Julian wrote:
My radio does not like low temperature. When cold (e.g. less than 50
deg. F), the SSB modulation is bad. Its a sort of brumming noise
superimposed on the audio. Strange, if I change to AM or FM, the
modulation is good, under same low temperature conditions. So, it
seems that the microphone is OK.

What I do now is to heat the radio using a hair drier until the SSB
modulation is OK. In a cold room, I need to do this every 15 minutes
or so.

Any ideas of what causes this, or how to fix it?

Thanks,

Julian

Sounds like maybe an oscillation. In any event... this sounds like a
job that will require a scope and schemetic. I don't see that you have
any other choice but to take this one in for repair.

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