[Hallicrafters] microphonics

[Walt Cates]

Chris,

Microphonics is a tough failure to breach, and it is a failure. There are many causes. Miss-alignment can cause it. crystalized carbon resistors can cause it. The piezo effect in disk capacitors and other components can cause it. Bad grounds can cause it. Cold solder joints can cause it. Tubes can be microphonic. dirty and corroded tube sockets and connectors can cause it.

Gently tapping components can sometimes localize the problem. If all else fails, disable any AVC or AGC then start at the audio output and back up. That is, disable the detector stage and see is the microphonics goes away. If not disable the last I.F. stage and test for microphonics. Keep backing up until you find the offending stage. 

In the case of microphonics on only 1 or 2 bands of a multi band receiver, then determine what circuits are common only to those bands. 

OPINION: To my limited knowledge, none of the Hallicrafters gear made it into production with an inherent microphonic condition. So if it is microphonic then there is a failure.

Best Regards, Walt Cates, WD0GOF, http://www.myhamshack.com/WD0GOF/<http://www.myhamshack.com/WD0GOF/>
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