I have noticed that the bias voltages have been wandering on all 4 tubes. Not a lot. Set at .496, for example, it might wonder up to 51 or so. Sometimes they are down in the .47 range, even though they were set at .50 previously. This will happen in a day or two of operation, running 4 to 6 hours. I check the bias after the amp has been on for at least an hour.
I was out of town for 10 days and my wife reported she was listening and heard a loud pop or bang. She shut it off.
I got home and turned it on. It sounds OK. But one of the output tubes now is biased at 0.62 and the range of adjustment won't let me get it any lower.
Any of your comments or suggestions would be appreciated. I'm a wiz with a soldering iron and can follow directions but I don't have a great deal of electronics knowledge.
Thanks!