I have a POWER 1 amp. I have tried the Svetlana KT-88's and pulled them out in favor of the stock Svetlana 6550C tubes. I then e-mailed PartsConnexion about this, and they informed me that I didn't really have Svetlana KT-88s. What I bought was basically Sovtek tubes, made in the Reflektor factory. Apparently, because of some legal issue, REAL Svetlana KT-88's are sold as "SED Winged-C KT-88" tubes. PartsConnexion recommended JJ Tesla KT-88's most highly for the POWER series amps. I have a set arriving tomorrow and will post again with my findings. I haven't tried replacing the 6922's yet, but I plan to try that soon. My inclination is to get Electro-Harmonix gold pins to replace the stock Sovteks. I've considered going the NOS route, but every time I think about it seriously I feel the neon "sucker" sign going on over my head.