Just some mean mains hum - what's wrong?

I've had trouble with valves/ tubes popping (probably oxide in the sockets or so, I think) and a glitching guitar cable. Then my amp went dead, apart from a mean 50Hz hum that responds to the volume control of my guitar. Thinking the cable finally gave up on me I fixed that and thought that would have solved the problem. Not quite so.

Any idea what the problem is? The fact the noise responds to the controls of the guitar baffles me. The guitar cable runs into my multi fx unit as first port of call if that helps.

Pre-amp: Egnater M4
Power-amp: Mesa Fifty/Fifty
FX: TC electronic G-system

Do you have the M4 in the insert loop of the G system ?

I'm having the exact same problem in my RM100. Here's hoping for some help!

if your running a g system in the effect loop of the amp or preamp, i highly recommend cutting the ground from one end of the cable from either the send or return to the effect loop. it basically will lift the ground loop that is causing the hum from the g system. that or try balanced cables.

You could also try one of these. http://www.ebtechaudio.com/he-2des.html

I run the smaller 2 channel unit with my GSP1101 in the loop of my RM100 for humming and squealing. Works like a charm and cheap on the Bay.