My (TriodeUSA) ST70 is clipping on both channels at around 22W as carefully measured by oscilloscope. Only the phase splitter has been changed (to a nicely balanced 12AU7A) since buying the amp used. Came with new looking JJ EF806Ss and EL34s. I changed out the phase splitter because the negative half of the signal was distorting long before the positive. With the RCA clear top 12AU7A the waveform is symmetrical but still clipping around 22W.
Lately, the left channel bias is moving day to day. I aim for .700 on each side. I check after about two hours or so of listening. One day the left will be at .675 (right moved up slightly as expected but not by as much) and the next day it will be at .715, right lower by a bit again as expected. Is this excessive movement day to day?
Is it time for new power tubes, new EF806Ss, or both?
Or should I be investigating other areas?