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I know this issue has been beaten half to death. And yes, I did read the previous postings. But I still have a couple of questions. I am about to replace the output tubes on my C-J Premier 12's (8 total) and want to get this right. First, are there ANY problems or disadvantages to replacing 6550's with a KT88 or KT90 tubes? Second, can I get recommendations for a tube that gives excellent imaging and a clear, extended high-end? I am not too concerned about a bass response. Thanks!
Follow Ups:
Prem 12s? Did someone say Prem 12s. I've got four of 'em juicin' a pair of Maggie 1.6s (I've also had a Prem 11A and still have a pair of very nice-sounding Bill Thalmann updated CJ MV-75s). I've rolled nearly every type of KT88/6550/etc., 5751, and 6FQ7/6CG7 through them. There're lots of good sounding combinations among these tubes, and combination is the key. Don't forget the 5751s and 6FQ7/6CG7s. I've found that changing just one can change everything.You've got a very nice system, and I like the room too ;) My system, and everything else, is of course different from what you have, but here's some of what I've found. At this moment, my Prem 12s are happily burning through Sylvania 3-mica black plate 5751s, 1950s-vintage Sylvania 6CG7 (bought from Jim), and welded-plate GE 6550As. I think, in the context of my gear, room, and ears, I haven't found a better sounding tube complement, and I think the system sounds just great. GE 6550As, welded or crimped/stapled plate types, do serve up great bass quality and quantity.
There are some other combos that're also up to the same par. The welded plate GEs I think sound more refined/tonally characterful than the crimped plate types. These GEs also sound good with old, cheap GE fully-shielded 6CG7s or Tung Sol 6CG7s. Any variant of GE black plate 5751 also sounds good, and I think the gray plate Sylvania 5751 is at least as good-sounding as the typically more pricey black plate. I also like the 2-mica black plate RCA 5751. Plugged in together with this selection of 6CG7s and 5751s, Sylvania 6550s also sound great.
Another favorite arrangement for me is with SED 6550Cs. I was a bit surprised I'd like this power tube at all given my previous experience with it. It can be as Jim, and others have reported, including myself, soft, rolled, and flabby. I'm not precisely certain what made the difference, but I've had very nice results with this tube, though when used with different 5751s and 6CG7/6FQ7s than mentioned previously. The GE 3-mica blackplates and plain old GE 6FQ7s (CJ's OE 6FQ7; the one with the round holes at the plate bends the filament bridge wire) together with the SED 6550Cs give a very nice result. I find that these particular small tubes are on the more lean'ish side with more HF energy, where the other small tubes in the previously mentioned complement are on the softer side. If I plug in SED 6550Cs to the first-mentioned tube complement I get something softer, so much so that the resulting sonics are out of my preference range.
A lot of other power tubes can sound good. Yes, the EI KT-90 can be great, on the leaner side, as is similarly the EH KT88. But both can be very good. I agree with Jim's survey assessment on the sonics of the EH KT88. The JJ KT88 is likewise leaner and delicate but also bass-shy. I don't use a subwoofer, and the Maggies don't reach very far down in the LF nether regions, so I'm looking for all the bass performance I can get. I've not found a liking in this current system, strangely, for the Tung Sol 6550. I have all 3-hole types. They've been spectacular installed in some other systems, but in what I'm using today they're just utterly lightweight.
I'm a very big fan of everything from Shuguang. Love'em. I've used the ST-bottled, Tung-Sol look-alike 6550s, the KT88-98, and the square-bottled KT88/KT100 (or whatever this thing is; it seems to wear all kinds of labels). All are fabulous. But I've also had more problems with them than any other output tube I've used in my CJs. GEs, Sylvanias, Tung Sols, and the Eastern European tubes have been durable and reliable. EHs, SEDs, Sovteks, good EIs - all great. I can't quite say the same thing about Shuguang tubes I've used. I haven't had trouble with KT88-98s, but I have had with the other, and earlier, types.
There's no problem running either 6550s or KT88s in the Prem 12s. Yes, every once in a while you may end up with output tubes where you can't get the bias LEDs to turn off. I've only had this happen with SED 6550Cs.
Don't forget the small tubes. Says my experience, they all have to play well together. There're many combinations that can sound great.
Ciao.
- SJ
I am sorry but JJ KT88 are anything but bass shy. JJ and KT90Ei are the best in this area actually and I tried virtually all KT88/6550 in two different amps. It's also in any way not lean.
Seems your amp fights with your speakers.
tantra
The SED and the EH and the Penta shuguang are all excellent tubes..THe last mentioned is my personal favorite in many amps but the trouble is you cant get them and Penta is selling the holed version from my understanding at the same price which is dirty tactics as far as Im concerned.
The SEDs are nice but they are pricey for what you get..The EH KT88 once broken are superb and some say they are better than the SEDS and Im hearing this more and more..Also consider the Tungsol 6550s which are very good sonically and are also a new sensor product.
Jim can help you out here because he pick and choose the best ones for you and match them.
You can replace 6550s with KT-88s or KT-90s, that's no problem. However, the last years of KT-90 Ei production is very poor quality and I don't recommend them.If you are looking for an extended and smooth top end the tube I recommend to people is the EH KT-88. You saw some other recommendations for the SED 6550C, but others here will say the 6550C is soft and rolled off on the top end. That would tend to indicate it is quite listener and system specific. The EH on the other hand is universally known as a tube with a bit more top end energy - and while the bass is very tight and well controlled, it's less in terms of quantity.
I have a lot of experience with the EH, I use them in the Citation II amps I redo.
Jim:
Can I use the LED bias indicators on my C-J premier 12's to bias KT-88's? The amp was designed for 6550's. If not, do you (or anyone) know how to measure bias voltage on C-J amps?
Thanks!
The LEDs don't care what tube is in there, so they'll do fine. All that matters is the current passing through the tube which is measured and the LED circuit responds.
I bought a set of the P/S 'SCs to replace the ValveArt (Shuguang) '88s in my ASL 'Canes, but I heard no differences, due perhaps to replacing with like-sound tubes (and also to my tin-earedness).
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
Jeff
The VA are pretty clean sounding and they are shuggies but they have had some quality control issues with those at times..Of course the ones Im speaking are 4 years old but they are new and I had two that were microphonic from the same batch supposedly.A lot of changes were made so I gave them another chance.
Most on this Asylum will tell you if you're looking for the best HF performance then go with the SED 6550Cs. KT-90s are the best, but only IF you can get the older versions that are no longer in production.
...as in Ei is no longer making tubes.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
but I don't have CJ12's. Additionally the SED's are rugged. I've yet to have one have a catastrophic failure and damage the amp. KT88's have a totally different tonal quality, a bit bloated in the midbass and uneven in the upper mids/highs (which can sound pleasantly additive with some other equipment). I find the 6550's to be the more neutral of the bunch. The KT90's are a tad too cool for me, although many like them a lot (Mine are old EI's). FWIW
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