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Ampeg SVT Classic with two mismatched tubes, issues

Discussion in 'Amps and Cabs [BG]' started by bovine mind, Mar 30, 2009.


  1. bovine mind

    bovine mind

    Jun 17, 2008
    San Francisco
    i bought my 1999 Ampeg SVT-CL from someone inside the music community around me i thought i could trust, and in my fever to get the amp into my studio, did not open the back to check if all tubes were the same. i could only try the amp in the seller's studio with a single 15" cab. i had my doubts but bought it anyway after the guy confirmed it had been retubed a little over a year ago. as far as i understand "retube" should mean an entire matched set. he showed me the receipt, which lists 6 tubes at around $250, so i assumed he was correct and brought the amp home.

    days after running it with an ampeg 810 at 4 ohms i noticed difficultly keeping the bias lights green. the top left light would fade to red right after adjusting and eventually would stay lit.

    i experienced low volume and a distorted tone, and still do.

    this weekend i finally managed to get the amp to tech who removed the grill and immediately noticed two mismatched tubes, which leads me to believe the seller may have blown a couple and replaced them after the initial proper retube.

    since he sold it to me with the words "retube" and receipt shown confirmed, i feel cheated. he should have mentioned the two mismatched. now i've got a $200 retube on my hands.

    my questions is, how detrimental to the amp, [ and how quickly ] is it to just replace two tubes instead of the whole set?
     
  2. Shouldn't be too much of a problem as long as the tubes are within a similar range of each other, even if they aren't too close you should be able to bias them fine.

    What I would be worried about is what caused an amp to blow a couple tubes not long after getting a new set put it? Could be an underlying problem :(
     
  3. bovine mind

    bovine mind

    Jun 17, 2008
    San Francisco
    interesting. i was still sold the amp under the assurance it had been retubed, and to my understanding that should mean a full matched set.

    he's still working on the amp, but so far nothing seems wrong but the retube needs.
     
  4. bovine mind

    bovine mind

    Jun 17, 2008
    San Francisco
    Just spoke to my tech, he says the amp has 4 magnavox tubes and 2 sovtek, and that it's a bad idea to mismatch tubes in an SVT as they're such powerful amps. any opinion on that?
     
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The label isn't a problem if the tubes behave the same. but different labels reduces the liklihood that they have similar characteristics, unless they come from the same factory. These surely did not.....

    Magnavox tubes should be old US tubes, maybe new, maybe well-worn-in. Sovtek will be newer, and probably not very close to the same characteristics, as the insides are likely to be visibly different in shape, and tubes work by the geometry of the innards. Same general action, different in details.

    I'd put the chance of close similarity suitable to be "matched" at "low", which is unfortunate, since the magnavox tubes may be of vastly higher quality than the Sovtek, but you don't have a full set of them. You DO have a dilemma.

    The best thing to do is find a decent tech, one who isn't scared of tubes and SVTs , and who can competently assess the matching. Maybe you hit the jackpot, but I doubt it.

    As for the seller, it's perfectly possible HE is ignorant of tubes and tube lore, and thinks he got a great deal on the retubing........ or not. He might have got the shaft from his tech.
     
  6. monkeybassist

    monkeybassist

    Oct 3, 2002
    Denver, CO
    Endorsed by Ampeg, DR strings, strong relationship with Surine basses
    I had an SVT-CL and had problems blowing power tubes right from the get-go straight from Ampeg. I ended up carrying spare 6550s with me just in case, at one point I borrowed a totally different tube from the guitarist (EL 34? Marshal amp) which carried me through the 3rd set much to my surprise. Then one day I decided to put a bigger fan at the back of that amp and lo & behold I never blew another tube again. I played it many times per week for another year or so before selling it. Maybe they just didn't put in a powerful enough fan, or possibly it was poor placement, I'm not sure but you might want to try another fan at the back, I initially used a little fan just clipped to a post or something and pointed right at the tubes in the back then later installed a bigger fan grounded with an on/off switch so there was no fan running while it was in standby mode heating up.

    Good luck.
     
  7. If it's an overheating problem it'd probably be the effect of the heat on the internal electronics.

    Subbing an EL34? Hmm . . . (not what I would have done!)
     
  8. monkeybassist

    monkeybassist

    Oct 3, 2002
    Denver, CO
    Endorsed by Ampeg, DR strings, strong relationship with Surine basses
    Not what anyone would have done, but I finished the 3rd set and it sounded fine. What would you have done? No PA mind you, and no back up amp.
     
  9. I have a backup amp so that doesnt happen :p
     
  10. bovine mind

    bovine mind

    Jun 17, 2008
    San Francisco
    thanks very much for the information.

    thankfully the seller included the receipt for the retube. it clearly shows "6x6550" and a price around $250, which is almost certainly a full matched set. i called the tech [#1] and he confirms he installed 6 matched winged C.

    when tech #2 opened the amp, none of those tubes were inside. i sincerely doubt tech #1 would install tubes of different brands and not tell the owner. now i'm probably going to have to pay for the repair as it's been two months since i bought the amp used, when the guy i bought it from obviously replaced all the tubes and showed me a receipt showing the original retube. i should have checked, but i knew very little about tube amps at the time and trusted the guy as he's a part of the music community here.

    i called last night and tech #2 confirms there is some other damage from the tubes going out, they fried some other components when they failed. i'm fuming.
     
  11. monkeybassist

    monkeybassist

    Oct 3, 2002
    Denver, CO
    Endorsed by Ampeg, DR strings, strong relationship with Surine basses
    I have plenty of backup amps, just none at the gig. And given the choice between the guitarist's EL 34 and the Peavey 'tonemeister' you have listed in your gear I'd be using the mis-matched tube.:rolleyes:
     
  12. Nothing at all wrong with the Peavey Firebass. If you don't like the sound, then fair enough.

    I'd rather go for one set with a different sounding amp, granted, not getting the tone I ideally want, but still putting out sound. Rather that than swapping in a tube that can't handle the voltages of the amp and risk blowing something major in sed amp. But on saying that, maybe that's just me being reasonable :rolleyes:
     
  13. While I don't agree with subbing an EL34, it CAN take the voltage. As I recall it'll handle 800V. Instead of subbing I'd have probably pulled the bad tube and one from the other side of the OPT and run with four outputs. Not ideal but you have to get through the night.

    Paul
     
  14. I thought the EL34's maxed out a hundred or so volts lower on the plate? Either way, I wouldnt have done it.
     
  15. +1 EL34's I put in an old 70's Aus.amp all blew pretty quick- had to get JJ KT77's which were superb!
     
  16. monkeybassist

    monkeybassist

    Oct 3, 2002
    Denver, CO
    Endorsed by Ampeg, DR strings, strong relationship with Surine basses
    Not only did it make it through the 3rd set, it sounded good. The guitar player joked that we should swap tubes, thinking he had some kind of mojo I didn't somewhere. When I brought it in to the tech the following Monday he couldn't find anything wrong anywhere aside from blown power tubes. They were EH tubes which I later found out were Chinese made. After getting an extra fan on the back like I said earlier though, the problem was pretty much permanently fixed and it ran great 'till I moved on and on through more and more gear. The SVT-VR I have now (US made) has a huge fan from the factory. The only thing I did to that was install a kill switch for standby warmup, great sounding head.
     
  17. dgovaerts

    dgovaerts

    Dec 22, 2004
    maybe the next time anyone buys a used tube amp, just buy it and keep in mind that you have to service it, so you know you get your budget right.
     
  18. 800V max plate voltage is correct and about 27W plate dissipation.

    Paul
     
  19. Bassmec

    Bassmec

    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    Winged C's you bought, disappearing Willie nilli!, cant have that, call the fooking police, this is theft cant let wrong-uns like that get away with it.
    Bollox If I do a service I expect it to add value.
    Sharia Law is what we need, search his premises if he has a set of six svetlanas in his possession he is going to have to do without his left hand technique from now on.
    :bassist:
     
  20. rbonner

    rbonner

    Sep 25, 2008
    6550 is 44 watts diss, so the 27 is a huge step down.
     

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