6550 vs KT88 vs KT90

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.

I am using Ei(Yugo) KT90s currently. Please be advised there are 2 KT90s, the older version, and the newer(current) version(3rd generation). The two are NOT compatible. Also, beware the prices of KT90s are really high. The reason is the factory was bombed during the 1999 NATO campaign. I have heard no positive news regarding improvement in this situation. The KT90 is the largest non-triode ouput tube used in our hobby. It offers the most power and bass response of the three tubes discussed in this thread. However, there is also a negative to this, it will not physically fit into MANY amplifiers, as it is too tall. This is not an issue with exposed tube amps(such as Jolida, Jadis, etc.). The old version was criticized for being bright and harsh. The new(current) version does not engender the same response. I would submit that someone at all interested in 6550 tubes should use KT90, if possible. KT90 betters the 6550(A or C) in all areas. The KT90 also is a bit tubier in its midrange, yet offers an extended(the most of any tube?) treble. The 6550 is the least loved of the bunch, by many tube lovers. It is a good tube for a neutral(like Audio Research) sound. But that does not make for a cult following. If a sweeter tone is desired, at the expense of power and bass response, the KT88 should be tried. Both Svetlana and JJ(formerly Tesla and Teslovak) versions are excellent. The Svetlana brand are a little warmer. E34L is a higher output version of EL34 from JJ. Otis is correct about them. Use these if you are searching for the "classic" tube sound. Warm, euphonic, less control of the bass frequencies, etc. Svetalana EL34 are the warmest, followed by JJ EL34, then by JJ E34L. In general order from warm(and sweet) to neutral: EL34, E34L, KT88, KT90, 6550. In order of price: EL34, E34L, 6550, KT88, KT90. EL34 are half the cost of 6550. E34L a little more than EL34. KT88 cost a bit more than 6550. KT90 a good bit more expensive than KT88. Note: JJ E34L and KT88 tubes are available in clear(standard), red, or blue glass, so you can even use them as mood lighting.

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