Transistors, Large and Small
We often see photographs of amateur
radio stations that include old vacuum tubes.
These photos were intended to illustrate the key components
that we used in our transmitters in days gone by.
Wonderful old tubes like the 304-TL, the 807, or the 813, or
even older gems are common in such photos.
4-1000 "pulls" from AM broadcast transmitters are popular.
Some collectors have build varnished wood stands to
better display their old vacuum tubes. A great web
site for this is that of the Tube Collectors
Association. See http://tubecollectors.org/
I don't have any old tubes, at least that I could easily
find. The first transmitter I built that had
much power used a 6146, and that's still a current part.
Being more of a solid-state experimenter, even in my own
history, it was more productive for me to look for old
transistors. I have the usual collection of
CK722, 2N107, and 2N170 receiver parts. There
were also some other small signal gems that I've collected,
including a few power parts. The best power
transistor discovered is quite interesting and probably a bit
unusual. This gem was given to me in the 1960s by
Dick, W6CQI (sk). He was the owner of a chain of
electronic parts stores in the Bay Area of California when I
lived there. He had connections that gave him some
interesting parts. The transistor is shown in the photo
above. This part, marked as a 4-50 DPT 992, was
made by Pacific Semiconductor Industries, or PSI.
Hence the Greek letter Psi that was their corporate
logo, shown on the transistor. The
transistor weighs almost one pound. The collector
flange is 2.6 inches square while the cylinder that houses the
part is 1 inch high by 2.2 inch diameter. The three
leads coming out of the ceramic are for the base and
emitter. There were two emitter leads.
The photo above includes two plastic 2N3904
transistors. One is the traditional leaded
TO-92 package while the other is a SOT-23 surface mount
package. Two additional PSI transistors are
included. One is a TO-5 2N697. The
other is a larger TO-8 package RF power part, the
2N1709. I remember running some of those
parts on 40 meter CW.
I was curious to see if this monster part, which was built in
1962 or 63, would still act like a transistor, so I measured
the DC beta. With a collector current of 1.1 Amp
(3.9 V on the collector) the beta was 34.
It's an NPN part and certainly seems to be
silicon. At 1.1 A, the base-emitter voltage was
You might see this early 1960s part and suspect that it
was just a large industrial element, perhaps even
Germanium. Not so. This was a
silicon RF power transistor. At one time I
had a copy of the report for the research program that
generated this part, but the report is long
gone. I do remember that this part was
specified for an output of 300 Watts at 20
MHz. It was tested in a water cooled
environment. I recall that this part
contained one-half of a silicon wafer. The
wafers were probably no larger than 2 inch diameter, if not
smaller. The report described a higher power
cousin that had a full wafer and was capable of twice the
power. I don't remember the supply voltage
An unusual circuit topology was sometimes used (shown below)
with experimental power transistors in that
era. The transistor is operated with a
grounded collector. There is then no need for an
insulator, making this an optimum thermal
environment. An input transformer, T, allows DC
isolation and also allows RF drive power to be applied between
the base and emitter. A negative supply, attached
to the emitter through an RF choke, provides the bias for
power generation. An output network attached
to the emitter extracts the output power.
That network is between emitter and
collector. So this is still a common
A slight modification will allow the
transistor to be biased as a Class A or AB
A friend, Bob/N7FKI, was lurking on
the web and discovered a couple of great sites that treat the
PSI parts, as well as numerous other very interesting
components. The base site is that of the
I've just started looking at this one and it appears that it's
loaded with fun stuff.
The other is a link fro that above which deals directly with
Pacific Semiconductor Industries. This is in the
form of an oral history of Sanford Barnes:
Shown below is another photo of the monster transistor, here
sitting on top of a vintage transceiver, itself a relic by now.