter, a sudden sharp sound will

cause the relay to "latch" open.

A crystal microphone cartridge, or a

magnetic headphone element can be used

as a microphone with the circuit shown

LI I

Fig. 10. Radio control can be achieved with sim-

ple detector. Tune Cl, Li to desired frequency.

in Fig. 9 (C) . The diode and transistor

are the same as in the previous circuits.

The Sensitivity control is set in the

same manner as in the circuit in Fig.

9 (B).

The acoustic relay circuits shown here

are moderately sensitive, requiring a

fairly loud signal for operation. Where

extreme sensitivity is needed, Super -

Sens can be coupled to a 3- or 4- transis-

tor audio amplifier. The hookup would

be the same as in Fig. 9 (A) .

Radio Control. Super -Sens can be op-

erated by remote radio signals provided

that a suitable control circuit is con-

nected to its input terminals, as shown

in Fig. 10.

The values of tuned circuit LZ and Cl

are chosen to resonate at the desired

control frequency. A general -purpose

(Continued on page 141)

Fig. 9. Sound -actuated relays can be made. If microphone is low- impedance type, use circuit (A);

high- impedance pickups work well in circuit (C); a low- or high -impedance unit can be used in circuit (B).

38 ELECTRONIC EXPERIMENTER'S HANDBOOK

F

FREEZE

MOTION

WITH

SOUND

Like to try your hand at the

fascinating field of high -speed

photography? All it takes is

a simple trip unit and a strobe

HAVE YOU ever wondered just exact-

ly how glass breaks, liquids splash,

balloons burst, or a ball bounces? The

electronic flash trip unit featured here

will answer these and a host of other

intriguing questions that can only be

explored through the use of high -speed

photographic techniques.

Adaptable to almost any camera and

electronic flash, this simple sound -actu-

ated unit provides a means of obtaining

Sound -actuated unit (lower right) flashes strobe as

first balloon, hit with dart. bursts. Insert shows

drop of milk hitting black background; mike was 10"

away, sensitivity of trip unit reduced to just half.

By ROY E. PAFENBERG

unusual and striking photographs. The

experimenter, research worker, or tech-

nician will find it a valuable low -cost

laboratory accessory, and the student

can use it as the ideal basis for a

science project and /or science fair ex-

hibit. Although the fact is not widely known,

the 1 /1000 to 1/2000 second flash dura-

tion of the conventional hobby or pro-

fessional electronic flash unit is fast

1966 Fall Edition 39

Trip unit fits neatly in 2%" x 21/4" x 5"

box; since layout is compact, it's best

to copy author's model. Strobe light is

the inexpensive unit described in text.

enough to capture all but the highest

speed events on film. The problem is

one of timing. With the method de-

scribed here, sound produced by, or

associated with, the event to be photo-

graphed is used to trigger the electronic

flash. Since the camera shutter must be

open, photography is done in subdued

lighting or in a darkened room. After

the flash captures the high -speed event

on film, the shutter is manually closed.

The exact instant the flash occurs

relative to the noise that actuates it

can be controlled by the way in which

the microphone is positioned. Since

sound travels relatively slowly, placing

the microphone close to, or away from,

the object will introduce an adjustable

time delay.

Construction. In essence, the flash trip

unit incorporates two stages of audio

amplification (a single 12AT7) that

triggers the 2D21 thyratron in response

to sounds picked up by the microphone

( see "How It Works," page 42 ) . Since

a thyratron acts like a switch or short -

circuit when it conducts, it fires a flash

unit connected to J2.

Although the sound -actuated trip unit

may take any form that gives due con-

sideration to layout, wiring, and the

shielding requirements of high -gain am-

PARTS LIST

Cl, C2, C4- 0.005 -14., 500 -volt ceramic disc

capacitor

C3, C5- 10 -µf., 25 -volt electrolytic capacitor

C6- 20 /20 -µf., 150 -volt dual electrolytic capaci-

tor

D1- 500 -ma., 400 -P1V silicon diode

11, 12 -Phono jack, single -hole mounting type

R1- 2.2- megohrn, % -watt resistor

R2, R5- 220,000 -ohm, ;4-watt resistor

R3 500,000 -ohm potentiometer, audio taper,

with s.p.s.t. switch S1

R4, ñ7- 1000 -ohm, Y2-watt resistor

R6- 470.000 -ohm, % -watt resistor

R8- 47,000 -ohm, ;-watt resistor

R9 -27 -ohm, V2-watt resistor

R10-2200-ohm, ;4-watt resistor

SI- S.p.d.t. switch; part of R3

TI -Power transformer: primary, 117 volts;

secondaries, 125 volts a 15 ma., and 6.3 volts

(rig 0.6 amp. (Staneor PS -8415 or equivalent)

V1 -12AT7 vacuum tube

V2-21)21 thvratron tube

1 -2W x 2',-.i" x 5" Minibox

1 -7 -pin miniature tube socket with shield

1 -9 -pin miniature tube socket with shield

1- Crystal lapel microphone (or similar)

Misc. -Knob, terminal strips, solder lugs, hard-

ware, grormnets, a.c. line cord, wirr, solder, etc.

plifier circuits, the prototype unit is

neat, compact, and rugged. The two

tubes (V1 and V2) and tab -mounting

filter capacitor C6 are mounted on top

of the 21/4" x 21/4" x 5" Minibox used

as a chassis, while the power transform-

er fits inside and as close to the back as

possible. Sensitivity control R3 and mike

input jack J1 are at the front of the box;

output jack J2 (for connection to the

40 ELECTRONIC EXPERIMENTER'S HANDBOOK

{

VIA

¿5¿R1

SM G

R2

220K

vlB

125T 716

C2

.005yf. 7

R3

S00

V2

2021 6

y f. 5,7

R4 IK

C3

105 í

25V

R5

220 R6 R7

470 IK

C5

IOUf. RB

25V

J2( TO

STROBE

SHUTTER

CABLE

47K

TI

R9 DI

2711 RIO

2.2K

IW

C6A

20yf.

150V

C6B

20yf.

150V

V2

4

VI

4 9 5

Two stages of audio (Vla and Vlb) amplify mike input to trigger 2D21 thyratron (V2).

TI RI

RIO DI R9 R2 R4 VI C4 C2

C3 C5 V2 R5 R6 R7 SI R3

JI

Locate T1 as close to the back of box as possible; note location of tube sockets, and

mounting hole for C6. Jack J2 (for strobe connection) is hidden at rear of box.

strobe shutter cable) and the a.c. line

cord entry are at the rear.

Two two -lug terminal strips are used -

one for mounting silicon diode DI and

the other for terminating the a.c. line

cord. Chassis ground connections are

made to soldering lugs installed under

the tube socket mounting screws. Use

insulated hookup wire for connecting

the a.c. switch and filament circuits;

1966 Fall Edition

the balance of the wiring can be done

point -to -point using component leads.

It's a good idea to use spaghetti on the

leads as required to avoid possible

shorts.

With the components mounted and

wired, carefully check your work before

installing the tubes and applying power.

Check to see that the tube filaments

light, and measure the B -plus at the

41

+300V

-300V

FLASH TUBE

RI 4MEG.

C2

10001f. .020

3 MEG?

TO

CAMERA

SHUTTER

CONTACTS

u

TRIGGER

TRGNçç, c. ; ;

Flash shutter contacts are polarized. Check with a

voltmeter, and connect positive side to V2's plate.

junction of R1O-C6b. It should be slight-

ly in excess of 150 volts. Finally, check

for a reading of approximately 3 volts

at pin 2 of the 2D21. Secure a crystal

microphone such as the Lafayette Radio

99 G 4510 and terminate its cord in a

phono plug.

The Flash Unit. The small schematic on

this page is a simplified diagram of a

typical electronic flash. Normally, the

camera shutter discharges capacitor C2

-charged through isolating resistors R1

Mike was one foot away for photo of golf ball fall-

ing into bowl of water. Fracture pattern of bulb is

seen below; despite its looks, it exploded violently.

42

and R2- through the primary of trigger

transformer Ti. The very high voltage

pulse produced by TI's secondary is

applied to the external starter anode

of the flash tube, partially ionizing the

gas inside it. The energy stored in Cl

flows through the ionized gas, producing

an intense flash of light. In this applica-

tion, the shutter leads from the flash unit

are connected to J2 of the trip adapter.

The cord and connector are wired so

that the positive terminal from the flash

is connected to the 2D21 plate.

Almost any electronic flash unit will

work with the trip unit, so if you al-

ready own one or can borrow one, you're

in business. If you must buy one, re-

member that a.c. power will be required

HOW IT WORKS

As shown in the schematic on page 41, the in-

put signal from a high -impedance crystal micro-

phone is amplified by a conventional 12ÁT7 (V1)

twin- triode audio amplifier. A sensitivity control,

R3, is provided between the first and second

audio stages, and serves to determine the input

signal level required to trigger V2, the 2D21

thyratron trigger stage. This stage serves as an

electronic switch to close the contacts of the elec-

tronic flash unit. The firing circuit voltage de-

veloped in the flash is used as the plate supply

voltage for the 2D21. Resistance network R7 -R8

biases the cathode of the 2D21 to a positive value

of approximately 3 volts. When the positive peak

of the audio signal applied to the control grid of

the 2D21 appreciably exceeds the cathode bias,

the tube conducts or fires, triggering the flash unit.

The power supply is entirely conventional. The

6.3 -volt winding of Tl supplies filament voltage

to V1 and V2, while the output of the 125 -volt

winding is rectified by D1 and filtered by C6 -R10

to supply bias voltage and 150 volts of B -plus for

the audio amplifier plate circuits.

for the trip unit, so it would be foolish

to pay extra for a battery -operated

flash. Small but adequate a.c.- operated

flash units are quite reasonable -the

unit shown in the photo on page 40 is

available from Spiratone, Inc., 135 -06

Northern Blvd., Flushing 54, N.Y., for

$12.95 plus postage.

Take a close look at the camera shut-

ter on your flash unit, and secure an

extension cord to fit it. Cut the camera

fitting off of the other end, strip the

wires, and turn the flash unit on. Touch

a voltmeter set to a high range to the

bared leads, and observe the polarity.

Connect the positive lead of the cord

(Continued on page 142)

ELECTRONIC EXPERIMENTER'S HANDBOOK

Why depend on batteries

when you can get

all the energy you need

free of charge? How?

LET THE SUN POWER YOUR PORTABLE

By HOMER L. DAVIDSON

1966 Fall Edition

YOU CAN USE the sun to power your

small transistor radio -or, if it's

raining, you can use a 100 -watt light

bulb. The only other element you really

need is International Rectifier Corpora-

tion's "Solar Pac," which can be hooked

up to charge the radio's battery, or to

operate the radio, or to do both. The

"Solar Pac" comes in two models:

SP5C26C (4.5 volts at 26 ma.) and

SP9C13C (9 volts at 13 ma.) , and is

available from electronic supply houses

for $9.95.

There are many ways you can connect

the solar pack to your radio. You may

43

want to add a switch (see schematic) to

provide a choice of either solar or bat-

tery power. Or you can simply connect

the pack's 6" leads to the battery con-

nections inside the radio. You can even

use the solar pack as a plug -in supply

by connecting an earphone jack and

cord to the pack, removing the existing

wires from the radio's earphone plug,

and running a pair of wires from the

plug to the battery connections.

Mounting the pack is no problem as it

is supplied with mounting pads which

can be attached easily to any radio case

Hook up a couple of alligator clips to the leads of

the solar pack to make easy -to- connect power supply.

By connecting the solar pack in parallel with the

battery, you can charge the battery while operating

the radio, or run the radio without the battery.

The earphone jack connections of your transistor ra-

dio can be modified to accommodate the solar pack.

44

TO

RADIO

SLIDE SWITCH

Li! IET

9V

SOLAR PAC

Your portable can be switched to either battery or

sun operation by adding a slide s.p.d.t. switch.

or cover. But for a more permanent in-

stallation, place the pack against the

plastic back of your radio, outline its

shape with a scribe, carefully cut out

the required area with a knife -tipped

soldering iron or jeweler's saw, fit the

pack into place, and seal around the

edges with cement.

If you plan to use the solar pack as

a universal power supply for more than

one radio or transistor project, add

alligator clips to the pack's leads for

easy handling. Should circumstances re-

quire lower voltages than that provided

by the solar pack, insert an inexpensive

100 -ohm potentiometer in series with the

output to reduce the voltage.

Once you know how much resistance

you need in a given circuit (by measur-

ing the pot's resistance in the circuit),

you can substitute a fixed resistor. Add

a resistor only when no battery is in

the circuit, and only when the unit is

to be used out -of- doors. A resistor is

not required indoors as you can move

closer to or further away from the light

source to obtain a desired voltage. -J-

The solar pack can be cemented to the radio case,

and the leads can be slipped under the case flap.

ELECTRONIC EXPERIMENTER'S HANDBOOK

BUILD...

THE $UPERX PULSE POWER

PACK FOR NO RAILROAOT G

By KOODROW POFE

Design Er,g'ne3r,

Z_ollins Radio Canpcny

...ail.' pet the feel ,)r the rezl thin j

S AY Mr. Mocel ?ailroad Engineer, can

yoga atnrt your 10 o without jamping

to 1.) _cole miles psr hour? You can, you

know, without ecui ping your .oconD-

tive with eywtee.s Dr high gear ratios.

How? Easy . . . just build and use a

new transistor tl-_rcttle power pack on

your pike for the ulïimate in mo lei rail-

roading

With it ycu get pulse *Dower for

smoother stall -free starts, and your loco

can crawl, or hi -ball, or couple -without

crashing. You also get lots of power to

operate signal lights, switch machines,

or other accessories ... all with circuit

overload protection.

Just What is Pulse Power? To under-

stand pulse power, you must first under-

stand the nature and operation of the

conventional d.c. power pack. Your loco

is equipped with a tiny d.c. motor that

operates off power supplied to the tracks

by the power pack. When you man the

throttle, which is nothing more than a

rheostat, you are regulating the voltage

across the track, and hence the motor

speed.

Assume your throttle is turned all the

way down and your loco is sitting still.

You now begin to turn up the throttle,

gradually increasing the voltage applied

across the tracks. But notice, your loco

does not start immediately; it waits

until the proper operating voltage is

reached, and until all magnetic and

mechanical locking has been overcome.

By this time the voltage is too high for

a slow, smooth start, so the loco lunges

ahead.

Figure 1 shows, graphically, how late

a typical loco might start after you be-

gin cranking up the throttle. You will

note that a certain minimum voltage

must be reached to overcome the inertial

load on the motor before it will even be-

gin to turn.

Now let's assume you are using one

of the latest power packs to hit the

scene -you know, like the one we're tell-

ing you about right now -your loco will

start to crawl, like real trains do, the

moment you hit the throttle. How come?

Well, with pulse power you get maxi-

mum voltage in the form of narrow

pulses the instant you flip the primary

power switch. This is shown, graphical-

ly, in Fig. 2. Here the average power

consumed by the motor is a direct func-

PARTS LIST

Cl- 1000 -µf., 15 -volt electrolytic capacitor

(Sprague TVL 1165 or equivalent)

C2, C3- 0.47 -µf., 35 -volt capacitor (Kernet

KR47C35K or equivalent)

C4- 1 -µf., 35 -volt capacitor ( Kemet K1C35K,

or equivalent)

Dl, D2, D3, D4, D6, D7- 1N2069 silicon diode,

or equivalent)

D5-1N276 diode, or equivalent

FI -1- ampere fuse

11 -#47 lamp, 6 -8 volts, 0.15 -amp.

12, 13 -12 -volt, 1.2 -amp. automobile dome lamp,

or equivalent (two required)

Q1, Q2, Q3, Q7 -2N404 transistors

Q4, Q8- 2N1382 transistors

Q5, Q6- 2N456A transistors

RI, R6- 2200 -ohm, / -watt resistor

R2, R3- 22,000 -ohm, % -watt resistor

R4 -Not used

R5- 6800 -ohm, ,A-watt resistor

R7- 10,000 -ohm, 2 -watt carbon potentiometer,

linear taper

R8- 390 -ohm, 1/z -watt resistor

R9, R15, RIO- 1000 -ohm, % -watt resistor

R10, R14- 10,000 -ohm, % -watt resistor

R11 -10 -ohm, 1/2-watt resistor

R12- 1000 -ohm, 2 -watt carbon potentiometer,

linear taper (with switch S3)

R13- 330 -ohm, V2-watt resistor

SI- D.p.s.t. slide switch

S2- S.p.s.t. slide switch

S3- S.p.s.t. switch (mounted on R12)

S4- D.p.d.t. slide switch

TI -Power transformer: primary, 115 volts; sec-

ondary, 12.6 volts with center tap, (Stancor

P -8130, or equivalent)

I- Cabinet (Bud AC- 1613 -A or other suitable

sized cabinet)

Alisc- Fuse clip; pilot light holder; red lens

(Dialco series 1006); binding posts (4 -2

red, 2 black); throttle knob (Raytheon

175- 6 -2G); crawl adjust knob (Raytheon

90- 3 -2G); power transistor mounting kit (Mo-

torola 31K -15)

Fig. 1. The ordinary power pack is nothing more

than a full -wave rectifier whose output is a pulsat-

ing d.c. voltage with peaks that look like the wave-

form above. For most locos, the average power re-

quired for starting is much too high for a smooth

start, and the trains pull out with a sudden jerk,

and at a speed not akin to real railroading.

46

Fig. 2. The pulse power pack produces a train of

narrow pulses in addition to variable d.c. power.

The pulses are fully visible when the throttle is

turned down, but disappear gradually as the throt-

tle voltage builds up to full power. Instant rise

of pulse from zero to maximum provides immediate

power to operate train when crawl knob is turned up.

ELECTRONIC EXPERIMENTER'S HANDBOOK

05

251382 254564

FM.

-oo6Ò66boo

-

MP PJN,

NOTE

AT I. 4LL 5E5J57055 ±10X1 /25

2 N4 INTENTION4L.'.r OMITTED CONTROL <<

-

Fig. 3. Crawl control R7 adjusts pulse width to give desired crawl speeds when S2 and S3 are turned

on. Throttle R12 is part of a voltage divider that drives emitter followers Q7 and Q8 with varying d.c.

i2v

A ov-

1

i2v

B 3V

_L_

C 3v

Fig. 4. Pulses rise to maximum as soon as power

is turned on (a), providing immediate train start.

Crawl knob adjusts pulse width for varying train

loads and desired crawl speeds. Throttle adjusts d.c.

at emitter of Q8 (b) to run train at desired speeds.

With throttle turned down (c), pulses appear prom-

inently, then fade away as d.c. is turned up.

1966 Foll Edition

tion of the pulse width which you ad-

just with a crawl control. This varies

the circuit RC time constant.

How It Works. From Fig. 3 it is ap-

parent that pulse power, which makes

your trains run like a dream, calls for a

rather sophisticated circuitry. Let's give

the circuit a once -over and see what we

mean. First, we have transformer T1

stepping down the 117 -volt a.c. primary

power to approximately 12.6 volts. This

12.6 -volt supply branches off to jacks

J1 and J2, where it is available to oper-

ate switch machines, signal lights, and

other accessories. Some of this power is

also tapped off and applied to the bridge

rectifier circuit (D1 through D4), from

where it will eventually operate your

trains.

The 6 -volt #47 pilot lamp (11), wired

from the center tap to one side of the

transformer secondary winding, is mere-

ly an indicator to tell you when the

power is on. You can break down the

rest of the power pack into its pulse

forming and control circuits. the vari-

able d.c. circuit, and the short -circuit

protection circuit. If you care to, you

47

can throw in polarity switch 84 (forward

and reverse) for good measure.

The Pulse Circuits. These circuits be-

gin with Q1 and Q2 which comprise a

free -running multivibrator. The collector

of Q2 puts out a 60 -cycle square wave

which is fed through S2 and S3 to pulse

generator Q3 for conversion to narrow

pulses. These pulses are then amplified

by Q4 and appear as shown in Fig.

4(a). CRAWL ADJ potentiometer R7

adjusts the pulse width to suit varying

train loads and desired crawl speed. The

CRAWL ON -OFF switch (S2) is used to

disable the crawl feature, if desired.

Switch S3 is ganged to the main throttle

so that it cuts off the pulses when the

Fig. 5. This layout and accom-

panying dimensions are valid

only if the recommended Bud

cabinet is used. Lay out, drill,

and punch all holes as shown.

If you use another cabinet,

this layout can still serve as

a guide. The transistor mount-

ing holes remain the same, re-

gardless of cabinet dimensions.

throttle is turned all the way down to

where you hear a "click."

Variable D.C. Circuit. In the variable

d.c. function generator circuit, R12 and

R13 form a variable voltage divider, the

output of which is fed to emitter fol-

lowers Q7 and Q8. The emitter followers

provide a low impedance source for the

voltage. The output voltage at the emit-

ter of Q8 is variable from about 3 volts

to 12 volts, as shown in Fig. 4(b), de-

pending on the setting of R12, the speed

control potentiometer.

Diodes D6 and D7 are used to mix the

two functions (pulse and variable d.c.)

together. The pulses and variable d.c.

are fed to emitter followers Q5 and,.Q6

rn

5/8"

3/8 "DIA 3/8"

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48 ELECTRONIC EXPERIMENTER'S HANDBOOK

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Rear view of transistor power pack showing location

of power transistors Q5 and Q6. Be sure to use a

rubber grommet to protect line cord from damage.

which provide a high current output.

Their output waveform is as shown in

Fig. 4(c).

Short Circuit Protection. Lamps 12

and 13 in the emitter circuit of Q6 pro-

tect the entire unit against accidental

short circuits or overloading. Together

with a red jewel mounted on the front

panel, they also double as a track short

indicator. These lamps are of the or-

dinary 12 -volt auto dome light type,

each rated at 1.2 amperes. Putting them

in parallel, however, increases the cir-

cuit capacity to 2.4 amperes.

When the filaments are cold, the lamps

exhibit a very low resistance, and there-

fore act like a piece of wire. When your

loco or other load begins to draw about

1 ampere of current from the power

pack, the lamps begin to glow and their

filament resistance goes up rather sharp-

ly to form a protective load for the

power pack. Thus, even if the output

leads at J3 and J4 were to be shorted

together, no damage would result to the

power pack. But because one of the

lamps is mounted under the red jewel,

you would know there was an overload

when it lit up.

The FWD -REV switch (Si) is an

ordinary d.p.d.t. switch wired to reverse

the polarity of the d.c. voltage as it is

flipped from one direction to the other.

Construction. Assuming you have ob-

tained the Bud cabinet called for in the

Parts List, you now proceed to lay out

and drill the holes as shown in Fig. 5.

After drilling all holes and deburring

them, mount the power transistors on

the back panel, making certain you use

the mica strip and washers supplied

with the mounting kit to insulate the

transistors from the case.

Figure 6 shows the general layout of

the wiring and other circuit components.

Electrolytic capacitor Cl should be

wrapped with electrical tape to insulate

it from the case. Notice that it is

mounted with a plastic clamp.

The circuit board is made from a

piece of 23/4" x 63/4" Vectorbord. Ob-

serve the location and mounting position

of 11 and 12. Bring out long leads to the

panel mounted components, and use a

(Continued on page 137)

50

CIRCUIT

BOARD

STANDOFF

With bottom plate removed, laced wiring

harness can be tucked away to one side

during repair or maintenance of the unit.

The component circuit board is supported

with metallic or insulated standoffs. To

install the line cord, thread free end

through grommet at rear of cabinet. Sep-

arate ends of cord back 12 inches and tie

into a knot to take up any strain on cord.

ELECTRONIC EXPERIMENTER'S HANDBOOK

BUILD THE LI'L DUSKER

This light sensor turns your lights on

at dusk, and off at dawn,

automatically- without a timer

By DON LANCASTER

HERE'S A CLEVER, useful, and eco-

nomical photoelectric controller you

will want to build. Li'l Dusker, the "light

watchman," will earn its keep turning on

lights for you in dark driveways, stair-

ways, and halls at night, and then turn-

ing them off at dawn when they are no

longer needed. And while you are away

from home, Li'l Dusker will turn on that

important "there's somebody home" light

that will deter all but the most persistent

intruder.

But Li'l Dusker has many more tal-

ents. It can serve as an automatic door

opener, or a light- operated relay. And

if you want an automatic flasher with

adjustable frequency, or a low -cost touch

control for a desk or table lamp, call on

Li'l Dusker.

About the Circuit. Although Li'l Dusker

acts like a magician, the circuit is really

1966 Fall Edition

a simple one, as Fig. 1 shows. It is just

a d.c. power supply (R1, Dl, and C1) ,

and a limiting resistor (R2) , a cadmium

sulfide photocell (PC1) , and a d.c. relay

(K1) , all connected in series.

The cadmium sulfide photocell has a

low resistance in the presence of light

and a high resistance in darkness. This

characteristic enables the Dusker to tell

night from day. Therefore, as light in-

creases with the break of dawn, the

photocell resistance decreases, increasing

the current in the relay coil, and causing

the relay to pick up.

The relay sensitivity -the light inten-

sity that will cause the relay to pick up

-is established by the value chosen for

the current -limiting resistor (R2) . The

circuit application determines which set

of relay contacts is used. For dusk -to-

dawn control, the NC ( normally closed )

51

SOI

100W

MAX. LOAD

Fig. 1. For dusk -to -dawn control, connect load

circuit to the NC relay contacts; for photocell re-

lay application, connect load to the NO contacts.

PARTS LIST

CI- 4 -µJ., 250 -volt electrolytic capacitor

D1- 130 -ma., 400 -P1V rectifier (RCA 40265 or

equivalent)

K1- Phillips -Advance #1524 -1C relay, 24 -volt,

1100 -ohm coil, 1 amp contacts (Newark 60 F

1749 or equivalent)

PC1- 200 -volt, % -watt radium sulfide photocell

(RCA 4403- Allied Radio 7 Z 435 or Polaris

Maj -1- Allied Radio 7 Z 565)

PL1 -100 -volt, 2 -pole standard plug (Amphenol

61 -M or equivalent)

R1 -15 -ohm, Y2-watt resistor

R2- 10,000 -ohm, 2 -watt resistor

S01 -110 -volt, 2 -pole universal receptacle (Am-

phenol 61 -F or equivalent)

1--Case made from Millen 74400 octal base and

shield (Newark 40 F 734)

Misc. -"Pop" rivets (4), 17 "- square piece of

1/16" single -sided PC board, funnel eyelets

for PC board (24), %" x %" aluminum sheet

(2), 2" x 11/2" plastic sheet or film, glue or

sealant, wire, solder

contacts are used; for door -opening op-

eration, the NO (normally open) con-

tacts are employed instead.

Construction Pointers. Li'l Dusker can

be encased for mounting on a windowsill

or anywhere outdoors, and can be plugged

into a standard wall receptacle or octal

socket. In Fig. 2(A), the Dusker has its

own line cord and is mounted on a win-

dowsill where it can "look" outside. For

general outdoor use, BX, ROMEX, or

other approved wiring can be brought in

through the top of the unit. To make

the Dusker weatherproof, the outlet can

be recessed and the entire unit mounted

as shown in Fig. 2 (B) in a sheltered

area. If Li'l Dusker is to serve as a door

opener, the case is used as it comes, with

only slight modification. You can then

make a companion light source, perhaps

with a 6.3 -volt filament transformer and

an automobile 6 -volt lamp bulb and sock-

et. You might want to add a low -cost

LINE

CORD FEET

(A) WINDOW SILL

BX OR ROMEX

RECESSED SOCKET

(B) OUTDOOR

O

_OCTAL PLUG

(C) INTERRUPTED BEAM CONTROL

LIGHT SOURCE

0

(D) PLUG IN

Fig. 2. Select one of these four case configurations

for the Dusker. For table or desk lamp touch

control applications, the outer casing is not used.

lens to focus the beam and thus provide

for greater separation between the

Dusker and the light source.

For touch control applications, you

can omit the case altogether and mount

the circuit directly inside the base of a

table or desk lamp.

Construction Details. Using a Millen

#74400 octal base and shield, cut the

case for the plug -in configuration follow-

ing the details given in Fig. 3. In addi-

tion, two mounting brackets will be re-

quired. These can be made out of a small

strip of aluminum sheet cut as shown in

Fig. 3 (D) . Drill the holes first, then

52 ELECTRONIC EXPERIMENTER'S HANDBOOK

bend the bracket into shape using long -

nose pliers, or a vise, if one is available.

You will also need a piece of tough

plastic film to serve as a protective win-

dow for the photocell. Acetate, Mylar,

or anything similar will do. Avoid using

brittle material that will crack or break.

The parts are mounted on a small

(1%- inch -square) printed circuit board

laid out, drilled, and cut as shown in

Fig. 4. Eyelets are used in the holes

where shown to give the circuit board

some extra ruggedness. The aluminum

brackets are riveted to the circuit board

SHIELD

3/4"

3/4" 3/4"

PUNCH

I /8'

DRILL

(2)

°

1/8° DRILL(2)

MATCH DRILL

TO ORIGINAL

BASE HOLES

J

PLASTIC

WINDOW

I/4-*-1

I/8"DRILL

.(21

L J

BASE

(IF NOT REQUIRED

DISCARD OCTAL PLUG

AND MTG. FROM

ORIGINAL UNIT)

I I/2"-H 1-9/64" PUNCH KEYED OR

(B) 1-5/32" ROUND

ALUMINUM BRACKET

(2 REQUIRED)

8

1/16"

DRILL 1/4

(2) 7/8

(D)

Fig. 3. The base and shield of case are cut and

punched as shown. Then they are finished with

lacquer or paint, or are anodized. The two brack-

ets at bottom are made from 1/32 -inch alumi-

num sheet. Window is made from heavy plastic

film such as Mylar; avoid using brittle material.

1966 Fall Edition

* I /16" DRILL(4) MATCH

TO BRACKETS

DO NOT EYELET

UNTIL ASSEMBLED

`

I) _

*USE 5/64'

DRILL (5)

DO NOT -10.

EYELET *

3/4"

I /16 "DRILI(15)SET

WITH

UNNEL EYELETS

1 -3/4"

Fig. 4. This is foil side of printed circuit board.

Numbers in parentheses indicate holes required.

( A)

FOIL SIDE

Fig. 5. Here's the component layout. Photocell PC1

is mounted on the foil side of the circuit board as

shown in (A). All of the other parts are mounted

on the bare side of the board as shown in (B).

in the locations indicated in Fig. 5, again

using eyelets.

The photocell is glued to the back of

the printed circuit board with silicone

53

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ollllnllmlllll luullu0l11111u1

immateliMMAMMINI

IlIIlIIfiNU

N S01 1011,

ALUMINUM

BRACKETS

EYELETED TO

7PO BOARD AND

POP RIVETED

TO CASE

I I

PLASTIC WINDOW

GLUED AND THEN

RIVETED IN

PLACE

Fig. 6. After all the parts are preassembled on

the circuit board, and the unit has been fully

wired and tested, install the plastic window and

pop -rivet the aluminum brackets to the case shield.

rubber sealant (Fig. 6) . The plastic

window is glued in place and allowed to

dry before the aluminum brackets are

riveted on.

Before making connections to the re-

lay, refer to the Special Applications

section at the end of this article to deter-

mine the proper relay terminals to em-

ploy. In general, the NC contacts are

used when decreasing light must ener-

gize the load, and the NO contacts are

used when increasing light is to energize

the load.

Checkout and Final Assembly. Before

final assembly, you will want to check

out the circuit to make sure it works the

way you want it to. For this you can

use a flashlight or other suitable light

source. If it becomes necessary to change

the sensitivity of the unit, change the

value of R2 as necessary. But you can

decrease the sensitivity by merely re-

ducing the amount of light reaching the

photocell. A filter made of colored cello-

phane, Polaroid material, or tinted ace-

tate placed over the light window will

work well.

Once you have obtained just the right

sensitivity for the particular application,

complete the assembly by "pop " -riveting

the circuit board and bottom plate to the

case. Once pop- riveted, the Dusker be-

comes tamperproof and there's no way

to take the case apart without using an

electric drill. If it becomes necessary to

open the case again, use a ', " high -speed

bit to drill out the rivets.

Once assembled, operation of the

Dusker is a snap. Just plug it into a

convenience outlet, plug the load or lamp

into its receptacle, and away you go.

Special Applications. For operation as a

light flasher, the Dusker must be wired

as a dusk -to -dawn control. This makes

it essentially an oscillator with negative

feedback. The Dusker must be positioned

25-100W

BULB

COM

117 VAC

S0 -60C PS

LINE CORD

DI

R2

CI PCI KI

Le, NOTE SI IS SPST

MICROSWITCH

Fig. 7. This low -cost touch control circuit can

easily be wired to any desk or table lamp by adding

a microswitch across PC1. To turn on lamp, touch

Si gently. To turn off lamp, bring hand near PC1,

shielding it from light. For proper operation, PC1

must be shielded from other strong light sources.

in such a way that the light shines in its

"eyes." Initially, when the light is off,

the photocell turns it on: the Dusker

"sees" it and turns it off again. This

cycle can go on as long as the unit is

plugged in. To adjust the on -off rate

(frequency), adjust the amount of light

that gets fed back. Changing the bulb

size will usually do the trick.

For "touch control" operation, mount

the circuit board (less case) in the base

of a lamp so that only the lamp light -

(Continued on page 139)

54 ELECTRONIC EXPERIMENTER'S HANDBOOK

BUILD

SOLID -STATE SLOT CAR

SPEED CONTROL

Turn your slot racing car into a

mighty fast cat, yet maintain absolute

speed control every inch of the way

S IMPLE TO BUILD, inexpensive to

own, a dream to operate! We're

talking about a transistorized slot rac-

ing speed controller that lets you run

your model racing car almost like the

pros do at Le Mans. From the instant

you start, all the way through the slop-

ing, winding, pretzel- shaped speedway,

till your car zooms across the finish

line, you'll enjoy the full pleasure of in-

By JAMES FISHBECK

stant and complete control over your

racing car's speed and performance.

Because the push- button type of speed

controller controls the car's speed by

applying a series of pulses, the accelera-

tion is in steps, rather than through a

smooth, linear variation from low speed

to top speed. This new solid -state speed

controller uses a carbon potentiometer

wired to a d.c. amplifier to provide a

smooth variation in resistance, which

gives your car finger -tip speed control

and all the power it needs to perform

with style and class.

How It Works. The speed controller

consists of a dual amplifier and two

separate potentiometer throttles -one

for each amplifier (Fig. 1) . Each am-

plifier output drives a separate lane of

the speedway.

Potentiometer R1 is shown connected

across the d.c. power pack supplied with

the racing car set. Its center tap is wired

to the base of emitter follower Qi, there-

by controlling the output of this stage.

The output of Q1 is directly coupled to

the base of Q2, the power output stage,

which supplies power to the track

through Fi. The other amplifier oper-

ates in the same way.

Since the power pack is nothing more

than a step -down transformer feeding

into a full -wave rectifier, it puts out an

unfiltered d.c. which is quite suitable to

run racing cars. Because the transistor

amplifiers do not perform well with pul-

sating d.c., a filter capacitor (C1) is put

across the power pack output to filter

out the ripples before they get to the

amplifier.

If you operate a speedway with more

Fig. L I n this two -lane

speed controller, each chan-

nel is a mirror image of the

other. The speed control po-

tentiometers are mounted

on individual chassis, and

are connected to the ampli-

fier circuit by long cables.

For compactness, mount the

slot racer power pack on top

of the amplifier chassis.

than two lanes, you can build a separate

amplifier for each lane with no degrada-

tion in performance (as long as you

don't exceed the wattage rating of the

power pack) . Just be sure you use identi-

cal components in all the amplifiers and

speed control potentiometers.

Construction. Except for the two speed

controller potentiometers, all parts, in-

cluding the power pack supplied with

the slot racing set, are mounted on a

2" x 5" x 7" aluminum chassis (Figs.

2 and 3 ) . The two speed controller po-

PARTS LIST

(.1 -- 500 -µf., 25 -volt electrolytic capacitor (1

null Dubilier BBR 500 -25 or equivalent

Fl, F2-1-ampere fuse (Littelfuse 3AG)

Ql, Q3 -2N109 transistor

Q2, Q4 -2N554 transistor

RI. R3- 5000 -ohm carbon potentiometer, linear

taper (IRC -CTS 011 -114 or equivalent)

R2, R4- 1000 -ohm, 1 -watt, 10% resistor

TS1- 4- terminal screw -type terminal strip

(Cinch -Jones 17 -4 or equivalent)

1 -2" s' 5" .c 7" aluminum chassis base (Bud

AC-402)

c 2 .e I ! s" aluminum Miniboxes

Pod CU-3017A)

Misc.- -Two miniature fuse posts (Littlefuse

342014), multiple- conductor intercom cable,

power pack from existing racing set, two

knobs, mounting hardware, transistor sockets.

rubber grommets, hookup wire, etc.

56 ELECTRONIC EXPERIMENTER'S HANDBOOK

Fig. 2. Large chassis allows plenty

mounting the power pack. Use mounting kit for Q2

and Q4, and be sure to mount Ql and Q3 on sockets.

Cables at sides of chassis go to speed controllers.

of room for

tentiometers are mounted on individual

31/4" x 21 /s" x 11 %" aluminum Miniboxes.

After drilling, punching, and deburring

the chassis, insert rubber grommets

through all cable entrance holes.

If your power pack is too large to fit

on the size chassis recommended, get a

bigger chassis. The size suggested hap-

pens to be convenient, but you have

complete freedom to select the packag-

ing that best suits your needs. Inciden-

tally, the layout of components is not

critical, either. Just use good practices

to come up with a professional looking

job. You must mount the two small

transistors (Q1 and Q3) on sockets,

however, and you must use mounting

kits for the power transistors (Q2 and

Q4). After you have mounted each poten-

tiometer on its Minibox, wire it up as

shown in Fig. 1 using the three -con-

ductor flexible cable ( you can make the

cable any length you wish) . Connect

the other end of the cable to the main

chassis.

Check It Out First! Having completed

all your wiring, you are now itching to

fire up the unit and race away . . . but

1966 Fall Edition

don't, yet. You'd better go over all the

wiring, very carefully, and check it out

against the schematic. Above all, you'll

want to make certain you haven't re-

versed any of the leads to the power

pack, as this could play havoc with your

transistors. If everything's okay so far,

wire the output terminals to the track

and plug the unit in.

If either car runs in the wrong direc-

tion, reverse the track leads to that

lane. Do not reverse the leads at the

power pack to correct this condition.

Should either controller potentiometer

work backwards, that is, if the car in-

creases speed when the knob is rotated

counterclockwise, reverse the two cable

leads across the potentiometer end ter-

minals. If one car tends to run slowly when

the potentiometer controlling that car is

all the way off, one of the transistors

in the amplifier associated with that

lane is defective. To determine which

transistor is at fault, remove the smaller

transistor (Q1 or Q3) from its socket.

(CAUTION: always turn the power off

when removing or inserting any transis-

tor.) If the car still runs slow with the

transistor removed, replace the larger

transistor. If the car doesn't run at all

now, replace the smaller transistor. -MI-

Fig. 3. This underchassis view shows parts layout

and wiring. Capacitor Cl is wired across the power

pack output to provide filtered d.c. to the ampli-

fiers. Use rubber grommet at all cable entrances.

57

BUILD THE

ELECTROLOCK

By MURRAY E. COULTES

A keyless wonder -

you just dial

the secret combination

to open it

THEY SAY daisies don't tell. Perhaps

the same can be said of the "Electro-

lock." Unlike conventional locks which

give tell -tale sounds when the right com-

bination registers or which can be easily

jimmied, the Electrolock is electronic and

can't be opened by anyone but yourself.

It uses no key; instead, you dial the four

correct digits, and presto -it opens.

As seen in Fig. 1, the Electrolock is a

series circuit consisting of a battery, a

solenoid, a push- button switch, and four

rotary switches. The plunger of the sole-

noid is connected to a small barrel bolt,

and a small spring holds the bolt closed

when the solenoid is not activated. But

when you dial the right four numbers

and depress the push button, you com-

plete the circuit, current flows through

the solenoid, and the plunger pulls back

the barrel bolt. When the push button is

released, the spring pulls the bolt into

the closed position again.

There are many ways in which you can

construct the Electrolock. The combi-

nation that will open the lock depends

on the switch connections you use. Usu-

ally, a 4.5 -volt battery suffices, but for

more snap you could try a 6- or 9 -volt

battery.

Drill a hole through the barrel bolt

the same size as the hole through the

plunger of the solenoid, and fasten them

together as shown in Fig. 2. Be sure to

drill the hole parallel to the knob so that

the bolt will not be turned down when

the plunger is connected to the bolt. The

spring is fastened between the screw

connecting the solenoid plunger and bar-

rel together to another screw mounted

External battery can be connected to the banana

jacks to overcome a weak internal battery. However,

the lock cannot be opened without the combination.

on the barrel lock frame. If you can't

find a suitable spring, use two or three

smaller ones tied together.

To operate the Electrolock, dial the

correct combination and depress the

push- button switch. The bolt should

58 ELECTRONIC EXPERIMENTER'S HANDBOOK

11

100

90

12

Si 2

SI 03

S5

2-- 3

SOLENOID

1

12

its

100 /2

941 O S3

8 4 8 4

7 5 7 5

6 6

12 12

11 1 I II I

10 2 10 2

9QS2 53 90 S4 3

8 4 J^2 S 4

7 5 7 55

6 81 l /

4.5V

Fig. 1. Any combination can be made by selecting

different switch positions. As there are more than

20,000 possible combinations, chances of "picking"

the lock are discouraging. Furthermore, if you add

a fifth switch, you can get 248,832 combinations.

PARTS LIST

B1 -4.5-volt battery

11, 12- Banana jack

S1, S2, S3, S4- 12- position rotary switch

SS- Push -button switch, normally open

1 -6 -volt d.c. type solenoid (Guardian Model 11

or equivalent)

Misc.-Barrel bolt, aluminum strip battery

mount, machine screws, hookup wire, solder

BARREL BOLT

4 -40 MACHINE SCREW

SOLENOID

Fig. 2. Spring holds barrel bolt in closed position.

Solenoid retracts the bolt when the proper combi-

nation is dialed and the push button is depressed.

snap open. If it doesn't, check your wir-

ing, particularly the switches. You may

have to adjust alignment and spring

tension to get smooth, positive action.

You've probably guessed the reason for

putting the two banana jacks on the

1966 Fall Edition

SI VI V2

Fig. 3. Align barrel bolt with solenoid to obtain

smooth action without bolt rotation. Battery and

switches can be mounted in any convenient position.

front panel. In case the battery inside

the unit hasn't the energy left to open

the lock, you just connect a fresh battery

across the terminals and dial the combi-

nation. Remember, you can't open the

lock if you forget the combination. -[3

59

DON'T PANIC...

PUSH

THE BUTTON!

7t

Don't you dare

build this box

.... unless you want to

create pandemonium

By BRUNO M. LARSEN

TS PANIC siren is guaranteed to set

1 he most blasé individual or "stuffed

shirt" on his ear, and cause the unwit-

ting "victim" who sets it off a moment or

two of embarrassed concern. For it is a

certainty that if this box is left alone

60

some venturous soul will be tempted to

throw that switch. And when he does,

you are sure to see a panic in the making.

Once the main switch is thrown, and

after a one- or two -second delay, the

box lets out a wailing sound akin to that

of a fire engine, ambulance, or police

siren. Lights go on and, within a sec-

ond or two, start to blink like mad. The

"victim" will snap the switch back to

OFF, only to find, to his chagrin, that

the switch has no effect whatsoever on

the rising siren wail, or on the lights.

If the switch thrower can keep a cool

head, he'll "push the panic button" -the

one innocently labeled SQUELCH -and

ELECTRONIC EXPERIMENTER'S HANDBOOK

sigh with relief as the siren starts on its

downward wail. If he releases the but-

ton while the siren is dying down, as he

probably will, the siren immediately

starts up again, whereupon the "victim"

quickly presses the panic (SQUELCH)

button again. But this time he isn't tak-

ing any chances -he's going to keep his

fingers on that button until the sound

ceases completely. As it does, he smiles

triumphantly. (All this time the lights

are still blinking -the squelch button

has no effect on the lights.) Once again

he releases the button -and once again

the siren starts.

What the "victim" doesn't know is that

the contraption will go off by itself once

the main switch is thrown to OFF and

a preset time has elapsed. Every time

he throws the switch he recycles the

panic box, and when he presses the but-

ton he only interrupts the sound, with-

out affecting the cycle.

How It Works. The secret of the panic

box is a delay incorporated in the ON-

OFF switch that causes the siren and

light circuits to remain activated for

from 60 to 90 seconds after the switch

is turned off. Pressing the SQUELCH

button is the only "known" action that

can be taken to start the siren on its

downward wail.

The heart of the panic box is a siren

module (Fig. 1) connected to a speaker

and a battery. The module contains a

relaxation oscillator (Q1) and a direct -

coupled output stage (Q2) . The oscilla-

tor creates a tone which rises from 5

to 3000 cycles within 30 seconds, and

creates a downward wail after the delay

switch shuts itself off.

Switch S1 is a concealed slide switch

that is normally left ON. It is used only

Fig. 1. Secret of continuous panic -

making noise output is the built -in

delay in switch S2; outwardly it

seems to be an ordinary on- and -off

toggle switch. Switch S1 is concealed

and normally left on. Only you know

where to find it and shut the thing

off in case of panic. Panic button

S3 has no effect on the delay action

of S2 and opens the siren circuit

only as long as it is held down. If

the victim's patience runs out before

the delay cycle is completed, he is

most likely to recycle the unit so

that it will not cut out by itself.

1966 Fall Edition

r

SIREN

MODULE

S3

SQUELCH

PUSH BUTTON-El

Fig. 2. Observe

color -coded leads

coming from the si-

ren module, and

connect as shown.

The lamp circuit

and its batteries

are optional and

can be omitted.

This circuit has

been included only

for psychological

effect. Lights have

built -in blinkers.

r

L

GRN

RED

BLK

YEL

SPKR

SI

SLIDE SWITCH

BI +

B2 +

52 ON-OFF

--' 83 +1-KD

11--1 Ba +F- L2

-J

NOTE:CIRCUIT WITHIN DOTTED LINES

MAY BE OMITTED WITHOUT

AFFECTING OPERATION OF

SIREN MODULE

by those in the know to shut the works

down. You can have fun in another way

-leave the switch off and your "victim"

won't be able to victimize someone else.

An 8 -ohm, 21, PM speaker serves as

the siren horn, and the entire unit is

powered by two or four 9 -volt batteries,

as shown in Fig. 2. Two of these bat -

teries-in parallel -provide power for

the siren, and the other two -also in

parallel -provide power for the lights.

Construction. The box, a 61'16" x 5932"

x 2 íI" plastic meter case, houses all the

components, including the speaker and

the batteries. The box also functions as

a resonant cavity and greatly amplifies

the siren sound. What's more, the same

BL

- _ _

tl

loudness is maintained during the up-

ward and downward wails of the siren.

Other types of enclosures can be used,

provided care is taken to select a box

that will resonate properly. Metal boxes

are generally poor resonators, while

wooden boxes make ideal resonators. The

SLIDE

SWITCH

SI

SPEAKER

Speaker and "hidden switch" are mounted on back

of box. Better chain the box in place lest your victim

heave it out the window when the alarm sounds off.

arrangement of the components is left to

the discretion of the builder.

The slide switch (Si) can be wired so

that it opens only the siren cycle, or

both the lights and the siren. To make

this switch less conspicuous, the pro-

PARTS LIST

Bl, B2, B3, B4 -9 -volt transistor radio battery

(Eveready 216, or equivalent)

Li, L2-4.9 -volt, 0.3 -amp. flasher bulb (GE -407

or equivalent)

Sl- S.p.s.1. slide switch

S2- 60- second delayed action light switch (Lafa-

yette Radio 34 R 3805, or equivalent)

S3- Normally- closed momentary push -button

switch

SPKR -2;_ ", 8 -ohms speaker (Philmore TS -25,

or equivalent

1 -Siren module (Lafayette Radio 19 -0105, Ol-

son Radio TR 71, or Saxton Iii -iron Model

IIS available at parts distributors)

1 -6- 15/16" x 5 -9/32" x 2- 5/16" plastic meter

case (Allied Radio 87 P 886 or equivalent)

1- Matching panel (cover) for above case (Allied

Radio 87 1' 888 or equivalent)

2 -Bulb sockets with red- faceted jewel lenses

(DIALCO 510M or equivalent)

4 -Type 5D battery clips (Cinch -Jones, or

equivalent)

4- Battery brackets (Keystone No. 95, or equiv-

alent)

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

terminal strips

62

PANEL

LAMPS

SALCIA'

PUSH BUTTON

S3

S IDE

SWITCH

sl

SPEAKER

CLAM P

SPEAKER

TIME

DELAY

SWITCH

SIREN

ODULE

BAI SERIFS

12 OR 4

(SEE TEXT)

Parts layout and box dimensions are not critical.

Paint the outside fireman's red and use large bold

letters. Battery mounting brackets are optional.

truding stem can be cut off flush with

the plastic box. You can use 6 -32 hard-

ware to mount the components, or you

can fasten them permanently to the box

cover with pop rivets.

The small speaker has no mounting

holes or flanges (actually, there are a

number of speakers available with

mounting holes) , but you can use a cou-

ple of mounting clips with washers to

secure the speaker to the back cover of

the meter case. Before mounting the

speaker, drill a number of holes in the

mounting surface to vent the speaker

cone to the outside of the enclosure.

Size of the holes is not critical. Also,

to make certain that the batteries clear

the main ON -OFF switch and the light

sockets, install battery mounting brack-

ets near the edge of the box cover.

There is nothing critical in the wir-

ing. Nor is there anything functional

about the blinking lights, which are in-

cluded purely for psychological purposes

-you can omit this circuit if you wish.

The outside of the box can be finished

and stenciled in any manner you wish.

For example, the SQUELCH button can

be labeled PRESS HERE, or PANIC

BUTTON. Or WARNING, DANGER,

etc., can be substituted for CAUTION.

Setting the Trap. Make sure that the

concealed slide switch is in ON position,

and the master ON -OFF switch Is set to

OFF. Then lay the box in a conspicuous

place, and be ready when the fun starts.

Happy panic ! -®-

ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER

2

AUTOMOTIVE

ELECTRONICS

1966 Fall Edition

Only 21 /2 years ago, when POPULAR ELECTRONICS

published a product -by- product analysis of the transistor-

ized ignition market, there were about 30 different manu-

facturers in business. And they were offering products

based on 11 different designs. Thirty months later there

appears to be only a half dozen active manufacturers

selling three or four different designs. What happened?

The answer to the above question is plain and simple -

the 1964 transistorized ignition systems were dropped

like the proverbial hot potatoes. Some systems were so

poorly designed as to be almost unbelievable. One or two

apparently unscrupulous manufacturers turned in a "fast"

buck and got out of business. The good products suf-

fered because of class association and several manufac-

turers switched to the production of other goods. But

possibly the one major contributing cause to the downfall

of transistorized ignition was that many 1964 circuits

weren't the very best.

The Editors of EEH have had the opportunity to exhaus-

tively test the only logical answer to the transistorized

ignition problems -the capacitive discharge circuit. In the

pages that follow are the plans for one of the best igni-

tions systems we have ever published. Although special-

ized components are called for, this is one system (among

the two or three that survived from 1964) that we feel

deserves your unqualified attention.

64

NOW! A UNIVERSAL CD IGNITION SYSTEM Murray Gellman

69

PROTECT YOUR CAR'S ELECTRICAL SYSTEM Charles Erwin Cohn

70

HEADLIGHTS -ON ALARM Thomas R. Yocom

71

AUTO VOLTMETER SHOWS YOU'LL GO Joseph Tartas

63

NOW! A UNIVERSAL

CD IGNITION SYSTEM

By MURRAY GELLMAN

Modified unit fits

12- or 6 -volt cars,

including

positive ground ignition

Because of the excellent response to the

article on a "Transistorized Capacitor

Discharge Ignition System" by Murray

Gellman (in the 1966 Spring Edition

Of ELECTRONIC EXPERIMENTER'S HAND-

BOOK), the author has provided construc-

tion details to modify the basic 12 -volt

negative ground circuit for operation

with 6- or 12 -volt positive, or 6 -volt

negative ground ignition systems. On

page 66 you'll find some representative

excerpts from our reader mailbag, with

the appropriate answers. THE EDITORS

WHETHER YOU ARE the owner of a

foreign car with a 6 -volt ignition sys-

tem, or an American car with a 12 -volt

positive or negative ground ignition, you

can now enjoy the advantages of in-

creased gas mileage, quicker starting

even in cold weather, longer life for

breaker points and spark plugs, and

more power at high speeds with a tran-

sistorized capacitor discharge ignition

system. You can build the system from

scratch for the car you presently own,

and modify it later, if you wish, to fit

any other car you might buy. The 12-

volt negative ground system (and how

to build it) was described in the 1966

Spring Edition of the ELECTRONIC Ex-

PERIMENTER'S HANDBOOK. The following

instructions tell you how to modify the

basic design to fit your car.

Six -Volt Negative Ground Ignition. The

basic 12 -volt transistorized capacitor

discharge ignition system can be modi-

64 ELECTRONIC EXPERIMENTER'S HANDBOOK

r

01

1N2615

04

C2

Iyf.

H.V.

TO

DIST.

03

MCR1605-6 A

2NI100

TO

IGNITION

SWITCH

C3 50y

ICI

4yf.

2 5611

RESISTORS

IN PARALLEL

DI

IN463

C6

132yf. RS

1.81<

D5

1N2615

C4

226f.

TC5

OyI.

TO POINTS

IN DISTRIBUTOR

G

T 3 R7

100f1

R3

660K

2 .OND

Fig. 1. In this positive ground ignition system, the d.c. resistance of pulse transformer T2 replaces resistor

R6 in negative ground circuit. Also, positions of R1 and R2 are reversed, as is polarity of diode Dl.

Component side of positive ground circuit board

showing parts location and orientation. All compo-

nents are color- coded, and the appropriate colors

marked on the circuit board to facilitate assembly.

fled to operate on six volts by making

the following changes : (1) add another

10 -ohm resistor in parallel with R1; (2)

add another 820 -ohm resistor in parallel

with R2; (3) short out R6 (27 ohms)

by connecting a heavy jumper wire across

it; and (4) replace the SPC -4 trans-

former (T1) with six -volt transformer

SPC -4A (available from SYDMUR, P. 0.

Box 25A, Midwood Station, Brooklyn,

N.Y. for $14.95).

1966 Foil Edition

Positive Ground Ignition. To convert

the 6- or 12 -volt negative ground system

to positive ground (see Fig. 1) using the

same printed circuit board, the collector

center tap must be removed from ground.

This can be done by cutting the copper

strip above and below the letter G with

a single -edge razor blade. Hold a clean

soldering iron -one having no solder on

the tip -on the copper strip next to the

letter G. Remove the strip using the

razor blade. Drill a hole (using a x$52

TOROID CORE

Fig. 2. Fabrication details of positive ground pulse

transformer. Shown are a completely assembled

unit, the ferrite toroid core, and coil assembly forms.

65

MORE ABOUT CAPACITOR DISCHARGE IGNITION SYSTEMS

Q Can I substitute a new ignition coil with

a 250:1 turns ratio for my 100:1 coil now

in the car?

A Yes, but you wouldn't gain enough to

merit the extra cost. Your present coil

used with a CD system will produce ade-

quate voltage at all engine speeds.

Q Must the "condenser" across the breaker

points be removed?

A No. It does no harm -leave it there.

Q I want to wind my own toroid transformer.

How about revealing the winding details?

A Sorry, but this transformer is something

special and a patent has been "applied

for" to cover its construction.

Q What temperatures will the CD system

withstand?

A It has been tested at 60 degrees below

zero (F) and 200 degrees -plus under the

hood.

Q

A The transistors are rated to operate above

Why no heat sinks on the transistors?

Fig. 3. Pulse transformer

is wound on ferrite toroid

core with 300 turns of

bifilar -wound #40 Polyure- RED

thane insulated wire. Wire

terminals are soldered to

the lugs on the coil form.

Q

A

Q

A

Q

A

Q

A

the ambient temperature under the hood,

and, besides, the metal box acts as a heat

sink.

Must I replace the distributor cap and ig-

nition wiring harness?

You might find it advisable to clean out

the cap and check the harness for breaks

or worn spots. Replacement is not a pre-

requisite.

Do I change the engine timing?

No. Just be sure it meets the manufac-

turer's specs. The CD system will not up-

set the timing.

Must I use a printed circuit board?

Why not? What have you got against

space -age engineering?

I used your transformer in another CD

circuit that I saw published this year. The

transistors gave up the ghost. What hap-

pened?

The toroid in this CD system was designed

to match the transistors. Substitution

could lead to a lot of headaches.

FERRITE

TOROID

CORE

2CT

RED

GRN

TO TI

CENTER

TAP

01

BARRIER

STRIP

Fig. 4. Wiring details of transistors and barrier strip

connections for positive ground ignition system.

Terminal marked A- connects to ignition switch.

66

bit) in the copper strip ?!I -inch away

from the end that was cut, and another

hole near the letter Y in the ground

strip. Then, using a #42 bit, drill a hole

above the letter U on top of the printed

circuit board; this hole is used to mount

the pulse transformer (T2).

The pulse transformer is made by

winding 300 turns of bifilar -wound #40

Polyurethane insulated wire on a ?í, -inch

ferrite toroid core. (See Fig. 2.) After

the wire is wound, it should be placed in

a form and the leads connected to the

lugs (see Fig. 3) . The wire leads can be

wrapped around the lugs without remov-

ing the insulation (the heat melts away

the insulation), and then soldered. After

this is done, the form is placed in a

small cup form and filled with epoxy

cement. (SYDMUR will supply the tor-

oid, form, and cup form for $2.50, or the

completed pulse transformer for $4.50.)

The pulse transformer reverses the

polarity of the incoming negative pulse

to the positive pulse that is required at

the gate to make the SCR conduct. No

attempt should be made to drop the B+

(Continued on page 74)

CIRCLE NO. 1 ON READER SERVICE CARD---31.

PROTECT

YOUR CAR'S

ELECTRICAL SYSTEM

By CHARLES ERWIN COHN

Forty -five -cent 1111k pPov ides ¡ e i der-the-hood fire protection

M OST VEHICLE lighting and elec-

trical accessory circuits are well -

protected by fuses or circuit breakers.

However, the main feedline which con-

nects the battery to the generator and

to all circuits, except the starter, and

the circuit wiring up to the fuse block

or circuit breaker very often go unpro-

tected. Should a short occur at a point

ahead of the protective devices, the high

currents would cause extensive wire

damage, battery damage, and possible

fire. At a cost of only 45 cents, it is now

possible to minimize this hazard. A fus-

ible link introduced by Chrysler Corpora-

tion on its 1965 autos can be adapted

for use in any car equipped with a 12-

volt battery system. The part number

is 2580389, and it can be obtained from

any Chrysler dealer.

The link is a short length of 16 -gauge

wire which behaves like a fuse. Because

the regular wiring in the car is much

FUSIBLE

LINK

=12v

FEED LINE

STARTER

SOLENOID

TO

STARTER

Insert fusible link between battery

and main electrical feedline. Should

the link fail for any reason, you can

reconnect the main feedline as before.

1966 Fall Edition

heavier, the link will burn out before the

regular wiring has a chance to do exten-

sive damage in the event of a short. At

30 or so amperes, the link runs hot ; and

at about 40 amperes, it quickly melts.

Normal total current requirements in a

car rarely exceed 30 amperes. For the

system to operate again, once the link

fuses, it must be replaced. Special heat -

resistant insulation is used to safely con-

tain the hot link.

As shown in the diagram, the link is

connected as close to the battery in the

electrical system as possible. It should

not be inserted in the starter circuit.

Usually, the link can be attached to the

"hot" terminal of the starter relay. As

a safety precaution, disconnect the bat-

tery before you install it, and reconnect

the battery after the job is done.

Disconnect the feedline from the sole-

noid, and connect the end of the link

with the larger terminal lug to the sole-

noid and the other end to the feedline.

A small nut and bolt can be used to

connect both wires. All connections

should be firm. The junction of the link

and the feedline should be taped, and

positioned so that it will not accidentally

cause a short circuit.

In the event the link gives way when

you are miles away from a service sta-

tion, reconnect the feedline as it was

originally -after you have cleared the

short circuit. -C-

69

HEADLIGHTS -ON ALARM

Alarm sounds if thé lights are left on

) after the ignition is switched off

By THOMAS R. YOCOM

HOW MANY TIMES have you jumped

into your car, turned on the ignition

switch, ready to go somewhere, only to

have nothing happen -a dead battery!

Why? Because the lights were left on

after the car was parked; during the

winter months the chance of this hap-

pening is greatly increased. You can put

this annoying situation behind you for

good by installing a "Headlights -On

Alarm." It is small enough to be tucked

under the dashboard, and it will sound

an alarm if you leave your lights on

when you turn off the ignition switch.

How It Works. A warning bell or buzzer

goes on when current runs through relay

Should you forget to turn off your lights when

you turn off the ignition switch, the alarm will

sound -unless you install a disabling switch (S1).

PARTS LIST

DI, D2, D3, D4- 1Á'34A diode or equivalent

K1 -5000 -ohm remote -control relay, s.p.s.t., pull

in at 1.4 ma., drop out at 1.2 ma. (Lafayette

99 R 6091 or equivalent)

R1, R2 -2400 -ohm, 1/2-watt resistor

S1- S.p.s.t. switch (optional -see text)

1 -12 -volt buzzer

K1. When the ignition switch is turned

on, a small current on the order of 5 ma.

will flow through R2. No current can

flow through K1 because D2 is reverse -

biased at essentially full battery volt-

age. The ignition system and any other

electrical devices connected through the

ignition switch operate in a normal

manner.

When the parking or driving lights

are turned on, current runs through the

lights as usual, and also goes through

R1. Current cannot go through K1 be-

cause of the reverse -biased condition of

D2. However, if the ignition switch is

turned off, the bias on D2 is removed,

and if the headlight switch is still on,

current will run through K1, D2, and R2,

and energize the relay to turn on the

alarm.

Diodes D3 and D4 prevent interaction

between the parking and driving lights ;

otherwise both lights would go on when

either light switch was closed.

Installation. Parts can be mounted on

a small chassis or clustered around the

relay. The alarm circuit shown in the

schematic is for cars having a negative

ground electrical system. For positive

ground systems, reverse the polarity of

all the diodes.

Should you want to operate the lights

without having the alarm sound off and

without having to turn on the ignition

switch, break the line at point X in the

diagram and add Si.

Another innovation is to use the tail-

light circuit instead of the headlights

and parking lights. Since the taillights

go on when either the parking or driving

lights are on, you only need to monitor

the taillights. In this case, eliminate D4

and connect the anode of D3 to the tail-

light bus instead of to the driving lights

circuit.

70 ELECTRONIC EXPERIMENTER'S HANDBOOK

AUTO

VOLTMETER

SHOWS

YOU'LL

GO

Keep tabs on your

charging system -

catch battery failures

before they happen

By JOSEPH TARTAS

EVER stop to wonder what your auto-

mobile battery voltage is? "Why

twelve volts, of course," you say (un-

less you have a 6 -volt system and an-

swer "six ") . It seems like a silly ques-

tion -until you examine it closely. The

fact of the matter is that battery volt-

age varies over a range centered around

12 (or 6) volts: Exactly what it is, and

when, are facts that can tell you a great

deal about the health of your car's elec-

trical system.

If your car or boat is equipped with

an ammeter or indicator light, you

might automatically assume that you

need only be concerned when the "Bat-

tery" light stays on, or if the meter

shows discharge when the engine is run-

ning. While it is important to know,

as these devices indicate, that your gen-

erator is supplying a charging current

to the battery, it is equally important

to know the battery voltage under load

and no -load conditions, as well as the

voltages actually available at the starter,

ignition system, etc. Voltage drop

across cables can be enough to cause

trouble. The voltmeter can tell you

where your trouble is without "cut-

ting" into any of the circuits. It can

also alert you to potential trouble.

Storage Battery Theory. Let's review,

for a moment, the typical characteris-

tics of a lead -acid storage battery. It

consists of several cells each having a

potential of about 2 volts. The exact

voltage of each cell will depend on the

proportion of acid to water in the elec-

trolyte, and the condition of charge or

discharge of the cell.

One standard method of checking a

lead -acid cell is to measure the specific

gravity of the electrolyte. This electro-

lyte is a mixture of sulphuric acid and

distilled water with a specific gravity of

1.260 at 77° F for automotive service,

and ranging from 1.275 for heavy in-

dustrial uses to 1.210 for batteries in

standby or emergency service. The spe-

cific gravity is measured by means of a

hydrometer. The open- circuit voltage of

the cell is directly related to its specific

gravity :

Voltage = specific gravity + .84

A voltmeter, therefore, can be used to

continuously monitor the specific grav-

ity of the battery as a whole.

Because the proportion of water to

acid is increasing as the cell discharges,

the specific gravity is gradually reduced

(water alone has a specific gravity of

1966 Fall Edition 71

This illuminated voltmeter is one of several

types for use in cars. Panel meters will also

serve; in some cars, they can be mounted in

dash. Meter above is sold by Lafayette Radio.

1.000) and the relative state of charge

will be indicated by the hydrometer

reading. For the sake of accuracy, the

correct specific gravity is designated at

77° F, with a small correction factor of

about 15 points for temperature varia-

tions over the usually encountered

range of 32 to 110 °. Some hydrometers

have a built -in thermometer with the

necessary correction indicated.

As a cell discharges, the terminal

voltage begins to drop due to internal

resistance. The heavier the current,

the greater the internal voltage drop

and the lower the terminal voltage due

to the heating effect on the battery re-

sistance. If there is excessive resistance

in the battery cables due to broken

strands in the conductors or poor termi-

nal connections (due to loose or cor-

roded joints), there is a further drop

under high current drain conditions,

and little voltage appears at the starter

terminals or at other equipment such

as the radio or lights.

One voltage appears at the battery

terminals under no -load conditions, a

lower voltage under starting conditions

(or with the lights, heater, or radio

on) and a still lower voltage at the

starter or equipment due to the nor-

mal cable drop. When an ammeter is

used as the indicator, it will show at a

glance whether or not there is a load

on the battery by its discharge rate,

but it does not give any indication of

the battery voltage or its condition of

charge, nor does it indicate excessive

IR drops.

The "idiot light" does not even give

this amount of information, but usually

tells no more than the fact that there

is an output from the generator. When

it is lit, the generator output is nil or

inadequate. When the light is out, the

generator output exceeds some preset

current level at the generator terminals.

Neither the ammeter nor the light

necessarily show battery condition.

Enter the Voltmeter. A d.c. voltmeter

connected directly to the battery termi-

nals will tell you at a glance the charge

condition of the battery, the condition

of your voltage and current regulator,

and if the generator is functioning

properly.

A typical 6 -volt battery will read 6.3

volts with no load when fully charged.

If it reads below that, the percentage of

charge left will depend upon current

drain, the length of time the discharge

occurs, and the final voltage acceptable

(the point at which the battery is con-

sidered discharged but not damaged) .

The final voltage, below which the cells

are considered exhausted, depends upon

the time and discharge current rate. This

final voltage may vary from 1.0 to 1.85

volts per cell, but the most used value

is 1.75 volts for typical applications.

Any of several voltmeters can be used

in an automobile or boat. An 8- or 10-

volt d.c. voltmeter is suitable for a 6-

volt system, and a 15 -volt meter for a

12 -volt system. There are a number

of special meters available from auto-

motive supply and electronics parts

houses, some types already mounted in

brackets, with or without a panel light,

and some types that include trouble-

shooting charts. These meters have ex-

panded scales to make it easy to read

battery voltage while driving.

One type that includes both illumina-

tion and trouble- shooting information is

the Lafayette Radio voltmeter (Stock

No. 11 R 8002) ; another is the Stewart -

Warner "Volt- Guard." The latter is ad-

vertised as a voltmeter and electrical

system analyzer, which, in effect, is

what it really is. The Stewart -Warner

meter has a meter bracket and light

socket, but these are sold separately as

accessories.

Unlike the regular d.c. panel volt-

meter, the automotive types draw about

50 ma. of current, but this small drain

is insignificant compared to the current

capacity of a car battery. The normal

leakage across the top of the battery

72 ELECTRONIC EXPERIMENTER'S HANDBOOK

due to dirt and acid probably equals or

exceeds this drain. The meter is wired

directly to the battery terminals with

small -gauge insulated wire ( #20 is

more than adequate) ; alternatively,

the ground lead can be connected to the

engine block where the battery is con-

nected. In either case, the meter leads

should be soldered to solder -lugs and

connections to the battery or block

should be clean and tight.

It is a good idea to check voltages at

the various terminals (battery, engine

block, voltmeter on panel) with a port-

able voltmeter or VOM to determine if

there are any undesirable voltage drops

in the cables or connections after the

meter is installed. You may avert trou-

ble later on.

What the Readings Mean. Each time

you start your car you should check

your indicator lights and watch the volt-

Simple gadget for turning over engine consists

of two clip leads connected to normally -open

push -button switch. Leads are connected to

starter control terminals of starter solenoid.

meter for abnormal indication. Remem-

ber that the battery drain is heavier in

winter and the battery voltage (if you

keep your car outside) will be lower to

start with. (Continued on page 147)

BATTERY VOLTAGE TABLE

BATTERY VOLTS! ENGINE OFF OR

IDLING2 ENGINE STARTING

(Battery Condition) ENGINE RUNNINGS

(Generator Condition)

Below

5.0 Below

10 or

no read.

ing

Dead or disconnected

battery, meter dis-

connected or not

wired properly

Disconnected, defective, or improperly wired

meter. If the engine will start, or run, the

battery is not at fault

4.5.6.0 9.12

6 -6.4 12 -12.8

6.7.7.6 13.5.15.2

Undercharged battery; Normal range for

engine might not start winter and summer

Fully charged

battery. Generator

and regulator oper-

ating properly

Normal for short

period after driving

due to battery "surface

charge," or meter reads

high

Generator not charging,

regulator not working, or

current drain from equip-

ment (lights, radio, etc.)

exceeds generator output

Battery fully charged, but

generator or regulator not

working properly

Normal when battery,

generator, and regulator

are working properly. Meter

reading varies with charge

in battery, engine speed,

temperature, and regulator

setting

Above

7.6 Above

15.2 Voltage regulator contacts

stuck together, or voltage

regulator set too high.

File and clean contacts and

check battery fluid for level

and specific gravity

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

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

3. Normal driving speeds.

All voltages are approximate, and will vary with temperature, condition of regulator contacts,

accuracy of meter, and other conditions.

11111111 !IIIIIIIIIiIIIIIIIIIIII11111111 IIIII, í'.911I II 'll. III'.ìll . II üll Illlldll!IIIII " ".. I. 9Jllilllll:'IIII it Illh 1111 ": °'I.

1966 Fall Edition

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time without damaging the leatherette.

Record Cases are available in three sizes: for 7 ", 10" and

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The Tape Cases or the 7" Record Cases (with catalog

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74

IGNITION SYSTEM

(Continued from page 66)

from the power supply in order to supply

a positive pulse to the gate. This would

result in regeneration of the SCR due to

large current feedback.

Wiring the P -C Board. With the pulse

transformer completed, proceed with the

wiring of the printed circuit board. The

only changes that are made to the nega-

tive ground circuit are as follows. In

order for the transistors (QI and Q2)

to be properly forward -biased, it is nec-

essary for resistors RI (10 ohms) and

R2 (820 ohms) to shift positions; R1

replaces R2 and R2 replaces Rl. Capac-

itors Cl (4 µf.) and C3 (50 pf.) are re-

versed in polarity so that the plus (+ )

side of the capacitors are grounded.

Diode D1 (1N463) is reversed so that

the anode goes to the plus ( +) mark

on the printed circuit board. The 27 -ohm

gate current limiting resistor (R6) is

not required since the d.c. resistance of

T2 takes its place.

Cut two 11/2" long pieces of heavy wire.

Insert the end of one wire in the hole

vacated by R6, and the end of the other

wire in the remaining hole. Now, con-

nect the free ends of the wires respec-

tively to terminals 1 and 3 of trans-

former T2. The center lug ( white dot) on

the pulse transformer goes to the hole

in the ground strip (near the letter Y) .

Installation. The wired printed circuit

board and capacitor C2 (1 ;cf.) are

placed in the cabinet. Wires from G as

well as from the emitters go to ground

on the barrier strip. The wires coming

from H and the collector center tap go

to A- on the barrier strip, the A wire

to coil plus ( +) and F wire to PTS on

the barrier strip. The wires coming from

B, C, D, E and the transistors are con-

nected as shown in Fig. 4.

Other items available from SYDMUR

are a complete kit for negative ground

ignition, including a specially made cab-

inet ($44.50) , and a completely wired

system ($60.00) . A kit for positive

ground ignition can be obtained for

$47.50.

ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER

3

OPERATION

ACTIVATE

How to get

moving toward

a successful career

in the

field of electronics

PART 1:

GETTING YOUR TRAINING

IN RESIDENT SCHOOLS

(see page 83 for an analysis

of home -study training)

By KEN GILMORE

4 ..

IN Whippany, New Jersey, Richard J.

Ewalt carefully checks out a complex

piece of computer test gear he helped de-

sign. The equipment will become part of

the Nike -Zeus anti -missile system de-

veloped by Bell Laboratories, Ewalt's

company.

In Edwards, California, Loren E. Hir-

man sets up a series of subcarrier os-

cillators in a telemetry system. The de-

vice is used to transmit data from planes

being tested by Hirman's company, Gen-

eral Dynamics.

In Albuquerque, New Mexico, Harry

F. Chaney shoves a batch of tubes

on a special test board into an oven,

checks their performance at different

heat levels to see how they'll operate

under extreme temperatures. He works

for the Electron Tube and Semiconduc-

tor Devices Division of Sandia Corpora-

tion, a leading company in atomic energy

development.

1966 Fall Edition Photos taken at RCA Institutes by Christopher Sheridan 75

All three of these men -Ewalt, Hir-

man, and Chaney -are electronics tech-

nicians, vital members of today's elec-

tronics team. For men -and women -

interested in electronics, it's a good team

to join. The industry is advancing rapid-

ly; new people are needed badly. Pay is

good, working conditions usually top

rate, and jobs are almost universally

interesting.

But there's a catch. If you're un-

trained, don't bother to apply. A few

decades ago, a bright young man could

pick up enough know -how working

around the local radio repair shop to

qualify for a job chasing electrons. Or

he could work in a plant and with a

little study on the side eventually learn

enough to get promoted to an electronics

job. But no more. Today, you've got to

know what you're doing. That means

a good technical school education.

The first thing to decide is where you

want to fit into the electronics picture.

In general, today's technical school pro-

grams are designed on three different

levels.

Engineering Technology. To become

an engineering technician, you'll spend

two to three years at one of the top tech-

nical institutes, a junior college, or a di-

vision of a regular four -year college

that provides an engineering technology

program. In most cases, you'll end up

with an A. S. (Associate in Science),

an A. S. E. E. ( Associate in Science,

Electrical Engineering) , an A. A. S. (As-

sociate in Applied Science) , or some

similar degree. The course will cover

virtually the same areas in math, the

sciences, and engineering that regular

electronics engineers study. And as with

engineers, you'll spend most of your

time- 60 to 80 percent of it -in class.

Lab courses account for the other 20 to

40 percent.

Toward the end of your training, you'll

have the opportunity to specialize. At

New York's RCA Institutes, for exam-

ple, you can become an expert in com-

munications or computers. At Capitol

Institute of Technology in Washington,

D. C., you might choose communications

engineering, nuclear instrumentation, or

control systems as your field of con-

centration.

The engineering technician's program,

while at college level, is designed for

the man who wants to work with hard-

ware. "It depends on what he wants to

do after graduation," says Edward Nor-

man, Capitol's Dean. "Does he want to

hold down a desk and let paper be the

prime result of his effort? Then he'd

probably be happier as an engineer. But

if he wants the more practical type of

employment where he can actually get

his hands on a few parts now and then,

he'd probably like being an engineering

technician better."

"There is heavy emphasis on math

and physics in an engineering technology

course," adds Mike Terzian, Dean of Ad-

ministration at RCA Institutes. "Since

it's a college level course, a student can

get credit for most of the work he does

if he should later decide to go to college

for an engineering degree.

"Meanwhile, after a little over two

years, the man who finishes our T -3

course [RCA's program at the engineer-

ing technology level] is ready to go to

work. The majority of our graduates

get jobs in research and development.

A project engineer will design some-

thing -say a piece of data processing

equipment which is supposed to meet

certain specifications. Now it's up to

the engineering technician to build the

prototype from scratch. He punches out

the chassis, lays out the circuit, builds it

and tests it to see if it meets specifica-

76 ELECTRONIC EXPERIMENTER'S HANDBOOK

"Just how far

you're able to get

depends on .. .

how hard you're

willing to work"

tions. If not, he may recommend modifi-

cations."

"Engineering technicians also do other

types of jobs," says Richard Ungrodt,

Dean of Engineering of the Milwaukee

School of Engineering. "They might be

part of a team that works out production

techniques. And some of them work in

sales and maintenance. You'll frequently

find engineering technicians assigned

to computers, for example. In the old

days, you'd find an engineer doing this

job, and sometimes you still do. But a

lot of this work can be done by top -level

engineering technicians. So they're really

doing engineering level work."

Industrial Technology. "This program is

designed for the fellow who wants to do

service type work," says C. L. Foster,

president of Central Technical Institute

of Kansas City, Missouri. "He may

maintain two -way radios in a fleet of

trucks, or enter the broadcast field. Or

he may work for the same company as

the engineering technician, doing work

on a less complex level."

"There's not so much math in his

curriculum," says RCA's Terzian, "and

there's more lab work. His training is

aimed toward analysis and troubleshoot-

ing, rather than design. It's a good

course for the guy who doesn't have col-

lege in the back of his mind, and there's

a steady demand for people with this

training."

A man preparing for an industrial

technician's job may spend a year to a

year and a half in school. He'll get a

diploma or certificate when he finishes,

but if he ever decides to go to college,

he'll have to start at the beginning; his

credits won't be transferable.

Service Technology. A service techni-

cian may work in a service shop, trouble-

shooting radio and TV sets and hi -fi

gear. In industry, he might do routine

1966 Fall Edition

production testing or wiring on a pro-

duction line. But because his skills

aren't up to those of the engineering or

industrial technician, he's not able to

compete for jobs as well as his more

highly trained colleagues.

"As the demands of industry have

increased in the last ten or fifteen years,"

says Mike Terzian, "technicians have

needed more training. The man with

only a service technician's background

isn't likely to be able to hold down more

than a routine job. And demand isn't

too strong; sometimes we have trouble

placing them."

"The only place we offer a radio and

television servicing course per se is in

our night school," says J. J. Gershon,

Dean of Chicago's DeVry Technical In-

stitute. "We feel that competition being

what it is, our graduates need more than

just a background in radio and TV."

Of course, it's one way to get started

in electronics. If you can't afford to

take a longer course, you might become

a service technician, then go on with

further schooling on a part -time basis

after you get a job. Generally, a ser-

vice technician's training takes 6 to 12

months of full -time schooling, up to two -

and -a -half years in night school.

Can I prepare for a technician's job

through home study?

The answer to this controversial ques-

tion depends on whom you ask. Gen-

erally, most schools agree that you

can't reach the engineering technician's

level or get an associate degree through

the mail.

"There's no comparison between resi-

dent and home -study training," says

DeVry's Gershon. "Resident training is

certainly more desirable. But if a man

has a family or can't leave a certain

area, then he has no choice. He can

77

profit from home study, even though he

can't attain the same level that he could

in resident school."

"Home study is more oriented toward

radio -TV servicing and manufacturing -

assembly line work -than residence

schools," says Harry Rice, Dean of RCA

Institutes home study division. "But

home study graduates also get jobs as

broadcast engineers and technicians in

industry, and they open their own busi-

nesses."

A different view is taken by one resi-

dent school official who asked that his

name not be used. "I don't recommend

correspondence training to any young

man who is seriously interested in a ca-

reer in electronics," he says flatly. "If

he's lucky, he might get a job on a pro-

duction line doing routine wiring or test-

ing. But it would be very difficult for

him to get a real technician's job."

Some schools take another view. "The

main difference between residence and

correspondence schools is that in resi-

dence school you learn the material in

a much shorter time," says Norman of

Capitol Institute. "And, of course, the

lab work can't be the same." Capitol

Radio, a home study school formerly

affiliated with Capitol Institute, requires

that a home -study student be actively

working in the electronics industry.

Therefore, the reasoning goes, he

doesn't need the same laboratory work

as students fresh out of high school.

But this is a unique requirement on the

part of Capitol Radio.

Foster of Central Tech also claims

advanced standing for his home -study

curriculum. "Our home -study program

very closely approaches the engineering

technician's program," he says. "We

can't say it's absolutely equivalent, be-

cause we do not go into higher math and

practical laboratory work is limited.

But a home -study graduate is certainly

prepared for a job at the industrial

technician's level."

How's the job outlook?

If you're trained as an electronics tech-

nician, job finding won't be a problem.

The Technical Institute Division of the

American Society for Engineering Edu-

cation estimates that some 16,000 engi-

neering technicians are graduated each

year. But the Bureau of Labor Statistics

of the U. S. Department of Labor places

the demand at about 80,000 a year. That

Training You'll Need For Various Jobs In Electronics

TRAINING JOBS QUALIFIED FOR* DEGREE OR LENGTH OF TRANSFER CREDIT

LEVEL CERTIFICATE TRAINING TO COLLEGE

Service

technician Radio -TV service

Communications trouble-

shooting, maintenance

Broadcast engineer

Sound system trouble-

shooter

Assembly line wiring

Routine production line

testing

Certificate 6 -12 months No

Industrial

technician Field service technician Certificate

Computer technician

Junior R &D engineering

technician

Communications installa-

tion, maintenance

Broadcast engineer

Production line testing

supervisor

1.11 /2 years No

Engineering Field service technician

technician Computer technician

R &D Engineering technician

Senior engineering

technician

Associate engineer

Certificate

or Associate

Degree

2 -3 years Yes (exact number

of credits trans-

ferable depends

on college)

There may be some overlap, but in general each level of technicia, s fitted for a certain range of duties.

78 ELECTRONIC EXPERIMENTER'S HANDBOOK

"The engineering technician's program ... is designed for the man

who wants to work with hardware."

means more than five jobs available for

each man trained.

Milwaukee School of Engineering says

it could easily place twice as many grad-

uates if it had them. RCA reports that

90 percent of its industrial and engi-

neering technicians have jobs lined up

even before they graduate. The other

ten percent aren't looking for jobs;

they're foreign students returning home,

young men going into the service, and so

on. Other top schools report a similar

situation.

By the way, the door is open for girls.

"They can work in electronics as well

as men," says Terzian. "And in most

places they have no trouble getting a

job."

How much can I make?

Starting salaries vary, of course, in

different parts of the country, at differ-

ent companies, and for technicians with

varying amounts of training. Generally,

though, an engineering technician might

start in the vicinity of $500 a month.

Some, of course, don't make that much ;

others make more. An industrial techni-

cian might earn $50 or $75 less to

start with; a service technician could

average about $325 a month.

There's almost no limit to how far

you can advance, and most technical

graduates tend to do well. DeVry made

a survey recently of 43 graduates picked

at random. They had graduated from

two to fifteen years earlier. About 35%

were in military service or just out, or

were in the process of attending other

schools, or just didn't answer. Of the

remainder of these 43 graduates, two

had become vice presidents of com-

panies, three held the title of chief

engineer, one was a principal engineer

(assigned to handle projects other engi-

neers couldn't), six were engineers, and

one was working toward his master's

degree. Other titles: one senior design

engineer, one supervisory engineer, one

district engineering sales manager, one

international marketing manager, one

field service administrator, four engi-

neering assistants, two technical staff

assistants, and one senior technical

writer.

Sometimes technical school graduates

even reach top management positions.

Cyril J. Statt, who graduated from Cen-

tral Technical Institute in 1940, is now

manager of manufacturing at General

Electric's computer plant in Phoenix,

Arizona. And Richard Wainwright, a 1954

graduate of Capitol Institute of Tech-

nology, is president of his own company,

I -TEL, Inc., of Wheaton, Md, which de-

signs and manufactures microwave fil-

ters. Just how far you're able to get

depends on your ability, your training,

and how hard you're willing to work.

What does it take to qualify

for a technical school?

While schools vary somewhat in their

admission requirements, most of them

that will train you to be a high -level

engineering technician accept only high

school graduates with at least a C aver-

age. They usually also require one or

two years of algebra, one of geometry,

and one of physics or chemistry.

Requirements do vary, though. Mil-

waukee wants a background with four

years of high school math through trigo-

nometry; others have their own addi-

tional requirements. It's a good idea to

check with schools you're interested in

while you're still in high school, so your

courses can be tailored to meet the re-

quirements. If that's not practical, then

get all the math and science you can. But

don't neglect English, either. Most

schools emphasize technical report writ-

ing. Many schools give entrance examina-

tions. If you're not up to the minimum

level in any subject, you may be re-

quired to take remedial courses before

you can enroll in the regular technician's

program.

If you enter industrial or service tech-

nician's training, some or all of these

requirements may be waived. Check with

the schools you're considering for en-

trance requirements at the various levels.

Incidentally, most physical handicaps

won't stop you in electronics. One that

1966 Fall Edition HANDBOOK 79

"If you're trained ...

finding a job

won't be a problem."

4, ..

v, % ..,, How much will it cost?

r,a, r r Generally, tuition for an engineering

technology course, lasting two to three

years, will cost anywhere from a little

under $2000 to almost $3000. You can

pay as you go along, by the week ($20-

$25) or by the month or semester. Two -

year courses, naturally, tend to cost less

than three -year programs.

Living expenses vary considerably, de-

pending on the city. RCA Institutes, for

example, estimates that it costs students

$30 to $50 a week to live in New York.

Central in Kansas City, on the other

hand, says that students get along for

$25 a week. All schools will help you

find a place to room and board; some

have school dormitories.

Incidentally, the tuition at a given

school is generally the same, no matter

what level training you're taking. The

difference comes in length ; you'll spend

six months in some of the simpler ser-

vice technician's courses, three years in

the more rigorous engineering technol-

ogy programs.

If the total cost of going to school and

living in a city away from home is too

much for your budget, you might be able

will keep you out of some jobs: color

blindness. Many technicians must be

able to read the color codes on resistors

and other parts.

And don't think you have to be fresh

out of high school to qualify. Many

schools have older students who worked

for a while before deciding what to do.

RCA had one graduate in 1960 who had

been a locomotive engineer for 20 years

when he quit his job to become a techni-

cian. He has recently been promoted by

his company to the job of master tech-

nician, and was invited this year to read

a technical paper describing some of his

work at a conference of military elec-

tronics experts.

ELECTRONIC EXPERIMENTER'S HANDBOOK

to work part time. "At least 75 percent

of our full -time students work," says

Foster of Central.

"If a student wants to work," adds

Gershon of DeVry, "we'll help him find

a part -time job. A student who works

can usually earn enough to pay for either

his tuition or his living expenses, but

not both. On a normal day, he'll spend

two hours in lab, four hours in class,

and have two or three hours of home-

work. That's eight or nine hours on

weekdays, and then we load him up

with homework for the weekend. So

anyone who wants to work in addition

to this heavy load is going to be a busy

fellow."

Terzian of RCA agrees. "It's very

difficult to work and complete the T -3

program. But some students do it."

Ungrodt of Milwaukee is more pessi-

mistic. "It's really practical only if a

student is willing to take more than two

years to get through a two -year course.

If a student works half time -20 hours

a week -and is a very good student, he

might be able to carry a 14- credit load

instead of the usual 18 -20 quarter hour

credits. But he shouldn't plan to do it

on a regular basis."

If you do have to work, though, most

schools have facilities for helping you

find a part -time job that will interfere

least with your studies.

How about holding down costs by

starting your training through the mail,

then finishing up in residence? You'll

have to check with the individual school

here. Central has a regular program

designed to let you learn as much as

possible at home, some others will

work out such a schedule on an in-

dividual basis, others discourage it. But

if the school you want to attend does

offer such a plan, you can cut down the

total cost of your technician's training

by taking advantage of it.

How do I choose a technical school?

It isn't easy. There are hundreds of

schools across the country that teach

electronics ; some are excellent, others

barely passable. And it's not always

easy to tell which is which.

If you must stay at home, and if your

town has only one school, then you have

no problem. You'll take whatever is

available, and hope it's a good school.

But if you can pick and choose, here are

some guidelines.

First, if you're still in high school, go

to the guidance department. Chances

are they'll have detailed information

about many schools both in your neigh-

borhood and farther away. Second, if

you're going to take an engineering tech-

nology course, find out whether the

curriculum at the school you're consider-

ing is accredited, either nationally or

regionally. Ask local educators -school

or college officials -about regional ac-

creditation. For national listings, see the

Where To Write For More Information

section of this article. Lack of accredita-

tion doesn't necessarily mean it's not a

good school, but you'll want to check

more carefully if the school isn't an ac-

credited one.

Third, write the schools you're consid-

ering and ask for their catalogs. Com-

pare the courses listed. You'll find that

some schools offer a far broader pro-

gram and courses on a much higher

level -calculus, digital circuits, micro-

waves, telemetering and servomecha-

nisms, for example -than others. Even

among accredited schools, some ob-

viously give far more than others. Inci-

dentally, you'll generally find that those

with broader courses take longer -and,

of course, cost more. Finally, check the

faculty listing. Faculty members of top -

rated schools have impressive qualifica-

tions, both in academic degrees and ex-

perience.

1966 Foil Edition 81

The man who finishes ... is ready to go to work."

WHERE TO WRITE FOR MORE INFORMATION

National Directory of Schools and Vocations. Miller &

Brown, State School Publications, N. Springfield, Pa.

One of the most complete lists of technical schools.

$12 in hard cover, or see at library or vocational

counselor.

List of Accredited Curricula Leading to First Degrees in

Engineering Technology in the United States. Engineers'

Council for Professional Development, 345 E. 47 St.,

New York, N.Y. 10017. 25 cents.

Characteristics of Excellence in Engineering Technology

Education. Professor W. Leighton Collins, Executive

Secretary, American Society_ for Engineering Education,

University of Illinois, Urbana, III. 61801. 25 cents.

The Engineering Technician. Secretary, American So-

ciety for Engineering Education, University of Illinois,

Urbana, Ill. 25 cents.

How To Choose Your Technical Institute, by Hartung.

Bellman Publishing Co., Cambridge 38, Mass. $1.00.

The following can be ordered from National Council of

Technical Schools, 1507 M St., N.W., Washington 5, D.C.:

Directory of Approved Technical Institute Courses. Free.

Admission Requirements for Approved Technical Insti-

tute Programs of Higher Education. A review of the

high school background best suited for success in

technical institute programs. 5 cents.

Code of Minimum Standards. This code sets forth the

requirements of the NCTS for approval of Technical

Institutes. 3 cents.

The Electronic Technician. Electronics has become a

major field of employment with electronic technicians

in great demand. This monograph details the work of

these technicians and the industry which employs

them. 5 cents.

The Engineering Technician: His Education, Entrance

Into Industry, and Place on the Engineering Team. A

set of charts placing the technical institute program

and the engineering technician in proper relations. 5

cents.

The Technician and the Engineer. Reprint of an address

by Dean C. J. Freund, University of Detroit. 3 cents.

The Technical Institute: Its Relation to Engineering

Education and Trade Training. Reprint of an address by

the late Dean C. W. Beese of Purdue University. 9 cents.

Have I got what it takes

for technical training?

Experienced teachers and administra-

tors at the best technical institutes can

tell almost at once whether an enrolling

student is going to complete his tech-

nological training successfully. Certain

characteristics show up in almost every

successful student. Here are the signs

some leaders in the industry look for:

Norman of Capitol Institute of Tech-

nology: "Good math background or apti-

tude. Inclination toward practical work.

And a great deal of motivation."

R. E. Baird of the Oregon Technical

Institute: "While in school, he will work.

If he doesn't understand, he will let you

know in no uncertain terms, and will

hound you until he does understand. He

really wants to learn."

Terzian of RCA Institutes: "First, a

sincere interest in the field. Second, self

discipline; the ability to sit down and do

the assignments, prepare the reports, do

the homework. He doesn't have to be

exceptionally brilliant, but it helps if he

enjoys math and physics and is good at

them."

Gershon of DeVry Technical Institute:

"Perseverance and desire are more im-

portant than high academic ability. I'd

rather give the poorer student who

wants to work a lot of help to bring him

up to the proper level than have the

gifted one who won't work or just isn't

interested."

Foster of Central Technical Institute:

"We look for a man who is primarily in-

terested in technical rather than research

type employment. He'll have to like to

work with his hands."

Ungrodt of Milwaukee School of Engi-

neering: "Ability to work and interest

in the subject matter. He should be a

good math and science student. But the

ability to work is the most important

thing. A man who wants to get some-

thing can really work. And he has some-

thing when he's through."

What he has, of course, is the key to a

career in electronics. Do you have the

qualifications? If so, pick out a good

school and prepare yourself for a life-

time of employment in one of the most

exciting fields on earth. -ice

82 ELECTRONIC EXPERIMENTER'S HANDBOOK

OPERATION

ACTIVATE

If you can

only study at home,

you still can obtain

excellent training

to become an

electronics technician

PART 2:

HOME -STUDY TRAINING

By KEN GILMORE

IN electronics today, it's what you know .

that counts. There's no room for the

half educated, the basement tinkerer,

the guy who isn't serious enough to pre-

pare himself with a first -rate educa-

tion. And preparation is just the beginning;

learning doesn't stop once you're on the

job. One educational authority, borrow-

ing the language of nuclear physics, esti-

mates that the "half- life" of even the

best technical education is just ten

years. To put it another way, 50 per-

cent of what you learn today will be as

out -of -date as the crystal set ten years

from now.

All of this adds up to one thing: If

you want to be a member of today's

fast -moving electronics team, you'll have

to get good basic electronics training,

then keep re- educating yourself from

there on out.

There are two ways you can get a

technical education. One is to attend a

regular electronics residence school -a

trade school, technical institute, or col-

lege. It's a good way -especially for

basic training.

But suppose you can't. There's no

school in your town, or you have a fam-

ily to support and can't leave your job.

Or you just don't have the cash to go to

a full -time school or college. These days,

you can get a first -rate electronics edu-

cation at home. Scores of top -notch cor-

respondence schools now offer an in-

credibly rich variety of courses, designed

to make you anything from a radio re-

pairman to an expert in space communi-

cations. And once you're on the job, edu-

cation through the mails is one of the

best ways to keep your knowledge up

to date.

Before you go rushing off to the near-

est post office to get your application in,

however, you'll have to make a couple

of basic decisions: (1) Exactly what

kind of job -among the many fascinat-

ing ones available in the field of elec-

tronics-do you want to land, and (2)

Which school, which courses, will best

prepare you to reach this goal?

To make the right decision, you need

information. And that's what you'll find

in the following pages. The Editors

have talked to scores of education au-

thorities across the country; we've

queried home -study school officials and

talked to their students and graduates.

Here are their answers to the questions

you'll be asking:

What can I learn at home?

The answer is- almost anything. Vari-

ous schools approach the subject of

electronics in different ways, at different

levels. Some concentrate in one area.

Hollywood's Grantham School of Elec-

tronics home study division, for ex-

ample, specializes in preparing you to

get an FCC First Class Radiotelephone

license -your ticket to a job in radio

or TV broadcasting or as a communica-

tions technician. Massey Technical In-

stitute of Jacksonville, Florida, and

Chicago's Coyne Electronics Institute

emphasize training that will help you

go into the radio -TV service business on

your own.

International Correspondence Schools

(ICS) of Scranton, Pennsylvania, on the

other hand, offers a wide variety of

courses: electronics fundamentals, hi -fi

and stereo servicing, radio -electronic

telemetry, industrial electronics, and

many more. At Chicago's DeVry Tech-

nical Institute, you can choose among

all the standard courses and such up -to-

the- minute fields as computer technology

and space and missile instrumentation.

Many schools offer courses on several

levels. "We advise beginners to take

courses in one of our career programs,"

says Jack W. Friedman, director of the

RCA Institutes Home Study School.

"These courses begin with basic elec-

tronics and lead through advanced

material in television, communications,

automation and industrial electronics,

transistors, or electronics drafting. Our

advanced courses, on the other hand,

serve more specific needs, such as help-

ing a technician update himself or move

to a higher level."

Some schools offer only advanced pro-

grams. "Many courses are keyed for the

rank beginner," says G. O. Allen, presi-

dent of the Cleveland Institute of Elec-

tronics (CIE) . "Courses of that type

serve a much -needed purpose, but we

prefer to leave the manual training to

them. For the man who has progressed

well beyond the intermediate level, we

offer a college -level course in communi-

cations engineering." Courses at Philco's

Technical Institute in Philadelphia and

Capitol Radio Engineering Institute in

Washington are also designed for the

working electronics technician or gradu-

ate engineer who wants to upgrade his

skills or keep up to date in this fast -

moving field.

What jobs can I prepare for?

There's almost no limit. Home -study

graduates of Central Technical Institute

of Kansas City, for example, hold such

positions as engineering technicians in

aerospace research and manufacturing,

TV cameramen, studio and recording

technicians, maintenance and operating

technicians with airlines, police depart-

ments, railroads, and public utilities.

Some own their own radio -TV repair

shops. Virtually every major electronics

company in the country and many small

ones have on their staffs men working in

research and development, in manufac-

84 ELECTRONIC EXPERIMENTER'S HANDBOOK

turing, in testing -men who got their

training or updated their skills through

correspondence study.

Take a few isolated examples from

one school -National Radio Institute in

Washington, D. C. NRI graduate David

F. Conrad of Reseda, California, is a

senior engineering aide for Litton Sys-

tems; he checks out magnetic recording

devices for a living. Robert L. L'Heureux

of Southboro, Massachusetts, works for

the data -processing division of Minneap-

olis- Honeywell. Walter G. Higgins of

Portland, Oregon, was a mailman when

he studied electronics at home; after his

course, he transferred to the Department

of the Interior as an electronics tech-

nician and now maintains UHF and VHF

communications links. Jim Davis of

Long Branch, New Jersey, troubleshoots

transistorized chopper -stabilized d.c.

amplifiers at Electronics Associates, Inc.

The list could go on endlessly.

Most schools claim that between 90%

and 100% of their graduates obtain em-

ployment in electronics. Says R. Parma

of National Technical Schools in Los An-

geles, "About 30% of our students are

currently employed in electronics. These

students feel that they lack the technical

skills to achieve advancement in their

company. Another 60% of our students

are employed outside of electronics, but

desire to change their jobs because of

the increasing opportunities in this

industry."

How long does it take, and how much

will it cost?

Time to completion depends on three

main things : the contents of the course,

how fast you learn, and how much time

you put in. Here are some typical ex-

amples.

Major programs at Capitol Radio En-

gineering Institute (CREI) in Washing-

ton, D. C., take about three years to

complete for the average student study-

ing two to three hours a day. Costs -

depending on the subject -hover in the

vicinity of $500 to $550 for the entire

course. DeVry estimates that the av-

erage student studying its $560 course

seven to ten hours a week can finish in

a year and a half. At CIE an FCC li-

cense course costs $325 and ordinarily

takes nine to ten months. Coyne's TV

servicing course costs $165, will occupy

the average student a year and a half.

National Technical Schools in Los

Angeles offers a 150 -lesson master course

in radio, TV, and industrial electronics

for $367. Each lesson takes three to

four hours, and National Tech urges

students to finish at least one a week.

Most, however, move faster and complete

the course in one to two years.

All times quoted above are average;

some students learn faster, some slower.

Put in twice as much time, and you'll

finish twice as fast. Most schools have a

time limit on finishing, too, but will

grant an extension if you need it.

One final point: Most schools give

substantial discounts for speeded -up pay-

ment, even lower prices for cash in ad-

vance. All prices given here are for the

most extended payment plans the schools

offer on a so- much -down, so- much -a-

month basis.

By the way, you don't have to hesitate

to pay in advance. All reputable schools

have fair refund policies if something

happens to keep you from finishing.

Once I've received my diploma,

are jobs easy to get?

Will the school help me land one?

If you don't already have a job in elec-

tronics (many home -study students do) ,

most schools will help you find one. Many

have formal placement bureaus (some

invite you to use their services for the

rest of your life) ; others will simply

forward your grades and a letter of rec-

ommendation to prospective employers,

leaving the bulk of the job up to you.

No reputable school, of course, guar-

antees you a job on graduation, any

more than reputable universities do.

1966 Fall Edition 85

Just how hard -or how easy- you'll

find it to land a job with good pay de-

pends on several things. The training

you select is one of the big ones. Natu-

rally, you can't expect to get the same job

-or the same pay -after finishing a six -

month course in basic electronics as you

could after a comprehensive three -year

course in industrial electronics or ad-

vanced communications systems.

One vital factor in job hunting is fre-

quently overlooked. CIE's Allen puts it

this way : "For CIE and other well -

trained students," he says, "job place-

ment is not much of a problem -if they

will face realities. It seems obvious, but

many young men from rural areas or

small towns expect to find suitable em-

ployment at home. They may find it, but

they should be prepared to go to the job

-the job will seldom come to them. A

college graduate seldom works in his

home town. The same is true of a high-

ly- skilled professional."

Can home -study graduates compete for

jobs with those who get their training in

resident schools? "What we're really

talking about here," says John Sivatko

of ICS, "is what does the employer think.

If an industry is unfamiliar with the

quality of home -study training, there

may be some prejudice against it. The

competence of the students is not that

different; the attitude of the employer

is the pertinent factor."

W. A. Robinson of DeVry makes an-

other point. "The resident student has

the advantage of meeting recruiters from

various industries who come to the

school to interview. The home -study

student, however, must go to the em-

ployer for his interview. Where home -

study programs compare closely with

resident programs, employment will

probably depend on how effectively the

student presents himself to a prospec-

tive employer."

In the past, some employers who hired

resident -school graduates regularly were

hesitant about putting home -study grads

on the payroll. To some extent, the sit-

uation still exists. "It is only fair to

say that correspondence education does

not yet receive the recognition it should

as adequate preparation for initial em-

ployment in the field," says CREI Execu-

tive Vice President L. M. Upchurch. But

the situation is changing -rapidly. "I'm

happy to say the closed -door attitudes

exhibited by many employers in the past

have been cast out by progressive com-

panies," says D. A. Lockmiller, Execu-

tive Secretary, National Home Study

Council. "Now we hear this question:

'What does he know and can he use it

well ?' That's a far cry from the old in-

sistence on pedigree -Where did you go

to school ?' "

Correspondence school graduates have

achieved high- ranking positions in busi-

ness and industry, too. The national

service manager of a large mail order

store is a veteran of home study, as are

many radio and TV station chief engi-

neers, manufacturers, and company ex-

ecutives. In fact, some educators think

that men and women with enough drive,

ambition, and self -discipline to complete

correspondence courses are likely to be a

notch above average. Recently, just on

a hunch, ICS sent questionaires to sev-

eral thousand company presidents

around the country, asking how many

were former ICS students. About half

answered. And of those, an astonishing

seven percent were, indeed, ICS alumni.

If all former correspondence students

had been counted, the number would

have been higher.

How about pay?

It's impossible to give precise figures ;

there's too much variation according to

geographical area, amount of training,

branch of industry -even the state of

business. But here are some samples

that will give you an idea of the range.

The U. S. Department of Labor's Occu-

pational Outlook Quarterly shows av-

erage technicians' salaries in private in-

dustry starting in the vicinity of $4900

a year. Also, ICS reports that its grad-

uates average $80 -$110 a week.

The range, however, can be far wider.

"Some of our recent graduates are well

over the $10,000 -a -year level already,"

says Allen of CIE. "At the other ex-

treme we have men who, because they

are not willing to relocate or enjoy a

certain type of electronics work, are

making as low as $2 per hour."

Don't overlook the possibility of work-

ing for the federal government. Elec-

tronics technicians from GS3 to GS9

earn from $4005 to $9425. You may want

to apply for a civil service rating at the

86 ELECTRONIC EXPERIMENTER'S HANDBOOK

O0

®om

o

end of your

qualify.

There's virtually no limit to what you

can make. Start your own business and

your ultimate earnings are determined

only by the sweat you're willing to put

into it and your ability as a business-

man. You can advance rapidly working

for others, too. Listen to Charles J.

Roesle of Washington, D. C.:

"Six years ago I was at the end of any

advancement at $5500 per year. But

after completing a National Radio In-

stitute course I passed a Civil Service

exam for an Electronics Production En-

gineer at $7000 per year. In May, 1961,

I was promoted to Guided Missile Project

Officer at $9000 per year. Recently, I

was promoted to Guided Missile Super-

visor, with a salary of $11,500 per year."

Incidentally, while you're dreaming of

future riches, you can begin making

your home -study course pay its own way.

Peter Cooke of Coyne surveyed the

school's 500 most recent graduates not

Illustrations

by John Hanna

schooling to see if you can

1966 Fall Edition

long ago and asked each one how much

money -if any -he had made repairing

radios and TV sets in his spare time be-

fore he finished his course. Among them,

the 500 students had picked up more

than $100,000 while studying. That's an

average of better than $200 each -more

than the total cost of the course.

Can I qualify for enrollment?

You can for most home -study courses

if you can read and write and really

want to get into electronics. The only

additional requirements come from

schools that offer advanced courses.

For example, CREI expects students

to have a high -school diploma and a job

or prior experience in electronics. The

whole course, in fact, is designed for the

working technician who wants to in-

crease his skill and his pay check, not

for the beginner.

Several other schools have similar re-

quirements, virtually all for advanced

courses. It wouldn't do you much good

to take a course in servomechanism

theory if you weren't yet on speaking

terms with Ohm's law.

How can I pick the right school for me?

It isn't easy. There are hundreds of

schools across the country offering thou-

sands of courses. Prices, estimated time

to completion, and many other factors

vary widely. But the job, while difficult,

isn't impossible. Here's advice from the

experts on how to proceed.

Says William B. Callahan, president of

Chicago's Commercial Trades Institute:

"Look for the schools offering courses in

the field you want to study. Compare

tuition prices, look for accreditation,

state licensing, and a good Better Busi-

ness Bureau record." Adds J. F. Thomp-

son of NRI: "Compare prices, faculty,

and reputation. If you're still in doubt,

Where can I get more information?

For more information on who of-

fers which course and on accredita-

tion, write to the National Home

Study Council, 1601 Eighteenth St.,

N. W., Washington, D. C. 20009, and

ask for the Directory of Accredited

Private Home Study Schools. It's

free.

87

Should kits be included in a home -study course?

A good case can be made either

way. "At best," says M. E. Hough-

ton of DeVry Technical Institute, "a

kit is a laboratory, a teaching device

that's carefully built into the rest of

the course. Our students don't just

assemble a kit. Eventually they

understand exactly why the kit is

built as it is."

Another point in favor: The kits

to be constructed in many courses

are multimeters, signal generators,

scopes, and other useful test instru-

ments. If you're planning to go into

servicing, these instruments can

form the basis of your equipment.

Some schools, such as Coyne Elec-

tronics Institute, feel that kits aren't

necessary. A kit's primary purpose,

the school maintains, is to familiarize

the student with actual electronic

hardware. "But most of our stu-

dents begin to repair radios and TV

sets almost immediately," says Peter

Cooke of Coyne. "So they don't

need kits."

Capitol Radio Engineering Insti-

tute offers another reason for the

non -kit course. "While we recognize

the value of properly integrated kit

construction in conjunction with cor-

respondence study, we know that

many of our students would find the

use of kits impractical because of

military restrictions, travel, space

limitations, and so on," says L. M.

Upchurch, Jr. "Further, since our

students are already employed in

electronics, their daily work fre-

quently gives them the advantages

they might otherwise get from work-

ing with kits."

One guideline, then, might be this:

If you're a beginner with no elec-

tronics experience and no prospect

of having a chance to work with

equipment during your course, you'll

probably do well to select a course

with kits. If you will be working

with equipment, or if you're already

a practicing technician taking ad-

vanced courses, then kits are far

less important, and in many cases

may not be needed at all.

And, of course, there's one other

important aspect: Courses without

kits, all other things being equal, are

certainly far cheaper than those

with kits. Some schools offer courses

either way.

write one or more graduates." Many

schools will supply lists of graduates.

David Lockmiller of the NHSC offers

this thought: "First, the school should

be accredited by a nationally- recognized

accrediting agency. There may be one

or two good schools that are not ac-

credited, but it is difficult to evaluate

these schools. Look for such things as

proof of performance, price, length of

the course. Examine a sample lesson,

check the employment features. No one

of these criteria is conclusive, but they

will help you to reach a final decision."

When you're making comparisons,

don't overlook some of the special or

bonus features a school might offer.

Some of these "extras" may not be of

value to you, but check to see what's

being featured by the school in addition

to the regular curriculum. Here are

some examples -by no means complete:

Consultation service. If you have a

problem on the job -say in the design of

88

a circuit or repairing a particularly

knotty trouble -some schools will have

a whack at helping you solve it.

Schematic service. One school main-

tains a file of more than a million sche-

matics -from old Atwater -Kent radios

of more than three decades ago to the

latest color TV sets. For a small fee,

the school will copy any schematic and

send it to you -an invaluable aid in

troubleshooting.

Course tailoring. Some schools fit the

course precisely to your needs. If you al-

ready have some background in math or

electronics, you can get a series of tests

from some schools to see where you

stand. Then you start at the right place

and don't waste time repeating material

you are already familiar with.

Special devices. A midwest school

supplies a projector and training films.

Another school sends a transistor trainer

-a special board that allows you to rig

experimental circuits rapidly. Some

ELECTRONIC EXPERIMENTER'S HANDBOOK

schools offer programmed lessons; others

supply slide rules and other devices to

help you learn. No one feature should

determine which course you select, of

course, but consider them along with all

other factors.

What does it take to complete

a home -study course successfully?

No reputable school will tell you it's

easy. But it can be challenging, interest-

ing, rewarding. The completion average

for home -study students is higher than

the national college average. The drop-

out rate in colleges is high in some

cases going up to a peak of 80cí' but

one out of every three students com-

pletes his home -study course.

Why do so many fall by the wayside?

"The two most important reasons," says

G. O. Allen of CIE. "are motivation of

the student and length of the course in-

volved. For example, we conduct many

courses for industrial concerns. These

1966 Fall Edition

courses often take from 18 months to

two years. Despite this rather formid-

able assignment, we frequently have

completion percentages for individual

companies as high as 90 to 95 percent -

sometimes 100 percent. These men are

highly motivated because the company

provides funds and often company time

for training, and is certainly in a posi-

tion to influence the student's future

employment. On the other hand, we

sometimes encounter completion rates as

low as 10 to 15 percent for students en-

rolling individually for these same

courses. Self- discipline simply does not

produce the same results as discipline

administered by an employer. In some

courses that run up to three years, we

experience similar results from our

group enrollments, but an even lower

completion rate for individual students."

Despite these gloomy statistics, you'll

have a lot going for you. "Any reputable

school will do all it can to help the stu-

dent finish the training he has selected,"

says DeVry's W. A. Robinson. "Most

schools keep a steady flow of inspiration-

al and motivational material in the mail,

particularly to students who lag. In fact,

most schools bend 'Over backwards of-

fering extra help to those they feel need

it. In the final decision, however, it is

the student himself who makes the de-

cision to complete his training."

"The difference between a completer

and a non -completer," adds R. Parma of

National Tech, "is the degree to which

he allows himself to procrastinate. Pro-

crastination is the student's worst en-

emy, but the fault does not always lie

with the student. Home study competes

with the family, sports, TV, etc. But

whether or not a student completes his

course depends on how he rationalizes

the importance of his time and career."

Just who can benefit from home study?

"Anyone who is interested in improv-

ing himself," says Robinson of DeVry.

"Anyone who will bend his mind and

back to the task," adds Hal Kelly of the

National Home Study Council.

"The question should be," says John

Sivatko of ICS, " `Who can benefit from

study ?' Home study is just a tech-

nique. If you can benefit from any kind

of learning, you can benefit from home

study."

89

There's no doubt that the country

needs more trained people. "Our eco-

nomic progress today is being hampered

by an increasing shortage of skilled men

and women," says NRI's Thompson. "At

a time when four million people are job-

less, newspapers are crammed with ads

for workers who can connect an elec-

tronic circuit, program a computer, ser-

vice aircraft and missile equipment -or

even qualify for training in hundreds of

new skills that were unheard of 20 years

ago. To put it another way, there would

be virtually no unemployment if today's

four million jobless obtained the skills

to match business and industry's needs."

Correspondence education could play

an increasingly important role in train-

ing men and women for tomorrow's ever-

more- demanding jobs. In fact, the whole

notion got some pretty high -level en-

dorsement recently, as President John-

son voiced this opinion: "Home -study

courses are an important link in the

ever -lengthening chain of educational

services our nation provides for its

citizens. They represent an important

resource in our society's commitment to

provide unlimited opportunities for every

American to reach his highest potential."

"We need correspondence education in

this country now more than at any time

in our past," says G. O. Allen of CIE,

who is also the recently -elected presi-

dent of the National Home Study Coun-

cil. "We have a tremendous shortage

of classroom facilities and qualified

teachers, and this shortage is bound to

get worse. Correspondence education

can easily help fill the gap."

Maybe it can fill a gap in your life, too,

and start you on a rewarding career in

the important and fascinating field of

electronics. 40

Should I study at home or go to a residence school?

If you're looking for controversy,

this is the question to ask. Of

course, if you have a job and a

family and can't simply take off and

go to a residence school, your choice

is easy. You'll study by mail.

But what if you do have a choice?

There's no doubt that home study

has important advantages. Among

them : You can study in your spare

time, at odd hours, or while travel-

ing. You don't have to leave home

or lose income. You can study at

your own pace. You don't miss

classes; they wait for you if you're

sick or busy. You can move from

one city to another without missing

a beat. And home study is certain-

ly far less expensive than residence

training. You'll probably spend less

for an entire electronics course

lasting two years or more by mail

than for one semester in college.

But would you learn more in a

regular classroom? Actually, the

evidence shows it's the other way

around. One study by the dean of

the College of Education of the

University of Michigan showed that

correspondence students did slightly

better on exams than others who

learned the same material in the

classroom. Several other studies

showed similar results. "You learn

by doing, not by copying someone

else," says Richard S. Frazer, presi-

dent of Christy Trades School. "You

learn more thoroughly because you

do it all yourself."

Then should you study by mail in

preference to residence school? "If a

home -study student is willing to put

forth some effort toward self -im-

provement, we feel it is comparable

to the best resident -school training

to be found," says J. F. Thompson

of National Radio Institute. "It de-

pends on the individual," says John

Sivatko of International Correspond-

ence Schools. "Some people can get

more out of a home -study course

than they can in residence, and vice

versa." G. O. Allen of Cleveland

Institute of Electronics agrees.

"Much depends on the person," he

says, "his goals and motivation, his

geographical location, his time

availability, the nature of the sub-

ject to be learned, etc. I will state,

however, that other things being

equal, I do believe the student who

learns through a good home -study

90 ELECTRONIC EXPERIMENTER'S HANDBOOK

program not only learns better, but

retains it longer."

But C. L. Foster of Central Tech-

nical Institute says : "We recom-

mend resident school training if it

is at all possible. If resident school

is not practical, we recommend

home -study courses because we be-

lieve that worthwhile education can

be obtained through home study."

And W. A. Robinson of DeVry Tech-

nical Institute brings up another

point: "Some types of training are

offered at a more advanced level in

our resident school than through

home -study programs. In such cases,

we could not provide equivalent

home -study training."

Finally, L. M. Upchurch, Jr., of

Capitol Radio Engineering Insti-

tute sums up his feeling. "We do

not know of any authoritative com-

parative study of correspondence -

as opposed to classroom -learning

that has indicated any significant

superiority of class attendance. Sev-

eral studies, on the other hand, have

shown slightly better results from

home study.

"Comparing correspondence and

classroom study of technical sub-

jects is difficult in one respect:

laboratory work. Because CREI

students are, as a condition of en-

rollment, employed in the field of

electronics, we know that to a con-

siderable extent their practical ex-

perience gained on the job is a

satisfactory substitute for super-

vised laboratory work. This is not

invariably true, however.

"In any case, we would not ordi-

narily recommend correspondence

study to a prospective student with

the qualifications, the means, and

the opportunity to attend a good

residence school in the same field.

(Nevertheless, there are some stu-

dents for whom home study would

be the better choice.) Neither would

we claim that the average corre-

spondence student completing our

course is as well prepared as the

average graduate of a comparable

program in residence.

"The value of home study," Mr.

Upchurch concludes, "is not as a

competitor of residence school in-

struction, but as a valid educational

method for individuals who want

and need further education, but

whose circumstances are such as to

make class attendance undesirable

or impossible."

1966 Fall Edition 91

NOW YOU CAN EASILY ADD

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OR FILM SHOWS WITH

POPULAR PHOTOGRAPHY'S

EXCITING NEW

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PICTURE EVENING"

1

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SOUND FOR LL-

A PIC.I'URE EVENING

"Sound For A Picture Evening"

Consists of selections from the music masters

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No matter how good your film and slide shows are, sound will

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fessional. But, it has to be the right kind of sound. Although

any musical record can be used as a background for your film

and slide shows, few, if any, can match the variety of actions,

situations, and scenes inherent in most shows. That's why

Popular Photography created this album. It's ideal for almost

every mood captured by your camera. Whether your show i5

simple, elaborate or somewhere in-between- "SOUND FOR A

PICTURE EVENING- provides a final, professional touch to

make it a complete success.

A POPULAR PHOTOGRAPHY

EXCLUSIVE

The "Sound For A Picture Evening" album has been produced

by the editors of Popular Photography exclusively for our read-

ers and is prepared by the Custom Services Division of Capitol

Records. This outstanding album cannot be purchased in any

store and is available by mail only to the readers of Popular

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ALBUM CONTENTS:

17 SPECIFIC MOOD MUSIC

BACKGROUNDS

8 TRACKS FOR SPECIAL

SOUND EFFECTS

THEMES TO MATCH YOUR

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3 FILM OPENINGS: Grandiose, Sweet and Gentle and

Dramatic 3 FILM CLOSINGS: Epic Finale, Hollywood

Style and Gentle 11 THEMES: Happy -Go -Lucky Gay

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slide show a resounding success. You will find helpful tips on

how to build an effective sound track, choosing the right back-

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organizing your show, editing and much more.

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where to find the exact band you want. Eliminates guesswork,

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la must for every slide and film show impresario)

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POPULAR PHOTOGRAPHY -Dept. SD

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Please send me albums at $3 98 each. My

check (or money order) for $ . is enclosed. I

understand that you will pay the postage. (Add 75g to

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CHECK ONE: MONO STEREO

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Sorry-No charges or C.O.D. Orders EEH.66

92 ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER

4

AUDIO

STEREO

HI-FI

PROJECTS

1966 Fall Edition

Six months ago, when the introduction to this chapter in

the Spring 1966 Edition of the ELECTRONICS EXPERI-

MENTER'S HANDBOOK was being written, the Editors

discovered that Dave Weems had had speaker enclosure

projects in the six preceding issues. With one more proj-

ect in the Spring Edition, and two different designs in

this Fall Edition, Dave has certainly carved a niche for

himself and ranks -in our estimation -as the number one

designer and writer on build -it- yourself hi -fi speaker en-

closures. A tip of our hat to Dave!

Besides enclosures, the Editors selected for publica-

tion in this edition of EEH the "Hi -Fi à Go -Go" color or-

gan circuit developed by Don Lancaster. At first glance,

this circuit might appear to compete with our cover photo

project, but the two construction projects are quite dis-

similar. The "à Go -Go" lamps are high -wattage bulbs, as

compared to the low- intensity but very attractive Christ-

mas lights of the Wortman project on page 21.

94

TOTEM POLES FOR STEREO David B. Weems

99

HI -FI À GO -GO LAMPS Don Lancaster

105

THE "CINDERELLA" David B. Weems

109

SOLID -STATE 6 -WATT AMPLIFIER FOR 10 BUCKS

Charles E. Fenoglio

112

UNIQUE 99¢ SPEAKER ENCLOSURE John N. Ayres

93

MOST stereo speaker systems are sim-

ply two mono speakers connected to

a stereo amplifier. Any good system,

when duplicated, can be expected to per-

form well in stereo. But good stereo pre-

sents unique requirements.

The first requirement is that the sys-

tem be able to provide perspective, or

give direction to the sound of individual

voices or instruments. Some of the

early stereo recordings seemed engi-

neered for this purpose alone, with the

result that we got a "ping -pong" effect.

It was probably exaggerated effects such

as this one that caused some audiophiles

to condemn stereo hi -fi as inferior to

mono hi -fi. Regardless of the misuse of

directionality, however, without it there

would be little reason for stereo record-

ing and reproduction.

There are a number of factors which

influence the ability to locate sound

sources, such as the difference between

sound intensity, waveform, and arrival

time at each ear. Another factor, and

one which influences the others, is the

ratio of arrival times of direct to re-

flected sound. If this ratio is made very

high, the sound source can be easily

located. In an extreme case, the ping -

pong effect is the result, with the music

coming from two widely spaced "holes

in the wall."

A second important requirement for

good stereo sound is an apparent enlarge-

ment of the source. One way to accom-

plish this is to simply enlarge the source

itself, i.e., use a large multiple speaker

system. Another way is to utilize re-

flected sound ( reverberation) to augment

the direct sound from the speakers.

Properly utilized, reverberation can give

the effect of a sound source even larger

than the room itself.

Other requirements for stereo include

the suitability of room acoustics, of

course, as well as the usual high -fidelity

characteristics of wide and smooth fre-

quency response, low distortion, good

transient response, and wide dynamic

range.

Control of Reflections. It would appear,

in looking back over the above require-

ments, that there is a conflict. For di-

rectionality, we need a high ratio of

direct sound to reflected sound, but for

enlargement, we need a mixture of re-

TOTEM

POLES

FOR

STEREO

Go the "Sweet Sixteen"

one better with a

column speaker system

and a separate

bass speaker enclosure

By DAVID B. WEEMS

94 ELECTRONIC EXPERIMENTER'S HANDBOOK

fleeted sound with the direct sound. The

trick, then, is to control the reflections.

One way of controlling reflections is to

limit the dispersion of sound to one

plane, either horizontal or vertical. The

choice of which to use is an easy one

since horizontal dispersion gives good

distribution of sound over the listening

area, whereas vertical distribution does

little except bounce the sound waves off

the floor and ceiling. If we can limit

dispersion in the vertical plane and in-

crease it in the horizontal plane, we can

achieve two benefits; more efficient use

of sound energy and an opportunity to

control the ratio of direct sound to re-

flected sound simply by positioning the

speakers properly.

Excellent horizontal dispersion of

sound can be obtained from a vertical

line source. A single loudspeaker acts

like a point source, radiating sound in

the form of a spherical wave. which

spreads out in all directions at once. The

sound wave propagated from a line

source, however, travels outward in a

cylindrical pattern. If we use several

speakers to produce the sound and mount

them in a straight line, we can approx-

imate a line source. By making the line

a vertical one, we can concentrate the

sound into horizontal dispersion and con-

serve some of the energy that a point

source squirts out in the vertical direc-

tion. Reflections from ceilings and floors

are minimized.

A vertical column, of course, is not a

new idea in sound reproduction; column

speakers have been known and appreci-

ated for years by the manufacturers of

public address systems and by the sound

engineers who install them. Perhaps one

reason for the acceptance of column

speakers by public address people was

the fact that their p.a. systems had to

be used in such impossible acoustic en-

vironments as half -empty gymnasiums

with their hard reflective surfaces.

"Sweet Sixteen" Concept. The benefits

of using multiple small speakers for low

distortion are well argued by the pop-

ularity of such systems as the "Sweet

Sixteen" (POPULAR ELECTRONICS, Jan-

uary and April, 1961) . Critics of these

multiple speaker systems insist that they

produce no measurable low frequency

bass or extreme highs. However, pro-

1966 Fall Edition 95

For awhile, when the "totem poles" were being devel-

oped, the workshop looked like a hi -fi supply house.

The single woofer gave way to separate woofers.

ponents go right on building Sweet Six-

teens, indicating that there are benefits

that can't be measured. One reason, per-

haps, is the apparent enlargement of the

sound source. Those who have heard a

multiple system usually admit that the

speaker arrangement does have some-

thing to offer.

One deficiency multiple speaker sys-

tems have is that the speakers must be

mounted in a concentrated pattern, such

20"

18 1/2" - I

29'

I-1/2"

as a square. This results in identical

distances between identical speakers,

which causes certain points in their fre-

quency range to be boosted or cut, and

peaks or valleys appear in the response

curve. These variations are measurable

and have contributed to the criticism of

the whole idea of multiple speakers.

An obvious answer to this deficiency

is to use the Sweet Sixteen concept where

it is strongest and to eliminate its weak-

nesses. The prescription for changing

the Sweet Sixteen into something really

great is to install a crossover network,

add woofers and tweeters, and string the

mid -range speakers to create a line

source of sound.

Speaker Selection. If you already have

a Sweet Sixteen system that you want

to update, you can split the speakers

into two groups of eight each. Ten speak-

ers were used in the system shown here

to obtain an 8 -ohm impedance, but omit-

ting one pair would not appreciably affect

performance.

Either 4- or 5 -inch speakers can be

used with the design shown. If you are

buying new speakers, choose them by

magnet weight rather than size. Avoid

consideration of arbitrary phrases such

as "heavy duty," "heavy magnet," etc.

Magnet weight should be about 1 ounce

or more. Actually, magnet weight by it-

self is not a foolproof way of determining

magnet size. Look for the gauss rating

-the larger it is, the better.

16 I /2"

2"

PORT i+3/4" 2 "-

0

6 -1/4'

I" 23-

6-I/4"

/2'

D ID

1 NI-I/2"F00T

3- /2"

zz"

DUCTS

i

3/4X3/4"

CLEAT

1 "X2'

(3/4X1 -1/2 ")

CLEATS

P281

3/4'X3/4'

CLEAT

I.- i

INSIDE VIEW

RIGHT SIDE

COVER REMOVED

3/4, I-1/2"

These drawings show

all the necessary wood-

working details. A Bill

of Materials is given

on page 98. Width and

depth of the ports in

the combined bass

speaker enclosure are

somewhat critical as

ports are cut for the

Electro -Voice speak-

ers. The author at-

tached poles to his

column speakers so

the systems could be

rotated and aimed at

the audience. Sound

radiation from column

speakers is mostly

horizontal with little

vertical dispersion.

96 ELECTRONIC EXPERIMENTER'S HANDBOOK

33

The small speakers can all be of a

single brand and model, but a slight im-

provement will be gained by using two

different brands. If you do, pair off the

unlike speakers and connect them in

parallel, then connect these pairs in

series. Ten speakers, each having a 3.2-

ohm voice coil, provide a final impedance

of 8 ohms when wired in this manner.

There are small foreign -made speakers

available with 8 -ohm voice coils. If you

want to use some of these, you'll need

a different wiring arrangement. To ob-

tain an impedance of 8 ohms, you can

parallel three speakers in one set, and

wire three sets in series for a total of

nine speakers to handle the mid -range

instead of ten. For a 16 -ohm hookup,

use eight 8 -ohm speakers -four parallel

pairs in series. Don't try to use speakers

of mixed impedance ratings in the same

system unless you are sure you can de-

sign a circuit that will provide equal

power to each speaker. You might end

7-I/2'

4" OR 5"

SPKRS.

TWEETER

CONTROL

TWEETER

MIDRANGE

CONTROL.

60"

61 -1/2'

3/8"

t 3/8"

22" 27"

DAMETER OF SPEAKER HOLES IS 3-1/2" FOR 4' SPKRS.

4 "FOR 5' SPKRS.

TWEETER HOLE IS 2- 15/16"

up with one or two speakers doing all

the work.

While you can substitute other woofers

with good results, the Electro -Voice

SP8B specified in the Bill of Materials

is highly recommended. It was the final

choice over the other 8 -inch woofers that

were tested for this particular applica-

tion. Of course, you can use separate

woofer systems, or other quality brands

of woofers in the manufacturer's enclo-

sures, if you don't mind having two

woofer cabinets plus two columns in your

living room. The compelling reason to

put the two 8 -inch woofers in a single

enclosure is to keep the cabinet popula-

tion within acceptable limits. You also

gain the advantage of mutual coupling

between the two woofers with improved

low- frequency performance.

There is an alternative, though, par-

ticularly if you have an amplifier that

will tolerate mixing of the two stereo

channels (some transistor amplifiers

won't) . The alternative is to use one

woofer for both channels, but the woofer

should have either a dual voice coil or

an added mixer transformer to which

the bass from each channel is fed. For

the latter method, a possible choice is

the Electro -Voice XT -1 transformer with

an E -V SP12B either in the manufac-

turer's enclosure or in "Mr. Thuras' Mag-

ic Box" ( Spring, 1966, ELECTRONIC Ex-

PERIMENTER'S HANDBOOK) .

It is also possible to substitute other

tweeters for the University T -202 spec-

ified, but you must check for similar

wide -angle dispersion characteristics

first. (Note that the totem pole control

of dispersion angle is essentially for mid-

range sound.) The T -202 has its own

built -in filter network and is hooked

directly across the output of the ampli-

fier. If you substitute a tweeter with-

out a high -pass filter or with a filter

operating at a different crossover fre-

quency (other than 3000 cycles), then

you'll have to change the wiring or the

crossover network to obtain the required

crossover frequency.

Some of you may note that the wiring

of the crossover network is unusual and

somewhat different than any shown in

University's instruction book. The

changes were made necessary by the use

of a 16 -ohm woofer and a tweeter with a

high -pass filter set at a frequency not

1966 Fall Edition 97

AMPLIFIER

16f10

8n0 TWEETER

CONTROL

-0-

o

5

N-2A

2 3 4

0-0 0

0 0

6 7 8

N-28

I 2 3 4

>-O 0 0

0 0 0 0

5 6 7 8

L PAD

TWEETER

In wiring a "totem pole," this diagram must be followed.

Be sure to phase the mid -range speakers so that all of

the cones move in the same direction at the same time.

covered by the manual. As used here,

the University N -2A acts as a frequency -

dividing network operating at 350 cycles,

and the N -2B serves as a low -pass filter

at 3000 cycles.

BILL OF MATERIALS

Speakers and Accessories

2- Electro -Voice SP8B 8 -inch woofers

2- University T -202 tweeters

20 -4" or 5" mid -range speakers

2- University N -2A crossover networks

2- University N -2B crossover networks

2- University AP-8 controls for mid -range

speakers

Lumber for Two Columns

2 -6" x 60" pieces of 3" fir plywood (for

speaker panels)

4-4" x 60" pieces of 3" fir plywood (for sides)

4-4" x 7/" pieces of 34" fir plywood (for tops

and bottoms)

2-71/2" x 611/2" pieces of %" fir plywood (for

backs -optional)

Lumber for Woofer Enclosure

1 -18 1/2" x 231/2" piece of 34" fir plywood (for

speaker panel)

1 -181/2" x 271/2" piece of fir plywood (for

back)

2 -161/2" x 281/2" pieces of 34" fir plywood

(for sides)

1 -161/2." x 181/2" piece of 3" fir plywood (for

bottom)

1 -161/2" x 20" piece of Y4" fir plywood (for top)

2 -6" x 181/2" pieces of 34" fir plywood (for

duct panels)

2 -1/" x 22" pieces of 3" pine (for cleats on

speaker panel)

2 -1 /" x 26" pieces of 3" pine (for back

cleats)

2 -1 /" x 181/2" pieces of 3" pine (for back

cleats)

4 -3/4" x 141/2" pieces of %" pine (for corner

cleats)

Miscellaneous

104 -#8 x /" sheet metal screws (for small

speakers and crossover networks)

84 -#8 x PA" wood screws (for woofer enclo-

sure)

2 -Tool or "gripper" clips (to fit lamp poles,

if used)

Grille cloth, plastic veneer, glue, finishing nails,

fiberglass

98

MID RANGE

CONTROL

MID RANGE

4 4

liK WOOFER

A peek inside of an unfinished bass reflex cabinet

shows the two University N -2A crossovers attached

to the front panel. See the wiring diagram above.

Construction. The speaker enclosures,

both the woofer box and the columns,

are constructed from 3/4 -inch plywood.

The columns are quite simple in design,

and should cause no difficulty, but you

should wait until you decide whether you

need a back or not before putting on the

plastic veneer covering (see Speaker

Placement section of this article) .

(Continued on page 145)

ELECTRONIC EXPERIMENTER'S HANDBOOK

1114x À GO -GO LAMPS

WHY BE SATISFIED with just listen-

ing to hi -fi programs when for a

sawbuck you can have the added enjoy-

ment of seeing what you're hearing, and

intriguing all your friends. A pair of

ten dollar bills will get you two sets of

audio controlled lights to let your stereo

system really brighten up the place. For

those who want something different, it's

quite a conversation piece.

With the A Go -Go circuit, the bright-

ness of one or more incandescent lamps

is controlled by an audio signal. Its

full -range proportional control is capa-

ble of bringing the lights from full dark-

ness to full brilliance; the louder the

sound, the brighter the lamps. You can

use it to control up to 200 watts of light,

and with modification and a few dollars

more, up to 2000 watts. The unit is

about the size of two ice cubes.

How It Works. Sounds fed into J1 are

stepped up by Tl, rectified by D1 and

filtered by C2 only to become a control

voltage for trigger diode D3. (See Fig.

1.) It takes 30 volts to make D3 con-

duct. The time required to build up 30

volts on C3 depends upon the amplitude

of the sound and the values of C3 and

R2. The louder the sound, the quicker

the voltage buildup ; the larger the re-

1966 Fall Edition

Add a new

dimension to your hi -fi

... in color

By DON LANCASTER

sistor or capacitor, the longer it takes

to build up the voltage.

When D3 fires, it triggers the SCR

into conduction only if the SCR anode

also has a positive voltage on it. Once

the SCR fires, it continues to conduct

until the anode voltage drops down to

about 0. This happens each time the

line voltage waveform goes through

zero. The SCR will remain off until an-

other pulse is applied to its gate. The

sooner the gate pulse occurs when anode

voltage is present determines the amount

Fig. 1. Ratio of "on time' to "off time" of SCRI

changes in step with music levels, and brightens or

darkens different colored bulbs plugged into SOI.

99

I-3/4

11/4°

FOIL SIDE

ALL HOLES

#60 DILL

OR 3/64'DIA

Fig. 2. Printed circuit board is shown actual size to

help you make your own. However, almost any suit-

able chassis or breadboard arrangement can be used.

PARTS LIST

C1- 0.02 -s/., 200 -volt Mylar capacitor

C2- 0.05 -µf., 200 -volt Mylar capacitor

C3- 0.1 -14., 200 -volt Mylar capacitor

C4- 0.005 -µf., 600 -volt disc capacitor

DI, D2, D4- 1N4003 diode

D3- Trigger diode (Texas Instruments TI -42 or

equivalent)

/1 -Phono jack

RI- 33,000 -ohm, /2-watt resistor

R2- 39,000 -ohm, ,4 -watt resistor

R3- 200,000 -ohm, % -watt resistor

SCR1- 2N3528 silicon -controlled rectifier

S01-Chassis-mounted a.c. socket (Amphenol

61 -F or equivalent)

T1- Output transformer, 4 ohms primary to

10,000 ohms secondary (Thordarson TR -203

or equivalent)

1- Full -wave bridge rectifier module, 1.5 amp.,

200 volts (Motorola MDA942 -3)

1- Chassis -mounting a.c. plug (Amphenol 61 -M

or equivalent)

1 -Case (Millen 74400 or equivalent)

1 -2" square of 1/16" single -sided circuit board

Misc.- Silicon potting compound, hookup wire,

solder, pop rivets or screws

of time during each half -wave that cur-

rent can flow through the lamps plugged

into 201.

Neither the eye nor the lamps can fol-

low the 120 -cycle unfiltered pulsating

voltage out of the rectifier module, but

the lamps do respond in a proportional

manner. The brilliance of the lamps is a

function of the ratio of "on" time to

"off" time; or the louder the music, the

brighter the lights.

Capacitor Cl serves as a filter to pre-

vent the switching transients in the

A Go -Go from getting back into the

power line and causing AM -type radio

interference. The other components

optimize the circuit to prevent prema-

ture turn -on of the SCR and allow more

accurate proportional control by dis-

charging C3 before a new "on" cycle

begins.

As the audio is used for bias only,

little audio power is consumed. The

A Go -Go has high sensitivity and very

little volume is needed to drive it.

Construction. Start construction by

laying out and etching the printed cir-

cuit board shown in Fig. 2. Drill holes

and mount components as shown in Fig.

3. Watch the polarity -one wrong con-

nection can destroy the semiconductors.

After you've finished the wiring, con-

nect an a.c. socket and plug to the board

and test the A Go -Go with a 25 -watt bulb.

The bulb should glow slightly with no

audio. A fairly low level audio signal

should drive the lamp to full brilliance.

If this test checks out okay, test the

board using the lamps and audio source

(Continued on page 104)

NOTE' FOIL PATTERN

IS ON BACK SIDE

C2

C3

Fig. 3. Mount the jack and socke s in the case

before connecting them to the circuit. if space is

not a factor you can add more features. See text.

100 ELECTRONIC EXPERIMENTER'S HANDBOOK

HEATHKIT 1967 ;FREE!

I

WORLD'S LARGEST

ELECTRONIC KIT CATALOG!

mail this coupon to

get your copy

IHEATH COMPANY, Dept. 110 -9

Benton Harbor, Michigan 49022

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I

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easy to build ... save up to 50%

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NEW 12" Transistor Portable TV

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1966 Fall Edition CIRCLE NO. 10 ON READER SERVICE CARD 103

you plan to have in the permanent instal-

lation.

For best appearance and greatest sen-

sitivity, the display lamps should barely

light with no audio input. A different

background level can be obtained by

changing the value of R2; increasing its

value will decrease the background light

level. You might also experiment with

C2 -use too small a value, and you'll

have a choppy response; too large, and

the response will become mushy.

The components are mounted inside a

modified Millen octal base and shield.

Cut the shield to about 134 long (see

Fig. 4), and drill or punch a 1`'f ;4"

keyed or r;32" round hole in the top

for the socket. Drill a '744" hole in

one side of the shield for the audio

jack. Screws or rivets can be used to

fasten the two parts of the case.

Once you've wired the board, socket,

and audio jack, you can pot the circuit

in silicon rubber. To do this, turn the

A Go -Go upside down and place small

bits of tape over the inside openings of

J1 and 21. Then pour in about half an

inch of rubber and let it set. The printed

circuit board is then positioned in place

and another half inch of rubber added.

Complete the assembly by connecting

the plug.

Modifications. The A Go -Go operates

on 117 -volt, 60 -cycle lines and utilizes

incandescent lamps only. For the un-

modified unit, you can use a total of 200

watts maximum, but for cooler opera-

tion and longer life, 100 watts or less is

advisable.

If you plan to use a bigger package

than the modified Millen shield, you might

adá a 250 -ohm potentiometer in the input

circuit as a sensitivity control, and re-

place R2 with a 250,000 -ohm potentiom-

eter to serve as a variable background

control. A selector switch with several

capacitors (0.02 µf., 0.05 µf. and 0.1

µf.) to replace C2 will give you control

over lamp response.

More power is a snap, but it will cost

extra and you'll definitely need a bigger

(Continued on page 114)

Fig. 4. Octal base shield houses all components.

If desired, silicon rubber can be poured into the

case to keep the printed circuit board in place.

104 ELECTRONIC EXPERIMENTER'S HANDBOOK

ßß

Build The

D A"

By DAVID B. WEEMS

Half-cubic foot sealed enclosure costs under $10

IF YOU'RE thinking of putting down

$30 or more for one of those depart-

ment store "no name" speakers in a box,

wait. Here is a little hi -fi speaker sys-

tem that can save you money and will

probably sound better. At least you will

know what went into the box! And you

won't find a similarly well- constructed

enclosure with a good -quality small

speaker system on the market for any-

thing like this price. If your idea of

what $10 will buy in speaker systems is

based on what was available just a few

years ago, the Cinderella system will

amaze you.

The secret of the Cinderella is in the

design and construction of its XS -5052

woofer. This woofer's distinctive qual-

ities are noticeable in two ways. The

first is the obvious visual differences be-

tween it and a normal 6 -inch speaker.

Second, and more important, there is a

distinct aural difference, which can be

made apparent by a frequency test run.

Test Results. I set one of these woof-

ers on my workbench and hooked it up

for the usual bass resonance frequency

test, starting downward from 200 cycles.

Although most 6 -inch speakers resonate

at about 120 to 150 cycles, a few "hi -fi"

6- inchers have a bass resonance of

around 70 cycles, and, frankly, that is

where I expected this woofer to fall.

Low resonance is the crucial character-

istic for woofers to be used in small

sealed enclosures; the restricted air vol-

ume in such systems will raise the point

of resonance.

My eyes were glued to the oscilloscope

screen as the audio generator dial passed

70 cycles, then 60. Not until 48 -49 cycles

did the voltage across the speaker reach

a peak, indicating resonance. A remark-

ably low frequency for a $4 speaker.

The remainder of the system consists

of a small cone tweeter with its self -

contained capacitor which acts as a high -

pass filter, and an enclosure that occupies

1966 Fall Edition 105

17 1/2"

18'

L

10 -1/4'

5 -3/8" ¡ 6-3/8_H 4 -1/4 H

"A" SIZE ENCLOSURE

FOR ONE WOOFER- TWEETER PAIR

s 2 {"-1

19 I/2

18" T

Six -inch woofer costs only $3.95 but has surprising

low end response. Tweeter is not sold separately.

The Cinderella enclosure is caulked and sealed, re-

quiring use of sturdy front, top, back, and side

panels. The author was satisfied with 3/4 -inch pine.

2 -1/2"

3-1/2"

a'v2

2 -1/2'

"B" SIZE ENCLOSURE

FOR DUAL WOOFER TWEETER COMBINATION

ALL MATERIAL

3/4' THICKNESS

IÌ"

1-9-1/2-.1

.1

'1 3/4"

CLEATS

ALL MATERIAL

3/4'T HIC KNESS

Most builders may be satisfied with single woofer -

tweeter combination, but dual system sounds better.

BILL OF MATERIALS

-A" System -Total cost, $10

1- Woofer -tweeter combination (Stock No. XS-

TS-63, McGee Radio Co., 1901 lIeGee St..

Kansas City 8, Mo.; woofer available sepa-

rately as XS -5052 for $3.95)

2 -91/2" x 16" pieces of %" fir plywood for front

and back

1 -71/22" x 171/2" piece of 3/" clear pine for top

(1 x 8)

1 -7/)" x 16" piece of %" clear pine for bottom

(1x8)

2 -71/2" x 101/4" pieces of %" clear pine for .sides

(1 x 8)

2 -34" x 91/22" pieces of 3" pine (side cleats

for back)

2 -1" x 141/2" pieces of ." pine (top and

bottom cleats for back)

12 -#8 x 11/4" wood screws for back

8 -#6 x 1/2" sheet metal screws for speakers

1--1" x 24" s 30" sheet of fiberglass

[Misc. -#6 finishing nails (% lb.), caulking ma-

terial, glue, and grille cloth

"B" System -Total cost, $18

2- Woofer- tweeter combinations (Stock No. XS-

TS-63, McGee Radio)

2-12" x 18" pieces of %" fir plywood for front

and back

2 -11" x 191/2" pieces of 1" fir plywood for top

and bottom

2 -11" x 12" pieces of 3/4" fir plywood for sides

2 -1/4" x 12" pieces of 1/4" pine (side cleats for

back)

2 -1/4 x 161/2" pieces of 3.4" pine (top and bot-

tom cleats for back)

14 -#8 x 11/4" wood screws for back

16 -#6 x %" sheet metal screws for speaker

mounting

1 -1" x 24" s 60" skeet of fiberglass

Misc.-#6 finishing nails (1/2 lb.), caulking ma-

terial, glue, and grille cloth

106 ELECTRONIC EXPERIMENTER'S HANDBOOK

Nail side to bottom and front of the enclosure.

Good fit and a liberal use of glue are important.

only ''í sq. ft. of shelf space. The sys-

tem is called the Cinderella because.

while it bears no apparent pedigree, it

does show inborn quality. For example,

even in the small enclosure, the system

resonance is a little over 70 cycles. The

transient response is surprisingly good

for a low -cost system. As in all small

sealed enclosure systems, efficiency is

lower than in a large system, but a 7-

watt amplifier supplied all the sound

you would want in a very large but very

live room. The Cinderella is rated at

12 watts.

Budgeting Your Money. The enclosure

is sturdy, contains sufficient damping

material, and is thoroughly sealed. Any

one of these features may be missing

from a department store box. For the

skeptic, here is a rundown of how to

budget your money to build the Cin-

derella "A" system for only $10.

Speakers $6.90

Plywood for front and back .55

Pine for top, bottom and sides .75

Screws .26

Glue .25

Fiberglass .66

Caulking material .20

Nails .06

Total $9.63

1966 Foil Edition

That leaves 37 cents to squander on

grille cloth and trim. You can use screen

molding for trim (as I did -15 cents for

a cabinet) and decorator burlap will

serve as grille cloth at 49 cents a yard

(17 cents) . If anyone mentions finish-

ing the wood, you will find that 5 cents is

still available. and that is just about the

amount of shoe polish I used to stain

and "oil finish" the model shown. For

very little more, you can use a veneer

plastic, such as Contact. Or choose a

hardwood if you want fine cabinetry.

The sound can be improved by putting

two sets of the woofer -tweeter combina-

tion ($12.95) in one "B" size cabinet

(see page 52) at a cost of about $18.

Used in multiples, these little speakers

sound even better. There is more solidar-

ity in the bass and somewhat smoother

sound throughout the whole spectrum.

Also, the impedance curve tends to flat-

ten out when two woofers are hooked in

parallel.

In buying material, note that the

:'í" x 712" pine shown in the drawing is.

of course, what lumber yards sell as

"1 x 8 ". When you have cut all parts

to the specifications shown, set them up

as in the finished enclosure. At this time

you can trim any'of them that do not fit

satisfactorily. One of the economies in

this system, in time as well as money, is

the avoidance of many cleats which

would require the use of extra screws.

nails, and glue. The nailing system

shown in the diagram is quite adequate

for such a small enclosure, but a good

fit is necessary.

Construction. Begin construction by

nailing the bottom to the front, using

plenty of glue between these two parts.

Next, nail one end to the bottom and

front. Continue with the other end, and

finally nail down the top to the sides

and front.

The cleats for the back can now be

attached, using glue and nails as with

the exterior parts; but if you use the

same kind of nails, they must be cut

just short enough so they will not pene-

trate the outer surface of the sides and

top. A somewhat easier method is to

use a different nail, such as sheet rock

nails which have a large head and are

the correct length.

The joints should be caulked even

107

Front view of an experimental "B" system built by

the author to test front and side panel vibration.

This enclosure was built using cleats and screws,

unlike the plans on page 106. Fir plywood was also

used and the enclosure covered with a plastic ve-

neer. It was determined that gluing and nailing of

the panels would be adequate if care was exercised

in fitting the panels together. A grille cloth was

later installed to protect the speakers. Wiring of the

"B" speaker arrangement is shown below. Try the

8 -ohm tap instead of the 4 -ohm output of your

amplifier if the bass response seems a little thin.

TWEETER

RED

DOT

A SYSTEM

SYSTEM

rÌ

TO BA

AMPLIFIER TAP

TO an

AMPLIFIER TAP

Be sure to follow this wiring diagram to keep the

speakers in phase. Once the enclosure is sealed,

you may find it fairly difficult to change the wires.

108

though they seem to be thoroughly sealed

by glue. The caulking material can be

purchased in a cylinder for use with a

gun, or in a squeeze tube. Most building

supply stores have guns to loan, but

some rent them. Force the caulking ma-

terial along the joint and wipe away ex-

cess with a rag so it won't flow onto

the speakers.

The speakers are mounted and wired

as shown in the diagram. The back

should be drilled to allow speaker con-

nections to pass through. The wires can

be brought out through a small hole

which is later filled with caulking mate-

rial or sawdust and glue, but a better

method is to use small bolts as con-

nectors through the back.

Padding is extremely important in a

small sealed enclosure. Tests indicated

that the Cinderella's resonance could be

lowered 10 cycles or more and the bass

range greatly extended by the use of

proper padding. The whole interior of

the model shown is lined with a 1 -inch

layer of fiberglass. You can get fiber-

glass from most electronics stores; a

common size measures 1" x 24" x 60 ",

enough for two cabinets. Cut the fiber-

glass to fit all interior surfaces, except

the front baffle, and secure it in place

with tacks or glue. Then fold the re-

mainder of your sheet of fiberglass so

that it will fit into the enclosure loosely.

This should fill the enclosure.

Now fasten the back in place with the

screws specified, hook the Cinderella up

to your amplifier, and try on the "glass

slipper." That, naturally, is a suitable

wide range program source. When you

do, you'll be glad you didn't settle for

a pig in a poke. - 30

After filling cavity behind speakers with padding,

cleats should be caulked and back -nailed into place.

The usual household caulk works out just right.

ELECTRONIC EXPERIMENTER'S HANDBOOK

By CHARLES E. FENOGLIO

SOLID -STATE

6 -WATT AMPLIFIER

FOR 10 BUCKS

All -purpose push -pull audio amplifier operates on wide range of

input voltage and output impedance without bias adjustments

I F YOU would like to have a quality,

I low -cost amplifier for a hi -fi or public

address system -one you can use at

home or in your car, and can convert

into a speech amplifier, modulator, or

high -power intercom -then try your

hand at this transistorized "Six -Watter."

You can build it in less than two hours,

at a cost of about $10.00. All compo-

nents can be mounted on a printed cir-

cuit board, and construction is easy.

Several novel circuit features make

it possible to use few parts, eliminate

transformers, and achieve high efficien-

cy. A unique d.c. bias stabilizing net-

work eliminates the bias adjustments

normally found on this type of ampli-

fier and permits operation with a wide

range of supply voltages without modi-

fication.

The excellent low- frequency response

of the Six -Watter is due in part to the

absence of transformers and the use of

high -value coupling capacitors as well as

direct coupling. High -efficiency Class B

operation makes it ideal for use wherever

battery life is an important considera-

tion. Power consumption from a 12 -volt

battery under no- signal conditions is less

than ' watt.

While the amplifier can work on any

supply voltage ranging from 3 to 15

volts, the higher the voltage source, the

greater the audio power output you can

get. An input signal of less than 0.2

volt is sufficient to drive the Six -Watter

to full output. This is more than ade-

quate gain for most tuners, and crystal

or ceramic phono cartridges.

How It Works. Audio input is coupled

to the base of transistor QI through ca-

pacitor Cl. The amplified signal at Qi's

collector is direct -coupled to the base of

Q2. Here again, the signal is amplified

and directly coupled to Q3 and Q4.

Transistors Q3 and Q4 work in opposite

directions; while one is conducting more,

the other is conducting less -their out-

put signals are 180° out of phase with

each other. This type of circuit makes it

possible to drive a push -pull output stage

without the aid of a transformer.

The signals from Q3 and Q4 are di-

rectly coupled to Q5 and Q6 respectively.

Transistors Q5 and Q6 operate as Class

B power amplifiers. Balanced operation

requires that the product of the current

gain of Q3 and Q5 be equal to that of

Q4 and Q6.

The filter network, C2 and R4, pre-

vents audio voltage variations at point

1966 Fall Edition 109

C3

.

r

3

O INPUT

CI

109f.

RI 39K R3 02 05

IK 2N 305 2N554

w_ w.

OI

E

03

291304

C

R4 R5

IK IK

R7

47(1

39K

C2

I009f.

DI

IN2069 RB

47n

04

291305

06

29554

R6

680(1

FI

2 2AMP +

1

3 TO

15V

C3

10009 f.

L J

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

100K

TUNER gMPLIFIER neither transformers nor bias adjustments. It operates with supply

INPUT voltages of between 3 and 15 volts. An input signal of 0.2 volt is suffi-

cient to drive it to full output. Volume control can be added if desired.

SPKR

3.2R

(SEE TEXT)

PARTS LIST

C1- 10 -µf., 10 -volt electrolytic capacitor

C2- 100 -sf., 10 -volt electrolytic capacitor

C3- 1000 -µf., 15 -volt electrolytic capacitor

D1- 1N2069 (or any 750 -ma. silicon diode)

F1- 2- ampere fuse

Q1- 2N1694 transistor (or 2N167, or 2N2925)

Q2, Q4 -2N 1305 transistor

Q3- 2N1304 transistor

Q5, Q6 -2N554 or 2N2148 transistor

R1, R2- 39,000 -ohrn, / -watt resistor

R3, R4, R5- 1000 -ohm, 1/2-watt resistor

R6-680-ohm, fizz -watt resistor

R7, R8- 47- ohnz,' -watt resistor

1- Printed circuit board, available from Hazleton

Scientific Co., Box 163, Hazel Park, Mich.

48030 for $2.85 postpaid with all holes drilled

and for $1.95 postpaid uudrilled

2 -1%" x 21/2" x 1/16" heat sinks, copper or alu-

minum

A in Fig. 1 from reaching Q1's emitter.

This results in a high degree of d.c. sta-

bility without affecting the a.c. gain of

the amplifier.

Any speaker impedance ranging from

1.6 to 16 ohms can be used. Because

power output is a function of speaker

impedance, and source voltage, stick to

a 3.2 -ohm speaker and a 12 -volt source,

if possible.

Construction. You can make your own

circuit board, or purchase one for $2.85 ponents onto the printed circuit board as shown.

o-{R7 Y.:, 64R8)-0

r

0-(DI1)-0 0{R5)-0

`l R I }-o -1 R4 f"

0-( R2 Ye

QI Fo

\

13

<CI /// 1

Fig. 2. Carefully locate and solder all of the corn-

110 ELECTRONIC EXPERIMENTER'S HANDBOOK

Fig. 3. Use this full -size guide in making your printed circuit board. Space the transistors about 1/2" above

the board and hold transistor leads on top side of board with a pair of long -nose pliers when soldering.

(see Parts List) , or you can mount and

wire the components on a small (ap-

proximately 4" x 6 ") conventional type

chassis. If you use the board, locate and

solder the parts in place as shown in

Fig. 2. Space the transistors about 1/2"

above the board and hold the transistor

lead on

pair of

Heat

from a

the top side of the board with a

long -nose pliers while soldering.

sinks for Q5 and Q6 can be cut

' ill" copper or aluminum sheet,

17-17 /32

27/32

HEAT SINK

-I- 19/32- +29/32-I I

I/8"DIA 3 /1B DIA

r--31/32I-5/32H

21/2"

` TRANSISTOR

M r Iln-6-32'SCREW

111

HEAT SINK

II ~PC BOARD

NO.6 NUT

Fig. 4. Use thin copper or aluminum stock to make

heat sinks and mount with the transistor as shown.

1966 Fall Edition

and should measure 1V x 2! ". Drill

holes as shown in Fig. 3. Two holes are

used to mount each heat sink on the

board, and two are used for the transis-

tor pins. Paint the heat sinks black to

increase thermal dissipation. If you plan

to use the amplifier continuously at high

power levels and high ambient tempera-

tures, increase the size of the heat sinks.

Final Check. After completing con-

struction, feed a 6- to 12 -volt d.c. source

to terminals 2 and 4 (positive voltage

to terminal 2) and measure the d.c. volt-

age between point A and terminal 4.

It should be one -half the supply volt-

age. If it is not, RI and R2 may not be

matched closely enough. In this case,

temporarily replace R1 with a 100,000 -

ohm potentiometer and adjust the pot

until the voltage at point A measures

one -half the supply voltage. Then meas-

ure the resistance of the potentiometer

and replace it with a fixed resistor of

that value.

Modifications. You can add a volume

control to the amplifier by connecting a

potentiometer to the circuit between the

(Continued on page 140)

111

WANT a cheap, effective, and reason-

ably attractive enclosure for an 8"

speaker? Although the "99¢ Enclosure"

grew out of the need for a temporary

setup, the unit is quite appropriate for

permanent home hi -fi systems, especially

where positioning of conventional en-

closures for best stereo listening is ham-

pered by furniture placement or pecu-

liarities of the room's general layout.

The portability and durability of this

unit makes it practical to store a couple

of them out of the way, then move them

into position each time they are used.

The speaker used by the author was a

Lafayette SK -128, but any other full -

range 8" speaker would be equally ap-

propriate for use in this unique enclo-

sure. Construction can be completed in

five or ten minutes with the aid of a

drawing compass, measuring tape, and

penknife.

Construction. The "enclosure" is avail-

able, practically ready for use, in almost

any department or variety store, in the

form of a "Steri- lite" 44 -quart polyethy-

UNIQUE

99C

SPEAKER

ENCLOSURE

By JOHN N. AYRES

Simple

plastic baffle

uses inverted

wastebasket

-

lene wastebasket (U. S. Plastic Company

Model #1040). Prices may vary but the

pilot model was obtained at a cost of 99

cents. This container is approximately

20" tall and tapers from a diameter of

about 14" at the top to a little over 11"

at the bottom. It comes in three colors:

beige, turquoise, and yellow. The mate-

rial is sufficiently soft so that undesir-

able resonances are avoided, yet firm

enough to easily support the heaviest 8"

speaker.

The general idea is to place the waste-

basket on the floor, upside down, and

mount the speaker in the bottom. To pre-

pare the basket, first determine the ac-

tual diameter of the speaker cone (it

will be about 7 "), then adjust your draw-

ing compass to half that amount -the

radius -and draw a circle on the bottom

of the basket. Be sure the pivot of the

compass is in the exact center. Now,

using a penknife, cut the opening for

the speaker following the line as closely

as possible, but don't worry about minor

irregularities since the edge will not

show. Punch the mounting holes using

112 ELECTRONIC EXPERIMENTER'S HANDBOOK

Turn the wastebasket upside down

and cut out a hole

to pass the frame, but not the rim

of the 8 -inch speaker.

Holes in bottom of inverted basket

are ports to release

back pressure. Dress the enclosure up

with a decorative grille

(shown in right hand photo).

the speaker itself as a template ; a paper

punch or any sharp, pointed instrument

will do the job.

Using the Enclosure. Connect the

speaker leads to your amplifier, and sit

back and listen to a familiar record. You

will find the upward firing arrangement

quite desirable, for the sound spreads

out in all directions- obscuring the fact

that you are listening to a small 8"

speaker. Use of a pair of them imparts

an amazing stereo effect, totally elimi-

nating any "hole -in- the -middle."

A decided improvement in bass re-

sponse will be observed if the enclosure

is supported about two inches above the

floor. But instead of rigging up an elab-

orate support, the same effect can be

had by cutting six or eight equally

spaced 2" holes around the circumfer-

ence of what now serves as the bottom

of the enclosure ( originally the top of

the basket). Keep the holes as close to

the bottom as possible, using a tape

measure and drawing compass for layout

and a penknife for cutting as before.

This time, however, take pains to make

your cuts as clean as possible, since they

will not benefit from concealment as does

the big opening for the speaker. Very

fine sandpaper can be used to smooth

off the edges.

You can also install a suitable protec-

tive and decorative cover for the speaker

if you are willing to exceed your 99ç

budget. Radio stores have grilles for

wall or ceiling installations that will do

nicely. However, be sure the one you

select has an overall diameter not ex-

ceeding 101/2", so that it will fit the

basket properly. (Electro -Products'

#SG -8CO3 among others, makes a good

fit and is attractive as well). Four pan -

head machine screws, washers, and nuts

secure the works.

Bearing testimony to the value of the

finished product as both a unique, attrac-

tive conversation piece and an acousti-

cal device of commendable performance,

the author's dentist extracted his two

SK -128 speakers from their factory en-

closures and put them into a pair of the

99r wastebaskets.

1966 Fall Edition 113

THE WORLD'S

MOST DISTINGUISHED

PHOTOGRAPHIC ANNUAL

AND THE WORLD'S LARGEST SELLING

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For almost 20 years, in every corner of the world, the name

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Over 200 exciting pages of superb, provocative pictures -

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just $3 postpaid, when you check the

appropriate box on the order form.

IN IM - MI IN MEN -

Ziff-Davis Service Division, Dept. PA.

589 Broadway, New York, N. Y. 10012

Please send my copy of the 1967 PHOTOGRAPHY ANNUAL.

I am enclosing $1.50 plus 15c for shipping and handling for

the Regular Edition. ($2.00 for orders outside U.S.A.)

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PNf770GNAPNT

ANNUAL 1967

name 0LEAsE PRINT)

address EEH.E6

city

state zip code

1111111111=1=== IMP ti 1110 = = fi 1

HI -FI À GO -GO LAMPS

(Continued from page 104)

container. All you have to do is replace

the rectifier module and SCR with models

rated to handle the increased wattage.

The accompanying table lists components

needed for 200, 600, 1000, and 2000

watts. Cost of SCR1 and rectifier for 200

and 600 watts runs a little over four

bucks. But for 1000 watts it jumps up to

about $7, and for 2000 watts, $8.50.

MODIFICATION TABLE FOR MORE POWER

Power

Level

(watts)

Rectifier

Module Heat

Sink? SCR1 Heat

Sink?

200 1.5 amp.

Motorola

MDA942-3

No 2.0 amp.

RCA

2N3528

No

600 6.0 amp.

Motorola

MR1032B

(4 req'd.)

No 5.0 amp.

RCA

2N3228

Yes

1000 10 amp.

Motorola

MDA962-3

No 8.0 amp.

Motorola

MCR1305.4

Yes

2000 18 amp.

Varo Inc.

1N4436

Yes 18 amp.

Motorola

MCR808.4

Yes

How To Use It. There are many ways

in which you might use the À Go -Go

lamps. For instance, to make stereo lis-

tening fun to watch, you can install an

À Go -Go in each channel. In the right

channel use four red and two green 25-

watt bulbs; in the left channel use four

yellow and two green ones. Arrange all

the lamps in a row in a reflective en-

closure (crumbled aluminum foil will do)

or behind a translucent screen. The

green lamps should be in the middle,

the red on the right, and the yellow on

the left.

Audio signals for the À Go -Go can be

taken directly from the speaker leads. If

the sound is too loud for the amount

of light you want, try a lower imped-

ance tap on the amplifier or add a re-

sistor of 5 to 200 ohms in series with

the unit's input and the amplifier.

114 ELECTRONIC EXPERIMENTER'S HANDBOOK

CHAPTER

5

COMMUNIA

CATIONS

SWL

CB

HAM

1966 Fall Edition

Editors often have the feeling that they are making a

strong case for a particular story, or project, that they

"know" should attract widespread attention. When the

project doesn't catch fire, three questions come to mind:

was it a bad guess by the Editor, wasn't the story suffi-

ciently detailed, or did the project pass unnoticed? We

are convinced that Chuck Caringella's story on page 121

passed unnoticed -though there is every reason in the

world why it shouldn't.

In Chuck's story -it's really too simple to be called a

full -fledged construction project -he shows how any ham,

SWL, or CB'er with a receiver having a 455 -kHz i.f. strip

can make a vast improvement in receiver selectivity. This

is no gimmicky device, for the mechanical filter was de-

veloped about 15 years ago by one of the topnotch com-

munications equipment manufacturers -the Collins Radio

Company. We urge you to read how simple it is to add a

mechanical filter to your present receiver; then go ahead

and try it. When you do, you'll be in for a surprise.

116

THE CAMPER'S SPECIAL Hartland B. Smith, W8VVD

121

SUPER SELECTIVITY FOR YOUR RECEIVER

Charles Caringella, W6NJV

125

"WATCHDOG" MOBILE MONITOR Howard Burgess

127

DUAL -SENSITIVITY FIELD STRENGTH AND ABSORPTION METER

Robert N. Tellefsen, W7SMC /0

115

By HARTLAND B. SMITH

W8VVD

Battery -operated

80 -meter CW

transmitter for use

in the field, or

as a standby back

in the shack,

can be built for

less than $10.00

INEXPENSIVE medium -power r.f.

transistors make it possible to con-

struct a low -cost but effective dry -

battery- powered c.,w. transmitter. The

"Camper's Special" is a 3.5 -mc, portable

rig with an input rating of almost 5

watts, yet it can be built for less than

$10, plus batteries, key, and crystal.

Operating expense is insignificant, run-

ning in the neighborhood of three cents

per hour when ordinary Iantern batteries

are used as a power source.

While the transmitter is especially

well suited to operate miles from a con-

ventional power source, it also is a worth-

while addition to the shack of the con-

scientious ham who has been searching

for a simple rig for emergency backup.

Its signal is strong enough to provide re-

ception of solid copy at a distance of 20

miles or more on ground wave, and up

to 1000 miles when skip conditions are

optimum. Keep in mind that a 5- watter

is only two S -units weaker than a 100 -

watter. Performance, if the QRM isn't

excessive, can be surprisingly good.

116 ELECTRONIC EXPERIMENTER'S HANDBOOK

How It Works. Resistors RI and R2

form a voltage divider to provide a small

amount of forward bias for the base of

Ql. Current flows in the emitter- collec-

tor circuit and through Ll when the key

is closed. The application of power

causes the crystal to vibrate at its res-

onant frequency and varies the emitter

bias at an r.f. rate. If L1 and Cl are now

resonated near the crystal frequency and

Ql amplifies sufficiently to overcome cir-

cuit losses, the stage will go into sus-

tained oscillation.

Capacitor C3 couples the signal from

Q1 to Q2. Transistor Q2 and its tank

circuit (L2 and C4) amplify the signal.

Resonant tank circuit L3, C6 picks off

the signal and couples it to the antenna.

This is a basic master oscillator, power

amplifier (MOPA) configuration.

A tap on L3 matches the low imped-

ance of the antenna feed line to the high

impedance of the tank. When SI is open,

current flowing to the antenna passes

through pilot light Il, which serves as a

relative indicator of transmitter tuning

and power output. Tune all stages for

maximum brightness. Keep the switch

closed when on the air.

Construction. The larger half of a 5" x

4" x 3" Minibox is both chassis and front

panel for the transmitter. Since lead

length and parts layout aren't overly

critical on the 80 -meter band, you needn't

worry about precisely duplicating the

component arrangement. As long as

your version resembles the prototype, it

should perform satisfactorily.

In order to save both space and money,

mica trimmer capacitors are used for Cl,

C4 and C6. Mount these capacitors be-

hind 'Y' holes drilled in the Minibox

cover. Note that one trimmer terminal is

fastened to the plate which is directly

beneath the adjusting screw in each case;

fasten this terminal to a grounded solder

lug. Support the other terminal on a

one -terminal insulated tie strip. If you

don't like to do your tuning with a screw-

driver, solder .e +" lengths of ''. i" brass

shafting, salvaged from old volume con-

trols, to the capacitor adjusting screws.

1966 Fall Edition 117

Larger half of box serves both as chassis and front

panel. Shafts mounted on capacitors Cl and C4 ac-

commodate knobs to eliminate screwdriver tuning.

Then you can put knobs on the shafts, as

shown. A large soldering iron is needed

for this particular job. Don't let excess

solder dribble down and short out the

trimmer plates or damage the mica in-

sulation.

No socket is required for 11. Merely

press the bulb into a fix" grommet and

solder leads from S1 directly to the base

and tip.

Cover L2 with a layer of plastic elec-

trical tape and slide it part way into L3.

The exact position of the coil will be de-

termined later when the transmitter is

adjusted. As you wire the coils, make

sure that the collector end of L2 and the

ground end of L3 are nearest Q2. This

arrangement minimizes capacitive coup-

ling, thus keeping harmonic radiation at

a minimum. Put spaghetti over the lead

at the C5 end of L2. Thread this wire

through the center of the coil and then

run it over to the capacitor.

Since the transistor cases are 24 volts

above ground, be certain that the fins on

Q2's heat sink do not contact nearby un-

insulated objects. Bend the fins near TS2

and the edge of the chassis at right

angles so that there will be no chance of

them shorting out the batteries. For the

same reason, position Q1 where it will

clear the side of the assembled Minibox.

Before plugging the transistors into

their respective sockets, trim the leads

to a length of % ". Grip the wires tightly

with a pair of long -nosed pliers, close to

the transistor body, to take up the me-

chanical shock that results from the

snipping action. Failure to do this can

sometimes fracture the silicon wafer in-

side the transistor.

Center shield isolates oscillator from amplifier.

Coil L2 is suspended inside L3 and cemented in

place after it has been tuned for maximum output.

118

PARTS LIST

BI -Four 6 -volt lantern batteries in series

Cl, C4, C6 -80 -480 pf. mica trimmer capacitor

C2, C5- 0.01 -µf. ceramic disc capacitor

C3- 100 -pf. ceramic disc capacitor

I1 -#47 pilot light

L1 -22 turns of 420 wire, 1" diameter x 1%"

long, tapped 11 turns from C2 end (B. & W.

3015 Miniductor, or equivalent)

L2 -14% turns of #24 wire, 4" diameter x

%" long -see text (B. & W. 3012 Miniductor

or equivalent)

L3 -23 turns of #20 wire, 1" diameter x 1N"

long, tapped 7 turns from ground end (B. &

W. 3015 Miniductor, or equivalent)

01, Q2- 2N3053 transistor

R1- 82,000 -ohm, % -watt resistor

C5 L3 L2 LI C2 TSI

TS2 C4 02 RFCI C3 01 R3 CI RI

ELECTRONIC EXPERIMENTER'S HANDBOOK

TSI C3 RPCI 02 C4 152

C2 LI R2 L2 L3 CB CB

R2- 5600 -ohnr, % -watt resistor

R3- 150 -ohm, % -watt resistor

RFCI -2.5 -rah. r.l, choke

Sl- S.p.s.t. slide switch

TS1, TS2- Two -screw terminal strip

KEY- Telegraph key

XTAL -3.5- to 3.8 -mc, quartz transmitting

crystal

1 -5" x 4" x 3" Minibox (Bud CU- 2105 -A, or

equivalent)

1- Transistor heat sink (Wakefield Engrg. ÁF-

209)

Misc. -Knobs (3), crystal socket, 2?ÿ" x 3%"

shield (aluminum or tin), 1- terminal insulated

tie points (4), 2- terminal insulated tie points

(2), transistor sockets (2), grommet, solder

lugs, machine screws and nuts, wire, solder,

spaghetti, etc.

Bend fins on Q2's heat sink to avoid contact with

cabinet and leads. For best results, locate compo-

nents as shown. Lead dress is not too critical.

A 2W!ß' x 3 %' metal shield with a ','

mounting flange isolates the amplifier

from the oscillator stage. Either thin

aluminum or coffee can tin may be used

for the purpose. Drill a small hole near

the center of the shield to pass the spa-

ghetti- covered lead of C3.

Precautions: The amplifier transistor

generates quite a bit of heat during

normal operation. Consequently, never

use the rig unless a heat sink is slipped

over Q2, and don't hold the key down for

more than 15 seconds at a time while

tuning up. Watch the battery polarity,

too; accidentally reversing the battery

leads can destroy the transistors.

Adjustment. Connect a 100 -ohm, 1 -watt

composition resistor across the terminals

of TS2 to act as a dummy antenna. At-

tach a key and battery to TS1. Set Cl

at low capacity and tighten down C4 and

C6. Then open Si. Tune your receiver to

1 TS I

f.

0

IIIBI KEY

01602

" e

OE CO

*SEE PARTS LIST "

Transistor Q2 amplifies the output of Q1, which acts as a

crystal -controlled master oscillator. All coils, with the

possible exception of Ll, are tuned for maximum output. If

the oscillator does not "start" reliably, detune Ll slightly.

1966 Fall Edition 119

J ^;

/'-ROPE

72A TWIN LEAD/

46.5 OR 139.5

TO

TS2

ROPE

STRIVE FOR

MAXIMUM HEIGHT

II SPREAD

C

Sling the center of the antenna over the highest limb of a tree, and spread it as much as possible. The

more horizontal the line, the better. Radiation angle is north and south if the wire runs east and west.

the crystal frequency, and depress key.

Slowly tighten Cl until the oscillator

can be heard in the receiver. Do not ad-

vance Cl beyond the point where consis-

tent oscillation occurs each time the key

is pushed. Adjust C4 and C6 for maxi-

mum volume on the receiver. By now,

II should start to glow. Slide L2 in and

out of L3, while adjusting C4 and C6.for

the brightest indication. Then cement

L2 in place.

A milliammeter temporarily connected

in series with the key should read some-

where between 175 and 225 ma. with

both transistors plugged in. Removal of

Q2 should drop the reading to 10 or 15

ma. Now remove the dummy load and hook

up the regular antenna. Stick to the

specified dimensions. Do not attempt to

use a random length of end -fed wire, as

it will load the transmitter incorrectly

and will radiate a very poor signal. The

most important part of the antenna is its

center so far as height is concerned.

Consequently, as long as you have the

center at least 30 feet off the ground,

you can tie the ends to any convenient

tree or bush.

If possible, use a 461/2-foot feeder,

rather than a 1391/2-tooter. In either

case, however, do not coil up the ex-

cess line. Instead, let it "meander" back

and forth on its way to the transmitter

with no sharp bends.

Operation. Working with low power on

a crowded band requires a certain

amount of skill. When arranging sched-

ules with stations back home, try to

choose a time when conditions are opti-

mum between the two locations. If skeds

are impractical, pick a net frequency

where the gang has been previously

alerted to listen for your signals.

During random operation, don't bother

to call CQ. Wait for a strong station to

come on the air within 3 or 4 kc. of your

frequency and then tap out a reply. With

a little patience, and operating know -

how, you'll be surprised and pleased at

the number of QSO's that the Camper's

Special will produce. -l-

1Y0 ELECTRONIC EXPERIMENTER'S HANDBOOK

SUPER SELECTIVITY FOR YOUR RECEIVER

By CHARLES CARINGELLA

W6NJV

Mechanical filter sharpens

bandwidth for optimum

reception of AM, CW, and SSB

IF your receiver or transceiver employs

a 455 -kc. i.f. strip, sharp selectivity

can be achieved by substituting a recent-

ly introduced mechanical filter (Lafay-

ette 99 K 0123) for the first i.f. trans-

former to help you cope with today's

crowded radio bands. Several important

advantages make this installation highly

desirable.

Steep skirt selectivity makes it possi-

ble to overcome the masking effects of

strong or local signals as little as 5 kc.

away. Once the filter is installed, it

doesn't need to be adjusted while the re-

ceiver is in operation. No objectionable

effects such as ringing or hollow sounds

commonly associated with crystal filters

are present. The filter can be installed

in most vacuum -tube -type amateur, com-

mercial, or CB equipment. Finally, it

works well in AM, CW, and SSB receiv-

ers. How It Works. The mechanical filter

is basically an electromechanical device.

It consists of an input transducer, a

resonant mechanical section having sev-

eral metal discs, and an output transduc-

ers, as shown above. Both transducers

are crystal types. An electrical signal

applied to the input transducer is con-

verted into mechanical vibrations which

travel through the resonant mechanical

section to the output transducer, where

they are reconverted to electrical signals.

The selectivity characteristics of the

filter are determined by the resonant

metal discs. Each disc is carefully ma-

chined to extremely close tolerances to

make it vibrate at a desired frequency,

such as 455 kc. The discs are made of a

ferro- nickel chromium alloy for extreme

hardness and resistance to corrosion.

Each is supported by -and coupled to

the others with -a thin rod. The rod

runs the entire length of the filter, and

is attached to the transducer at each end.

Only those signals within the filter's

passband can get through.

Nominal bandpass characteristics of

the filter used in this project are shown

1966 Fall Edition 121

in Fig. 1. At 6 db down on the response

curve, the bandwidth is approximately

2 kc.; and at 60 db down, the bandwidth

is approximately 6 kc.

It is natural for mechanically resonant

elements, such as metal discs, to have

multiple resonances which allow spurious

transmissions through the filter at fre-

quencies other than those in the primary

passband. By employing conventional

type i.f. transformers at the input and

output ends of the filter, these spurious

signals are attenuated. Signal frequen-

cies of plus or minus 20 kc. from the

i.f. (435 kc. and 475 kc.) are cut by a

minimum of 40 db. Frequencies above

475 kc. and below 435 kc. are far enough

away from-the rest of the receiver's pass -

band to be blocked, and thus be of no

consequence.

Input and output impedance is 10,000

ohms. Capacitive coupling is required to

prevent B + on the input side from get-

ting to the output side, which is in the

grid circuit of the next stage, and to pre-

vent B-h from shorting to ground. In

order to minimize the number of connec-

tions to the filter, the bottom leads of

the windings in both transformers are

DB

o

20

40

60

80

-6]8

-60 DB

1 t I I I 1 , I

3

I

4 +

4 3 2 I O I 2 5

KILOCYCLES

Fig. 1. Bandwidth of 2 kc. at 6 db expands slowly

to 6 kc. at 60 db. Steep skirt characteristic makes

it possible to separate closely spaced stations.

already connected to the ground foil on

the filter's printed circuit board. Only

three connections are needed: plate,

grid, and ground.

TI

455KC

MIXE VI

613E6

K

AIM

IOOK

B+ AVC

MECHANICAL FILTER

a ASSEMBLY

MIXER

VI

68E6 A 1

RI 10K

IK

Jf. P G

GND

.016f.

C2 OOlyf. I

R2

I0K

100K

I.F. AMP

V2

65,56 5

I.F AMP

V2

6506

Fig. 2. Typical receiver first i.f.

stage before modification. Internal

circuitry of transformer can be ig-

nored. However, the frequency of the

mechanical filter should be the same

as the transformer to be replaced.

Fig. 3. In addition to the mechani-

cal filter, only two capacitors and

two resistors are added (within the

dotted lines). Once the filter is

installed and the remaining i.f.

transformers have been peaked, no

further adjustments need be made.

122 ELECTRONIC EXPERIMENTER'S HANDBOOK

L- SHAPED'

MOUNTING

CI RI R2 C2 G BRACKET

Fig. 4. Mechanical filter and added components are

grouped together into a subassembly and mounted ün

the same manner as the original i.f. transformer.

Fig. 5. Bottom view of receiver before the first

i.f. transformer (Ti) is removed. It is not neces-

sary to disturb any other part of the receiver.

Fig. 6. After the first i.t. transformer is removed,

the mechanical filter subassembly is installed, and

held in place by two screws. The board should be

made small enough to pass through chassis opening.

1966 Fall Edition

Construction. The only parts you will

need, in addition to the mechanical filter,

are two 10,000 -ohm, 1/2 -watt resistors,

(Rl and R2) , two 0.001 -pf. ceramic disc

capacitors (CI and C2) , a 1" x 1" piece

of Vectorbord or other suitable material,

six push -in terminals, and an L- shaped

mounting bracket.

Except for the removal of the first

i.f. transformer, all components and con-

nections in your receiver or transceiver

remain the same. A typical circuit before

modifications is shown in Fig. 2. Varia-

tions in component values or in i.f. trans-

former design in different receivers are

not critical and will not adversely affect

the installation of the filter. Figure 3

shows the same portion of the receiver

after the filter has been installed.

The actual filter and additional com-

ponents are mounted on a subassembly

as shown in Fig. 4. While it is not neces-

sary to shield the filter -its components

are already housed in metal cans which

have been grounded to the printed circuit

board -it is necessary to have a good

ground connection between the board and

the receiver's chassis.

The one -inch -square piece of Vector -

bord is bolted to the bottom of the L-

123

V2 '; T2

\MECHANICAL

FILTER ASSEMBLY:.

shaped bracket. Resistors R1 and R2

and capacitors Cl and C2 are mounted

on the board. The push -in terminals

serve to hold the components and the

connections to the receiver. Before and

after photos show how the subassembly

is mounted on the chassis. Check to see

that the board fits in the chassis open-

ing, to fully seat the bracket.

CLEAN

LAYOUT

TECHNIQUE

124

Fig. 7. Above -the -chassis view of mechani-

cal filter mounted in place of Tl. Inser-

tion loss is on the order of 1.5 to 3 db.

Alignment. Generally, once the filter

assembly has been installed, no further

alignment is necessary. However, you

might try to peak the remaining i.f.

transformers in the receiver. Just in

case the two transformers on the filter

have been diddled with, they too should

be aligned for maximum output at the

designated intermediate frequency. IA

TO GIVE your finished project that

professional look, take care not to

damage the painted surface of the cabi-

net when you locate the various mount-

ing holes. Cut a piece of graph paper

to cover the area to be drilled or

punched and seal it down temporarily

with rubber cement. Then lay out your

drilling pattern using a sharp -pointed,

soft -lead pencil. Centerpunch hole loca-

tions and drill (or punch) through the

graph paper. When all machine work -

including deburring- is finished, simply

peel off the paper pattern. Excess ce-

ment can be removed by rubbing the

surface with a finger or a soft eraser.

The resulting surface should be smooth

and clean. If you use decals or painted

labels, protect them with two or three

coats of clear lacquer or acrylic plastic.

-E. G. Louis

ELECTRONIC EXPERIMENTER'S HANDBOOK

"WATCHDOG" MOBILE MONITOR

A real watchdog, this miniscule tester

functions as a field strength meter, carrier-shift

indicator, and modulation checker.

The perfect companion piece for your mobile rig,

it also measures voltages and current.

By HOWARD BURGESS

THE "WATCHDOG" is a self- contained,

unpowered monitor to help you squeeze

the last legal milliwatt out of your trans-

mitter. The circuit was designed to en-

able measurement of relative field

strength, determine if carrier shift is

taking place, and give an audio check of

modulation quality. As a bonus feature,

the watchdog can serve as an emergency

d.c. voltmeter. If you rush out and buy

all new parts, you might be set back

about $9, but many -if not most -of the

necessary parts are probably right in

your junk box.

1966 Pall Edition

Construction. Because the greatest val-

ue of the Watchdog is in mobile opera-

tion, the circuit has been squeezed into

a 21A" x 13s" x 4" aluminum box (Pre-

mier PMC -1002) . A bigger -or even a

smaller -aluminum box could be used,

depending on the size of the 0 -1 ma.

meter. A 1?i" square face meter of the

imported variety was used. These meters

are commonly available and you should

have no difficulty in duplicating the exact

layout of the parts shown in the accom-

panying photographs.

Only two parts in the circuit need spe-

125

Because the Watchdog is a

passive network, it doesn't

require batteries or a

power supply to operate.

AN7. I

JI-11 500v

R3 J2

.51MEG-

W 20V

0-Ima.

J4

ONO

cial attention. One of these is silicon

diode DI, which must be suitable for de-

tector operation up through 30 mc. Ca-

pacitor C3 must be of the low- leakage

variety (Mylar -type) and must have a

capacity of at least 1.0 µf. The voltage

rating of C3 is not important.

The components built into the circuit

for voltage measurements are not an ab-

solute necessity and may be left out if

you wish. No effort was made to alter

the meter scale ; instead, a conversion

table was pasted on the back of the box.

One final construction suggestion: after

the case has been drilled and the meter

hole cut out -but before the parts are

mounted -spray -paint the box to match

the interior colors of your car. Spray

enamel paints are readily available at

all automotive supply stores.

Operation. The Watchdog has three

operating positions. With switch S1 in

the FS position, the watchdog becomes a

field strength meter and will indicate the

relative carrier level output of your

transmitter. A short piece of wire

plugged into the antenna jack, J1, is

more than ample to drive the meter off -

scale with even a 5 -watt input CB rig.

The Watchdog requires no tuning and

will work on any of the ham bands up

through 10 meters. With SI in the FS

position, the Watchdog can be used to

peak up the pi- network of your trans-

mitter or tune your antenna for maxi-

mum efficiency.

When SI is in the CS position, the

"talk power" of your transmitter is being

measured, and the circuit has become a

linear detector. It will be necessary to

close -couple the output of the transmit-

ter to the Watchdog by bringing a lead

126

PARTS LIST

C1-500-pl. mica capacitor

C2- 0.1 -sf., 200 -volt capacitor

C3- 0.001 -4. ceramic disc capacitor

C4 -1 -µf. low- voltage capacitor

Dl -1X54 diode

I1. 12, 13. 14, 15-P hono tip jack

16-Miniature phone jack

L1- 0.75 -mh. r.f. choke

MI --0 -1 era. d.c. meter (1 . " square)

RI- 18,000 -ohm, 1,1,watt resistor

R2- 1000 -ohm. h -watt resistor

R3- 0.51- megohm, 1-watt resistor

R4- 20,000 -ohm, /watt resistor

SI- Single -pole, 3- position switch

l -1 /8" s 2 ¡g" r 4" aluminum box

Dlisc.- Insulated tic point, wire, solder, cte.

from J1 close to the transmitter. If the

transmitter is well shielded, or very low

powered, it may be necessary to place

the end of the lead inside the case of the

transmitter. The coupling between the

Watchdog and the transmitter should

be arranged so that the meter reads

about 0.8 ma. The exact reading is not

important -just be sure that the cou-

pling is not too tight to damage the

meter.

If the transmitter is properly modu-

lated, the meter should have a slight

upward kick for normal voice transmis-

sion. The movement of the meter needle

should not be more than 10c,í, of the un-

modulated (about 0.8 ma.) value. A

larger than 10% upward kick indicates

overmodulation, and a downward shift

says that the transmitter has insufficient

drive to the final amplifier.

(Continued on page 150)

Parts placement depends on size of meter used. With

a very small meter, lay out components as shown.

ELECTRONIC EXPERIMENTER'S HANDBOOK

DUAL- SENSITIVITY

FIELD STRENGTH

AND

ABSORPTION METER

By ROBERT N. TELLEFSEN

W7SMC /!6

PERHAPS the simplest yet most under-

estimated item of test equipment

found in the ham shack is the absorption

meter. It's impossible to calculate the

number of hams who have been spared

FCC pink tickets for being on the wrong

band because they took care to monitor

their own frequency. But this is just one

of many applications of the field strength

and absorption meter, or "wavemeter."

It can be used as a neutralization indi-

cator or as a null indicator for adjust-

ing balanced modulators in SSB trans-

mitters. It can also be used to determine

if an oscillator circuit is working, and to

compare transmitter signal output before

and after adjustments are made.

Easy to build, the absorption meter

consists of a variable -tuned single tran-

sistor amplifier powered by a 11 -volt

Only four coils are needed to cover the 160- to 6-

meter amateur bands. Whip antenna extends effec-

tive range of the field strength and absorption meter.

1966 Fall Edition

penlight battery. (It works with and

without the battery; with the battery in

the circuit, sensitivity increases by a

factor of 10.) Resonance is indicated by

a front -panel -mounted 0 -1 ma. meter.

Four plug -in coils are used to cover the

160 -meter to 6 -meter bands.

Parts cost is less than $8 and it

shouldn't take you more than an evening

to put the whole thing together.

How It Works. A small amount of r.f.

energy is absorbed by tuned circuit Cl,

LI when the coil or antenna is placed in

the vicinity of an r.f. field. The amount

of energy absorbed depends upon the

strength of the r.f. field, the extent of

coupling of the meter to the field, and

the resonant condition of the meter's

tuned circuit.

COIL TABLE

160 Meters

Ll = 140 turns of #32 enameled wire

L2 = 13 turns of #32 enameled wire

80 and 40 Meters

Ll = 44 turns of #26 enameled wire

L2 = 6 turns of #26 enameled wire

20 and 15 Meters

Ll = 171/2 turns of #22 enameled wire

L2 = 3 turns of #22 enameled wire

10 and 6 Meters

Ll = 41/2 turns of #18 enameled wire

L2 = 1 turn of #22 enameled wire

Use Am phenol 24 -5H forms

127

The r.f. energy in the tuned circuit is

coupled to the base of Ql by L2, and is

detected in the base -emitter circuit, as

shown in Fig. 1. The greater the signal

strength, the higher the meter reading.

Detection and current flow take place

even when S1 is off. By switching S1

on, the battery is placed into the circuit

and permits Q1 to function as a transis-

tor amplifier instead of just as a diode.

Sensitivity goes up because of the tran-

sistor's gain characteristic. It takes only

1/10 as much signal to obtain full -scale

deflection when the battery is in the

circuit.

Construction. A 21/4" x 21/4" x 4" alumi-

num box (Fig. 2) houses all the compo-

nents except the plug -in coils and a whip

antenna. Parts can be located as shown,

or in any other convenient arrangement.

However, it is necessary to observe po-

larity of the meter and battery. A 1 /a "-

diameter plastic clamp and a right angle

Fig. 1. Base -emitter circuit of Q1 functions as a

simple diode detector when battery is not con-

nected; with battery, sensitivity increases tenfold.

PARTS LIST

B1 -1.5 -volt penlight battery

CI- 50 -pi. variable capacitor (Hammarluud

HF -50 or equivalent)

C2- 0.005 -µf. disc ceramic capacitor

71 -5 -pin miniature socket (Amphenol 78 -S5S or

equivalent)

72 -Phono tip lack

LI, L2- Plug -an coils (see Coil Table)

M1 -0 -1 ma. mete.,

Q1- 2N2924 transistor, or equivalent

Sl-S.p.s.t. slide switch

1 -2' /y" x 2 4" x 4" aluminum box (Bud

CU -21034 or equivalent)

Misc.-5-prong polystyrene plug -in coil forms

(4), knob, solder, etc.

128

Fig. 2. When mounting components, consider clear-

ance space required for the variable capacitor. Tape

battery ends to prevent contact with metal case.

bracket serve as a battery holder. The

battery ends should be taped to prevent

electrical contact with the sides of the

box. Since the transistor leads are soldered

into place, be sure to heat -sink the leads

when soldering. Wind the four coils on

% "- diameter polystyrene plug -in coil

forms using the data in the coil table.

Avoid overheating the coil pins, as the

plastic melts easily.

Calibration and Use. Calibrate the ab-

sorption meter with a signal generator

or grid dip oscillator. Plug in the appro-

priate coil, loosely couple the absorption

meter to the signal source and rotate

the variable capacitor to obtain a maxi-

mum meter reading. Then mark the dial

scale. By selecting frequencies at the top

and bottom ends of the band, you will be

able to determine quickly if your trans-

mitter is within legal limits. The pur-

pose of the absorption meter, in this

case, is to spot the band rather than an

exact frequency within the band.

You can make a dial by cementing a

small piece of white paper to the box as

shown, and marking it with an ink pen.

Low meter readings can be raised by

switching in the battery, or by increasing

the coupling, or both. Signal pickup can

be through the plug -in coil, or from the

whip antenna when it is plugged in. -IN--

ELECTRONIC EXPERIMENTER'S HANDBOOK

METHODS

THE BEST OF TIPS & TECHNIQUES

GADGETS

REWIRE RECTIFIER SOCKETS

FOR QUICK TUBE SUBSTITUTION

The rectifier tube sockets in your power sup-

ply can be modified to accommodate different

tubes by wiring them as shown in the dia-

gram. Be care -

PLZTE PLATE f u l not to

f exceed tran

II former and

e, tube ratings

r when substi-

Fzj.. tuting tubes.

,111 Fi The tubes that

can be used include: the 5AR4, 5AS4, 5AT4,

5AU4, 5AW4, 5AR4, 5AZ4, 5CG4, 5R4, 5T4,

5174, 5V3, 5V4, 5W4, 5X4, 5Y3, 5Y4, 5Z4, 5931,

6087, and 6106. -Jinn Vasbinder

TOOLBOX GIMMICK

HAS 1001 USES

This handy gimmick for your toolbox can re-

place a fuse holder, hold a cartridge rectifier,

connect an antenna lead -in to a TV set, and

serve as a heat sink or

as a third hand for sol-

dering. It can even be

used to hold construc-

tion notes or a sche-

matic near a project

being worked on. The

gimmick is made with

two clips and a small

(3 -4) terminal strip. To

secure the clips to the

strip, remove the fasten-

ing screws from the

clips and pass them

through two terminals. Hold the clips in place

while you tighten the screws. You can attach

a couple of leads to the screws and install a

similar gimmick or separate clips on the other

end of the wire to serve as a jumper or

"quickee" patch cord. -Albert Koehler

ADJUSTABLE RESISTOR KEEPS

MODEL RACER ON TRACK

Racing model cars has become a popular in-

door sport for grown -ups as well as for the

kids, but Pop usually winds up repeatedly

replacing cars that Junior lets fly end over

end as he cranks the rheostat control to full

throttle. Such "accidents" can be prevented

by inserting a 20 -ohm, 10 -watt, variable -tap

1966 Fall Edition

resistor in series with the rheostat, thus limit-

ing the speed of the car. The resistor is

adjusted to keep the racer on the track at

full throttle. A switch connected in parallel

with the resistor will eliminate it from the

circuit if Pop and his friends want to get

down to some serious racing. -Ken Greenberg

GELATIN MOLDS AND RUBBER BALLS

SHOCK -MOUNT HI -FI EQUIPMENT

Make use of several homemade air suspen-

sion mounts to isolate your record player or

other hi -fi equipment from annoying vibra-

tions - particularly

those which travel

along the floor and

hi -fl furniture. Each

mount consists of a

small gelatin mold,

a woodscrew, a

washer, and an air -

filled rubber ball

just large enough to

fit into the wide end

of the mold. Drill a

hole in the bottom

of the mold just

large enough to ac-

commodate the

screw. Place washer

between the screw

head and mold, and

screw the mold into

place on a side of the base. Then cement the

rubber ball in place inside the mold. If the

sides of the base are too thin to hold the

screws, you can build up the cabinet with a

block of wood. -Harry Goldman

iw DDDSCREW

AIR FILLED

RUBBER CALL

HAND VISE "FOOTS"

CHASSIS ON THE BENCH

A small hand vise can

be used to support a

radio, amplifier or TV

chassis in almost any

convenient position, to

facilitate assembling

or servicing. If more

"feet" are needed, two

or more vises can be

employed. Three or

four vises will support

a record changer and

enable you to observe the

and below the deck. action both above

-H. Lee per

129

110101...8 doieu tools gor

Oozefls of lobs

in a fly

vocket set!

Really compact, this new nut

driver /screwdriver set features 12

interchangeable blades and an

amber plastic (UL) handle. All are No.99PS -50

contained in a slim, trim, see thru

plastic case which easily fits hip pocket. Broad, flat

base permits case to be used as a bench stand.

Ideal for assembly and service work.

7 NUTDRIVERS:

3/16 -, 7/32 ". 1/4 9/32 ". 5/16 ".

11/32", 3 /8" he. openings

2 SLOTTED SCREWDRIVERS:

3/16' and 9/ 12" tips

2 PHILLIPS SCREWDRIVERS:

1 and a2 sites

EXTENSION BLADE:

Adds 4" reach to driving blades

HANDLE:

I r;`,F Shockproof. breakproof. Eaclu

sive. positive locking device

holds blades firmly for turning.

- - permits easy removal

WRITE FOR CATALOG 167

I

JICEELITE®.

XCELITE INC. 54 BANK ST., ORCHARD PARK, N. Y.

Send Catalog 162 with information on 99PS -50

name

address

city state & zone

130 CIRCLE NO 30 ON READER SERVICE CARD 1

RELAY GATHERING DUST?

BOTTLE IT UP FOR PROTECTION

Relays that must be used in dusty locations

are subject to failures resulting from dirty

contacts. To prevent such failures, enclose

your relay in an airtight housing. Suitable

housings can be

made from a

variety of con-

tainers such as

screw cap jars,

coffee cans

with plastic

snap -on covers,

or for the real-

ly small relay,

small vials. The

lid, or cap, of

the container

with relay at-

tached is

mounted on the

chassis, and the wiring for the relay is run

through a hole in the cap which is then

sealed. Finally, the container is screwed or

snapped onto the cap to effectively seal the

relay against dust. -Win. B. Rasmussen

TWISTED PAIRS COME EASY

USING A HOMEMADE DIE

Here's a way to make professional -looking

twisted pairs which are often used in wiring

filament and a.c. circuits to minimize radi-

ation or pickup of stray signals, hum, noise,

etc. Obtain a short brass rod about Vi" in di-

ameter and drill three holes in it as shown in

the diagram. Hole size depends on the gauge

of the wire you intend to twist; side holes

should be drilled at angles of less than 45° for

best results. To use, simply insert the two

wires in the side holes and pull them from the

center hole. Connect one end of the wires to

be twisted in a. vise and place the die in a

hand drill. Then simply rotate the drill and

work the die along wires until the lengths of

wire are properly twisted. -Rontun A. Scheidel

ISOLATED LINE VOLTAGE

FROM FILAMENT TRANSFORMERS

Experimenters are well aware of the dangers

of a hot chassis, such as the a.c. /d.c. radios

and the transformerless TV sets. Besides

shock hazard, test equipment can be dam-

aged when you're working on a hot chassis

that isn't isolated. Two 6.3 -volt transformers

ELECTRONIC EXPERIMENTER'S HANDBOOK

can be connected back -to -hack to do the work

of a 1 to 1 isolation -type transformer, as

shown in the diagram. A certain amount of

noise filtering is also realized from this type

117

Yac

of hookup. But don't drive any equipment

which requires more wattage than the lowest

watt -rated winding. The transformer case

and one side of the low- voltage windings can

be grounded; however, the hookup will work

satisfactorily without the ground connection.

-Robert B. Kuehn

FILM SPOOL MAKES

SAFE METER ADJUSTMENT TOOL

When it is neces-

sary to straighten

indicating meter

pointers or to make

slight adjustments

of meter springs, a

delicate tool and a

delicate touch are

required to avoid

damage to moving

parts. An empty

camera film spool,

with one flange re-

moved and the tips

which held the

flange filed down,

will do the job; the slot in the spool shaft

fits over the meter pointer. A second spool

can be used to hold the pointer near the coil

or at any other suitable location. -H. Leeper

SINK -DRAIN STRAINER

PROTECTS SMALL SPEAKER

Small perfor-

ated sink drain

strainers - the

type found at

corner hard-

ware shops -

make excellent

protective

grilles for

small speakers.

Chrome - plated

and convex in

shape, they

come in many

sizes and sell

for about 25

cents each. To

install one, glue it

of epoxy cement.

1966 Fall Edition 131

in place with a few drops

-Henry R. Rosenblatt

There's GOOD NEWS Today!

PRICES REDUCED

on the famous

MARK TEN SCR

IGNITION SYSTEM

Factory

Assembled

ONLY

OR IN

EASY -TO- ASSEMBLE

DELTAKIT ONLY

$4495

$2995

ppd.

Here's why DELTA offers you

these unparalleled savings!

You read it in the June 1965 issue of this magazine!

"First SCR Ignition System in mass production."

Now Delta - the ORIGINAL manufacturer and the

largest - offers this price reduction due to high

production levels. Thousands have purchased and

installed our remarkable automotive system. We at

Delta can now pass along our lowered manufacturing

costs to you - with extra savings in addition to the

Excise Tax reduction effective January 1st! Save on

gas. Increase the life of your points and plugs.

Dramatically improve your car's acceleration and

general performance. Buy the ORIGINAL, and for

less! ORDER TODAY!

DELTA DELTA PRODUCTS, INC.

P.O. Boa 1141EEHGrand Junction, Colo. 81501

Enclosed is $ Ship prepaid. Ship C.C.D.

Please send: Mark Tens (Assembled) a $44.95

Mark Tens (Delta Kit) to $29.95

SPECIFY -0 Positive Negative 6 or 12 Volt

Ground Ground

Car Year Make

Name

Address

City, State Zip

DP 6 -E CIRCLE NO. 5 ON READER SERVICE CARD

smAlrg , a- an

mt '.`. C:r. ..` tn

mr_2) tet,; enw afpturing series

._.j.

/ A

i

...the day Wrappington Tapely yelled "Eureka," ran into

is work shop, slid a cone -shaped Mueller flexible clip insu-

ator over each end of two wires, before splicing, then slid

he insulators back together just before wrapping with tape.

The high dielectric insulators not only improved insulation

t the splice, but made it very easy to remove and replace

he covering for inspection of the joint. What new things

ave you found to do, with Mueller Clips and Insulators?

At Jobbers everywhere.

rite factory for FREE clip samples and complete, FREE clip catalog.

1600A East 31st Street Cleveland 14, Ohio

CIRCLE NO. 17 ON READER SERVICE CARD

LEARN ELECTRONICS

AT HOME

IN YOUR SPARE TIME

It is fun to learn when you can set

your own pace. Whether you want a

beginner's course that teaches the basic

fundamentals of solid state and tube

electronics, or an advanced course that

will equip you to move up the ladder

in your chosen field of electronics, you

can select just the courses you want to

take ... and take those courses at your

OW11 speed.

EARN MORE, learn about Missiles,

Computers, Transistors, Automation,

Printed Circuits.

Over 30,000 graduates now employed

by industry. Resident school also avail-

able at our Chicago Campus. -Founded

in 1934.

Send for our FREE course catalog.

VETERANS: Write for full information on training.

AMERICAN INSTITUTE OF

ENGINEERING & TECHNOLOGY

1137 -1139 W. Fullerton Parkway- Chicago, Illinois 60614

132 CIRCLE NO. 2 ON READER SERVICE CARD

HYBRID ADAPTER PATCHES

PHONO PLUG TO COAX CONNECTOR

Phono plug connections can be made di-

rectly to equipment having coaxial termi-

nals of the SO -139 type, thus avoiding hum

and stray r.f. pickup from exposed leads.

The necessary adapter is constructed from

a Cinch -Jones 81A or Switchcraft 3501F

phono jack,

and an Am-

phenol PL -259

coaxial plug.

Straighten the

lugs of the

phono jack and

remove the fi-

ber base. Grind

the base down

to a diameter of 1;2" and remount it -but

leave the lugs extended. Then solder a 2"

wire to the jack's center lug and cover with

protective tubing. Insert the wire into the

plug's center connection and solder. Final-

ly, bend the outer shell and solder. Be sure

not to short out the inner connections to

the shell. -F. W. Chesson

HEAT -SHRINKABLE PLASTIC

COVERS COMPONENTS COMPLETELY

We often run the risk of short circuits for

the sake of miniaturization. For instance,

when mounting a capacitor or resistor on a

printed circuit board, it's a common practice

to bend the

lead parallel to

the component

and mount the

component

standing erect.

A real space -

saver -but

that long lead

is a potential

troublemaker!

One neat way

- - - - - of preventing a

short is to cov-

er the component and the lead with a plas-

tic "Fit- Cap," such as manufactured by the

Alpha Wire Co., and apply a bit of heat.

The shrinkable plastic reduces in size, grips

and insulates the component.

-- -Byron G. Wels, K2AVB

SINGLE -TRANSISTOR

AUDIO MONITOR

Designed for low -level monitoring of tuners

and tape decks whose output signal requires

an external amplifier to be heard, this

ELECTRONIC EXPERIMENTER'S HANDBOOK

A COMPLETE SELECTION OF ANNUALS, YEAR-

BOOKS, DIRECTORIES AND HANDBOOKS from the

world's largest publisher of special interest

magazines. They're all editions that have

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moment to review the titles still available.

You're sure to find many of your favorites.

PHOTOGRAPHY ANNUAL

A selection of the World's finest

photographs compiled by the editors

of Popular Photography.

212 pages -24 in full color.

1966 -$1.25.. _ #1

1964 - $1.25...... #3

vP1MTOGIRPNY

R8IRERM0.=

PHOTOGRAPHY DIRECTORY

World's most complete

photographic buying guide.

1966 - $1.25.._.___ #22

1965 - $1.00... _._ #23

STEREQá'HFfl

71RECTORY

STEREO /Hi F DIRECTORY

Complete buyers guide for virtu.

ally every Hi Fi component man.

ufactured.

1966 -$1.25___. #29

1965 - $1.00...._..._ #37

::.ELECTRONIC

EXPERIMENTER'S

ELECTRONIC EXPERIMENTER'S

HANDBOOK

Many challenging projects for the

electronics hobbyist.

1966 - Spring Edition-41.25 #36

1965 - Fall Edition -$1.25 ._. #9

1965 - Spring Edition -$1.25 #14

1964 - $1.00 _ #13

TAPE RECORDER ANNUAL

Everything you need to know about

tape recording including a complete

directory of mono and stereo recorders.

1966 - 1965 - $1.00.._ #31

POLAROID LTNL

PHOTOGRAPHY

Complete guide and only

comprehensive and up-lo -date

handbook an Polaroid Land Pho-

tography.

1966 - $1.25--- __. #24

1963 - $1.00.._. _. #25

CAR b DRIVER YEARBOOK

A complete buyers guide covering sir.

tually every car available in the United

States ... Road tests ... Technical

specifications . Accessories and

performance equipment buying guide

Guide to racing with action -

pecked photos.

1966 - $1.25_.._..... #15

IaRTAS-k.AT/W4

...= aPRVIWNa

MANOBOOK-1966

ELECTRONICS INSTALLATION

AND SERVICING HANDBOOK

The only complete guide for servicemen

and hobbyists to every major phase of

consumer electronics servicing.

1966 - 91.25....... #32

SKIING INTERNATIONAL

YEARBOOK

A luxuriously illustrated com-

pendium of 1965's important

events ... A timely forecast of

the excitementpacked 1966 sea

son-by the editors of Skiing

Magazine.

TO PLACE YOUR ORDER, circle the num-

bers of the annuals you wish to receive on

the coupon, clearly print your name and

address and enclose your remittance. Please

be sure to enclose an additional 150 ship-

ping and handling for each copy ordered.

Add 500 per copy for orders outside U.S.A.

1966 Fall Edition

1966 - $1.25....... #26

Ziff-Davis Publishing Co. -Dept. SD

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

I am enclosing $ for the annuals circled below. My remittance includes

an additional 15g per copy for shipping and trundling (50g for orders outside '

U.S.A.). I understand quantities are limited and orders will be filled on a first

come -first served basis.

i'wvirinöw ro -_

n trmoees etrv -

.4411111

INVITATION TO PHOTOGRAPHY

A unique 116 page guide to better pic-

ture taking by the Editors of Popular

Photography. Basic down -to -earth ad.

vice that helps you eliminate costly

trial and error, time -consuming guess

work. 20 complete, het -end -photo

packed articles in all.

1966 - $1.25._._- ... #35

FLYINO...

FLYING ANNUAL

The most valuable aviation yearbook

ever compiled . . Pilot reports .

Aircraft directory . .. How to buy

used airplane . Navcom. directory

.. Learn to fly section.

1966 - $1.25...__..., #27

1965 -51.25........ #28

FLYING TRAVELGUIDE COMMUNICATIONS

Here's the first really useful HANDBOOK

guide to flying vacations. Every- The most complete and up-to.

thing you need to know about: date guide to the exciting world

lodgings. restaurants, resorts, of specialised radio communia- -

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activities, airport facilities 1966 -$1.25..... #18

e ens fun, price information,

special information for the gals 1965 - $1.00.... #19

-and much more. 1964 - $1.00 #20

1966 -$1.25__. #34 1963 - $1.00.._. #21

1 3 9 13 14 15 17 18 19 20 21 22 23

24 25 26 27 28 29 30 31 32 34 35 36 37

1 Name.

Address

City State

Payment must be enclosed with order.

1

LEH -66 ,

Zip Code I

133

PRI

on a subscription to

POPULAR ELECTRO

12 exciting $ 50

months only

At the regular subscription rate these same 12

issues would cost all of $5.00! BUT NOT FOR

YOU. Your cost is only $2.50- HALF -PRICE!

Every month POPULAR ELECTRONICS brings you a

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You'll enjoy being right on top of the fast -growing

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ered and transistorized equipment -and much more.

Construction projects galore! Clear -as- crystal dia-

grams guide you each step of the way through fun -

to -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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Amateur Radio and SWL

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Transmitters and Transceivers

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Antennas

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Build -It- Yourself

Antenna, 40- Meter, for Small Roof

Antenna Aadapter, Power Line

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Double -Duty EICO 772

Hula- Hoop -a Ham or CB Antenna

Idento- Minder

O- Multiplier, Nuvistor

Screen Modulator, One -Tube

Transmitter Crystal Switch, Plug -in

2 -Meter Simple Superhet

simple "audio monitor" doesn't provide

much gain, but will match an 8 -ohm speaker

to the program source. A power transistor

is used in an emitter follower circuit as

DELCO

DS -501

(OR EOUIV.)

OUTPUT I -I /2

TOR 3V

FM TUNER

GND

shown. The amplifier runs on a 1.5- to

3 -volt battery and no heat sink is neces-

sary. - Crud Du)tn,lil

TRANSISTOR BATTERY HOLDER

MADE FROM TWIN PENLIGHT CLIPS

You can easily construct a holder to accom-

modate the popular 9 -volt transistor battery

by modifying a

twin AA hold-

er. With just

a pair of pliers,

bend and break

off the inside

prongs of the

holder's U-

clips to make

room for the

larger battery.

Then bend the

outside prongs

inward so they

can get a good

grip on the battery. When inserting the

battery in the holder, be careful not to

short the terminals against the frame of

the holder. -Art Trouffer

"MAGIC" TAPE MARKS

CABLES LIKE MAGIC

A professional -looking lead or cable marker

can be made with Scotch "Magic" tape. You

just print the desired information on the

tape using al-

most any me-

dium and wrap

it around the

cable. For du-

rability, the

tape should be

long enough

to cover the

printing a cou-

ple of times when wrapped around the

cable. Better contrast can be obtained by

sticking a small strip of paper on the tape

behind the printing. -Don E. Watson

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CIRCLE NO. 25 ON READER SERVICE CARD

1966 Fall Edition 135

Because you've got to SEE it to BELIEVE

it... we will send you a FREE sample!

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CIRCLE NO. 4 ON READER SERVICE CARD

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ELECTRONIC COMPONENTS

N. Y.. N. Y. 10012 212

CIRCLE NO. 29 ON READER SERVICE CARD

BEEF UP THOSE FLOPPY

RABBIT -EAR ANTENNAS

If the small swivel balls inside of the tele-

scoping -type antenna mounted on the rear of

your TV set should break through the plastic

case, you can put

them back in place

with two small met-

al strips. Drill a 1/2"

hole in each strip to

allow the antenna

sections to pass

through, shape the

strips with tin snips

to fit inside the

case, and insert

them between the

swivel balls and the

top of the case as

shown. Make the

center screw just snug enough to provide suf-

ficient friction to hold the antenna elements

at any desired angle when they are fully ex-

tended. -Homer L. Davidson

111111111011.111111

USE FERRITE CORE RODS

TO BOLSTER INDUCTANCE

Say you've just wound a coil, soldered it into

a circuit, and find you need more inductance.

What do you do? Just insert a short length of

ferrite core into the coil form. Then adjust it

for the correct inductance and cement it in

place. The same technique can be used if you

need a few extra turns of wire on a ferrite

COIL TAPE OR

CEMENT

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

iiii1iui u,uiuuuuau1iunuuiu1, ' /In

u

i, SHORT LENGTH OF

FERRITE CORE

core. Simply tape or cement a short length

of ferrite core to the coil end as shown; this

will have the same effect as adding more

turns to the coil. -Art Trauffer

ADD PUSH -BUTTON ZEROING

TO YOUR OHMMETER

You can add an instant zeroing feature to

your ohmmeter by inserting a push- button

s.p.s.t. switch in the ohms or positive input

line to the

range selector

of the meter.

Break the ex-

isting line go-

ing to the input

jack and con-

nect the nor-

mally closed

contacts across the break, with the fixed pole

toward the jack and the movable throw

toward the meter. Wire the normally open

ELECTRONIC EXPERIMENTER'S HANDBOOK

contact to the common input line. Depress-

ing the button will now short both input ter-

minals of the meter and enable you to set the

ohms -adjust control to obtain a zero reading

without having to remove the test leads from

the circuit under test. -Stanley E. Bammel

U- SHAPED CLAMPS

HOLD COAX TO CIRCUIT BOARD

To connect a coaxial cable to a printed circuit

board securely, form two U- shaped clamps of

heavy -gauge wire. Make one U -clamp wide

enough to fit

snugly over the

insulation;

make the other

one slightly

narrower to

hold and con-

nect the braid.

Position the

coaxial cable

and drill five

holes in the

board as

shown. Then

insert the cable

and clamps,

and solder the

clamp in contact with the braid to the braid

and to the circuit board. -Don Lancaster

PULSE POWER PACK

(Continued front page 50)

different color wire for each lead to

avoid confusion. It's also a good idea to

lace the wires as shown, to facilitate

mounting and removal of the circuit

board.

As a final word, observe that the two

1" standoffs are secured with the bottom

screws of the power transistors. If you

happen to use metal standoffs, do not

let them come in contact with any of

the components on the circuit board. If

you can get non -metallic standoffs, you

should do so.

Operation. After you have completed

the wiring, check out the unit thorough-

ly before plugging it in, and thus save

yourself from a possible headache later

on. Connect the output jacks (J3 and

J.ç) to the tracks (at this point polarity

doesn't matter).

Before turning the power switch on,

set the CRAWL switch (S2) to the off

II

changing

channels?

expanding your

commercial

operation?

STOCKED IN DEPTH BY LOCAL & MAIL ORDER DISTRIBUTORS

1966 Fall Edition

CTS Knights, Inc. has

the right crystal for

all CB applications.

CTS Golden Line CB

crystals are manu-

factured to the same

exacting specifica-

tions as military units

an accuracy of

±.003% of fre-

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and are unaffected

by wide temperature

extremes. All crystals

are made from virgin

quartz ... only "first

cuts" are used.

CTS KNIGHTS, INC.

(Formerly the James Knights Company)

SANDWICH, I L L I N O I S

a subsidiary of CTS Corporation, Elkhart, Indiana

CIRCLE NO. 3 ON READER SERVICE CARD

I 37

50 SIMPLE

ELECTRONIC PROJECTS

YOU CAN BUILD NOW!

NO EXPERIENCE NECESSARY

1 Pick up a copy of Semitronics 96 -page book

called "Electronic Projects" at your electronics

or hobby dealer for only $2.00. It contains step -

by -step instructions to build 50 simple electronic proj-

ects right in your own home ... even if you never worked

with electronics before. All are described in simple lan-

guage, clear diagrams and are easy -to- build.

2 If you want a complete, all -in -one- package kit,

here are ten you can start with. Available kits

are: Crystal diode receiver transistor radio

code instructor electronic metronome electronic organ

home broadcast station clearance light flasher big

voice megaphone battery eliminator and an automa-

tic light control.

011 Parts for all electronic projects in this magazine

and all Semitron projects are available from your

Semitron Electronic Center now on display at

your local electronics distribution or hobby center. This

Semitron Electronics Center has over 100 different elec-

tronic components: semiconductors, resistors, capaci-

tors, relays, speakers, meters, hardware, tools, e c

IDEAL FOR BEGINNERS OF ALL AGES

With the new Semitronics handbook ...

"Electronic Projects," any student, be-

ginner or hobbyist can have the fun and

excitement of building electronic proj-

ects that work -even if you never worked

with electronics before. Semitronics

makes it simple with this illustrated

handbook and easy -to -find parts, all

available at low cost from your dealer's

Semitron Electronics Center.

LOOK for the Semitron Electronics Center

at Your Local Dealer or send $2 for your

Projects Book (includes postage and

handling) to: ELECTRONIC

PROJECTS

Semitróñics Corp.

265 Canal St., New York, N.Y. 10013

Send copies of Project book

at $2.00 each, postpaid.

Send information on electronic hobby

kits & name of dealer nearest me.

Name

Addresq

Zip

City /State Code

position, and flip the DIRECTION switch

(S4) to FWD. AIso, turn the THROT-

TLE control fully counterclockwise but

without turning off the switch that's

ganged to it ( you will hear a distinct

"click" if the switch is turned off).

Now, flip the PWR switch to on. If

the trains move at all, R13 is too high

in value and must be reduced. Suc-

cessively try a smaller resistor (reduce

the resistance by about 10% in each

step) in place of R13 until you find one

that will just cause the train to stand

still. When you do, leave that resistor

in. Slowly rotate the THROTTLE clock-

wise ; the train should start up and run

forward. If it runs backwards, simply

reverse the leads to the tracks.

Turn the throttle counterclockwise, but

without flipping S3 off. Then turn the

CRAWL ADJ knob fully counterclock-

wise and flip CRAWL switch S2 to on.

Your train might growl .a little but it

should not move. Now slowly rotate the

CRAWL ADJ knob clockwise until the

train begins to crawl real nice and slow.

As you give it some throttle, your train

will increase in speed realistically -as if

it were coming out of Grand Central

Station.

Slow down the throttle as you come in

to a station and let the train crawl a bit.

When you are ready to stop, just rotate

the throttle fully counterclockwise until

S3 clicks off for a full stop. With a bit

of practice you'll soon be driving your

train like the old pros and enjoying

many hours of real pleasure. Man, that's

railroading! -

LUMEMIN STEALS THE SHOW

( Continued from page 17)

highest pitched note when it is fully il-

luminated. Similarly, maximum volume

is obtained when the volume photocell

(PC2) is completely in the dark, and

minimum volume when it is exposed to

the brightest light.

If you happen to be a skilled musi-

cian, you should be able to play a recog-

nizable tune with as little as a half- hour's

practice. Generally speaking, however,

considerable practice, skill, and patience

are required to play the Lumemin, as

CIRCLE NO. 26 ON READER SERVICE CARD

138 ELECTRONIC EXPERIMENTER'S HANDBOOK

with other musical instruments. Trem-

olo, vibrato, sliding tone, and similar

special effects can be obtained.

Possible Circuit Variations. After using

the Lumemin for a while, you may find

it desirable to change certain component

values to meet your individual playing

techniques. As you can see from Fig. 2,

the lowest pitched note that can be pro-

duced depends on the value of R1, while

the highest pitched note for a given

light intensity depends on the value of

R2. Therefore, the ratio of these two re-

sistors establishes the basic tonal range

of the instrument. With the presently

assigned values, the instrument's range

is about three octaves, the lowest fre-

quency being about 800 cycles (this

will vary with component tolerances).

If you want to drop the lower fre-

quency limit, use a larger value resistor

for R2. The exact value will have to be

determined experimentally. One way to

do this is to put a potentiometer in place

of the resistor, and adjust it for different

effects. Later you can either leave the

potentiometer in the circuit at the de-

sired setting, or you can measure the

resistance at the desired setting, and

substitute an appropriate resistor.

In some cases, it may be necessary to

change the value of R3. Here a larger

value resistor will reduce the output

volume, while a smaller value will in-

crease the loudness for a given light

level on PC2. Values as high as one meg-

ohm and as low as 250,000 ohms can be

tried. There seems to be no end to the num-

ber of circuit changes you can make.

For example, you can arrange a bank of

different value resistors for both R1

and R2, and, by means of an appropriate

switching circuit, select the best com-

bination for the piece to be played. One

other possibility is to combine the Lume-

min's circuit with a modular audio am-

plifier and loudspea a single cabinet

as a self- contained 'rument. Finally,

for more precise performance, you can

incorporate a built -in light source by

mounting a suitable lamp over the photo-

cells. Regardless of the final modifications

you may wish to make, or even if you

use the design as is, the Lumemin can

provide you with many exciting hours of

music and sheer pleasure. 3-

LI'L DUSKER

(Continued from page 54)

and no other room light- shines on it.

Add a microswitch across the photocell,

and connect the relay so that increasing

light energizes the load (Fig. 7). The

microswitch wilt short out the photocell

when pressed.

Here's how the touch control works :

While the light is out, the photocell

"sees" no light and the relay is not ac-

tivated. A gentle touch of the switch

energizes the relay and the light goes on.

The photocell "sees" the light and holds

the relay energized. The light stays on.

Now, how do you turn the light back off ?

Just pass your hand between the bulb

and the photocell to create a shadow.

Presto! The lamp goes out and stays

out.

FREE POO' PAN Inrlotes,

WORTH Transistors

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10 ELECTROLYTICS ('¡

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06 TRANSISTOR RADIO SETS'

s

c.ifsdrlver. p.p .-. .

Cl 10 LITTLE 'LYTICS e1

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25 GERMANIUM DIODES 2

IN34.INd. 1Ní,0 no test +1

50 QNE-WATTERS Si

resistors, asst. values, ó torn

40 WORLD'S SMALLEST S' resistors, i.',W. to 3 esce

5 2N107 TRANS'TRS si

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40 DISC CONDENSERS S1 f

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25 TOP HAT RECTIFIERS, S1

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75 HALF WAITERS el resistors, asst, a^á too...

10 CK722 TRANS'TRS s1

Raytheon. pnp, 110 test,,.

Cl 15 NPN TRANSISTORS 1

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0 TRANSFORMERS

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100 PRINTED CIRCUIT;'

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vnp, stut. .31) to 40ÚV .

C10 TRANSISTOR SOCKETS

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15 PNP TRANSISTORS S1

CK722, 2N101. sent cases.

per vale 1 lb. CATALOG 10e

P.O. BOX 942 E

SO. LYNNFIELD, MASS,

1966 Fall Edition CIRCLE NO. 21 ON READER SERVICE CARD 139

Thinking of college and

a space age career?

Send for this booklet on

ENGINEERING TECHNOLOGY

AND ENGINEERING

Learn how you can prepare for a dynamic

career as an electrical or mechanical engi-

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For your copy, just mail

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MSO

Milwaukee, Wisconsin 53201

Milwaukee School of Engineering

Dept. EX -966, 1025 N. Milwaukee Street

Milwaukee, Wisconsin 53201

Please send the "Your Career" booklet.

I'm interested in

Electrical fields O Mechanical fields

Name Age

Address

City State ZIP

MS -ass

CIRCLE NO. 16 ON READER SERVICE CARD

6 -WATT AMPLIFIER

(Continued from page 111)

signal source and amplifier input as

shown in Fig. 1.

If plans call for the amplifier to be

employed with a low- impedance input

device, say about 1000 ohms, reduce the

value of Ri-or even eliminate it. This

will give you a substantial increase in

gain. There's no point in reducing the

value of R4 for a high- impedance input,

as no appreciable gain will be realized.

A 150 -ohm resistor placed in series with

C2 introduces negative feedback, and

lowers the output impedance still more,

and reduces distortion, but sacrifices

gain. The higher the resistance, the

greater the feedback and the lower the

gain.

BIAS NETWORK

_A closer look at the biasing arrangement of the

various transistors in the Six- \Fatter is needed

for a better understanding of how the circuit oper-

ates and how balanced operation can be achieved

even if the d.c. current gain of the transistors

differs.

Resistors R1 and R2 maintain the bias voltage

at the base of QI at approximately one -half the

supply voltage. If the voltage at point A in Fig. 1

drops. the potential difference across Ql.s base -

emitter junction increases and causes Q1 to con-

duct more heavily. The greater current flow

through R3 increases the voltage drop across R3,

and incnases the forward bias of Q2. This makes

Q2 conduct more heavily and increases the for-

ward bias on Q3 and Q5, at the saine time de-

creasing the forward bias on Q4 and Q6.

Transistors Q5 and 06 act like a voltage di-

vider across the power supply, and the biasing

action just described reduces the dynamic resist-

ance of Q5, and increases the dynamic resistance

of Q6. This raises the voltage at point and

tends to restore it to its former value.

If, on the other hand, the voltage at point a

rises above normal, the forward bias on Q2 de-

creases, reducing the bias on Q3 and (15, increas-

ing the bias on Q4 and (76, increasing the dy-

nantie resistance of Q5, decreasing the dynamic

resistance of Q-!, and, finally, decreasing the

voltage at point .1 to its normal value.

Diode DI also affects the bias of Q3 and Q4.

'rhe voltage drop across Dl places a small for-

ward bias on 03 and (14. which in turn places

a small forward bias on QS and Q6. This for-

ward bias reduces crossover distortion and serves

to thermally stabilize the amplifier. Changes in

voltage drop across the diode due to changes in

temperature tend to compensate for similar tem-

perature changes in the base- to-emitter voltages

of the transistors. The voltage drop across Dl is

essentially independent of supply voltage and

therefore is able to maintain the same bias over

a relatively wide range of supply voltage.

ELECTRONIC EXPERIMENTER'S HANDBOOK

The amplifier's high- frequency re-

sponse can be substantially improved by

substituting 2N2148 transistors for the

2N554's in the output stage. They cost

about $1 more each ; the 2N554's were

used because of their low cost. Should

you decide to substitute "bargain" tran-

sistors for Q5 and Q6, you may run into

higher than normal leakage currents.

To overcome this situation, you can con-

nect a 100 -ohm, Iii -watt resistor between

the base and emitter of Q5 on the bottom

side of the board.

If you plan to use the Six -Watter as

a narrow -band speech amplifier, reduce

the value of C2 and place a small capaci-

tor in parallel with R5 to cut the ampli-

fier's response at both the high and low

ends. The amplifier can also be used as a

modulator for small transmitters. An

ordinary output transformer connected

backwards makes a reasonably good

match as a modulation transformer. Use

an output transformer which can match

the impedance of the final stage of your

transmitter to the amplifier's nominal

3.2 -ohm load. -®-

SUPER -SENS

(Continued from page 38)

diode (1N34A) and an npn transistor

(2N169) can be used. Adjust the Sensi-

tivity control until the relay just closes

in the absence of the radio signal. An

incoming radio signal will open the relay.

Bench tests with the remote control

circuit were made using a standard AM

broadcast -band ferrite -core antenna coil

(Superex "Vari- Loopstick ") for LZ and

a 270 -pf. ceramic capacitor for Cl. With

a relatively short antenna, positive relay

operation was obtained when a strong

local broadcast station was tuned in.

Photocells of all types can be used

with Super -Sens to make it respond to

variations in illumination and color. In-

visible infrared rays can be used as in-

truder alarms. Smoke detectors and in-

dustrial counting devices can also be

made. Regardless of the intended ap-

plication, whether specific or general,

the only limit to Super -Sens is your

imagination and skill. -J-

r HOW TO

IMPROVE YOUR

o TWO-WAY RADIO!

The right communications microphone may

double the talk power of even the finest trans-

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be eliminated -reliability improved -

intelligibility increased by proper

microphone selection.

Write for our helpful

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1966 Fall Edition

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SETTING NEW STANDARDS /N SOUND

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CIRCLE NO. 9 ON READER SERVICE CARD

141

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CIRCLE NO. 12 ON READER SERVICE CARD

FREEZE MOTION WITH SOUND

(Continued from paye 42)

to the center conductor of a phono plug,

and the negative lead to the shell. Con-

nect the plug to J2 on the trip unit.

Operation. Any camera can be used

with the trip unit and flash as long as

time or bulb exposures are possible. If

your camera has only a bulb shutter po-

sition, you'll need a locking -type shutter

release cable. A 35 -mm. camera is ideal

for use in high -speed photography. Fine

cameras are available at reasonable

prices, depth of field is excellent, film

costs are low, and you can project your

results in the form of 35 -mm. color

slides.

Set your experiment up in a room that

can be darkened somewhat. While total

darkness is not required, the lighting

level must be reduced to the point where

room illumination will not register on

the film during the period the shutter

is open. Install the electronic flash on

the camera and mount the camera on a

tripod. Focus the camera on the object

to be photographed and adjust the cam-

era iris for normal flash exposure of the

film used at the object -to -flash distance.

Follow the instructions supplied with

the electronic flash for this setting.

Position the microphone near the ob-

ject to be photographed -the distances

given for the various photos shown in

this article will give you a rough idea

as to how mike placement affects results.

Advance the sensitivity control on the

trip unit until the noise developed by

the event to be photographed triggers

the flash. Now dim the lights, open the

camera shutter, initiate the event, note

that the flash fires, and close the camera

shutter. If you want to record a time -

graduated series, move the mike away

from the object to be photographed in

increments of a few inches and shoot a

series of photographs.

The results that can be achieved with

this simple piece of equipment are al-

most unbelievable. If the initial results

are short of your expectations, keep

experimenting. Make sure that extrane-

ous noises are not tripping the flash pre-

maturely. Good shooting! -i0--

ELECTRONIC EXPERIMENTER'S HANDBOOK

1

y

e

TOTEM POLES FOR STEREO

(Continued from page 98)

The woofer enclosure is somewhat un-

orthodox, but very easy to build, par-

ticularly if you plan to cover it with a

plastic veneer. First cut out all the parts,

and before joining the major compon-

ents, glue and screw the cleats to their

proper places on the sides; this will

eliminate the need to struggle with them

later inside the cabinet. Attach the cross

cleats to the rear of the top and bottom

pieces, and you are ready to glue and

screw together the top, bottom, and sides.

Next, make the speaker cutouts in the

proper locations in the front, then glue

and screw the duct panels to each end

of the front panel. Slip the front panel

into the enclosure and secure it in place.

If you are covering the sides of the en-

closure, you can fasten the duct panels

more securely by driving some finishing

nails through the sides directly into the

edges of the duct panels.

Grille cloth and molding can be selected

to fit in with your decor, and you can

add feet or legs to the basic enclosure

as desired. Both crossover networks are

mounted just above the lower duct as

shown in the photo. After you mount

and wire the speakers, the enclosure

should be padded with "kimsul," felt,

cotton batting, or fiberglass wrapped in

cheesecloth. Don't pad within the duct

area, but other exposed surfaces of the

back, sides, top, or bottom can be covered

as desired, leaving no two opposing sur-

faces uncovered. If you wish, the totem

poles can be attached to decorative pole

lights or other room dividers.

Wiring Considerations. Wire the nine

or ten mid -range units first, so that they

can be handled as a unit. They must

be checked first for proper phasing, and

a single flashlight battery will do for

this job. Connect it in series with the

speaker, reversing the leads if necessary,

until the speaker cone moves forward

when the circuit is completed and to the

rear when broken. Now mark the speaker

terminal to which the positive battery

terminal is connected. This marked ter-

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CIRCLE NO. 27 ON READER SERVICE CARD

1966 Fall Edition 145

BUY SPEAKERS FOR YOUR

"CINDERELLA" SPEAKER

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FROM McGEE FAMOUS 6"

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CIRCLE NO. 14 ON READER SERVICE CARD

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CIRCLE NO. 19 ON READER SERVICE CARD

minal will correspond to the red coding

or " " sign on the other speakers.

Follow the wiring diagrams, and make

a final phasing check between the units

in a channel and between the two chan-

nels. For an excellent method of phasing

a complex system such as this one, see

"Phasing Speaker Systems" by John

Dewar (POPULAR ELECTRONICS, Septem-

ber, 1965) . If you don't have an audio

generator available, any good recording

will do. First, check the phasing in each

channel, reversing the leads of either the

woofer or mid -range unit, then the

tweeter. If you use a dummy load in the

other channel, as suggested by Dewar,

be sure that its switch is turned on to

avoid having an open circuit. For the

final phasing of the two channels, a mono

record is probably more useful than a

stereo record.

Speaker Placement. Now you have to

make a decision on speaker placement

and whether to enclose the backs of the

columns or not. For maximum disper-

sion of sound the back panel should be

eliminated, but placement is somewhat

more important in that case due to

sound reflections from the rear. By

experimenting with various locations for

the columns as well as by aiming them

at various angles, you will appreciate the

enormous range of possibilities, some of

which should solve any acoustic problems

your living room can present.

When the columns are aimed outward,

toward the side walls of the room, max-

imum reverberation is obtained in the

listening area. If the sound is consis-

tently too "big," or too reverberant and

nondirectional, a back should be used.

Also, if it is necessary to place the

columns very close to a wall with the

front parallel to the wall, it is advisable

to cover the back with a 1 -inch layer of

fiberglass or other open acoustic damping

material. (This material is always nec-

essary when a back is added.) The more

experiments you perform, the closer the

final system will match your special

acoustical situation and tastes.

The totem pole system offers superb

stereo from any good stereo source, but

for a final test put on a good stereo

record of a large orchestra or chorus.

It is in reproducing massed instruments

or voices that this system excels. -IN-

146 ELECTRONIC EXPERIMENTER'S HANDBOOK

AUTO VOLTMETER

(Continued from page 73 )

Once the engine is running, the volt-

age should rise to full charge at higher

speeds, gradually coming down to the

lower running limit, which indicates

that the battery has fully recharged

from the starting drain. The final regu-

lated voltage varies with temperature

due to the temperature- sensitive ele-

ments built into the voltage regulator

itself, so it's a good idea to consult the

service manual for your own car to

acquaint yourself with the range of

voltages for the expected range of tem-

peratures normally encountered by the

accessories under the hood. Tempera-

ture could vary from 20° below zero to

150° F when you start off on a subzero

morning and then drive in the early

afternoon sun with a 180° thermostat

in the cooling system. An occasional

idling period at a long traffic light or

busy intersection could send the temper-

ature up quite high, even in cold weather.

Acquaint yourself with the high and

low voltage limits for a good battery

with the engine running, for both sum-

mer and winter, as well as the meaning

of abnormal indications and how to

recognize them. The battery voltage

table shows typical voltage ranges for

both 6- and 12 -volt systems. Note the

relationship between the two sets of fig-

ures: The values for a 12 -volt system

are approximately double those of the

6 -volt system. This is understandable,

when you consider that both are made

up of the same type of individual 2 -volt

cells. Because of normal deterioration in

the plates of the battery, small par-

ticles flake off and fall to the bottom of

the cell. As this process continues, the

resistance of the battery goes up, and

it is often possible to predict failure of

a battery long before it dies. Under the

usual starting conditions, the battery

drain is not too excessive, and the bat-

tery will charge up normally. However,

the time that it takes to regain the

charge will increase as deterioration

gets worse.

When the first cold weather comes,

1966 Fall Edition

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CIRCLE NO. 28 ON READER SERVICE CARD

the demand upon the battery is con-

siderably greater, and due to the large

internal resistance, the voltage at the

battery terminals is small. The battery

must dissipate the power expanded in

its internal resistance in the form of

heat. If this heat is great, the plates

buckle and the cell shorts and breaks

down. It is interesting to note that

most battery troubles show up during

the first cold spell of winter.

A thorough check of a doubtful bat-

tery can be made as follows:

1. Check the liquid level, and measure

the specific gravity of each cell before

adding any water. Regardless of the

state of charge (as indicated by the

specific gravity), they should all read

about the same. (The gravity will vary

with the level of liquid.)

2. Unless the battery is discharged or

near the lower limit voltage, measure

the voltage across each cell while turning

the engine over by means of the start-

ing switch. (Disconnect the high -volt-

age lead from the coil to prevent the en-

gine from starting.) This puts a heavy

load on the battery and simulates actual

starting conditions. If, under these con-

ditions, each cell reads low but there is

less than .1 volt difference between any

two cells, the battery is good. If the

voltage is low, the battery needs charg-

ing. If the cell measurements differ by

more than .1 volt, the battery should

be replaced.

3. Reconnect the high -voltage lead to

the coil and start the engine. Measure

the voltage across the battery with the

engine idling. Now race the engine.

The voltage should rise sharply from

open- circuit voltage to normal charging

voltage (depending on the state of

charge of the battery) and drop back

again as the engine slows down.

If the voltage does not increase

sharply, the fault lies in the charging

system (either the generator or voltage

regulator). If it increases but remains

high when the battery is known to be

fully charged and good, the voltage

regulator contacts are stuck closed.

Prolonged running under these condi-

tions can damage the battery. One

symptom of this trouble is the need for

excessive refilling of the cells with dis-

tilled water.

ELECTRONIC EXPERIMENTER'S HANDBOOK

The lack of charging may indicate

nothing more than worn generator

brushes (or open rectifiers in alternator

circuits), a dirty commutator, or burned

or pitted contacts in the voltage regula-

tor (the voltage regulator consists of a

cutout relay, a current regulator ele-

ment, and a voltage regulator unit, all

with contacts) . The correct method of

cleaning and adjusting these contacts is

outlined in the manufacturer's service

manual. Quite often, a gas- station at-

tendant will replace the whole unit

rather than attempt a minor adjustment

or cleaning of the contacts in a voltage

regulator.

A convenient gadget for turning over

the engine while working under the

hood consists simply of a momentary -

contact push- button switch, a pair of

wire leads long enough to reach across

the car (about 6 feet should be ade-

quate) and a small battery clip on the

end of each lead. The leads are con-

nected across the starter control termi-

nals of the starter solenoid. The push-

button then does the same job as the

ignition switch, but the engine will not

start with the ignition switch in the off

position. With this gadget, the high

voltage lead need not be disconnected

from the ignition coil.

The Payoff. You may be interested to

hear that, as this article was being writ-

ten, the author discovered that his

charging system was not functioning -

with the help of a panel -mounted volt-

meter. The "Charge" panel light would '

come on, but as the engine speed in-

creased with the car rolling along the

highway, the light became very dim and

appeared to have gone out. As a mat-

ter of fact, everything seemed normal-

except the voltmeter reading, which was

slightly under 12 volts.

Naturally, the charging system failed

on a Saturday when the auto service

department was closed (according to

"Murphy's Law ") . However, close and

continuing checks of battery voltage

showed that there was adequate charge

left in the battery to last the weekend

if all driving was done during the day,

and if accessories were not used. By

Monday, the voltmeter had more than

earned its keep! -®

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CIRCLE NO. 31 ON READER SERVICE CARD

1966 Fall Edition 149

Read What the Experts

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CIRCLE NO. 13 ON READER SERVICE CARD

150

MOBILE MONITOR

(Continued from page 126)

The last switch position is for a modu-

lation check (MOD) . The Watchdog cir-

cuit has now become an r.f. voltmeter

with a time constant long enough to

show audio modulation peaks. The cou-

pling between the Watchdog and the

transmitter must be adjusted to give a

meter reading of about 0.5 ma. (unmod-

ulated carrier) . On high level modula-

tion peaks, the meter reading may al-

most double; and on positive modulation,

the peaks should reach the 100x, (1.0-

ma. point) .

The operator can check his own modu-

lation quality by plugging a headset into

the A.F. jack on the front panel of the

Watchdog. Turn S1 to the CS position,

and what you will hear in the headset

will be a perfect reproduction of the sig-

nal being transmitted. At your home

station, the output of this jack can be

used to feed an oscilloscope to look for

residual a.c. hum, parasitics, or distor-

tion.

Emergency Voltmeter. In an emergency,

the Watchdog may be used as a volt-

meter by connecting test leads to the tip

jacks mounted in one end of the box. In

series with the tip jacks are resistors

R3 and R4, providing a 1000 ohms -per-

volt range at two different voltage scales.

With the test leads connected to tip

jacks J3 and J5, the meter scale can be

converted into a range of 0 -20 volts.

With the leads between tip jacks J4 and

J5, the meter scale can be converted to

a range of 0 -500 volts. In addition, tip

jacks J6 and J5 can be used to connect

the 0 -1 ma. meter to any transmitter that

has built -in current multipliers and pro-

visions for tuning up with a low -range

milliamp meter.

VOLTAGE CONVERSION TABLE

Meter Reading 20 -Volt Scale 500 -Volt Scale

(ma.) (volts) (volts)

0.2 4 100

0.4 8 200

0.6 12 300

0.8 16 400

1.0 20 500

ELECTRONIC EXPERIMENTER'S HANDBOOK

ELECTRONICS MARKET PLACE

FOR SALE

IT'S SUPERCALIFRAGILISTICEXPIALIDOCIOUS, Free in-

formation on Kit -of -the -Month Club and new catalog of

etched circuit boards and radio books. Many exclusive

items. Leader Enterprises, Box 44718KL, Los Angeles

90044.

RECTIFIERS & TRANSISTORS -Send for catalog of semi-

conductors and other components, 10¢. Electronic Com-

ponents Co., P. O. Box 2902, Baton Rouge, La.

SURPRISE ELECTRONICS EQUIPMENT $5, $10 PACK-

AGES, TANG, Box 162, FRAMINGHAM CENTER, MASS.

01701.

CANADIANS: Giant Electronic Experimenters' Catalogs.

Rush $1.00 (Refunded). ETCO Electronics, Dept. E.E., Box

741, Montreal.

GIANT TESLA COIL- FORTY -INCH SPARKS! Complete

plans $5.00. Details and color photo 50f. Huntington

Electronics, Inc., Dept. K, Box 9, Huntington Station,

Shelton, Conn. 06484.

FREE confidential bargain parts catalog. KNAPPYS, 3174

8th Ave. S.W., Largo, Florida 33540.

CANADIANS -Free Copy -Electronics By ETCO- Exciting

Electronics Mailorder Magazine. ETCO, Dept. E.E., Box

741, Montreal.

FRAME & DISPLAY 60 C.B. cards in plastic. Send only

$1.00. Guaranteed. TEPABCO, Box 198J, Gallatin, Tenn.

37066.

TUBES

ELECTRONIC TUBES -LARGEST STOCK IN USA. ELEC-

TRONIC COMPONENTS AND EQUIPMENT. WRITE FOR

"BARRY GREEN SHEET" CATALOG. SEND 100. Barry

Electronics, 512 Broadway, N.Y.C., N.Y. 10012. (We also

buy unused tubes, and good commercial equipment.

Write details.)

TUBES °{ All types: HiFi, Ham, Industrial, TV. All brand

name -brand new. Lowest prices in country. List: VAN -

BAR Distributors, Box 444K, Stirling, N.J.

FREE! WHOLESALE RADIO TUBE CATALOG, LARGEST

LISTING IN THE WORLD. MANY OTHER BARGAIN

ITEMS. CeCo, 120 West 18th Street, New York, N.Y. 10011.

INFORMATION -how to rebuild Picture Tubes. Box 2134,

Hammond, Indiana 46323.

TAPE AND RECORDERS

INSTRUCTION

LEARN MORSE INTERNATIONAL CODE ALPHABET IN

HALF HOUR. Mail $1.00 check or money order for la-

minated, pocket -size fifty word mnemonic to: MNEMON-

ICS ASSOCIATES, 56 Grand Street, White Plains, New

York.

ENGINEERING and Art Degrees earned through home

study, Electronics, Mechanical, Liberal Arts. When writing

specify course desired. Pacific International College of

Arts & Sciences, primarily a correspondence school.

Resident classes also available. 5507 -C Santa Monica

Blvd., Hollywood, Calif. 90038.

MOVIE FILMS

PROCESS your own movies at home. Save money! Have

fun! Free catalog. Superior, 444 -46N. Wells, Chicago,

Illinois 60610.

EMPLOYMENT INFORMATION

GET a Government Job -pass any Examination, Free de-

tails. W.P. Parrish Co., 6118 East 52nd St. North, Kansas

City, Mo. 64119.

BUSINESS OPPORTUNITIES

ELECTROPLATING Equipment, Supplies, Instructions.

Home workshop and Industrial. DC Power Units from 10

Amps, to 3,000 Amps. Transformers, Meters, Rectifiers.

100 Amps., $29.50. Send $1.00 (Refundable) for Formu-

las, Equipment Guide, Catalog & Schematic. HBS, Dept 8,

3543 East 16th Street, Los Angeles, Calif. 90023.

INVENTORS

INVENTIONS WANTED. All Types. Global Marketing Ser-

vice, 2420V 77th, Oakland, Calif.

RON'S STEREO TAPE CLUB, 449 East 7th St., Red Wing, MAGIC TRICKS

Minn. 55066.

TAPE RECORDER accessories. Make yours or buy com-

pleted. 101/2" reel adapters, tape lifters and automatic

shutoffs. LEROI ELECTRONICS, Marengo, Illinois.

WANTED

WORLD'S finest Professional Magic, Tricks, Jokers, Puz-

zles. Giant illustrated Catalog. (164 Pages) Only 10¢. Vick

Lawston's Magic, 4018Z N.E. Fifth Ave., Ft. Lauderdale,

Fla.

CASH -for old ignition type model airplane engines. Box MISCELLANEOUS

111, Hamilton, Ohio.

RUBBER STAMPS

RUBBER ADDRESS STAMP $1.00. Signature $2.88. Cata-

log. Jackson Stamps, 1433 Winnemac, Chicago, III. 60640.

PERSONAL PROBLEMS got you down? Worried about

world conditions? Learn to control your life and affairs

through proper use of cosmic law. Free literature. Write

today! LEMURIAN FELLOWSHIP, Dept. 612, Box 397,

Ramona, California 92065.

1966 Fall Edition 151

UNUSUAL BARGAINS

SCIENCE FAIR HEADQUARTERS

Bargain! 3" Astronomical Telescope

See the stars, moon. phases ,'t \,,gin: -. planets

close up! 00 to 180 power- fanefu. Sit. Palomar

Reflecting type. Unusual Buyl Equipped with

Equatorial mount; finder telescope; hardwood

tripod. Included FREE: "S'L'AB MART":

272 -page IIANDBOOK OF HEAVENS ":

"110W TO USE YOUR TELESCOPE" book.

Stock No. 85,050 -GD $29.95 pstpd.

4iá" Reflecting Telescope -up to 255 Power,

All -metal pedestal mount.

Stock No. 85,105 -GD $84.50 F.O.B.

Superb 6" Reflector Telescope

"i to 576 Power. Equatorial mount and Pedestal Base.

Stock No. 85,086 -GD $199.50 F.O.B.

SOLVE PROBLEMS! TELL FORTUNES! PLAY GAMES!

NEW WORKING MODEL DIGITAL COMPUTER

ACTUAL MINIATURE VERSION

OF GIANT ELECTRONIC BRAINS

Fascinating new see -through model computer actually

solves problems, leaches computer fundamentals.

Adds, subtracts, multiplies, shifts. complements.

carries, emorizes, unts, compares. scummier..

Attractively colored. algid plastic parts coolly

mbled. 12"s3i/2 "s4a r Incl. step -hy -step a sseni

bly diagrams. 32 -page ins, met Ion book erl g

operation, computer language (binary systems) rig

, progrmn,ni ng. problems and

15 experiments.

Stock No. 70,683.00 $5.98 Postpaid

DETAILED PROGRAMMING BOOKLET FOR EXPERIMENTS

Stock No. 9080 -GD 150 Pages) $1.00 Postpaid

New! Low -Cost! Complete!

Du PONT PLASTIC LIGHT GUIDE KIT

First Time Available Anywhere

Experiment with these amazing new Du Pont

plastic fiber optic light guides. 1001 uses

for mfrs., experimenters, hobbyists. Use for

exciting new projects and products. Guides

transmit light same as wire conducts elec-

tricity. Use to illuminate remote areas, mul-

tiple locations from single source, confine

light to small areas -with photo cells they count, select, de-

tect or sort by size, shape or color. More flexible than glass

-costs 80 to 90 S7 less. Kit contains 2' lg. guides (2 sizes),

penlight source, connecting adapter, concentrating lens, color

coding end dyes. polishing & capping materials, inst.

Stock No. 70,855 -GD (Kit) ......$10.00 Ppd.

FOUR GUIDES AVAILABLE SEPARATELY -

2 ft. up. (50c.65c ft.) Write for details.

BATTERIES GUARANTEED

RECHARGEABLE FOR 5 YRS.

Use these remarkable space -age Nickel-Cad-

mium batteries in flashlights, portable radios,

toy or flash guns. Obsolete all others! Low -

cost kit includes compact, highly efficient bat-

tery charger and 2 "D" size Ni -Cd batteries

guaranteed rechargeable to full power for 5 yrs. Poster out -

cells. Durablebl black

constant-doesn't

pl plastic carger 5axy x 3" with x lead-acid

plugs into standard wall outlet. Completely charges 1 or 2

"D" or "C" size batteries in 16 hrs. Light shows when unit

is charging -will not overcharge.

Stock No. 60,591 -GO ......................$9.95 Ppd.

Stock No. 60,592 -GD (Charger only) $5.98 Ppd.

Stock No. 60,593 -GD (Two "D" Cells only) $5.98 Ppd.

Fascinating Top Adaptation of Binary Digital Computer

BEAT "DR. NIM" IN ANCIENT GAME!

Not cast', but fun for all Thrilling for young-

-- stets. Challenging far adults- Teaches conipoter

fundamentals, without need for mathematical abil-

ity. To play, release 1 to 3 marbles for roll down

plastic game board through series of flipflop chan-

nels. Ifow you SET flipflops to begin and path of

travel for each marble, determines path of succeed-

ing marbles. All plays predictable. Now DR. NIM

oatonialirnllo plays 1, 2 or 3 marbles- If you can

u.fke him take the last marble you winl Game great for playroom

did parties, year -round fun- Durable red & white plastic 1l5/.t"

z 121 2" x 11í ". 24 -p. Instruction Booklet.

Stock No. 70,816 -GD $2.98 Ppd.

Order by Stock No. -Send Check or M.O.- Money -Back Guarantee

EDMUND SCIENTIFIC CO., Barrington, New Jersey

MAIL COUPON for FREE CATALOG "GD"

EDMUND SCIENTIFIC CO., Barrington, N.J. 08007

Completely New 1967 Edition. 148 pages

Nearly 4500 Bargains.

Please rush Free Giant. Catalog Gtr

Name

Address

City State Zip

ELECTRONIC

EXPERIMENTER'S

HANDBOOK

FALL 1966

READER

SERVICE NO. ADVERTISER PAGE NO.

I Allied Radio 67, 68

2 American Institute of Engineering & Technology 132

3 CTS Knights, Inc 137

Caner 147

4 Datak Corporation, The 136

5 Delta Products, Inc 131

6 DeVry Technical Institute 13

7 EICO Electronic Instrument Co., Inc I

8 Edmund Scientific Co 152

9 Electro- Voice, Inc 141

10 Heath Company 101, 102, 103

II International Crystal Mfg. Co., Inc 4

12 Johnson Company, E.F 142

13 Knight -Kit Div., Allied Radio 150

18 Lafayette Radio Electronics SECOND COVER

14 McGee Radio Co 146

15 Miller Co., J W 142

16 Milwaukee School of Engineering 140

17 Mueller Electric Co 132

19 Multicore Sales Corp 146

National Radio Institute THIRD, FOURTH COVERS

20 Olson Electronics Incorporated 148

21 Poly Paks 139

22 RCA Electronic Components and Devices 2

23 RCA Electronic Components and Devices 6

24 RCA Institutes, Inc 33, 34, 35

25 Sams & Co., Inc., Howard W 135

27 Scott, Inc., H.H. 145

26 Semitronics Corp 138

28 Sydmur Electronic Specialties 148

31 Telex 149

29 Warren Electronic Components 136

30 Xcel!te, Inc 130

CLASSIFIED ADVERTISING 151

CIRCLE NO. 8 ON READER SERVICE CARD

152 Printed In U.S.A. ELECTRONIC EXPERIMENTER'S HANDBOOK

BUILD, EXPERIMENT, EXPLORE, DISCOVER

WITH NRI CUSTOM- DESIGNED TRAINING KITS

BUILD YOUR OWN

PHONE /CODE TRANSMITTER

This is just one of seven training

kits programmed into NRI's Com-

plete Communications course. You

get actual practice in building your

own crystal -controlled, phone /code

transmitter and putting it on the

air. You experiment with modula-

tion, "clamping" circuits, key fil-

ters, other aspects of commercial

transmitter operation. Can be put

on the air simply by attaching an

antenna and complies with FCC

regulations. As with all NRI training

kits, you get the most modern fea-

tures and parts.

Join the Thousands Who

Gained Success with NRI

"I am Frequency Co-

ordinator for the 11th

Naval District. The

course was priceless."

J. J. JENKINS, San

Diego, Calif.

"Many thanks to NRI. I

hold FCC License, am

master control engineer

with KXIB -TV." R. L.

WOOD, Fargo, N.D.

"I am a Senior Engi-

neering Aide. Without

NRI I would still be

working in a factory at

a lower standard of

living." D. F. CONRAD,

Reseda, Calif.

Available Under

NEW GI BILL

If you served since January 31,

1955, or are in service, check

GI line in postage -free card.

r

BUILD ACTUAL ANALOG

COMPUTER CIRCUITS

Industry, business offices, the gov-

ernment and military all need

trained Electronics Technicians.

NRI's Industrial Electronics course

prepares you. You progress through

10 carefully designed training kits,

topping off your practical experi-

ence phase of training by experi-

menting with feedback control sys-

tems, analog computers and digital

computer elements. You actually

solve problems on this analog com-

puter you build yourself. This is the

practical, fast way to a good pay-

ing, career position.

BUILD A CUSTOM- ENGINEERED

TELEVISION RECEIVER

Want to earn $3 to $5 an hour in

spare time? Want your own part-

time or full -time business? In Ra-

dio-TV Servicing you learn to in-

stall, maintain, service radios, TV

sets, hi -fi and stereo, other home

Electronics equipment. In your

training are eight training kits, in-

cluding this complete, modern,

slim -line TV receiver. You build it

yourself, become familiar with

components and circuits, learn

servicing procedures ... and earn

extra money as you train. National

Radio Institute, Washington, D.C.

SEE OTHER SIDE

FIRST CLASS

PERMIT

NO. 20 -R

Washington, D.C.

BUSINESS REPLY MAIL

NO POSTAGE STAMP NECESSARY IF MAILED IN THE UNITED STATES

POSTAGE WILL BE PAID BY

NATIONAL RADIO INSTITUTE

3939 Wisconsin Avenue

Washington, D.C. 20016

1111

YOU GET MORE FOR YOUR MONEY

FROMNRI Below is an example of material included in just one NRI

course. Other NRI home study plans are equally complete.

AMERICA'S OLDEST AND LARGEST RADIO -TV,

ELECTRONICS HOME -STUDY SCHOOL

Compare if you like. You'll find -as have so many

thousands of others -that NM training can't be

beat. From the delivery of you; ;; -.t lessons in the

remarkable, new Achievement Kit sent the day we

receive your enrollment, to "bite- size," easily

read texts and carefully designed training equip-

ment ... NRI gives you more value. The picture

above dramatically illustrates the material in-

cluded in just one NRI course. Everything you

see is included in low-cost NRI training. But NRI

is more than kits and texts. It's also friendly, per-

SEE O7`HER SIDE

sonal services which have made NRI a 50 year

leader in the home study field.

Whatever your interest or need ... whatever your

education . . . there is an NRI instruction plan

in Radio -TV Servicing, Electronics or Communica-

tions to fit your needs; tuition rates to fit your

budget. Prove to yourself -your best home -study

buy is NRI. Mail postage -free card today. No

salesman will call. NATIONAL RADIO INSTITUTE,

Electronics Division, Washington, D.C. 20016.

National Radio Institute, Electronics Divisìoh

Washington, D.C. 20016 13 -096

Please send me your catalog. I have checked the field(s) of

most interest to me. (No salesman will call) PLEASE PRINT.

Television -Radio Servicing

Complete Communications

Industrial -Military Electronics

FCC License

Math for Electronics

Basic Electronics

Electronics for Automation

Aviation Communications

Marine Communications

Mobile Communications

JOB AND BUSINESS

OPPORTUNITIES IN

ELECTRONICS

COMMUNICATIONS

RAOIO TELEVISION

Check for facts on new GI Bill.

Name Age

Address Zip Code

City State

ACCREDITED MEMBER NATIONAL HOME STUDY COUNCIL

NOW 10

WAYS to

train at home

MAIL CARD

NO POSTAGE

REQUIRED

OVER 50 YEARS

OF LEADEF` HIP IN

ELECTRONICS TRAINING

Experimenters Handbook 1966 Fall

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