6550 vs KT88 vs KT90

Don't know the answer to your question on comparisons, but I run Svetlana 6550's in my Sonic Frontiers amp and love them. They are detailed, and smooth. In the SF, they don't have a strongly "tubey" sound because of SF's design. They produce a lot of bass, as well. I'm very pleased the the 6550 tube. The KT90 can be used in SF equipment, but require careful biasing, according to the manufacturer's tech, so you might be cautious in setting them up if you try them. I'd be curious to know how much you like them, if tried. Sovtek has had the KT88's for quite a while, but I've been so pleased with the 6550's that I haven't "rolled" them. Good Luck in your quest for info. I'll be watching. Stu

Hello, According to Kevin deal and others the KT-90 By EI seems to be the premiere output tube. The Svetlana 6550 is a solid tube and seems to be preferred over the Sovtek KT-88. I am interested to see a review of the New Svetlana KT-88. http://www.audionow.com/download.htm

I had VTL retube my Deluxe 300's w/ KT90s when they were first available as they had my amps for upgrades anyway. I think that was 6 years ago and they still are sounding good and biasing out fine. There were some dramatic improvents and tradeoffs from the stock 6550A's, though I did not have the amps very long before the repair/retube. My recollections on the differences are that the KT90's are more detailed and tighter bass in my amps at the expense of being more analytical and less "warm" sounding. Be careful, as I do believe there are 2 incarnations of KT90's that are not interchangeable. My tubes are designed to idle @ 300mv, and there are some that idle at twice that. I was on the phone with VTL 2 weeks ago and they told me that they are now usng what they feel betters them all, the 6550C's. By the way, if anyone wants to make me an offer on 14ea 6550A's (red VTL stamped), they are for sale. Unfortunately the only way to determine what YOU like with your amplification is the expensive way - try them all )that are compatible with your cicuitry). Good luck. Alan Tempe, AZ