OK, I'm thinking about changing the tubes out in my QuatraValve. It currently has four EH 6550's. I can't really afford to buy the big bucks NOS stuff right now and would like to try something different than EH's. I'm thinking of going to Bob at Eurotubes and having him send me some JJ KT88's and some new high gain 12ax7's. Here are my questions: Has anyone here done the 6550 to KT88 swap? Will I lose/gain power or be the same? How do they compare (generally speaking) sound wise to the 6550's? What other brands of 6550's or KT88's should I consider? Any input would be much appreciated!