6550 vs KT88 vs KT90

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

I love the treble and midrange of the EL-34 but find the bass unacceptably fat. I love the bass of the 6550C but not much more. Trelja, how does the bass and midrange of the KT-88 or KT-90 compare with the 6550C?

Notwithstanding the above comments, the sound of the tubes is dependent upon the amp. I had KT-90's in my prior amp (Jadis Defy7 Mk4) and now have Svet EL-34's in my Manley Designer Ref 250 mono's. The Manley's have simultaneously better bass (pitch, tightness, extension) and a more lush involving midrange and sweeter highs. I know the power specs are quite different (250++ w/ch for the Manley's and 100 w/ch for the Jadis), but they are similarly priced. I'm not an expert (in any way shape or form), but I do find this an interesting thread. BTW, is it possible to experiment with the 6550C's, KT90's, and KT88's on an EL-34 designed amp? Manley also has a Designer Ref 500 amp which uses 10 6550C's/ch vs. the Designer Ref 250's 10 EL-34's/ch. For what it helps, the Manley amps are "designed with high plate voltage/low plate current".