I tried Sovtek KT88 in several amps, and did not like the sound of that tube, period. The Svetlana KT88 sounds far better, and the EH KT88 is very good also, though not as romantic as the Svetlana. I believe the Vacuum Tube Valley KT88 shootout is about 2 years old. The JJ-Telsa KT88 was one of their top tube choices. It's a great tube & very powerful, but it was a little analytical in my VT100, which needs the warming up of the Svet KT-88.
Better than KT-88s?
The KT-88 has always been my favorite octal output tube, 6550s being too harsh and EL-34s being too soft at the frequency extremes. However I just re-tubed one of set of amps with Sovtek's new 6550WE (RAM-tested) and have been most impressed. They seem to have the magical midrange of the EL-34 but with much better frequency extension and much tighter bass. I was completely unaware of this tube until recently but to my ears the KT-88 has some serious competition. Anyone else have experience with this tube?