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
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
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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
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.
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.
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
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
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
Fig. 1. Jack Yundt's "Handy Audi" test instrument adapted from
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 devices.
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.
Handy 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
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
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 wish.
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.
Field 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.
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
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.
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
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.
Lansdale Tube 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.