1992 pittbull trouble

I have a vht pittbull classic 100watt head. The overdrive channel sound fizzy and is losing volume the clean channel sounds great. I have changed all tubes and rebiased the power tubes, changed all guitar and amp cords, still overdrive channels sound bad. any ideas thanks for any help

It's hard (for me) to say what could be the problem. You'll probably need to take it to a competent tech. Look for recommended techs in your area.

Hi, look at the preamp tubes. Are they all glowing? You can also try to clean and tighten the clamps on the preamp sockets.

Petr

All the tubes are glowing, one tube the 12AU7 when first turning on the amp it lights up real brite then goes to normal glow. The only tube that does this. The only tube I have not replaced waiting on a new one I ordered. Not sure what this tube does can't find much information on this amp. all the other tubes are 12AX7 preamp tubes. Would this 12AU7 effect the overdrive on the amp?