Fender 6G6-B Bassman hum

[rf7]

This amp has a hum on the Normal channel that is only heard when the volume is turned above halfway. Cranking the Treble pot makes it worse. Grounding the input to the first tube in that channel does not affect the hum. Grounding the top of the Bass pot does not affect it. It seems to be coming through the Treble pot into the Volume pot.

It looks like 60Hz on the scope.

Any ideas?

[Enzo]

Start moving wires around, particularly those to the treble pot, since it seems central to your issue. Most older pots will ground their case to the chassis by the mounting nut, but someone may have replaced that pot and now the rear cover of the pot is no longer grounded. Possible here?

[rf7]

Moving the pot wires for the Normal channel away from the Presence pot wire cut the problem down to an acceptable level. Thanks Enzo!