Thanks for the input guys. Running one 6550 and one KT88 per channel certainly sounds different than running all 4 tubes as the same type. As I would expect, it sounds like a cross between the 6550 and KT88. Running all 6550s, the sound is nice, but I would describe it as very warm, and not very authoritative in the bass. The bass quantity is there, but it's a bit flabby. Mixing the KT88 with the 6550 brought about tighter bass response, and more extension in the treble.
My only fear is that running one of each will ultimately reduce the longevity of both tubes. On the other hand, I may be able to get more use out of 6 tubes (2 KT88s, rotating the 4 6550s) than if I were to just run all 4 6550s until they burned out.
My only fear is that running one of each will ultimately reduce the longevity of both tubes. On the other hand, I may be able to get more use out of 6 tubes (2 KT88s, rotating the 4 6550s) than if I were to just run all 4 6550s until they burned out.