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.
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.
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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.
Looking to 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
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 resistor R3.
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.
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
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.
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.
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),
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
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
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.
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
- 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.
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