Tonight I played my Rivera K100 at practice for the first time. I installed brand new power tubes on Sunday, a matched set of GT E34L's rated #4, and biased the amp just under factory specs. Rivera calls for 40 mA, I biased to 38 mA. After practice I went behind the amp to unplug everything and noticed it was pretty warm back there. It doesn't appear the paint on the tubes wore off, and I could still touch everything (except the tubes, of course), but it sure seemed pretty hot. So, assuming the bias is set correctly what would cause a tube amp to run hotter than expected? I used my 8 ohm cabinet and set the amp accordingly. I used good speaker cable. Maybe this is all in my head?