Yes, 6550 is a sweet spot in tubes.
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I believe the 6550 and KT88 tubes are still needed even with the Tung Sol KT-120 or now the KT-150 tubes. When I started out with my Jolida JD-502P I initially got the amp because it could handle the KT-120s and there weren't any other manufacturers of the KT-120s. It would keep the tube rolling to the minimum. Well the curiosity got to me and I tried 6550 and KT88 tubes and have found nice differences between each.
Like DonJr said the more the merrier.
KT120s are absolutely reliable not only based on my own experience of using them daily for nearly 2 years, but also based on my having rarely ever seen anybody say otherwise even when I posted a question regarding longevity. I think we "need" 6550s and KT88s merely for tone options and not because KT120s are "terrible", because clearly that's nonesense if only based on the KT120's overwhelming popularity due to performance and an amazing lack of publicized tone or reliability issues. This (A'gon) crowd is hardly shy about opinions, and from what I've seen the KT120 is nothing if not utterly accepted. I've never seen a specific new-ish power tube (and until some recent Chinese versions these were a "one option" tube from Tung Sol only) be so quickly adopted by manufacturers where I can reasonably assume they wouldn't risk an amp design on an unreliable or "terrible" tube. I've also talked to service technicians from more than one local high end audio shop (and a few amp designers), and it "seems" KT120s are a well designed, reliable, and great sounding tube that has earned its place as a huge success in audio. Also, most professional guitar players (and high end guitar amp designers) use either 6V6, EL84, or EL34 based designs as the trend has moved away from KT88s and 6550s, except in a few higher power demanding bass amp designs.
I have asked my question because I would like to replace my current KT120 set of power tubes (because of the age).
I have Jadis amplifiers that can accept EL34, 6CA7, KT77, KT88, KT90, 6550, KT120 and probably KT150.
In the past I used 6550 in my amps and Gold Lion (reissue) KT88. I remember when I switched to KT120 about two years ago it was big WOW factor. Better dynamics, deeper bass, more lively and open sound. Since that I was not listened to 6550 or KT88 and I wonder if there is a good idea to go back to these old tubes - rather back to good Svetlana Winged C 6550 than KT88.
Maybe a better idea is to wait for KT150 tubes.
As for reliability I had no issue with KT120 at all, but had a lot of problems with KT88 Gold Lion including blowed cathode resistors.
I have an Octave V110 (designed for the KT120) and I have to say in terms of tonality they are my least favorite. IMO I think they are too forward in the mids and bright in the highs. Nice and punchy in the bass though. If I put more laid back/warmer input and drivers tubes in they can sound pretty good. Give me an original Tung Sol 6550 solid black or grey plate any day. If the TS KT120 is too big check out the Ei KT90 type2. IMO again similar but better than the KT120 but also more pricey and a lot less than the TS solid black or grey plates. The big thing the KT120's have going for them is their price.
Sure would like to see some specs and prices for the KT150.
Has anyone seen or tried these KT120's from Shuguang?
Something new I guess. Although I would rather see a KT120 from the Psvane side of the business.
Oh to answer the original question I think we still need 6550's and KT88's for the amps that can only take those. Otherwise I think the KT120 will be the new standard mainly due to it's cost and reliability. It's rated for a max plate voltage of 800 where most amps are under 500V on the plate. The V110 is running at 620V for the KT120's (540V for EL24/6550/KT88's). So at a 450 - 500 plate voltage you can push the KT120's harder.
This is my opinion and so far I am the only one who doesn't care for the TS KT120 sound. Ok I may be spoiled with the TS 6550bp and gp.
I contacted leisure-audio about the Shuguang KT-120s and they quoted me a price of $199/quad. I haven't ordered them because I just don't have the funds and honestly am up to my eyeballs in all sorts of KT-88, 6550 and Tung Sol KT-120 tubes. I think I've spent just as much money trying various tubes for my Jolida than what I originally paid for it. Oh well the joys and insanity of tube rolling...
I like the sound of my 6550 and KT88 sets, but KT120s seem to sound stronger in my rig, and they're larger, so there's that...I do wonder if Shuguang KT120s will be any different from Tung Sols, and recently noticed some Chinese "Gold Lion" branded 12AX7 tubes being made by license (so they say) from New Sensor...for about half the cost of Gold Lions. They really should make a KT120 with fancy gold lettering, gold pins, and a presentation box or they're missing an opportunity...my new Psvane 12AX7s had a great box which provides a comfortable home for the tubes they replaced, or a nice casket for burrying small twin rodents.
Regarding guitar amps, a lot of guitar players who have been around the tube amp block are going for lower wattage amps since you can squeeze the magic grease out of the power tube stage without relying on complete preamp tube saturation...I just bought an EL34 based Burriss Royal Bluesman that illustrates this wonderfully and will melt your brains if you push the 18 watts...my other fave amp (Reverend Goblin) has a "5 or 15 watt" switch and does the same with 6V6 power tubes. A beautiful thing.
08-24-13: Reynolds853What's the amp? KT120 is NOT a replacement for all KT88/6550 amps so have to be careful.
GL KT88 sounds fantastic and much better than all the 6550 I rolled but NOT reliable. They always take out resistors after blowing. Soldering is simple but got tired removing 45+ screws on a 110#+ mono so back to SS. Winter is coming so looking for amps design for KT120 or KT150. So far I've only heard positive comments from owners and respected designers I've spoken too.
The KT-120 is my second favorite tube in my Emotive Vita amps. My very favorite is the Genalex KT-77. No reliability problems with either type.
I think Atmasphere was more than a little unfair in repeating gossip about the KT-120 having reliability problems. Sure, there will always be the occasional defective tube and the unfortunate owner may vent his frustration. That's understandable. But after several years I haven't heard of any problems with the KT-120. By now word would have gotten out if this were true.
Old thread, but just ran across it. I have switched to NOS GE 6550A in my Bob Carver Black Raven 200 mono blocks. The improvement over the current production Russian tubes is incredible. I was going to try KT120s, but instead I bought another 14 NOS GEs. These are the favorite tube of Stu Hegman and Bob Carver and I see why. Bob loves to tell the story of when he asked Stu about Genelex KT88s and Stu raised his pinky and said "Watered-down British tea." If you are thinking of getting some new Russian tubes, now maybe the time. With oil prices so low and strangling the Russian economy, our response ( like the response if Jimmy Carter in 1980) may be to impose an embargo if Russia gets more agressive in Ukraine.
"With oil prices so low and strangling the Russian economy, our response ( like the response if Jimmy Carter in 1980) may be to impose an embargo if Russia gets more agressive in Ukraine."
Putin and his henchmen are the one's strangling the Russian economy with their blatant corruption and criminal activities, low oil prices are just exacerbating the problem for his people created by HIM. Agree, buy now before the inevitable embargo by this or the next administration and his response, doubling down. There is no palatable solution with that guy, he is just too ambitious and dangerous.