Sorry if this is explained somewhere but I searched and could not find. Most of what I've read elsewhere is too detailed for my simple mind. Can one of the valve people please tell me in simple terms what the fundamental difference between a KT88 and a 6550 is, specifically: 1) KT88 beam tetrode v 6550 beam output pentode? 2) can both of these be run in triode / ultralinear? 3) typical differences in sound signature / power output? 4) bonus question - does anybody know who makes the current production Brimar labelled valves? Feel free to treat me like I'm stupid Cheers.