Hi,
I recently installed a diy driver board(rev.B) in my st-70, which already had an older sds capboard installed. Since this upgrade the bias drifts, even after a 2 hour period. For instance, if after 2 hrs with it biased at say 45ma.
I turn it off, the next time I turn it on from cold the bias will start at 54 ma.
and slowly drop. Is this normal? Also after zero-ing the voltage between tubes, this value drifts as well, not alot, but enough to make me think somethings not right.
power tubes are sed winged c
drivers are a pair of rca cleartop 12au7
phase splitter is a tele 12ax7 smoothplate, all test strong
meter is a fluke 75
wall voltage is 120v
Also the voltages at all tubes is a little low
thanks in advance for any suggestions,
scott