I've been considering the advantages/disadvantages of a plexi-type amp built to run kt66 instead of el34. First off, I know that to some degree this is splitting hairs. It's my understanding that the power section offers no difference unless the amp gets cooking pretty hot. If I'm going to get an amp built though, I want all of the parameters just the way I want them. Frankly, I can't decide on the kt66 vs el34 power section. It then occurred to me that the kt77 might be the answer since (as far as I know) it can be optimally run on a transformer selected for an el34. This means that if I don't like it, there will only be minor tweeks to put in an el34, rather than a different transformer. Now, as for the differences between the tubes. Performance wise, is the kt77 more like the el34 or the kt66? It's my understanding that it's essentially a kt66 but with more pronounced mids. Is this the case? I have seen the archived threads that address this, but I'm still not clear on the issue. Maybe this is because no one is really clear on it. I.e., the differences are so subtle b/t the kt66, el34, and kt77 that it's hard to pinpoint what the differences actually are. Someone says that the kt77 essentially sounds like the el34. maybe this same person would say the same about the kt66. I don't know.