A couple of months ago I bought a Dennis Had Inspire SE "Fire Bottle" HO (high output) pentode based amp of recent vintage, and have been rolling various tubes through it…note that this sort of amp has only 4 tubes so rolling is el-cheapo. So far I've noticed differences between rectifiers…234B, GZ34, and a 5Y3S…interesting…more bass, less bass, soundstage changes, etc., and output tubes including KT88, KT77, KT150, 6550, and parts of an old toaster (not really, but uh…). The amp came with a NOS Amperex 6SN7GTB, and I tried another of the same type of Amperex of a different design (getters on the side or top or something) and those sounded identical. Everything seems to change a little or more than a little, and all of it is fun. Note this amp has lots of dynamic juice in its massive 12 watts per side, sounds better than any amp I've owned in over 5 decades of gear silliness, and proves once again that "everything I know is wrong."