Recently built 2 monoblocks. Built them first to make sure they worked, then added an autobias board (erhard audio). I wired leds so I can see the lights with the system closed up. On one of the monoblocks, after some amount of time - usually 45 minutes to 90 minutes, the 2nd light goes out. Only once have I measured the bias voltage when that happened and it was up around .8 instead of the .5 I set on the board.
- using kt88 tubes
- sprayed deoxit in the 2nd tube socket
- swapping tubes - problem stayed with socket 2.
When things start up all voltages on the sockets are consistent. Resoldered all connections to socket 2, and all connections related to installing the autobias board. Any advice on diagnosing this? Thanks.