The recent Vacuum Tube Valley magazine compared several KT88 and 6550 tubes. The top tube was a KT88, but the 6550s were very close.
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?