When were the best tube amps made?

Any amp that can't even reproduce a simple sine wave doesn't count. If the negative half of a sine wave doesn't go down as far as the positive half goes up the amp is non linear and may be musical but it's not fidelity. If it does that to a sine wave think how poorly it will do on much more complex music wave forms. By the way this means every single ended amp and it's not curable since it's inherent in single ended topology.

Since I've gotten mentioned in these discussions I'll cite a few good tube examples.

CAT has a superb reputation and I've heard this from other tube designers I know and respect.

David Berning is a genius. His ZTOL circuit is one of the few real amp inventions in decades and his amps are special.

And I'm biased(pun intended, since the designers were good pals) towards the now, defunct Melos amps. Tube monoblocks with over 400 wats in triode and 25 watts class A and a damping factor 0f 20 from tubes, all from just 4 output tubes is something special. And the 400 watt rating is one pulled back from higher ratings for reliability.

And I know I'm missing at least a few other good tube amps.