Transistor Topics - Heathkit TCR-1, MOBIDIC
April 1960 Popular Electronics
many years, Popular Electronics had a monthly column titled "Transistor
Topics" that reported on news in the world of those newfangled semiconductors.
To wit, this article from the April 1960 edition begins, "Each month,
more and more transistorized consumer products are developed as replacements
for vacuum-tube designs." The Heathkit TCR-1 clock radio is featured
for its six-transistor superheterodyne AM receiver circuit. A mechanical
clock is still used since other than using Nixie tubes, digital displays
were not commercially available. The MOBIDIC "super" computer is also
covered for its total transistorization. At about 4 feet wide and 6
feet tall, it is hard to believe that the "MOB" portion of the acronym
stands for "mobile."
April 1960 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 are hereby
acknowledged. See all articles from
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By Lou Garner
month, more and more transistorized consumer products are developed
as replacements for vacuum-tube designs. In view of this trend, a radio
kit recently introduced by the Heath Company (Benton Harbor, Mich.)
takes on special significance. Dubbed "Your Cue," Heath's TCR-1 is frankly
designed as a transistorized table-model clock radio. If desired, the
set can be converted into an attractive "portable" by fitting it in
an optional leather carrying case.
Battery-operated, and hence
completely shock-proof, the TCR-1 is as at home in the kitchen or bathroom
as it is in the living room, den, "rec" room , bedroom, or office. With
no dangling cord to plug in, the set can be placed anywhere rather than
near an electrical outlet.
Basically a six-transistor
superhet using p-n-p types in the common-emitter arrangement, the TCR-1
boasts a number of circuit innovations as well as several interesting
operating features. It tunes the AM broadcast band from 535 to 1620
kc.·and has a standard 455-kc. i.f. Its audio amplifier can deliver
a maximum of 300 mw. to its 4" x 6" loudspeaker, more than ample for
good room volume. Radio battery life is from 100 to 500 hours, depending
on whether standard penlight or mercury cells are used. A separate battery
powers the clock; operating life is approximately four months, using
a mercury cell.
Referring to the block diagram of Fig. 1, the set features a high-gain
built-in loop antenna and a tuned r.f. amplifier ahead of its converter
stage. This is in contrast to the more common practice of having the
antenna coupled directly to the converter, and it insures better image
rejection and overall sensitivity.
The trend to transistors has now reached the clock
radio with this all-transistor circuit by Heath. One battery powers
the radio, another powers the clock.
Although a single i.f. stage
is employed, adequate selectivity is assured by the use of a double-tuned
i.f. transformer. The d.c. component of the detected i.f. signal is
coupled back to the r.f. amplifier for automatic gain control (a.g.c.);
the r.f. stage amplifies the a.g.c. voltage which is then applied to
the i.f. stage.
The audio signal from the detector is applied
through the receiver's volume control to an audio amplifier which, in
turn, drives a push-pull output stage. The power amplifier is operated
Class B to insure minimum battery drain at low volume levels. A special
feedback network permits the entire audio amplifier to function as a
tone generator, supplying a pleasant "alarm" signal.
clock-actuated switch allows the user to choose any of several modes
of operation, depending on individual preferences. The set can be used
as a conventional radio whenever desired. At night, a special "Lull-to-Sleep"
control will turn it off automatically after a playing time of up to
60 minutes. The clock can be set to turn the receiver on automatically,
supplying either an alarm tone or a radio program. Used in the bedroom,
the TCR-1 permits the listener to go to sleep with music and waken to
either music or an alarm. In addition, an earphone jack is provided
for personal listening.
From the builder's viewpoint, the TCR-1
is fairly easy to assemble. A conventional chassis and point-to-point
wiring techniques are used. The instruction manual furnished is clear
and well illustrated with pictorial diagrams.
In the field of computer design, too, the transistor has virtually supplanted
the vacuum tube. Few - if any - computers in current manufacture or
in the design stage use tubes. Most use transistors, diodes, and other
solid-state amplifying and control devices.
Transistorized computer console, the "MOBIDIC," is
already under production at Sylvania for the U. S. Army Signal Corps.
One of the most versatile of military computers is Sylvania's
transistorized "MOBIDIC" (Mobile Digital. Computer - pronounced, naturally,
"Moby Dick." This computer is used extensively by the army for routine
business calculations as well as for such battlefield work as logistics,
combat surveillance, tactical operations, scientific and analytic computation,
map compilation, and determining artillery target assignment.
Readers' Circuits. The circuits in Fig. 2 were
submitted by readers from opposite ends of the continent. John Gottcent
of 173 Warwick St., Brooklyn 7, N. Y., sent in the circuit given in
Fig. 2(A), while the one shown in Fig. 2(B) is the work .of Larry Gorney,
K6EBX, of 1536 E. Ave., Q-11, Palindale, Calif.
glance, the two circuits appear similar. Both employ a diode and two
transistors; both are designed for operation on a 3-volt battery, both
tune the AM broadcast band; both use modified direct-coupling between
stages; both require an external antenna for optimum performance; both
employ standard magnetic earphones and, finally, both can be assembled
using standard commercial components. But with all these similarities,
the two circuits are nonetheless very different in operation.
Referring, first, to Fig. 2 (A), we see that John's receiver consists
of a conventional LC tuned circuit followed by a two-stage RC-coupled
audio amplifier which uses p-n-p transistors in the common-emitter arrangement.
Coil L1 is a standard ferrite loop-stick antenna coil (such as Lafayette
No. MS-11), C1 a common 365-μμf. tuning capacitor, and R1 a familiar
1-megohm volume control with s.p.s.t. switch (S1). Capacitors C2 and
C3 are 0.5-μf. and 0.01-μf. units, respectively; 200-volt paper tubulars
may be used. Any of several diodes can be employed - the popular 1N34
or, if you prefer, a 1N48, 1N68, or CK705. Transistors Q1 and Q2 are
both G.E. Type 2N107's. The 3-volt battery, B1, is made up of a pair
of penlight cells connected in series.
In operation, signals
picked up by the antenna are selected by tuned circuit L1-C1 and applied
to the diode detector. From here, the detected audio signal is amplified
by Q1 and coupled through R1 and C2 to Q2. Additional amplification
is supplied by the second stage, with Q2's output driving the pair of
magnetic earphones. Capacitor C3 serves as a high-frequency bypass across
Note that no effort has been made to supply
a separate source of bias current for Q1's collector. This current is
obtained through Q2's base-collector resistance; hence, Q2's leakage
resistance will play an important part in overall circuit operation.
In some cases, it may be necessary to interchange Q1 and Q2 (identical
types are used) or to try different p-n-p types for Q2 until best performance
Fig. 2. Diodes serve as detectors
in the transistorized receiver circuits submitted by readers John Gottcent
and Larry Gorney. Note use of regeneration in Larry's circuit (B.)
Larry's circuit, in contrast, takes advantage
of the complementary characteristics of p-n-p and n-p-n types of transistors
to achieve direct-coupling between stages. Referring to Fig. 2(B), Q1
is a popular p-n-p type (Raytheon's CK722) , while Q2 is Sylvania's
familiar n-p-n type, the 2N35.
As in the first circuit,
L1 is a ferrite loop-stick antenna coil and C1 a standard 365- μμf.
tuning capacitor. L2 is an "extra" winding added to L1 and consists
of 10 to 15 turns of 22- to 28-gauge enamel wire wound on L1's form
about 1/4" from the coil itself. Larry used a type 1N34A diode, but
other general-purpose units will work as well. Capacitor C2 is a 0.05-μf.
paper or ceramic capacitor; working voltage is not critical. Resistor
R1 is a 220,000-ohm, 1/2-watt carbon resistor, and R2 a common 500,000-ohm
potentiometer. Any s.p.s.t. switch can be used for S1-toggle, slide,
rotary, or push-button. As before, the 3-volt battery, B1, may be made
up of a pair of penlight cells connected in series.
operation, r.f. signals picked up by the antenna system are selected
by tuned circuit L1-C1, detected by the diode, and coupled through C2
to common-emitter amplifier Q1. Enough r.f. "spills" through the detector
and Q1 to permit feedback winding L2 to provide regeneration, increasing
circuit gain and improving selectivity. Transistor Q1's base bias is
furnished through R1. The amplified audio signal is applied through
regeneration-volume control R2 to Q2 which, like Q1, is connected as
a common-emitter amplifier. Finally, Q2's output drives the magnetic
Either of these circuits can be assembled on a conventional
chassis or on a Bakelite or fiber mounting board. Follow good wiring
practice, keeping the signal leads short and direct and observing all
d.c. polarities. Don't install batteries or turn the circuit on until
you have double-checked all connections for wiring errors and accidental
Both circuits give optimum performance when used with
moderate-length (25' to 100') external antennas; a ground connection
is optional. In strong signal areas, a shorter antenna may give satisfactory
results. Moderate-impedance (500- to 2000- ohm) magnetic earphones should
be used. In the second circuit-Fig. 2(B) - try interchanging L2's connections,
as in any regenerative circuit, using the connection which gives maximum
Product News. With the Citizens Band
"booming," Radio Manufacturing Engineers, Inc. (RME), Washington, Ill.,
has introduced a fully transistorized, hand-held transceiver for use
in the Class D Citizens Band. This compact instrument, about the size
of the familiar "Walkie-Talkie," incorporates seven transistors and
Webster Electric Company (1900 Clark St., Racine,
Wis.) , manufacturer of "Tele-talk" intercoms and "Ekotape" recorders,
has introduced a line of transistorized d.c. to d.c. power converters.
A typical unit, Type 2D12, has an input rating of 12.6 volts at 3 amp.
and can supply 250 volts d.c. at up to 100 ma.
(165-08 Liberty Ave., Jamaica 33, N. Y.) has issued the second edition
of its popular Semi-Conductor Directory. This useful publication, supplied
free on request, has been expanded to 36 pages and lists the latest
in diodes, rectifiers, and transistors.
That's it for now, fellows
- we'll be back next month with more news.