I did a lot of rolling on this class tube, kt88, kt66, 6L6, 7581a, 807A, russian tubes I don't remember the number of, and they all sounded different. It seems invariably I liked the new sound (human nature) at first but after going thorugh perhaps a dozen sets of tubes, I ended up back at the tube that the maker (Decware, Steve Deckert) had designed the amp around. Makes sense really.
Jerry