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
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.
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.
The TCR-1's 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.
"MOBIDIC." 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.
computer console, the "MOBIDIC," is already under production at
Sylvania for the U. S. Army Signal Corps.
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,
At first 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 the 'phones.
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.)
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,
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.
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 shorts.
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 gain.
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 one diode.
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
Lafayette Radio (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,
That's it for now, fellows - we'll be back
next month with more news.