persistent 60 cycle hum only on tube gear

I had hum like that that I could not figure out until I stumbled on the fact that the mesh network node was too close. Once moved to the other side of the room, the hum went away. In my case too close meant three or 4 feet away.

This is not helpful except in I feel your pain. I had that same problem with a pair of ARC amps years ago. I was not able to fix it no matter what I tried, so I sold them and stayed away from tubes for a long time. I have always been confounded by the hum of those amps. I hope you are able to fix the problem.

John 

@erik_squires 

Erik, I always enjoy reading your posts and replies.  You are very astute and intelligent, and your posts don't look down on others who may not be as up to date on the subject at hand.  Can you explain to me why an isolated ground is prohibited by the electrical code?  I am a babe in the dark when it comes to most things dealing with electricity -- I avoid that issue like the plague (I got a pretty nasty shock when I was a kid by a wire that wasn't grounded properly, so I'm pretty phobic about it).

I'll shut up and listen!  Thanks.

iFi makes a ground hum gadget. Sorry I don’t have model info, but it eliminated hum in my complex system.

I wondered and googled

"why is an isolated ground is prohibited by the electrical code?"  The result is to long to paste here. 

There is a rather exhaustive explanation of why it might be a bad idea.