Although I said there was no way to balance output tube sections in a previous post, I realized recently that I was mistaken. In the amp I built there is no way to adjust because I built the output loads with fixed resistors, however since the published schematic has adjustments in the output current loads, this can in fact be used to vary the cathode-to-plate voltage individually for each output section by slightly altering the current running through each section. The concept is, start with the output current loads fixed, adjust the cathode current sink to approximately zero the output plates, then vary the current loads to adjust the offset between + and - voltages for each channel. The three adjustments are interactive, so, it would probably be best to adjust one of the current loads to partially decrease the offset, the adjust the other in the opposite direction to further decrease the offset until that is balanced, then adjust the current sink to zero both plates.