Mark IV Ground Problem?

[hagcel]

So I have a ton of noise coming out of my lead channel.

With nothing plugged in I get no noise.

With a cable plugged in I get a fairly loud sizzle. If I touch the tip it gets really loud. If I touch the sleeve or base of the plug the sizzle goes away.

If I do nothing and just leave the cable hang there sizzling after about 5 minutes or so the sizzle disappears for about a second then comes back - and repeats this over and over...

If I dime the masters on the other channels I can get a hint of the sound.

Also, I just installed Mesa Yellow 6L6s but it was doing this before...

Thanks for any help!!

 

[swbo101]

Going to ask the obvious questions first. Have you tried different cables and different guitars?

 

[hagcel]

Oh yeah I should have included that. I tried different cables, tried the ground switch in A and B. Tried a few different guitars...

The weird thing to me is that the amp does it when no guitar is connected and that is disappears for a few seconds then comes back in, sizzling a little more roughly at first then settles in to a constant sizzle...

 

[swbo101]

One other thing, have you tried it in multiple outlets? I've heard of grounding issues that were related to an outlet.

 

[Boogiebabies]

Could be a preamp tube issue. Replace one at a time until issue resolves itself.