6550 vs KT88 vs KT90

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

I replaced my Svetlana 6550C with the new Svetlana KT 88 tubes for my Melos 11 ST 90 amplifier and there is a very big improvement in the bass, midrange, highs, power output, clarity etc. Also, Svetlana KT 88 sounds way better than my former GE 6550A. Regards. Slore

Well everyone is right so far. Confused? You should be. The basics. The KT 90 IS the same tube as the GA KT99A, thought to be a wonderful tube. The 90 provides about 15% more output power than a KT 88(more headroom). It also seems to extend the bass down about an octave. It also sucks out some of the midrange and provides less highs than the 88. There also seems to be increased intermodulation distortion in the 90 but that could be a product of poor matching. Lastly, the 90's are generally bullit proof. They will handle a much higher plate current which means they can be biased higher. I have little experience with 6550 save to say that they have a weaker bass than the 88's and a purer midrange. A tube that you may be able to use that you have not mentioned is the E34L. If the plate current of your amp is low enough these tubes will give you much more of what you have gotten into tube audio for. Far better midrange bloom and life. A purer tone, the best sound hands down HOWEVER, it is likely that you will reduce the output power of your amps by about 30%. If you can try these you should. Also they are cheap.

I have experince with both tube types. I have run both KT88's and 6550C's in Cary and Audio Research Gear. A KT88 will give you more top and bottom end at the expense of a more analytical mid range. If you are a R&R listener KT88's will sound better to you, for all else the 6550C's are superior, especially NOS types.