February 1960 Popular Electronics
[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Popular
Electronics was published from October 1954 through April 1985. All copyrights are hereby acknowledged. See all articles from
Topics was a monthly column that helped introduce and educate readers
to the relatively new topic of transistor design and troubleshooting.
The editor often presented questions from readers and answered in
layman's terms. This month's question came from a reader in Bogota,
Columbia, which in 1960, was a big deal. Nowadays we take for granted
how small the world is due to the Internet.
See all articles
By Lou Garner
It's hard to believe, but the transistor's
high efficiency and extended life span have turned out to be "too
much of a good thing" in one respect. The transistorized, solar-battery
powered transmitters used in artificial satellites can continue
to broadcast their data for years - which is fine, up to a point.
But as more and more artificial satellites and space probe rockets
are launched, the airways will soon become cluttered with an overwhelming
number of transmissions. Since there is a limited amount of space
in the radio spectrum, new satellites may find their broadcasting
being interfered with by signals sent out by satellites launched
To prevent this unhappy situation from occurring,
the Army Ballistic Missile Agency has had the Bulova Watch Company
design a special "silencer" to turn off solar-powered transmitters.
Assembled in a cube measuring about two inches on each side, this
interesting device weighs about two and one-half pounds. Fully transistorized
itself, it develops approximately one-billionth of one horsepower,
yet can be set to switch off a transmitter automatically after an
interval of from zero to nine thousand hours.
the future, we can envision larger artificial satellites spaced
in regular orbits around the sun, to be used as outer-space "mileposts"
or marker beacons by interplanetary cargo and passenger ships. Their
transistorized transmitters would be powered either by giant banks
of solar batteries or by nuclear "fuel cells" to insure adequate
output power. Reader's Circuit
. Our mailbag
frequently includes letters from POP'tronics readers in South America,
Europe, and Africa; and we've even received mail from as far away
as India. Interestingly enough, many of these readers are experimenting
with circuits-and using components just like those popular with
stateside hobbyists. The circuit in Fig. 1 was submitted by Alexis
Pertuz, a high school student in Bogota, Colombia.
circuit is that of a five-transistor AM broadcast-band receiver,
with U.S.-distributed components being used throughout. Essentially
a t.r.f. design, it includes a doubler-type diode detector and a
three-stage audio amplifier. A class AB push-pull output stage is
employed, and p-n-p transistors in the common-emitter arrangement
are used in all stages.
In operation, r.f. signals are picked
up and selected by tuned circuit L1-C1. A tap on L1 matches the
high impedance of the tuned circuit to the moderate input impedance
of the r.f. amplifier Q1, assuring minimum tuned circuit loading
and thus maximum circuit "Q" and selectivity. Transistor Q1's base
bias is furnished through R1, bypassed by C2, in conjunction with
emitter resistor R2, bypassed by C3. A small r.f. choke, L2, serves
as Q1's collector load, with the amplified r.f. signal appearing
across this coil coupled through C5 to the doubler-type diode detector
D1-D2. The r.f. gain is controlled by bypass capacitor C4 and series
Fig. 1. Five-transistor AM broadcast-band
receiver circuit submitted by reader Alexis Pertuz, of Bogota, Colombia,
includes doublertype diode detector and a three-stage audio amplifier.
From the detector, the resulting audio signal
is amplified by a two-stage resistance-capacity-coupled audio amplifier,
Q2 - Q3. Potentiometer R6 serves as an audio gain control. Large-value
electrolytic capacitors, C7 and C8, are used for interstage coupling
to prevent attenuation of lowfrequency signals.
audio amplifier stage, Q3, is transformer-coupled to the class AB
pushpull output stage (Q4, Q5) through T1. Output stage bias is
furnished by voltagedivider R9-R10 and series base resistor R8.
The push-pull stage, in turn, is coupled to its PM loudspeaker load
through impedance-matching output transformer T2. A small open-circuit
jack (J1), across the speaker, is provided for earphone operation.
The d.c. power is furnished by a 6-volt power pack, B1, controlled
by a s.p.s.t. onoff switch, S1, and bypassed by C11.
can duplicate the receiver using readily available components. Coil
L1 is a standard ferrite loopstick (Lafayette MS-330) and C1 is
a small 365-µµf. variable capacitor. L2 is a common 2.5-mh. choke.
All electrolytic capacitors should have a minimum working voltage
of 15 volts.
In the output stage, T1 is an Argonne Type
AR-175, with a Type AR-119 being used for T2. Any standard PM loudspeaker
may be employed-a small unit (2" to 4") for pocket-sized sets, a
larger unit (4" to 8") for better tone quality.
Q1 is an RCA Type 2N147 "drift" type, Q2 and Q3 are G.E. 2N107's
and Q4 and Q5 are RCA 2N109's. Almost any crystal diodes can be
used for D1 and D2; Alexis used 1N48's, but 1N34's or 1N34A's should
work as well.
TV tuner, now available from
General Instrument Corp., is much smaller and lighter in weight
than old-style tubeoperated tuner.
reference packs made by International
Rectifier come in miniature sizes for printed-circuit board
installation and larger sizes for conventional mounting.
Fig. 2. Outline sketch and mounting details of transistor heat
dissipator recently introduced by the International Electronic
The power pack is made up of four penlight cells connected in series
to furnish six volts. However, Alexis indicates that the receiver
will work satisfactorily on a 9-volt battery without circuit changes.
Neither circuit layout nor lead dress should be especially
critical, although the usual care should be taken to keep signal
leads short and direct. The receiver is suited to either "chassis-type"
or "circuit board" construction, depending on individual preferences.
Although provision is made for an external antenna, Alexis
indicates that the receiver has more than ample gain for the reception
of local broadcast stations using only its built-in "loop" (L1),
. "Pre-packaged" assemblies
using semiconductor components are becoming increasingly popular
for many circuit applications. Typical units are the voltage reference
packs manufactured by the International Rectifier Corporation (1521
E. Grand Ave., El Segundo, Calif.) . These are made in sizes ranging
from miniature units designed for circuit board mounting and providing
a single output voltage to larger units which can operate from a.c.
or d.c. sources and can supply two or more regulated outputs.
Voltage reference packs, in general, supply a known accurately
controlled d.c. output voltage which is maintained constant regardless
of variations in ambient temperatures or in input supply voltages.
They are used to replace standard cells or dry cell batteries in
such equipment as digital voltmeters, regulated power supplies,
potentiometric recording instruments, fire control systems, autopilots,
missile guidance control gear, and aircraft instrumentation and
communication equipment. Heat Dissipators
Excessive heat can destroy a transistor. Even a moderately high
temperature can bring about a deterioration in overall circuit performance.
Often, the problem is not so much that of high ambient temperature
as that of getting rid of heat developed within the transistor itself.
High power transistors used near their maximum ratings can become
quite warm. To help dissipate internally developed heat in semiconductor
devices, the International Electronic Research Corporation (145
West Magnolia Blvd., Burbank, Calif.) has introduced a line of especially
designed heat dissipators.
These units are made in a variety
of styles to match the most popular transistors and power diodes.
They are available through regular parts distributors and, in quantity,
direct from the manufacturer. A typical IERC heat dissipator, designed
for use with transistors in the familiar JETEC TO-3 "diamond" package,
is illustrated in outline form in Fig. 2. Overseas
. Semiconductor devices are being used in larger and
larger quantities in the design of foreign-made products. Here are
a few spot items received from our overseas sources.
- Nippon Audio Kogyo Co., Ltd., Tokyo, Japan, is manufacturing
transistorized telephones; each set is designed as an automatic
dial master phone and may call any of ten stations. And Toho
Electronics, also in Japan, has introduced a fully transistorized
- There are several items from Germany. Dr. med. Noeller,
Children's Hospital, Heidelberg University, has designed a subminiature
transistorized transmitter which, with its self-contained battery,
measures only 5/32" 1/4" over-all; it is swallowed by the patient
and transmits data on pressure, temperature, and the pH value
within the stomach or intestinal system. Grundig Radio-Werke
GmbH, Fuerth/Bay, is producing a miniature transistorized tape
recorder. And a Hamburg firm, Protona GmbH, has introduced a
fully transistorized FM walkie-talkie weighing only 25 ounces.
The Metropolitan Water Board, Sydney, Australia, is using a
transistorized indicator system for low-level sewage pumping
- In Leningrad, Russia, the Aerophysical Institute has reported
the development of a semiconductor thermometer which determines
the optimum planting time for wheat and corn.
. Aldens, a Chicago mail order house,
is advertising a 3-band, 7-transistor portable receiver which sells
complete with battery and leather carrying case for only $49.95.
The set tunes the AM broadcast band from 540 to 1600 kc. and short-wave
bands from 3.5 to 12 mc.
Motorola, Inc. has announced price
cuts in its line of Zener diodes. There is also news of price cuts
on power transistors made by Delco Radio.
The General Instrument
Corporation, (Chicopee, Mass.) has started large-scale manufacture
of fully transistorized TV tuners. These units use three Philco
microalloy diffused transistors (MADT) and offer a performance
comparable to that obtained from vacuum-tube operated tuners with
respect to gain, signal-to-noise ratio, and image and i.f. rejection.
Designed for operation on 12 volts, these tuners require only 8.5
Before too long, the Raytheon Manufacturing
Company, pioneer manufacturer of low-cost "experimenter's transistors,"
is expected to announce two new types-p-n-p units selling for under
90¢ each to the user.
That does it. See you next month.