2021-11-23 Replace Germanium With Silicon Transistors

I also remember those projects that used the CK722 and 2N107. The last few years I have been repairing older transistor radios with germanium transistors. I have had a few of them with bad germanium output transistors, and I’ve replaced them with silicon PNP transistors, along with a change in base bias resistors. They work good.

But where I’ve replaced the germanium transistors in the RF and IF circuits, I’ve had a lot more problems. The germaniums can’t do much above 3 or so MHz. But the silicons will too easily oscillate at 10 or more MHz. So I have to add resistors and capacitors to roll off the gain above the AM band and prevent the parasitic oscillations.

So one can build those old circuits that used germanium transistors and instead use the modern silicon transistors, but one has to be aware that silicons may be so much better that they tend to go into parasitic oscillations.

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