[Boatanchors] Receiver Hummm --

[GRANT YOUNGMAN]

I have two receivers which both exhibit the same hum issue to one degree or another.   I’m just not sure where to look.  One is a 51J-4, the other a Hammarlund PRO-310.  The J4 is the worse of the two.

Normally, when not tuned to a carrier there is virtually no hum in the receiver audio.  Both radios have new good power supply caps.  The hum — which is 60 Hz — only appears when a carrier is tuned, and appears to be somewhat proportional to carrier strength.  So I’m guessing something around the detector/AVC or a bias (half wave) supply, although even with AVC off it still occurs. The source is before the audio gain control — so detector/AVC/ANL (?).

Any suggestions where I should poke first?  I’m guessing this might be a fairly common problem, although I haven’t run into it before.

Thanks … Grant NQ5T