6550 vs KT88 vs KT90

I'll throw in my two cents, since I've got amps (Jadis JA 80's, vintage about 1990) which can use a few of the types mentioned. I agree with Greysquirrel that it depends on the amp involved. My amps won't run with the KT-90's (at least Frank Garbie said it would not be a good idea), and as between the KT 88s and 6550s, I prefer the former. The best 6550's I've used (old ARC Phillips and Svetlana 6550Cs; couldn't afford the Tung Sols, and the GE's just sounded ordinary) probably control the bass a little better, but ultimately sound leaner. On a rich balanced speaker (my old Duntech Princesses, for example), this was fine, but on a more neutral speaker they could sound too thin. The KT88s I use (old MO Valves) are much richer and more harmonically correct in the midrange, with good bass and a wonderful sweetness--the classic tube sound, I suppose. I'm curious as to how the new Russian KT88's stack up against the vintage tubes. My gut feeling is that the older Jadis amps were designed around the older KT88s; in fact, I believe the newer models may have been designed, particularly the transformers, around the KT90's. I've heard the newer Jadis amps with the KT90's, and they sound terrific. So I'd suggest you take the amplifier you want to use the tubes in into account. Hope I haven't confused you even more.......

Trelja: Thanks, I'll give that a try. On the reliability, the newer KT88s, particularly the Chinese lower grade makes, have had reliability problems. The vintage stuff is a different story. All the 6550s I've used in the JA80s have started going bad, and blowing the protective fuses, within a year to 14 months (in my ARC Classic 150s, the same Phillips tubes lasted 5 years). I've had the KT88s in there for over two years now with no problems. I must admit having a preference for the MO Valve KT88s, even over the KT90s I've heard in Jadis equipment; just a matter of preferring the darker sound, I guess. But the prices.....

I'd suggest you ask the manufacturer of the amps directly. The new Jadis have transformers optimized for the KT90s, but I believe that VTL amps can use both 6550s and KT90s, so I don't know if you have to have a transformer specifically designed for that tube. The manufacturer will be able to tell you what he/she thinks is the best tube for your amps.

Trelja, just a note to you to mention that Jadis replied that the KT90s can be used in my old JA80s. I may get a set for when I run out of the NOS KT88s. Anyone with experience on how the new KT88s stack up against the older ones, sonically?