Scope the bias supply too. Loss of filtration on that can cause plenty hum. ANd make sure the LV rail for the trem/reverb is clean too. The trem bulb could even inject some hum if the rail is hummy.
The volume control is right at the first stage, so the whole amp is between it and the speakers. DO the EQ controls affect the tone of the hum? if not the hum comes in after them. How about a hummy 6AN8? Pull the thing - the PI - and listen. Any hum now is pure power tubes.
Isolate the problem.
Power? That amp uses their 60 watt OT and 60 watt PT. That's a clue.