KT-88 KT-90 KT-100 6550 which has the best bass?

It depends how you describe best bass. In my experince with a Graaf tube amp, the 6550 was a warmer more musical sound but the KT-90s were more dynamic and punchier, but lost the magic in the mids. Could be the brand of tubes used also.

Happy Listening

I went thru the 'tube flipping' phase several years ago. In a c-j premier 11, I replaced the 6550 with a quad of the the kt90 series. Yes, I had some extended bass, but lost some sound stage. I really recommend using the tubes recommended by the manufacture of the equipment. The sound will be different, but not necessarly better!

I'm with Bigkidz. It depends on how you define "better bass".

I have KT88 and KT90 tubes, and consider the bass of both to be excellent, though quite different. The KT88 is punchier, warmer, and bloomier in the midbass by a significant amount, and not as extend. It is more classically tube. The KT90 is more evenhanded, leaner, taut, and extended. It's kind of like comparing the tube and solid state sounds. KT88 tube, KT90, more like solid state.

Again, depends in part on the electronics, though Joe and I both have used Jadis as a reference. In my JA80s, Joe's (Trelja's) and Peter's (Bigkidz) descriptions of KT88 vs. KT90 are accurate; I found 6550s (Svetlanas and Philips) to be a little fuller and warmer than the KT90s (EI Type 3), but nowhere near as rich and full as the KT88s (Gold Lions) and lacking the finesse of the other types in the midrange and highs (more of a brute force-type tube, may have a little more power). For rock at loud volumes, I'd go with either the 6550s or KT90s, depending on how lean or rich you like your sound.

Oh, David(by the way, how have you been?), I forgot to talk about the tube companies, since you mentioned EH and Svetlana.

In my experience, I have only tried the Ei KT90. They are no longer produced, thanks to the NATO bombing in the former Yugoslavia, but still available. It looks like EH is beginning to make them. It only makes sense, whenever you see a group of people fret over something no longer being available, it's wise to bring that product to market.

As far as KT88 goes, I prefer the JJ, which seem to have that punchy bass and beautiful tone. Svetlanas sound more neutral and 6550/KT90ish to me, though still a recommended tube.