Bardeen announced his invention of the transistor 10 years to the month before this article was written in
Popular Electronics. A decade later, engineers and scientists had revolutionized electronics for commercial,
military, and hobby applications. It seems strange to read here about applying transistors at high frequencies,
where the definition of "high" is in the hundred of MHz.
We've come a long way, baby.
[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. As time permits, I will be glad to scan articles for you. All copyrights (if any) are hereby acknowledged.
See all articles from
By LOU GARNER
a Merry Christmas to you . . . together with the sincere wish that your Christmas Stocking will be brimming full
with exactly what you would like old St. Nick to bring-be it a new car, new test equipment, or a whole cartload of
transistors and miniature components.
In the past few weeks our mail has included a lot of letters asking
about high-frequency operation of transistors. There's nothing especially mysterious about transistors at high
frequencies. The circuits themselves are quite similar to those used at, say, AM broadcast-band frequencies (550
to 1500 kc.) except, of course, for the values of components in the tuned circuits. But the important thing is to
have the proper type of transistor.
Tetrode transistors (see our May 1957 column) may be used up into the hundreds of megacycles. The highest
frequency tetrode available at this writing is Texas Instruments' Type 3N25 - this is a p-n-p unit with a cutoff
frequency of 250 mc. General Electric, too, offers a whole series of tetrode transistors the highest frequency
unit is the 3N30, an n-p-n transistor with a cutoff frequency of 120 mc. RCA is currently offering the highest
frequency triode transistor, the 2N384; this is a p-n-p unit with cutoff frequency of 100 mc. which may be used as
an oscillator up to 250 mc.
In general, r.f. transistors will serve as amplifiers up to, or slightly past,
their nominal "cutoff frequency" (at which their gain is approximately 70% of that achieved at low frequencies),
and as oscillators well above cutoff frequency. Take the RCA transistor as an example. With a cutoff frequency of
100 mc., this unit will provide 15 db gain at 50 mc. in a common base amplifier circuit. It provides unity gain at
The lowest priced high-frequency transistor as far as the home experimenter is concerned is probably Philco's Type
AO-1 surface barrier transistor. With a rated cutoff frequency of 30 mc., the AO-1 is offered at slightly under
$2.00 by leading mail order supply houses.
All of these transistors are suitable for receivers and
low-power transmitters. Unfortunately, no manufacturer is currently offering medium or "hi" power transistors for
use at high r.f. values.
Readers' Circuit. One- and two-transistor receiver circuits are extremely popular with
home builders. Almost all such circuits featured in past columns have used either detector-amplifier or simple
regenerative-detector arrangements. These circuits, at best, have limited sensitivity and, usually, just fair
This month, however, we have a most interesting "maximum performance" two-transistor receiver
circuit. Submitted by Gerald Le Fevre, of York Rd., Pavilion, N. Y., as his "favorite," this receiver has a
superheterodyne circuit. In addition, it uses a reflex arrangement, permitting one transistor to serve both as an
i.f. stage and as the audio amplifier. Coils L1 and L2 are Miller Types 2000 and 2020 respectively.
Fig. 1. Reader Gerald Le Fevre's two-transistor superheterodyne receiver.
Referring to Fig. 1, you will see that a Sylvania Type 2N94 r.f. transistor serves as a combination
mixer-local oscillator. The i.f. output signal developed across the primary of transformer T1 is coupled to the
i.f. amplifier stage, a second 2N94. T1 is a Miller 2041.
The amplified signal then goes from i.f.
transformer T2 (Miller 2042) to a 1N34A diode, which serves as the second detector. The resulting audio signal,
appearing across volume control R8, is "reflexed" back to the i.f. stage through audio coupling transformer T3.
Finally, the amplified audio output signal is applied across a pair of headphones. (T3 is an Argonne AR-100.)
Fig. 2. Two simple uses for a transistorized high-voltage "generator," suggested by
reader Charles Rakes: (A)
night light; (B) electric fence.
Base bias for the first stage is supplied by voltage divider R1-R2, operating in conjunction with emitter
resistor R4, bypassed by C5. Base bias for the second stage is supplied by voltage divider R5-R6 and emitter
resistor R7, bypassed by C7. R6 is bypassed by C6; other r.f. bypass capacitors are C4, C8, and C9. Operating
power is supplied by a standard 6-volt battery, B1 (such as a Burgess Type Z4).
Construction should pose
no problem for the experimenter who has assembled other simple transistor receivers. Gerald assembled his unit on
a 4" x 4" chassis, but suggests that a small Masonite board will serve as well. A Miller #2112 two-gang unit
serves as tuning capacitor (C1a/C1b). All resistors are "1/2 watt units, while all fixed capacitors may be small
disc ceramics or paper tubulars.
Transistorized code practice oscillators are currently available in kit form from, left to right, Knight
(Allied Radio), WRL Electronics and Lafayette Radio. See page 122 for details on all of these units.
If you assemble one of these receivers, be sure to keep your layout as "clean" as possible, with all signal
leads short and direct. Watch the battery polarity ... remember that the 2N94 is an n-p-n transistor!
Moderate-impedance (2000 to 4000 ohm) magnetic headphones should be used.
You shouldn't need an external
antenna for stronger local stations. However, for additional pickup, try connecting an antenna to the "hot" side
of the ferrite antenna coil (L1) through a 200-µµfd. ceramic or mica capacitor.
To align the unit for best
operation, use a standard r.f. signal generator. With a modulated r.f. signal, peak the i.f. transformers for m
aximum output at 455 kc. Adjust the oscillator trimmer capacitor (across C1b) for tracking at the high-frequency
end of the dial (around 1500 kc.) and the padder capacitor (C2) and oscillator "slug" (in L2) for tracking at the
low-frequency end of the band (about 600 kc.), "rocking" the tuning capacitor as you do so. If an antenna trimmer
capacitor is provided (across C1a), adjust this for maximum output above 1550 kilocycles.
Reader Charles Rakes, of 4419 Harrison St., Kansas City, Mo., has submitted a pair of interesting applications for
a high-voltage "generator" designed around a low-cost power transistor. Referring to Fig. 2, a CBS-Hytron Type
2N256 power transistor is connected as a modified "Hartley- type" oscillator. Base bias is determined by R1.
In operation, the a.c. voltage developed across the "primary" winding by the oscillator is stepped up by the
secondary and used to operate a small (15-watt) fluorescent lamp (A) as a soft "night light," or power an
"electric fence" (B) to keep livestock from straying.
Construction of the basic circuit is relatively
simple and the wiring is completely non-critical. R1 is a 22-ohm, 2-watt carbon resistor. B1 can be any standard
medium or large-sized 6-volt battery (such as a Burgess F4P1 or 2F4).
The combination oscillator/step-up
transformer (T1) is made from a discarded vacuum-tube audio output transformer. The secondary (low-impedance)
winding is partially unwound and center-tapped. It is then rewound and becomes the "primary" winding in the
oscillator circuit. The original primary winding (high-impedance) then becomes the high-voltage secondary winding,
providing the necessary boost.
Code Practice Oscillators.
Back in April, we reviewed currently available transistorized superhet receiver kits. As a result, we received
quite a number of requests that such "reviews" be a regular feature of the column . . . so here goes with a review
of transistorized code practice oscillators.
Of the various code practice oscillator (CPO) kits now
available, the KT-72, offered by Lafayette Radio (165-08 Liberty Ave., Jamaica 33, N. Y.), is the least expensive.
Catalog price is $2.99 (plus postage), including both batteries and a standard hand key. This kit assembles on a
small piece of perforated Masonite. The oscillator is designed for headphone operation only.
Allied Radio Corporation (100 N. Western Ave., Chicago 80, Ill.), offers a nice CPO which assembles into an
attractive black plastic box. It operates from a single penlite cell (included). The kit number is 83Y239 and the
catalog price is $3.95 (plus postage), less hand key and 'phones. This unit is also designed for headphone use
WRL Electronics (Council Bluffs, Iowa) offers a CPO with an easy-to-wire etched-circuit wiring board
which assembles in a sturdy aluminum case. Two penlite cells (included) power the circuit. WRL's kit sells for
$4.95 (plus postage), and is for headphone operation. The hand key and headphones are available as optional
Lafayette Radio is the only firm currently offering a CPO kit which provides loudspeaker operation. The
KT-118 kit assembles into a small plastic case not much larger than a package of cigarettes but which includes the
loudspeaker, transistor, battery, and entire circuit. Catalog price of the KT-118, less hand key, is $795 (plus
Lafayette Radio's two-transistor "Sunflex" receiver.
While a "sun battery" is not, strictly speaking, a transistor item, it is often used in conjunction with
transistorized equipment and, therefore, is of interest to Transistor Topics' readers.
Rectifier Corporation (1521 East Grand Ave., El Segundo, Calif.) , will shortly release a new silicon solar cell
with a lower cost per watt than previously available units. For full specifications, price and availability
information, write directly to the manufacturer.
Lafayette Radio's latest catalog offers a "Heliodyne"
silicon battery at $665 (plus postage). A multicell unit, this solar battery will supply up to 2.0 ma. at 3.2
volts in full sunlight. This is ample power for most small one- and two-transistor radio receivers or amplifiers,
and is considerably more than that supplied by standard selenium cells of comparable size and cost.
addition, Lafayette has announced a new two-transistor radio receiver kit, the "Sunflex," designed especially for
solar battery operation, It uses a highly efficient reflexed, complementary symmetry circuit which permits two
transistors to give the performance of three. Able to operate on standard penlite cells as well as a solar
battery, the KT-132 Sunflex receiver kit sells, less earphone and solar battery, for $11.95 (plus postage).
That's all for now, fellows. See you next year.