I just found out today that the bias changes alot after playing for a while. The other day I re biased my amp right up to about 37ma and I thought I would check it today after about a solid hour of playing it fairly loud and all of tubes read about 42ma, i was very supprised, I quickly stopped and turned them down a bit. They sounded kick *** but ive herd this can burn out tubes. Has anyone else had problems like this?