I have a Mesa "Buster" 2x10 Combo powered by (6) 6L6GC power tubes. LOVE it! The original tubes were Svetlana STR-454's, no longer available/used by Mesa. I recently had the amp re-tubed by Mesa with a new sextet, they now use Chinese STR-441's. The amp still sounds way GOOD, and I'm not a tube snob, however to my ears, there is a difference. It's my understanding the Mesa amps are designed to use their tubes only,-I also recall having seen some tube suppliers who made aftermarket tubes available that would be compatible with Mesa-Boogie. Having searched the 'net, I can't find any. Is anyone aware of any suppliers with Boogie-compatible Svetlana 6l6GC STR-454 tubes? PBG?? Anyone? Thanks in advance. 'Deal.