I have tried all three tubes. (A)sevtlana 6550C, sev KT88 and the KT-90 type 3 from kevin deal. Iam have spent 9 months with the sev 6550c, 1 month with the kt-90 and 1 month with the sev KT88 on my Jadis Defy 7 amp. The overall winner, in my opion, the Sevtlana KT-88. 2nd place the sev 6550 and my lease favorate were the Ei kt-90 type 3. The last was a suprrise since it has alot of hipe. Evem thouth the kt-90 had great bass and a more lively upfront sound it was the least musicsal. The KT-88 has a lush and sweet midrange and high frequencys. The sev 6550c have great base also with more bottom end slam, although it lacks the clarity and sweet midrange of the kt-88. Both are excellent current production tubes. As for the kt-90's buyer be wear. Some may like it and some may not. It sure sounds different. The Sevalana tubes in general are more musical but none are perfect in every way. It's always tradeoffs but overall most I feel will really enjoy the new Sev KT-88. Good Luck, John
