[Argus25]

I had not thought of testing the transistor's high frequency capability in what amounts to a grounded base circuit (10R base resistor is effectively grounded base) because it circumvents the Miller effect of the collector-base capacity because the voltage swing at the base is so small. But I guess it is the way it might be done to determine the Ft value.

I have never been sure how the manufacturer did the test for the Ft and just accepted the published value.Obviously in a grounded emitter circuit (from the AC perspective) the source impedance at the base will have a significant effect on the high frequency performance, the lower the impedance the better.

Most likely the test of a transistor for its high frequency capability should be in some sort of circuit that resembles the one it will actually be used in.

Of unmarked germanium transistors I have tested, most of them have probably been intended for audio work and were little use above 50 to 300kHz. So I have never trusted unmarked transistors to be of any use for RF work, but they could be I guess and worth testing them just in case they turned out to be RF types.

Apart from the AF178 which is now my preferred replacement for AF11x, there was another very good transistor in the same package that was used in some UK made radios (some car radios too), this was the AF185 suited to 12V radios. I collected some a few years back but oddly even then they had become incredibly difficult to find. I even got sent some fakes that I think we're re-labelled other devices. But the AF185 is a very good replacement for AF11x, that is is you can find any genuine ones.