Mesa Boogie Mark IV hum issue

[baerman]

I have a Mark IV that I replaced all the tubes in with JJ tubes. I plugged a Digitech GNX4 into it and used the Channel 1 to try to get some rectifier tones. About 30 seconds into my experiment I started getting massive amounts of what I can best explain as grounding noise. I disconnected the Digitech and played the Mark IV and still the noise exists on all 3 channels. The amp sounds fine with the exception of the hum. The amp is plugged into a Furman for power and someone,(an electrian), suggested that I try one of those cheap 3 prong to 2 prong adapters. Tried that and it didn't work. Also tried changing the ground on the back,(A/B switch). Do you guys think that it is possible that I damaged a tube? My dad has an old tube tester,(retired electrical engineer) and I will go that route, but if I damaged a tube or tubes which would it be 12ax7 preamp or 6L6 power tube? I'm planning on taking my amp in for service to have it gone through since it's 20 years old. I just like to know what kind of problem I may have because I don't want to be jacked around by someone who is just guessing and figured someone here may have some experience with this same issue. Thanks in advance

[avi8r2005]

check your instrument cable first. You may just have a bad cable. I had a mark IV and it also had a bit of humming to it as well. Also if you are playing close to any flourescent lights, TV, stereo or such, that can cause interference. If none of those are the culprit, try swapping around your preamp tubes if you have any spares.

[Metaldude30]

Yer first problem was plugging a digitech into a MarkIV, it probably went WTF and now is getting back at you for such blasphemy!

[baerman]

I know it was blasphemy, but I love the sounds in that GNX4. It's part of a smaller rig that I use with a Fender Combo. Just experimenting. I will try new preamp tubes. Thanks