what Robert said. While different tubes have different characteristics, its difficult to predict how different tubes will sound in different products. Heck you cant predict 100% how different samples of the same tube from the same manufactuerer will sound, let alone different manufacturers. I will say this however, I have heard more amp designs over the years, that got more things right than wrong, with KT88/6550s, EL34s, and 6L6 varients. But the thing is you never know until you try.