6550 tube vs KT88

Was wondering what might be some of the differences between these 2 tubes. I've heard 2 sets of 88's and was not a tube that fits my music, classical. i found the sound too compressed, too flat on fq's, dynamics were thin. Too warm, not detailed like the KT90 tube.
Is the 6550 a middle of the road between the 2?
Hows the timber? bass/mids/high separation?
The KT88 seems to blend the 3 too much.
Can't speak to the KT90's, have not heard them.
A while back, I was auditioning an Audio Aero amp. It could take either 6550's which worked in my Conrad Johnson Premier 11a or KT88's which came with it. My experience with my system showed the KT88's to be a more bass heavy and just not enough treble magic when compared to 6550's in that amp. Having said that the KT88's gave a great deal more detail than the 6550's but did not sing for a violin or have the clarity of a triangle or piccolo for my ears.
It was always a case of did I want more resolution of the singing voice. Hope this helps
Yes my limited experience of the 88's showed not much resolution for classical. Too smooth. Smooth being if you took the fq range as looking overa falt landscpe, you'd see few peaks and valleys. Bland IOW.
The 90's in my Jadis present descent bass/mids/highs and all 3 are separated, not mushed together like a 88 tube does. All 3 in equal balance. I'd say the highs are slightly limited with the 90's, but make up in a musical image.
I notice there are very few amps offering 90's.
I don't think I;d like the 6550's. seems got lucky, the 90 may be the ideal tube for my taste, offering dynamics.
I found zero bass with the 2 88 tubes I tested. Just a falt response, flat like the Kansas landscape.
I can see how tubes get a bad reputation vs a big ss amp.
>>I found zero bass with the 2 88 tubes I tested. Just a falt response<<

Perhaps bad tubes (possible but not probable); more likely a weakness elsewhere in your system. "Zero bass" is not a general characteristic of the 88. Your amp might be the problem.
>> I found zero bass with the 2 88 tubes I tested
agree w/ commercial member "Audiofeil". The KT88 tubes are anything but bass shy! I'm using EH KT88 in my JoLida 502A to very good effect. They sound better (more balanced over the entire audio spectrum) than the original winged-C Svetlana 6550 tubes.

One thing that you *need* to realize is that different amps take to different tubes.
By this I mean, for example, just because KT88 sound great in my JoLida does not mean that they'll sound as great in your CJ 11a or some other amp.

For the particular amp that you have several people have tube-rolled before & probably catalogued somewhere in these archives which output tube sounds best, better, good & fair. Same deal w/ my JoLida - the EH KT88 is reputed to work really well in this amp & I can 2nd this from my experience.
You probably need to search these archives; it'll be worth your while.
The EH KT88 is a bit bass heavy (you are correct) but it's soundscape is not flat like KS!
Post removed 
Thanks Tvad I'll order that issue. I think the issue here is that my Seas speakers area MTM design rated at 87db, so its just not a match for the KT88 I demoed nor the EH88's that I rolloed in my JOR.
db rating must be 90+ to be effective.
This is the one drawback with Seas speakers, few tube amps can bring out the dynamics. The Jadis is one that can meet these demands, as their web site says, "our amps can drive any speaker" and they can. I've put their smallest amp to the test.
Not sure how the Jadis 88 tubes image? vs the 90's I'm using.
The thing is, if I order a Jadis amp in the future, I may just stay with the 90, as I like the sound. And may not be willing to give up the characteristics of the 90 in order to gain some benifits of the 88's or 6550's.
Trade off's are a part of this audio realm. But if it isn't broke, don't fix it.

>> I think the issue here is that my Seas speakers area
>> MTM design rated at 87db, so its just not a match for
>> the KT88
I do not understand this convoluted logic! what does 87dB SPL/W/m have to do with compatibility with KT88 output tubes?

what is the bias voltage set at for the KT88 tubes?
(for example, in my 502A the recommended bias voltage for 6550 tubes is 50mV. However, KT88 work better in this amp when their bias is set at 55mV i.e. driven slightly harder).

As far as I can tell: you do not have sufficient power amp output wattage to drive is mid-low efficiency speaker. Correct?
If so, please do not blame your lack of output power wattage on the sonics of the KT88!
Post removed 
Tvad, I beg to differ on a nit. Bartock fan does "know wtf" he's talking about. He understands himself perfectly. The problem is that nobody else does!

Perhaps in his ability to judge the performance of tubes sans amps (other than his JOR) and drivers without speaker systems (other than his Thors) his is an idiot savant, perhaps sans savant. For the life of me I don't know why anyone evens bothers to respond to his posts, they always evolove into a testimonial for KT90's (since I guess he decided against the KT88 based Cayin) and the superlative Seas drivers. I believe that is his initial intent when he posts. Too bad the word introspection is not one with which he is familar. If it were not so sad it would be funny.

IMHO, FWIW, Amen, All praise to Allah, and God Bless America............
I'm only reporting my experiments as a note to others who can use the info I provide. I'm saying that when I rooled the 90's to a quad of EH88's, all the timber/dynamics/sepaaration of bass/mids/highs had virtually disappeared when compared to the 90's.
Maybe the issue is that when you roll the JOR to 88's, the amp needs to be biased properly. Not sure how biasing could bring the 88's resolution up to the superior dynamics of the 90's. Maybe the Jadis stock 90's are a highly select tube for this amp. Gabriel did say Jadis 88 replacement tubes are expensive, possibly fora resaon. Not all tube amps are equal, maybe not all 88's are equal.
I also demo-eda 88 tube amp recently and found the very same results in the sound vs the JOR/KT90's.
The orchestral was flat, no peaks valleys in dynamics of fq's. Blues/jazz hada increase in dynamics, but not equal to the JOR90, not even close.
I should point out that the JOR does have tone controls and i use them to the max, at say 95% open. When I have the tone controls at neutral, 12 oclock, then the Jadis sounds exactly/very close like the 88 tube amp i demo-ed.
Maybe some feel that's not true musical image with the treble up, which beams the highs/steely, cold. But its the way i like it. I love the tingle and sparkle.
With the tone controls up to 95/98 % open I get to hear recessed instruments in the orchestra that CANNOT BE HEARD when treble is at say 50-75% open. Bass is also greatly extended at 95% open.

Its like the apature on a camera, more open lets more light in. Here the tone open allows a greater band width and more music comes through.

So open 95% the music is alive in the room. At 75% open the music has a image that its in the next room.
btw I listen with vol control at a very comfortable 25% open, 9 Oclock, maybe a tad more, but rarely. Its too loud for my taste at 10 oclock. I should also mention even at 11 pr 12 oclock vol, the sound is clean, not distorted.
With tone open 98% and vol at mid way, then the music is shattering loud.

The 88 tube amp i demoed vol at 9 oclock or 12 oclock, had little effects. The seas's showed no change in response.
Its kinda like that Audio esearch VS110 with 8 KT88's/LS12 pre with the Magnaplanars i heard the other day.
the salesman said, "if I turn the ARC to 10 oclock or up all the way, its the same, the maggies will not respond to any increase in vol" And it did so, sure enough, no change.

It was at that time I realized impedence load, some drivers were beasts on amps. I also realized how powerful Jadis makes its amps, even the tiny JOR has its muscle.
Post removed 
Tvad, what ia m saying is that if i roll the 90's in my JOR to the 88's, the speakers will voice differently, different response.
this is all i'm saying. That each tube has different characterists. IMHO the 90 tube works best with seas drivers.
For some reason the 88 tube does not match the Seas's heavy demands with 87 db SPL.
Its too neutral, too "tube-y" ofa sound. The 90's bring out a solid response.
What is difficult about that.
Tell you what maybe I;ll rya pair of JJ's in the JOR see what gives.
Thanks Dave, i'm trying to understand these tubes. . I'm just want to get at the bottom of things here. As you know many opinions and posts on this site can be just as biased as some sound systems I've heard.
Lets just cut to the quick.
What are the EXACT characterists of a 6550, 88, 90?
Provided we are usinga amp source of high clarity, superior purity?

I realize this can't be done, as each speaker will voice differently.

I need to order that quad of JJ 88's and then I can feel better of my opinion on the 88's.
I'll try next month, as I'm still unemployed post katrina and cash is low.
"What are the EXACT characterists of a 6550, 88, 90?"
Wrong question. I have tried a few brands of new production 6550's and KT88's in my VTL's, and each kind sounded different. As anybody with a little tube rolling experience can tell you, there is no "one sound" for each tube type -- different versions with the same model designation are not physically or electrically (and hence sonically) equivalent, and that includes different brands, factories, and vintages.

I'm also not sure that your amp, apparently designed to use KT90's, is really a good candidate for KT88's as drop-ins. For instance, I know that my amps, which come stock with 6550C's, can't use KT90's without resistor changes, although KT88's are fine. And if your amp uses autobias, there may be no way for you to tell if the replacement tube type is not being biased in the proper range by a circuit not designed for it.

FWIW, in my amps a swap from SED 6550C's to EH KT88's produced improvements in essentially all the same areas you're complaining about, and the overall effect would be outstanding for a classical listener in my view. But although my speakers are also about 87dB sensitive, my amps are ~200w, and obviously everything else is different too. BTW, when comparing tubes you must make sure one set isn't wearing out, or still breaking in -- that will totally skew the results as well.
Post removed 
Post removed 
I was yanking your chain. I sensed a little frustration earlier. Yeah, Zaikes had it right.
Bombaywallh  slashing of my comments was spot on, back then I did not know what i was talking about in all things tubes. 
I am still learing,,but making  costly mistakes...Very long story,,but here goes,,I bought a  used Defy on Agon some years ago,,had Jadis's recommended tube the 6550 in the amp,,w/o listening to the tube,,i sold the 12 off and bought kt90's, Then sold those off, bought kt88's, (now running) and decided to buy KT150's fora *more robust sound/bigger sound stage** Wrong,,Now am selling off the KT150's (gonna takea  hit) , will hold with the KT88's ,,but will also now REBUY the 6550's..
yeah , going around in circles.
Just heard a YT vid of KT88 vs 6550,,I loved the mid/highs of the 6550,,the tube originally placed in the amp by Jadis,,,
I really think its the best tube for the amp, and for my classical midrange.

wow, i posted this topic some,,,14b years ago,,and comming back yet once again to finally finsih the shootout,,talk about time delay.
I am now locking these 2 supreme midrange cantors in battle.
The Defy had 6550’s, never listened to them,,I assumed the 90’s were superior,,so yrs later (amp sat up for 10 yrs as, i had no cash fora good preamp til only recently 2019,,amp bought in 2008),,so anyway,, went from kt90’s in 2019, to kt88’s, 2019/2020, now kt150’s for 2 weeks, now back to kt88’s,,and about to buy some used (new? bulk lots) 6550’s.
all my comments/opinions above are null and void, all my ideas are completely in-accurate, and invalid.
I like uru975’s post,, the YT vid did seem to show the 6550’s has a upper mid/high FQ clarity/sparkle that the KT88’s lack. as far as **Kt88’s superior in details** I have doubts that the 6550's  lack such details as expressed in the 88 resolution....,,,My comment the 88’s lack bass is completely inaccurate, 88’s have super bass. Bombay corrects this faulty opinion in his July 2006 post,
88 ’s have gorgeous bass resolution,,and reveal details of mid fq’s, but as i say,,will the 6550 offer equal mid fq details , PLUS a huge bonus of sparkle and a clean open *Live stageing* of vocals?? as did the JOR KT90 set up???
(But the EIKt90 has a screetchy high fq distortion,, yet the mid fq’s gavea true live muisc show right in your room.
This is what i am after now.
the Defy surely adds more fullness vs the JOR,, all i need do now is try to match the JOR/EIKT90 *live muisc show* feel.
My hunch is the 6550’s will approach this experience.
read Dentdog’s July 2017 comment.