WRONG OHM IN MY 210 65 12ax7. HELP!

Hallo, I solved all problems with blowing fuses. It was the tubes. I changed transformer (was NOT original) with a fantastic mercury magnetics (designed for this particular amp). So...it sounded fantastic for 3 concerts and 4 rearshals. my setup is gain channel 3, master 10. no pedals. last time I played it, I turned it on (in stand by mode) and then wait for soundcheck. about half an hour or so. when I taken it from stanbby mode and started to play it, the sound was out of focus, thin, with low volume and a really fast and buzzy decay. I checked the back panel and then realize the horrible thing: the ohm switch was in the 8 position (don't know why) and the tubes was glowing really red. Turned off the amp. switched to 4 ohm. and when I re-turning it on the sound was better, the tubes were normal in light, but after 2/3 min started to sound bad again.
turned it off for an hour or so (before concert), then played the first song of my gig (really loud), and for the second song I had to change the amp, according to my partner, the sound was horrible.
The day after I brought the amp to my tech, and stayed an hour with him playing the amp loud to check the problem. But this not happened. I explained the chronicle to my tech, so he checked all the inside,then measured the tubes and the transformer, but he saw nothing wrong.
Anybody had my same problem? Could a transformer with wrong ohm, come back good after a night (if the problem was the transformer)?

I would suggest first off checking the bias voltage. Were BOTH tubes glowing red or just one? If one, try checking and re-tensioning the socket. If both, maybe you're running them too hot OR the PI tube has gone flaky. The MM's in the past had a problem with the PI and would do this. It was one of the reasons that they went to the SS driver. Bias, re-tension, change 12ax7 to a KNOWN good one. Mike.