February 1960 Popular
Transistor 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.
[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. As time permits, I will be glad to scan articles for you. All copyrights (if any) are hereby acknowledged.
See all articles from
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 years earlier.
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.
Alexis' 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.
The second 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.
You 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.
Transistor 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.
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.
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 Research Corporation.
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
Reference Packs. "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 News. 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.
Product News. 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.
- 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 wirephoto transmitter.
- 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 stations.
- In Leningrad, Russia, the Aerophysical Institute has reported the development of a semiconductor thermometer
which determines the optimum planting time for wheat and corn.
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 ma. current.
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.