Transistor Topics: Semiconductors Other Than Transistors
March 1958 Popular Electronics
March of 1958 when this article appeared in Popular Electronics, learning
of semiconductor devices other than transistors was usually new to experienced
professionals as well as to hobbyists. Vacuum tubes still dominated
electronic products in the day. Companies like General Electric, Sylvania,
and RCA were the pioneers for development of Zener diodes, photodiodes,
SCRs, thyristors, etc. Exotic compounds like selenium, germanium, silicon,
and lead and cadmium sulphides were used. This article discusses some
of those devices.
March 1958 Popular Electronics
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 (if any) are hereby acknowledged.
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By Lou Garner
use of semiconductor devices other than transistors is expanding rapidly.
Such devices bear approximately the same relationship to the transistor
that industrial control tubes, thyratrons, heavy-duty rectifiers, phototubes,
and gaseous voltage regulators bear to the vacuum tube.
Small diode detectors and semiconductor power rectifiers have been used
for years - even before the invention of the transistor. In addition,
many special-purpose semiconductor diodes are either in current production
or are being developed. Available units include diodes designed to operate
at the Zener point as voltage regulators, and light-sensitive photodiodes.
The Zener diode is operated with a voltage applied in
its reverse (or high-resistance) direction at or very near to its nominal
"breakdown" (Zener) voltage. When the applied voltage increases slightly,
the diode's resistance suddenly drops from a moderately high to a very
low value. In conjunction with a fixed series resistor, such units can
serve as effective voltage regulators and are similar in operation and
application to the "VR" series of gas-filled voltage regulator tubes.
Photodiodes are made in a variety of styles and types.
Virtually all types of semiconductor materials are used in their construction,
including selenium, germanium, silicon, and lead and cadmium sulphides.
They range in size from Sylvania's minute 1N77A, a germanium photocell
smaller than a matchstick, to the large selenium "sun batteries" manufactured
by International Rectifier Corp.
Even General Electric
Co.'s Unijunction transistor is, in reality, a special-purpose semiconductor
device rather than a conventional transistor. Originally called a "double-base
diode," it has characteristics roughly like those of a small gas-filled
thyratron tube. G.E. is also developing a special silicon-controlled
rectifier which may serve as a possible replacement for both power relays
and medium-sized thyratrons.
In fact, almost all semiconductor manufacturers are designing and developing
new solid-state devices to replace standard thermionic tubes. RCA,
for example, is working on a "Thyristor," which may be operated either
as a bi-stable switching element or as a conventional high-frequency
currently being produced
by General Electric Co. include low-current silicon rectifiers (above,
right), and a silicon double-based diode (right, compared in size
with Life Savers). The tab protruding from the cap of the diode
serves as a ground for shielding purposes.
, such as these 1, and 3.5-watt units
available from International Rectifier Corp., make effective voltage
Fig. 1. Jack Yundt's "Handy Audi" test instrument adapted from POP'tronics
Fig. 2. Ronald Wilensky's simple field strength meter described
fully in the article.
Shockley's new "Bistable" diode is a four-layer
silicon device having alternate layers of n-type and p-type materials.
When a control voltage is applied to its two electrodes, it can be switched
from a high-impedance state with a resistance of from 1 to 100 megohms
to a low-impedance state with a resistance of less than 20 ohms. In
this respect, its action is much like that of a small neon bulb. It
can be used in similar applications, for example, in a saw-tooth oscillator
or pulse generator.
As designers and engineers learn more
about solid-state physics, you can expect to see more new semiconductor
Readers' Circuits. While a good many
home experimenters like to work on and to experiment with original circuits,
a high percentage prefer to adapt "standard" circuits they have seen
in magazine articles and books to their own requirements. Often, this
takes as much ingenuity and skill as is required to "dream up" a new
circuit. This month we are featuring a pair of interesting circuits
which our readers have adapted to their own needs.
Audi. S/Sgt. Jack W. Yundt (AF 14504821, 45 Ftr. Day. Sq., Box 473,
APO 117, New York, N. Y.) is, to use his own words, "an amplifier tinker."
When he saw Transtopic Experiment No. 15 in the February 1957 issue
of POP'tronics (page 85), he decided to turn the original circuit (a
simple code practice oscillator) into a multi-purpose audio test instrument.
He dubbed his completed test gadget "Handy Audi" (see Fig. 1).
It can be used as: (a) a code practice oscillator (CPO) with loudspeaker
output, (b) a CPO with headphone output, (c) an audible tone source,
and (d) an audio test signal source.
In operation, a single
n-p-n transistor is used as a common-emitter audio oscillator, with
transformer T1 serving both to provide the feedback necessary to start
and sustain oscillation and to match the transistor to a loudspeaker's
low-impedance voice coil. The feedback signal obtained from the transformer
is coupled back to the transistor's base electrode through d.c. blocking
capacitor C1. Base bias current is supplied through R1 and R2. Unbypassed
emitter resistor R3 serves to stabilize circuit operation. Operating
power is supplied by a 9-volt battery, B1, controlled by s.p.s.t. on-off
switch 81. The other components and switches permit the circuit's operation
to be modified for special applications.
All components used
are standard and should be readily available. R1 is a small potentiometer
- its taper is not critical. R2 and R3 are 1/2-watt resistors. C1 can
be a tubular paper or miniature ceramic capacitor. S1, S2, and S3 are
s.p.s.t. toggle or slide switches, while S4 is a d.p.s.t. unit. T1 is
an Argonne Type AR-119 transistor output transformer. The PM loudspeaker
can be a 3" to 6" unit with a 3- or 4-ohm voice coil. J1 is a standard
open circuit jack; BP1 and BP2 are binding posts. The power supply battery,
B1, can be a standard 9-volt transistor battery or 1 1/2-volt cells.
Sergeant Yundt assembled his unit in a plastic case about the
size of a table-model a.c.-d.c. receiver. Since neither lead dress nor
circuit layout is critical, however, you can use any size of case you
To use the completed instrument as a CPO with loudspeaker
output, connect a hand key to binding posts BP1 and BP2 and close switches
S1 and S2. With the key depressed, adjust R1 for desired operation.
If headphone operation is preferred, a pair of electromagnetic headphones
is plugged into jack J1, and switch S3 is closed. Switch S2 is opened
to silence the speaker.
For use as an audible tone source, the
key may be removed. Switches S1, S2 and S4 are closed, With this setup,
a steady tone is obtained from the loudspeaker. This is handy for such
purposes as checking microphone placement in p.a. installations.
Finally, to operate the instrument as an audio signal source, a
test probe (simply a shielded lead with a 0.5-.μfd. d.c, blocking capacitor
in series with the central "hot" lead) is plugged into jack J1. Switch
S2 is opened and switches S1, S3 and S4 closed. The audio signal obtained
from the probe can be used for signal injection tests of phonograph
amplifiers, p.a. systems, intercoms or other types of audio amplifiers,
including the audio sections of radio and TV receivers.
Strength Meter. If, at first glance, the circuit in Fig. 2 looks somewhat
like one of the simple diode and transistor receiver circuits you've
seen featured in past columns, don't be too surprised. Actually, it
is such a receiver, but Ronald Wilensky (KN2ZPV), of 920 East 17th St.,
Brooklyn, N. Y., has modified the basic circuit for use as an inexpensive
field strength meter.
In operation, r.f. signals picked up by
the antenna are selected by tuned circuit L1-C1 and coupled to a 1N64
diode detector, CR1. C2 serves as an r.f. bypass capacitor, insuring
that only the d.c. component of the detected signal is fed to the base-emitter
circuit of the p-n-p transistor. The transistor, in turn, is used as
a common-emitter d.c. amplifier, with its output indicated as a deflection
on the 0-1 milliammeter. Operating power is supplied by a 4.5-volt battery,
B1, controlled by the s.p.s.t. "power" switch S1. Series rheostat R1
serves as a sensitivity control.
Using readily available components,
construction is straightforward and should pose no problems. For best
results, Ron indicates that the instrument should be assembled in a
plastic case. L1 and C1 are chosen to cover the frequency band of interest
to the individual builder. For the 27.255-mc. R/C band, Ron suggests
that L1 be made up of 12 turns of #16 wire, wound on a coil form 5/8"
in diameter by 1" long. C1, in this case, can be a 25-μμfd. variable.
The antenna's length may be varied to suit individual requirements -
Ron used a straightened piece of "coat hanger" wire.
Sun Batteries. Some time ago, we announced that the
International Rectifier Corp. (1521 East Grand Ave., El Segundo, Calif.)
was planning to introduce a new series of inexpensive silicon solar
cells. These units are now in full production. They have an active area
of about 0.78 square inch.
Mounted and unmounted styles are
available in both "standard" and "selected" (optimum output) versions.
Prices range from $4.00 for an unmounted "standard" cell (Type No. SA5-PL)
to $8.00 for a mounted "selected" unit (Type No. SA5A-M). A standard
cell can deliver over 20 milliwatts into a 4-ohm load with an illumination
of 5000 foot-candles. Its open circuit voltage at this light level is
about 0.45 volt.
Product News. An important
step towards the standardization of transistor types has been taken
by Raytheon and Tung-Sol Electric. Both of these firms are now producing
several transistors under the same EIA-registered type number.
Another new transistor manufacturer has entered the field-Fairchild
Semi-Conductors Corp., Palo Alto, Calif. This new firm is sponsored
by the well-known Fairchild Camera and Instrument Corp. Present plans
call for the development and production of silicon diffused transistors
and other semiconductor components.
Zenith and Philco are now
producing fully transistorized portable short-wave receivers. Both are
multiband sets, and sell for well over two hundred dollars each.
RCA has introduced several new transistor types. The 2N404 is a
p-n-p junction transistor designed for use in switching circuits, has
a maximum collector current rating of 100 ma., a maximum dissipation
of 120 mw., and an alpha cutoff frequency of 4 mc. The 2N408 is a p-n-p
junction transistor intended for Class A and Class B audio service in
entertainment-type receivers; a pair of 2N408's in Class B push-pull
can deliver a 160-mw. output signal with a 9-volt power supply. The
2N407 is similar to the 2N408 except for basing.
Company, a division of Philco, has introduced a new series of MADT (Micro
Alloy Diffused-base Transistor) v.h.f. transistors. One of these units
will serve as an oscillator up to 1000 mc.
That's the show for
now, fellows. See you next month.