I'm a long time st-70 owner and first time poster, and I'm looking for some help in diagnosing a problem(s) with my amp.
Aprox. 6 years ago, I replaced a bad driver board with one of those sold by Triode Electronics. I also opted to run it in triode mode. All was well for a year or so, and then I put the amp in storage and didn't use it until last year. When I took it out of storage and put it back into use, I noticed that it didn't bias correctly -- I couldn't get it *lower* than about 1.95V when it was warmed up. Also, it would eat a rectifier tube every few months or so (which I would know had happened because it would start to blow fuses). Yesterday, I replaced a blown rectifier and after maybe an hour of use, the left channel of the amp went dead.
I've done basic troubleshooting (switching tubes, cables, etc) and that yielded nothing. I opened it up and tested voltages at 3 & 4 of the EL34s to check for a possible bad output transformer, and they were in the 530 - 540 range (which is high from what I am reading).
Okay, that's the extent of my knowledge. Undoubtedly, I should have explored the bias problem and the blowing rectifiers before something failed. Any help would be appreciated!