Ampeg SVT-CL - 6550 Tubes

Discussion in 'Amps and Cabs [BG]' started by Slpbass81, Sep 25, 2022.

  1. Slpbass81


    Dec 16, 2010
    Orlando, FL
    Endorsing: GHS Strings
    I need a new set of 6550 power tubes for my Ampeg SVT-CL. I currently have JJ’s but it looks like they are out of stock everywhere. Has anyone been able to find any or have recommendations of what brand I should switch to?
  2. Wasnex


    Dec 25, 2011
    Is Eurotubes out of stock?

    6550 - Eurotubes

    Previously I would have considered Shuguang 6550A, but they have been shut down for quite awhile. You might take a chance on Psvane as their engineers supposedly came from Shuguang. Vacuum Tube - 6550A, Classic Series, Psvane | Antique Electronic Supply ( stock is low.

    Pretty much all the other choices I know of are New Sensor (Russian). Many of the New Sensor 6550 and KT88 have a good reputation for tone, but are considered unreliable in amps that run high voltage like an SVT.

    I believe Ampeg put either Sovteks or Svetlanas in the 50th AV SVT. My believe is these tubes are very closely related, and sometimes the same tube. Sovteks have been around for a long time. They have a fairly good reliability rating, but some slag on their tone. I could be wrong, but I think the Sovtek design predates New Sensor.

    I believe @coreyfyfe put some Tung Sols in his SVT a few years ago :greedy:

    I would definitely avoid EHX 6550 or KT88. I bought a couple of used amps with these tubes and almost all of them were dead or failed quickly.

    I have I had to retube my vintage SVT today, I would probably go with JJ KT88.
    Vacuum Tube - KT88, JJ Electronics | Antique Electronic Supply (
    KT88 - Eurotubes

    Quite a few people have reported good results with KT88 in SVTs. I have never run them in an SVT, but I have a bunch of amps that run KT88, and JJs have been the most reliable and best sounding for me. Since they are not the OEM tube type, the amp could potentially be unstable, so no guarantees.

    Some people have really negative feelings about JJs and Eurotubes. The KT88s I ordered from them were really well matched and have run flawlessly after some initial hiccups. I put them in an amp that was bought as nonop. The amp ran fine on the bench for a couple of weeks, but when I put it on a speaker it started blowing fuses. I got the impression that it would be impossible to get the tubes replaced under warranty. Luckily I just needed to tighten up the pins in the tube sockets.
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  3. bobyoung53

    bobyoung53 Supporting Member

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  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    First question… are there identified issues with the current set, or are you changing their out “just because”?

    If there are identified issues with one or two tubes, you might talk with a pro tech to see if maybe they have a stash of a couple of tubes that might match up with what’s already in there.

    If changing them just because, or you read something on the internet that it “it’s the thing to do” or “all the cool kids are doing it”, my recommendation is to stick with the known good working set that you have.

    I see a lot of perfectly good tubes with over 50% of their useful life left changed out and then have problems with tubes in the replacement set. I just worked on an amp last week where this was the case.
  5. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    Yeah the tung sol reissues have been running strong for me in that amp for a while, but like @bobyoung53 said prices have gone way up on the new sensor stuff.
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  6. 20220205_162906.jpg
    Don't you wish it was 1990? :woot:
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  7. JeezyMcNuggles

    JeezyMcNuggles Supporting Member

    Feb 23, 2018
    Santa Maria, CA
    I suck, but nobody really notices
    You should switch to groove tubes... good luck
  8. jastacey


    Feb 8, 2009
    When I had a SVT-CL, I used Sovteks 6550's, they were the stock tube, from the factory, Seems like tubes have taken a huge leap in price, I'd get the tubes tested first, before spending $$ on new tubes, you didn't indicate why you need new tubes, so ....whats wrong with the amp?
  9. denton57

    denton57 Supporting Member

    Nov 1, 2005
    Back in Feb/March, I picked up a sextet of Groove Tubes from a reverb seller for like $179. I had a 50th anniversary SVT at the time but now have a 73 SVT with GE’s. Glad I bought a backup set but man, the GE’s are rocking. Hard to say, but this SVT seems to be way louder than any other SVT I’ve owned. But I’m glad I have some backups just in case...would have much preferred the TungSol RI’s, but they weren’t available at the time and I just felt like I had better buy before things got out of hand.
    bobyoung53 likes this.
  10. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    Yeah before poop really hit the fan in tube world I managed to snag a few backup sets for some of my amps. My SVT I’ve had backup tubes already, but for my others I bought a few quads of ruby and TAD rebranded tubes from any vendor still carrying them for reasonable prices. If I’m buying tubes normally I try to go with a set of preferred vendors and tubes, avoiding rebranded tubes in most cases. But if you’re buying rebranded stuff like GT, TAD, Ruby, Mesa, etc, the reliability of vendor is less of an issue. That’s what you’re paying for with the rebrand.
    Wasnex likes this.
  11. denton57

    denton57 Supporting Member

    Nov 1, 2005
    I have had nothing but great experiences with the RI TungSols. Have had them in a variety of amps, and currently have a new quad of 7581a’s in a 76 Bassman 100, and that amp is a keeper. Dead quiet, sounds fantastic. Those are great sounding tube heads.
    bobyoung53 likes this.
  12. dbsfgyd1


    Jun 11, 2012
    Mascoutah, IL
    It was better than the 70’s…LOL!!

    The set I have in my Eden WT 300v are newer, but I don’t have plans to use it much. Pretty soon, the market value of the tubes will be worth more than the amp.
  13. bobyoung53

    bobyoung53 Supporting Member

    I have a 1978 Ampeg B-15S with the original Magnavox branded 7027A's, it was in nice shape when I bought it so don't think it had a lot of use but that's 44 years. I also bought a '67 Bassman with what (I think) were the original GE 6L6Gc's, that was also in nice shape, even had a Fender CBS hang tag still on it, (don't ask me if that was on it for all those years, doubt it :laugh: but the owner may have packed it away), but they worked but one was really microphonic so they had to go.
    agedhorse likes this.
  14. bobyoung53

    bobyoung53 Supporting Member

    I had one Tung Sol 6550 tube go dead out of two sextets I threw in two SVTs, tech threw in another Tung Sol, sounded great, it's still in it. It must have been a dud as the tubes were less than a year old at the time.
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  15. bobyoung53

    bobyoung53 Supporting Member

    I bought an SVT head out here in Lima, Peru, Mickey Mouse capitol of the world, about twenty years ago, and it had six GE 6l6GCs from old Fenders, you could see the scrapes on the tube bases from the tube retainers and none of them glowed or showed any signs of distress which I was really surprised at, I thought the thing had been modded for them at first but nope. The amp actually sounded different, once I realized I pulled them right out and bought 6550's. One side was biased all the way hot and the other side was biased all the way cold too. I think the owner did that just to get rid if it, I only paid 300 bucks for it, still got it here now. It actually sounded Fendery to me, weird, you wouldn't think tubes would make that much of a difference.
    denton57 likes this.
  16. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    Follow the directions - exactly - in the SVT-CL owner's manual for setting the bias. If you can set it correctly, you probably are wasting money buying output tubes.

    If you do need tubes, I just checked and JJ 6550s are $300 for a matched sextet, KT88S are $330. I have JJ KT88s in my SVT-CL (it really did need new tubes), it sounds great and I wish I had an excuse to use it more.
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  17. bobyoung53

    bobyoung53 Supporting Member

    I guess I'll stay away from ebay. :laugh:
  18. denton57

    denton57 Supporting Member

    Nov 1, 2005
    Wow! Goes to show how robust tubes were back in the day as well as the amp for putting up with that.

    Mine has four GE branded and two GT branded but look identical in construction and really old. I’m assuming they were rebrands from the early days of GT. Anyway, I took it to a tech when I first got it prepared for the inevitable (the power tubes need replaced) but no...just a dw7 and the 6c4. I was so elated. Older guy, and made the comment “that amp sounds really good” when I was picking it up. Hoping I can ride these GE’s until I’m too old to lug an SVT.
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  19. bobyoung53

    bobyoung53 Supporting Member

    I can remember buying a set of Groove Tubes during the 80's for an SVT, not sure of which brand they really were but they really sounded good. Yeah I was amazed that those 6L6's weren't at least glowing cherry red, not even a hint, but I didn't play it for that long but probably left them in for a couple of days.
    denton57 likes this.