I'll make 2 suggestions. The first is the one you asked for, talk to Kevin at Upscale Audio, he'll have whatever you may need in tubes. Secondly, use KT90's instead of 6550's. I replaced 8 6550's in my amps with KT90's and the improvement was dramatic. I heard Svetlana's KT88 is a killer tube as well, and is another tube which could replace 6550's. Visit his web site, he breifly describes each tube and has pricing. I think you just need to type in "upscaleaudio" under a search engine and you'll be there. Good luck.
