though. I have read that the KT90's tend to have a more solid state sound and less of that tube warmth. I am sure someone will let me know if I am wrong.
It could depend on the KT90. I have the Ei KT90 type 2 and with the stock input tube they sound 'steely' in the highs. With the 5751 input the Ei's are amazing. And the power WOW. So I will say with the right compliment of tubes they sound very powerful and tubey. I haven't tried the EH KT90's.
As far as the Eat's the tubes that have a serial # that starts with 'D' had the most trouble. The pair I have that start with 'E' and they are rock solid. Just received some Gec KT88's and they sound very close to the EAT's.
Another great tube but very different (IMO the most 'tubey' sound) is the original Tung Sol 6550 solid black or grey plates.