120hz hum coming from all-tube system - but only at high volumes


I generally listen to my system at 8-9olcock on the volume dial.  A friend and I were pushing the dial up to 11-12 oclock and a fairly loud 120hz hum would start to appear after a while.

Bringing the dial back down would eliminate it.  You could then pushing it back up and it'd be fine for a bit and then then hum would reappear.

Do I have bad tubes somewhere?  Ground loop that only rears its head occasionally at high volumes?


(System is Manley Steelhead pre, Manley Mahi's mono amps, Forman Elite-15 PFi power conditioner, schiit yggdrasil DAC, Klipsch Forte IV speakers)
otherones
60 cycle… I am thinking is what you mean. All ground loops I have experienced have been at low volume or almost none. It is a trickle behind the scenes and does not increase in volume… it is like a, well little trickle of water behind the scenes. So, I don’t think that is what it is.
The power supply using rectifies and the 60 Hz gets doubled to 120 Hz… Hence I would be looking at the power supply side of things.

It could be a capacitor on the power supply side is bad, but that is mostly a guess.