@daniel777 I am not getting much of any heat build up. The tubes power dissipation seems to be low enough to not cause any issue. I believe less that 2 watts per 12ax7. I used my laser thermometer all over the chassis and one got maybe 1 degree over ambient, measured in room prior to starting the music, after an hour of running. Slid the top off to not disturb the air circulation and only hot spots were the tubes them selves at ~130f and the solid state components in the power supply. Near by components on the signal board did not seem heated at all.