Just when I thought 3rd time was a charm...I just received replacement power tubes for my amp. I put them in, and low and behold, the same friggin' problem. Any time I try to put in new power tubes for this amp, it starts crackling, popping, and making all of this static. What the hell could the problem be? The only tubes that seem to work are the original GT brand tubes that came in the amp (all models I've tried have been 6L6-GC type, exactly that the amp calls for). I measured bias both before and after the swap and adjusted after the swap to match the GT's bias. Both times I've tried to replace the tubes in this amp it's resulted in major failures (both times called for the output transformer to be replaced). I'm really not in the mood to deal with another amp tech right now, so I'll shop this problem out to you guys...anyone have any ideas?