As an aside, at Bell Lab’s press conference announcing the breakthrough silicon junction transistor, a comparison was made between it and a germanium transistor by using each as amplifier for music, first at room temperature, then immersed in boiling water. The germanium transistor lost its gain when heated up, the silicon didn’t. It was a selling point for the newer silicon device.

Apparently, though, it is not always the case as the unfortunate sales manager for Needco Cooling Semiconductors, LTD found out one day in 1960 when a similar demo was attempted…

A germanium transistor operated just too well at a recent press conference. As part of a demonstration of a new thermoelectric transistor cooler, General Thermoelectric Corp. of Princeton, N.J., immersed a transistor amplifier in boiling water. The company planned to show how, without a thermoelectric cooler, the boiled transistor would die.

The germanium transistor should have quit amplifying at 85°C. Obstinately, it continued to amplify at 100°C.

The sales manager of Needco Cooling Semiconductors, Ltd. (a Montreal firm which developed the high-efficiency cooler) assured the audience that the signal would soon die. After a minute of heavy silence he tried to coax the unwilling transistor to die. He jiggled the transistor in the boiling water and then began to rap the side of the vessel—gently at first—then not so gently. Finally, the president of Needco joined in and began rapping the water vessel while the sales manager turned to the output-monitoring scope, which he began adjusting and tapping. The scope continued to work well, as did the transistor—still. (Electronic Design, July 20, 1960, p. 25)

 

I would think that it would require a different transformer to enable a silicon transistor to work in that circuit since the silicon transistor needs a higher voltage to turn it on. That would be prohibitive.

I have used the NTE176 to repair a lot of these old tachometers and have not had any come back for any problems other than this particular one. I will be heating up the next few that come in to see what happens to them.

Ya'akov, I managed Intel's corporate demonstration group though most of the 90s. My team ran all of the demonstrations that Intel's top management did at public events plus at most of the trade shows. Your failed demo story really resonated with me.

I had nightmares for years afterwards about failing demos. One of my former coworkers insisted that I was suffering from PTSD.