Ay160 amp hum

[Spinner]

At end of ay160 rebuild.  I recapped TSU and shfa3.  All works as it should on record selection and playing.  Got a intermittent all in compassing hum on amp.  With the hum there is no music sound   A few times hum went away after first selection    Yesterday I took out selectomatic to look at and inspect wires for a short.  I took off all old fabric wrapping. all wires looked good.  I put back in.  First test I did not connect mute plug   Music played great out of both speakers with great volume control.   I turned off, plugged in mute plug and tested again.  Hum came back.   I turned off unplugged.  Hum still there when TSU powers up amp.   Looking for ideas.

[jukenorman]

I would say that you probably have some sort of ground loop. Also, iirc there is more to the mute plug than mute, there is also squelch. I think you need to trace the wiring from the plug back to the contacts which initiate mute and squelch, paying particular attention to searching for a stray ground where there shouldn't be one! You might be able to narrow down the source by connecting the pins in turn, using a small extension cable, to determine which one is introducing the hum.

Norman.