Hi; I've got a nagging problem with a 18W TMB MV head that I've had for several years and believe that it was constructed from a kit.
The noise problem comes as a sort of distorted hiss when the amp is well warmed up after a half hour of playing. It doesn't appear to come from the signal path but sounds like a bad tube does (more or less).
This happens as the amp is in the run mode and I'm not feeding a signal to it, whether the guitar cable is plugged or not.
I've re-tubed this thing more than once with fresh JJ's and just lately Mullard EL84's. Just can't figure what's going on and no amp technicians anywhere near.
Anyone experienced this or suggest possible troubleshooting tips.

Thanks...