Hum on Tube Amp - Can't find source

You don’t have the monos on separate receptacles, do you?

Any routers or wifi nearby? Dried out capacitors in amp power supply?

If you can disconnect everything and the amp still hums, I'd try a different amp.  Make sure it isn't the speaker that has the hum.  You've pretty much eliminated everything else.  

I guess you could put a power gneerator upstream such as a PS audio.  For a tube amp the Setllar 3 can be very affordable.

Jerry

There’s something going on if it’s happening to both of your amps.

A few weeks ago, my wife was in the basement and turned on a space heater. A while later, I turned on my integrated upstairs and it started to hum. It had never done it before and I had no idea she turned on the heater. It took me days before I figured out what had happened. I had to call the manufacturer.

They called it DC Coupling.

Do you have led lights?  Even Xmas lights can cause a hum.

HumX doesn't always work, cheater does.

@ervikingo 

Have a look through this document- maybe something helpful.

AES