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James Sweet wrote:
wrote:
wrote:

I have an old 8 gernamium transistor, protable AM radio that is noisy
on weak stations when cold. It works reasonably well when set it in the
sunshine and warms up. The problem seems to be the RF section since the
noise goes away when the volume is turned down. I'm suspecting the
germanium transistors may be the problem and wondering which one might
be replaced with a silicon variety to cure the temperature problems?

I'm not sure what all 8 transistors do. Two are in the output stage,
and another is used as a audio driver that drives the audio input
transformer.There are four RF coils, the usual oscillator (red) and
mixer (yellow) and white (1st IF) and (black (second IF). But that only
requires 6 transistors, and there are eight total. The detector is a
diode, so they didn't use a transistor for that. I haven't figured out
what the other 2 transistors do.

I'm thinking of replacing the oscillator transistor with a high gain
silicon variety to try and eliminate the temperature problems?

Any other ideas?

-Bill

Sounds like a perfect job for a can of freeze spray. Warm it up until
the problem goes away, then give suspect components a quick shot of cold.

Yes, good idea, but the can of freeze spray costs $10, and the radio
only cost two dollars. So I put the radio in the freezer for 30 minutes
and took it out and it didn't work at all. Then I applied a hot
sodering iron to the body of the oscillator transistor and it very
quickly started working again. Seems the oscillator doesn't run at low
temperature.

Would you guess the solution is a silicon transistor? or just adjust
the bias on the existing germanium transistor?

-Bill