January 1956 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Popular Electronics magazine ran
their "Transistor Topics" column for many years, and this is the third in the series. Unfortunately,
I do not yet have the previous two editions, but someday... Transistors were a relatively new phenomenon
at the beginning of 1956, so there was a lot to learn and a lot of people to teach about them. It might
have been easier to make converts of dedicated tube users if the JFET (junction field effect transistor)
had been commercialized before the BJT (bipolar junction transistor), since the JFET (voltage on the
gate controls current flow) acts more like the familiar vacuum tube (voltage on the control grid controls
current flow) than the BJT (current on the base controls current flow).
See other "Transistor Topics" in the series:
In opening the third installment of this department, we want to express
our appreciation for the many letters and cards asking that it be continued and that it be published
monthly. Many thanks to all who took the time and trouble to write.
Diode Rectifier Supplies
Power supplies for transistor experiments. The circuit in (A) is a simple hall-wave
rectifier, in (B) a bridge rectifier. and in (C) a simple voltage doubler. All of these circuits employ
the common 1N34 crystal diode.
The material below originated with Mr. Rufus Turner, Contributing Editor of POP-'tronics. We have
quoted directly from his letter to us.
"Transistors have become so closely associated with battery operation that the mere mention of a
power line-operated d.c. supply for a transistor circuit brings forth looks of amused astonishment.
"To be sure, transistors do permit long-life operation of some circuits which, when 'tubed,' cannot
be powered by batteries without running into expense. But there also are some places where it seems
pointless not to run the transistor from the power line. I saw an example in print recently. The subject
was a clever transistorized photo timer. Battery operated, of course, but why? The timer relay switched
the a.c. line on and off to an enlarger or print box. Since the power line had to pass through the timer
anyway, there seemed little point in ignoring it for transistor bias. Another familiar example is the
transistorized burglar alarm that sets off a line-operated signal but is operated from self-contained
batteries. You can name others.
"The striking features of the transistor are not lost, as many workers seem to fear, when the a.c.
line is used - where sensible - for transistor power. No matter from what source it receives its d.c.
bias, the transistor still is tiny, power-thrifty, non-microphonic, cool-running, practically indestructible,
"Because transistor current and voltage requirements are low, an a.c. power supply can be small in
size. This is compatible with transistor dimensions. A midget 6.3-volt filament transformer is entirely
adequate. Germanium diodes may be employed as the rectifiers, and miniature electrolytic capacitors
used for storage. Where voltages higher than 6.3 are needed, voltage multiplier circuits may be employed.
"The schematics show practical transistor power supply circuits employing germanium diodes. In each
case, T1 is a 1-ampere, 6.3-volt filament transformer. The circuits have been tested at a constant a.c.
input voltage of 115 volts and their d.c. output characteristics are given in the graph. Except in the
case of the doubler, the curves have not been carried beyond the current level at which the d.c. output
voltage falls to 6.3, the r.m.s. voltage of the transformer secondary.
"These circuits will be satisfactory, as given, for most low-drain circuits employing one or two
transistors at fixed operating voltages. For better voltage regulation (less fall-off of voltage as
the current increases) and higher output currents (such as will be required for multi-stage transistor
circuits containing bias resistor networks), Type 1N91 miniature germanium rectifiers may be substituted
for the 1N34 diodes, and the capacitor values increased. A 1N91 in the simple half-wave circuit with
C1 = 100 μfd. gives 60-ma. output at 6.3 volts d.c., contrasted to the 5 ma. at 6.3 volts obtained
with the 1N34 and 10 μfd. Output of the bridge, doubler, tripler, and quadrupler circuits likewise
will be improved.
This is a simple voltage tripler using readily available 1N34 crystal diodes.
Adding another capacitor and crystal diode to the circuit above enables it to operate
as a voltage quadrupler.
Circuit of the transistorized "radio add-on" unit suggested by Ed Noll. It is similar
to that outlined by Homer Davidson in our September 1955 issue.
"The curves in the graph were plotted from data taken in measurements on the circuits exactly as
they are shown here and without additional filters. In some transistor applications, especially sensitive
amplifiers, filters will be required. These may be of the simple, small-sized, resistance-capacitance
type. However, a sharper voltage fall-off must be expected as a result of voltage drop across the filter
Many thanks to you, Rufus, for the interesting ideas presented above. We hope that our readers will
take advantage of your schematics and suggestions. By the way, we have scheduled for early appearance
in this column a complete power supply unit for transistor experiments. It is a variable voltage supply
with an output of from 2 to 30 volts.
Speaking of power supplies, we might also report that another Contributing Editor is working on several
silicon solar battery hook-ups. Although the price of the "real" silicon battery is still high, we feel
that something concerning its use and application should appear in this column.
Another "Radio Add-On"
An additional suggested circuit this month comes from Ed Noll, whose many articles and books on TV
servicing and operation are known from coast to coast.
Ed brings to our attention the circuit shown below. It is used much like the original "Radio Add-On"
described in the September 1955 issue (page 48). In other words, the output is plugged into the phono
jack on a TV receiver. After the base-emitter detector is tuned up, it will bring in a single AM broadcast
station. Switching the TV receiver to the phono setting will enable the viewer to hear this station.
The advantage is two-fold: better fidelity from the AM station and greater use of the TV receiver during
The circuit is uncomplicated since many ferrite antenna coils are now sold with the tap shown in
the diagram. This tap is generally used for an external antenna. In this circuit it provides an additional
impedance match between the resonant circuit and the low impedance input to the transistor base-emitter
circuit. Don't forget that also in this circuit there is internal coupling in the transistor. The collector
circuit provides audio amplification of the rectified and detected signal.
Next month we go back to some receiver plans based on ideas suggested by you readers. Keep your letters
Posted January 18, 2017