Well today we fired it up and the bass amp worked great for about 45 minutes then just totally went to shit. Horrible distortion (VERY loud crackling and grating noises) kicks in when the amp is pushed to anything beyond quite operation. I'll try and replace the old tube tomorrow to see if maybe I got a bad tube. I hope the output section of the amp didn't get shorted out. The distortion comes out in the amps speaker level outputs and the balanced XLR as well. At first the distortion was heard as faint crackling in the PA then within 10 minutes the damn thing went nuclear and had to get turned off.

The old tube is a plain old Groove Tubes 12AX7. Could this malfunction be from not having the amp re-biased? I understand that the tube can wear a bit quicker but an hours worth of playing? I bought the tube from a local guitar store, but I honestly don't think the tubes where individually tested there.

I hope this doesn't get expensive

John