6550 vs KT88 vs KT90

From what I hear, these tubes are interchangable on most amps it seems that the 6550 is the least loved tube of the bunch. What are the sonic differences of these tubes? Thanks in advance for your reply.
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
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
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".
Great Thread. This is all very interesting to me having just bought my first tube amp, a Cary sli80. Ilove it, it's got 6550's, and I've been wondering whether to try some 88's. The first thing I decided to do was try different 6922's & 6SN7's. I wound up ordering some Tungsram 6922's and Raytheon 6SN7's. Looking forward to hearing a difference from my Sovtek & Chinese, at least I hope I hear a difference! The KT88's will be the next switch.
Krys, I found the KT90 to have the best bass of the three, far and away. Comparing the 6550 to the KT88, they are very close. I might say the 6550 to be a hair better, but that is probably only because of the KT88s sweet midrange. Drawing your ear to the mids(and possibly away from the bass just a bit).
Great thread Jman-- and so CIVIL. Hi Trelja and Greysquirrel. As a (sometimes) tube amp wannabe, I'm afraid I have nothing to contribute-- except questions. I have a SF Line 2 pre-amp and have done a little tube rolling with it, and I'm considering a SF Power 2 amp (I'm not really set up for mono-blocs). Is the amp design or the tube type more important, re: the comment Greysquirrel made on amp design? I read the Stph review of the Power 2, but don't remember what tube type is standard, just that it is quite neutral as opposed to tubey, but I've assumed that this can be changed with a simple tube change? Any comments on the Power 2 and its tubes? I especially appreciate peoples assessments of bass quality of the various tube types because I have a big SS amp with excellent bass (McCormack DNA-2DX). Hope this post isn't stepping on your thread. Thanks. Craig.
I think they are both equally important. The most important aspect of a tube amp(in my experience) is the transformers. It is by far, the most expensive functional part of a tube amp. This is what separates Jolida from companies like Air Tight. Yeah, they both use the same tube type(EL34, and same tube once you retube the Jolida), but there is something that prevents you from attaining that same level of sound for the two. Transformers are as different as anything else in the amp. If we would allow that interconnects have a major effect on sound, then we also have to give transformers their due. They have several orders of magnitude more length than a 1 meter interconnect. Like most cables, most use different wire, and different construction. We also have to consider the circuit design, parts quality, etc.(things we NEVER mention with tube amps). That being said, we take tubes seriously because it is the one area of the amp we can control. Like different brands of gasoline yielding different performance in our cars(we can't change engines). We get different sounds from different tubes. Garfish, if you need to maintain the level of bass you are accustomed to, you need to look at amps with the larger tubes(6550/KT88/KT90). But, please go out and listen to an EL34 amp. There is a tube magic in many of them that is quite addictive. You may find yourself with two setups.
Great post Trelja! Hi to you too, Craig! I agree that the transformers must be an important aspect of tube amp designs. So much depends on an amp's ability to recover (and not introduce nasty harmonics in doing so) from transients / dynamics (even relatively low level ones). They really make or break an amp. Though my experience is fairly limited (own a Manley, owned a Jadis Defy7, and listened in my system to ARC VT100 MkII and VT200), I can't deny the magic I'm hearing through my EL34 based Manley amps, especially with the Svet EL34's. Craig, my good friend has a DNA2 LAE with Rev A from Steve McCormack. It is by any solid state standard a top notch amplifier IMHO. I LOVE that amp. In several ways, I felt it bettered the ARC VT200. However, after listening to my amps for a few weeks in his system, he is making the switch to tubes. It is definitely worth the experimentation to find a tube amp that "does it for you". Good luck and great thread! Jordan
Sorry Craig, forgot to comment on bass. I think the bass from the DNA2 is tighter, but not better. Oddly enough, when directly comparing the ARC VT200 to my friend's DNA2, I thought the ARC better portrayed the sound of a double bass and other low frequency instruments. I won't wax on the "magic" of my Manley's, but I'd say the ARC is better than my Manley's overall. Tube amps can do bass "right" in the right system! Hope it helps. Jordan
The "Electronic industry" (Ei), has been rebuilt, however, the economic "sanctions" are still in place, and who knows how long? I may be able to get some KT-90, and other Ei products. E-mail me with the questions if interested!
Thanks for the offer Eldragon! Ei tubes are available. In fact, Jadis informed me that they see no potential problems with supply. However, the sanctions will probably hurt us in the USA. No one will care because this is such a minuscule hobby. But, last year the price of a matched quad of KT90s was $96(in a Stereophile ad), within 2 months it went to $150. I am not sure where it is now, but buying from a high end dealer or Jadis will be over $500(as of February, 2000). I am just happy they supposedly last way longer than we usually expect tubes to last.
Trelja; thanks much for the specific info. on the big amp tubes. Jordan, it was particularly good to hear your comparison of the DNA-2 with some good tube amps-- and glad to hear that tubes can be competitive in the bass. Thanks, and Cheers. Craig.
Trelja i guess you like your Jadis...? How detailed they are? I heard, earlier models had somewhat "sloppy" bottom? Regards!
Eldragon, I really love the Jadis. I have listened to many a product out there, and have EXTENSIVE experience with three in particular(Audio Research, Jolida, and Rogue). And, to me, the Jadis was a clear choice. I am somewhat surprised to hear the bass comments, because even when I had NO interest in buying a Jadis(late 80s - early 90s), the great bass(compared to other tube amps) was one of their main draws. I feel the bass is very good. Up there with any tube amp using 4 output tubes(can't compare to some of those BIG monsters using 16 or 32 tubes, obviously). And certainly, the best of ANY real world tube integrated. I believe it is a product of their massive transformers, large capacitance, and the KT90 tubes. It also has tone controls, so you CAN jack up the bass a bit, if ever needed. The amp is as detailed as I have been around. I hear things in music I have never heard before. CDs I have listened to hundreds(on various equipment) of times reveal new information. I am always amazed at cymbals, in particular. They are rendered with SUCH crispness, I always wonder why I haven't heard before. The detail may be a product of the passive preamp section. I like the combination of a passive preamp section into a tube integrated. The C - J CAV50 also does well using this combination. But, the Jadis is a MUCH better product. My main complaint with the C - J is its lack of power. Others complain about it being OVERLY warm, but I find that endearing of the C - J EL34 based amps. I imagine the Jadis could become quite warm with the Svetlana EL34s, if you are into that sound(I've yet to try).
Thanks Trelja, i have no reason not to believe you! It must be a great amp! Something i will seriously consider in the future! Regards!
I'll throw in my two cents, since I've got amps (Jadis JA 80's, vintage about 1990) which can use a few of the types mentioned. I agree with Greysquirrel that it depends on the amp involved. My amps won't run with the KT-90's (at least Frank Garbie said it would not be a good idea), and as between the KT 88s and 6550s, I prefer the former. The best 6550's I've used (old ARC Phillips and Svetlana 6550Cs; couldn't afford the Tung Sols, and the GE's just sounded ordinary) probably control the bass a little better, but ultimately sound leaner. On a rich balanced speaker (my old Duntech Princesses, for example), this was fine, but on a more neutral speaker they could sound too thin. The KT88s I use (old MO Valves) are much richer and more harmonically correct in the midrange, with good bass and a wonderful sweetness--the classic tube sound, I suppose. I'm curious as to how the new Russian KT88's stack up against the vintage tubes. My gut feeling is that the older Jadis amps were designed around the older KT88s; in fact, I believe the newer models may have been designed, particularly the transformers, around the KT90's. I've heard the newer Jadis amps with the KT90's, and they sound terrific. So I'd suggest you take the amplifier you want to use the tubes in into account. Hope I haven't confused you even more.......
Rcprince, you may want to e-mail Jadis regarding the use of KT90 tubes in your amp. They go out of their way to recommend KT90, and to avoid KT88 with me. They say they have seen reliability problems with KT88s. I have never had this experience. Quite the contrary. And, while Frank Garbie is very helpful, his information is often at odds with what I get from Jadis directly. So, again, I would ask THEM about KT90s in your amp. They always give me a response within a day or two. Good luck!
Trelja: Thanks, I'll give that a try. On the reliability, the newer KT88s, particularly the Chinese lower grade makes, have had reliability problems. The vintage stuff is a different story. All the 6550s I've used in the JA80s have started going bad, and blowing the protective fuses, within a year to 14 months (in my ARC Classic 150s, the same Phillips tubes lasted 5 years). I've had the KT88s in there for over two years now with no problems. I must admit having a preference for the MO Valve KT88s, even over the KT90s I've heard in Jadis equipment; just a matter of preferring the darker sound, I guess. But the prices.....
Trelja,which of the Rogue products have you used.Can you comment on svetlana 6550C Vs Sovtek Kt-88
Tml12, I have EXTENSIVELY used both the stereo and monoblock Rogue amplifiers. Wonderful sound, but not what I call "classic tube" sound. The new tube sound(Rogue, Jadis, Audio Research) is much more neutral, powerful, and extended(solid state sounding, at least to me). What people mean when they say the best of ss and tube amps are converging. The amps sounded more to MY liking with the KT88s. A bit more sweet. But then, I like syrupy sweet tube amps(even though my Jadis is not). I know you will say this is crazy, but I always preferred the Jolida 302B over all the other Jolida integrateds, and the Rogue power amps. But, that goes back to my sweet sounding tube preference. In reality, the Rogues offer MUCH more: power, neutrality, bass AND treble extension, etc. All of the things that "the absolute sound" is supposed to sound like. Just trying to be honest in regards to my bias.
I've learned a great deal from this thread and I have been having a great time tube rolling. My Audio Valve Challenger amps actually allow me to use ANY combination of 6550, KT88, KT90, or EL34 tubes so I have been mixing and matching to fine tune the sound (and generally driving myself crazy). I have not tried KT90s partly because of the expense but also because I am told they will only work optimally in an amp with appropriately designed transformers. Any thoughts?
I'd suggest you ask the manufacturer of the amps directly. The new Jadis have transformers optimized for the KT90s, but I believe that VTL amps can use both 6550s and KT90s, so I don't know if you have to have a transformer specifically designed for that tube. The manufacturer will be able to tell you what he/she thinks is the best tube for your amps.
I second the vote for the Svetlana KT 88 vs 6550 (haven't tried KT 90's). Just retubed my Aronov monoblocks with KT 88's from Upscale Audio and the improvements in the midrange and the top end are dramatic. If the bottom end is less defined, I sure don't miss it. Then again, my monitors only go down to about 45 Hz, and rest is handled by a powered sub.
There is so much good information on this thread that I made a hard copy of it-- thanks everyone. Craig.
Many thanks to all on this thread and especially to Trelja who REALLY knows his tubes. This is what all the threads should be like. Mark me down as another happy KT88 owner. Anyone for driver tubes?
Trelja, just a note to you to mention that Jadis replied that the KT90s can be used in my old JA80s. I may get a set for when I run out of the NOS KT88s. Anyone with experience on how the new KT88s stack up against the older ones, sonically?
Rcprince, I am happy you put the question to Jadis. As stated before, they really seem to love the KT90. They go out of their way to recommend it in their products. I think Frank Garbie is a great guy, and seems to offer a lot of help. I have however, gotten information from him that conflicts with what Jadis advertises or says. Particularly in tube substitution. He wasn't aware my Orchestra Reference or some other Jadis amps accept tubes other than what they came with. He has given me excellent help when I have gone to him. I know horror stories abound, but I have nothing but positive things to say. I am sorry but I can not offer anything in regards to old KT88s, as I have no experience with them. I apologize. Enjoy the tubes, Krys!
I am trying to replace my tubes that originally was KT90's on my Jadis orchestra reference integrated amplifier. Beside that the KT90's are quite good I am curious of experiencing the KT88's specially from Valve Art, hoping to have little warmer sound with still good bass and extended treble of the 90's. If you have any experinence It would be great help. Thanks
I experimented with Ei KT90v.3 a while ago with my then owned VAC PA100/100. Biasing problems frustrated me enough to permanantly distrust them. Now, over a year with my replacement to the VAC amp, I too appreciate the mix n' match possibilities with my Audio Valve Challenger monoblocks. They were delivered with Sventlana EL34's then I ordered (12) JJ KT88's. Fat bass became solid bottom end, a musical, sweet midrange connects the bass to extended high frequency clarity. The versatility of the amps allowed me to mix (4) KT88's w/ (2) EL34's in each amp. I haven't tried 6550's due to my satisfaction at this stage and $$ for yet another dozen of tubes.
Krys, I found the KT90 to have the best bass of the three, far and away.

Yeah but these Svet 6550's with Defy7 powering/new M Supreme SG caps, + Seas Thors new Munorf xovers  = bass like a  sub amp, So 6550's offer tons of bass.
But also, from what i ;'ve read on disc boards, beats out the 90 in terms of wider, more open sound stage. 
No i have to side with the 6550(=kt88, exact same tube) vs the 90, which may as you say be more clinical, detailed (less warm, warm to me means more mellow the reverse of warm is more attacking, more forward,,which if i recall the EIkt90's in my Jadis Orch Refer were more forward, attacking,,and,,harsh. The EH kt90 i am sure does not suffer from this harsh weakness as did the wayyy over rated EIKT90/  Glad that tube is now extinct. 
No I have to give the edge to the 6550/88 (same exact tube) over the nice, but no cigar,,KT90.

EL34's in each amp. I haven't tried 6550's due to my satisfaction at this stage and $$ for yet another dozen of tubes.

Don't need to roll to 6550's,
Your KT88's are in fact none other than,,,yep you guessed it, due to miniscle differences, same as mt Svet 6550's ,
IMHO the Svets6550's.  will shootout all other 88/6550's ever made.
In all categories,,including the most important characteristic, reliability. 
Built like tanks, sings like angels...

I am trying to replace my tubes that originally was KT90's on my Jadis orchestra

East EU tubes are like chinese power tubes, unrelaible, Those KT90EI's that came with the Jadis Orch Refer went bad after 1500 hours. = Junk  and  set the record for screechy harsh sounding. 
They fetch like $100 each now,,lol...
But when new, set the record for life like sound stage/female voice. WOW,, but hard to deal with the  steely highs. , The Svet 6550 has none of these issues. 
Its a tube you can <<relay on>> session after session,,and on and on, for years, = faithful tube. =  Gold winner.
experience on how the new KT88s stack up against the older ones, sonically

NOS Svet 6550(kt88) is ientical to the new production,, so don't pay high prices for *NOS Svet 6550s** Its snakeoil. 
No have not tried EH KT88's, vs Svet 6550's. 
Defy takes 12 tubes = not practical,,I did hear the Gold Lion's,,and found them to be a  bit lower vs the Svet's,. so i returned to vivatubes/12 GL KT88's,  with a  $150 restock generosity fee , and also previous 2 weeks, returned  vivatubes kt90's $100 restock gift fee,,,they said * please sir, go do business elsewhere*,,so I did and rebought for a  <<yep>>a   2nd time,, the Svet 6550's from a  California seller, and that is the end of my long  very expensive search for a  good power tube.

I second the vote for the Svetlana KT 88 vs 6550

It is exactly the same tube,, one can not win out over the other.
If anyone believes they are dif, its snakeoil.
Resurrected an 18 year dead thread, so you can respond (to yourself, repeatedly) about everything sounding the same?       The only thing, "the same" about the Svetlana 6550, that’s been made by Sovtek since SED’s St Petersburg (Winged =C=) plant burned down and took their manufacturing equipment with it (some years after this thread started/ended); is the name that Sovtek/New Sensor/Reflektor acquired.       Not saying it’s a bad tube.            Simply not the same tube.       Just as those that are now manufacturing, Mullard, Tung-Sol, Gold Lion/Genelex, etc, repops.      None of them are the same, or- sound the same, as the original valves.       I have noticed; some of the most reputable tube mongers that used to sell and and extol the virtues of the SED/Winged =C= brand tubes, aren’t selling the Sovtek repops.       Doug’s tubes does list Sovtek’s Svetlana 6550C as, "A great choice for people on a budget."        To each his own, of course!

Well I actually sold the original NOS /very low hrs, maybe 200 hrs, on the dozen sold  for $250,, and bought the KT90's, which I then(10 hours useage)  sold, bought 150s(10 hrs usage), returned, rebought 90's(10 hrs) returned, bought 6550s(10 hrs), returned, rebought 6550's and thats what I am running. 
Svet 6550's
which according to the Ebay seller's site specifically states,
The new Production Svet  6550 are *EXACTLY SPECIFICALLY PERFECTLY IDENTICAL/NO DIFFERENCE to the  NOS Svet 6550s*
I believe him
Why would he lie about it?
If you take the print off a  NOS and new prod svet 6550, could you tell them apart?
Of course not. 

You’re talking about an eBay seller:      "Why would he lie about it?"      Hilarious!        Provide a quad of unmarked, NOS original SEDs and the same, of the later Sovtek version, to install in my monoblocks (a quad each) and bring your wallet.      I’ve never been a big gambler, unless the odds and experience are in my favor.      btw: You couldn’t have heard the full potential of any of the new tubes you returned, after only 10 hours.