Thanks for the warm welcome and good info nivek! I sure am grateful, I can play with the amp tomorrow
I noticed the suggested bias values from the tech corner, really nice for Diezel to put them there. The 6550 and KT-88 use roughly the same bias value, I guess the 6550 is just a modernized version of the KT-88, but having the manufacturers spec sheet and then using the 75% from max current as a guideline should be the best way to bias it, then again I rarely go past 9'o clock on my amp so I doubt 1mA there or here will make an audible difference...
I'm going for the 2x sovtek KT-88 2x Sovtek EL-34 set but I'll see how it runs in 50W first, if it's good, what I think it will be, I'll use that setup for a few months. The winged C 6550's in the einstein do sound awesome, so apart from the premature failure of one, I think I can almost trust them as it might have been the tube retainer that caused the tube to get air in it and burn the filament.
Seems like they don't make tubes like they used to... This gets me to another question: Are groove tubes really any better, or is the price higher just because it says "Groove Tubes California" on the side? I mean if I invest ~300USD instead of about 200USD for a quartet of TAD's 6550's, or around 100USD for just some random 6550's or KT-88's off the shelf, will the GT's sound 3 times better or is it really marginal? I'm using the amp at home, through a 2x12" Celestion V30 cab, and I intend to change the tubes every year or every other year. I don't have a thick wallet, I'm still paying for the amp.
Oh, and better late than never, Merry Christmas! And a happier new year
Regards,
Kristjan