Transistors, Large and Small 
      31July2016

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 0.635.

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 used.   

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 emitter amplifier.

A slight modification will allow the transistor to be biased as a Class A or AB amplifier.  

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 Semiconductor Museum:
http://semiconductormuseum.com/Museum_Index.htm      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:
http://www.semiconductormuseum.com/Transistors/Hughes/OralHistories/Barnes/Barnes_Index.htm

Shown below is another photo of the monster transistor, here sitting on top of a vintage transceiver, itself a relic by now.