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SVT2 PRO volume issue

Discussion in 'Amps and Cabs [BG]' started by Mandril, Mar 6, 2008.


  1. Mandril

    Mandril

    May 10, 2006
    Madrid
    I have this SVT2pro I bought used two years ago, I think it's a 2000 model. The issue is that it started making a weird noise when turned on. It sounds right for a while, and then the volume starts to oscillate, it goes down & up for 4 o 5 seconds, sometimes 10, and then it stops and sounds right again, but after a few seconds the volume starts to oscillate again. Sometimes you can't even hear the bass. After a few minutes the whole thing stops and the amp sounds good. It's like it only happends while the tubes are warming up, but it always occurs when I turn the amp on, even if I let the amp getting warm in stand-by for half an our.
    So, I thought it could be the tubes, though the guy that sold it to me said he had just taken it to get the tubes replaced, so I took it to a tech, and change all the tubes that haven't been changed for 4 or 5 years! So I get home, I turn it on, and... same problem! :mad: Now when I turn it on, and same thing, volume oscillates for a few seconds till the amp is warm (after 20 mins or so). It is true that after replacing the tubes, the amp sounds awesome (once that is warm), but I'm concerned that it could deliver a bigger problem, and also I can't trust in it's reliability: I can't take it to a gig!!! I don't know if it's going to stop sounding in the middle of a song or something worst!
    So, after all this reading, does this happened to anyone else? Ever? Or someone knows why could this be happening? :crying::crying::crying:
     
  2. ZolkoW

    ZolkoW

    May 8, 2006
    Hungary, EU
    not an Ampeg player, but once or twice happened similar thing to me.. I think, it was only the speaker cable, which I have replaced since. or the guitar cable, I'm not sure.
    I had no problem since that.. hope this helps.

     
  3. maxbass

    maxbass

    May 22, 2002
    Milano Italy
    It is almost impossible to address correctly the problem without seeing and hearing what happens.
    I'd refer to a technician as soon as possible, once you can assume that the problem isn't elsewhere (bass electronics, jack, speaker cable, external effect...)
     
  4. Mandril

    Mandril

    May 10, 2006
    Madrid
    I've tried different basses, jacks, cables, cabs... and it's always the same thing...

    And I'm bringing the amp to my tech this weekend, but when I talked to him he seems a little confused, as he checked the amp and everything looked right when he returned it, and he doesn't knows what could be causing this problem... I guess he'll find out, but if someone has any tip on this, would be great!
     
  5. maxbass

    maxbass

    May 22, 2002
    Milano Italy
    How old are tubes?
     
  6. Mandril

    Mandril

    May 10, 2006
    Madrid
    new, the tech changed it a month ago, as it was my first thought...
     
  7. maxbass

    maxbass

    May 22, 2002
    Milano Italy
    Did you ever had the problem before replacing tubes?
     
  8. Mandril

    Mandril

    May 10, 2006
    Madrid
    well, it started about 2 months ago, so then I replaced the tubes, but the problem is still there
     
  9. maxbass

    maxbass

    May 22, 2002
    Milano Italy
    I'd change technician...:confused:
     
  10. Mandril

    Mandril

    May 10, 2006
    Madrid
    lol... he's one of the best tube techs in Madrid. Obviously if he doesn't repairs it this time, I'll try another one. The first time he only replaced the tubes, so I guess he'll figure something out.
     
  11. I wouldnt say he is one of the best techs if all he did was replace tubes.

    A good tech would have checked everything inside the amp. And only replaced tubes if they were needing replaced.

    I dare say, it might be that the old tubes were microphonic, and so are the new ones. Either that or he didnt replace all the tubes.
     
  12. Mandril

    Mandril

    May 10, 2006
    Madrid
    He did replaced all the tubes, as I have all the old ones... but the old ones were so heavy burnt that he probably guessed it was the major problem...

    but he also set up the bias, and checked the amp, but I guess he didn't noticed this issue, as it's quite irregular: some days it happens as I turn the amp on, other days it starts after 10 minutes, and even one day it didn't do it...
     
  13. Mr Matt

    Mr Matt Supporting Member

    Jan 18, 2005
    Washington State
    I had a problem similar to this on one of mine, but it was was more of a distorted declining volume issue.
    The tech I took it to cleaned all the 1/4" jacks on the back, preampin/out, effects loop, speaker jacks... with CRC electronic cleaner (turned off of course) & plugged in/out a 1/4" plug a few times, leaving it in until it dried.
    That did the trick for my issue, it turns out that the switching jacks on the Pro's sometimes get corroded for no apparent reason.

    It's worth $3.50 for a can to try!
     
  14. Mandril

    Mandril

    May 10, 2006
    Madrid
    Interesting... I'll try
     
  15. loend68

    loend68 Supporting Member

    Jan 14, 2008
    NH
    Endorsing Artist: Spector Basses, T.C. Electronics
    I had the same problem with two of these amps. After alot of back and forth with the repair shop, I believe they found issue with a preamp tube and one or more tube sockets. I'll see if I can find the repair bill.

    Good luck! It's a very frustrating problem.....
     
  16. glockrig

    glockrig

    Feb 28, 2008
    lafayette, la
    i had a similar problem with a hartke 350, and took it to a tech who pronounced it in good health, plugged in and fired it up on the spot when he said it was fixed, and it actually did the same thing with the tech there...i left it with him as he admitted that the amp didn't do that when he powered up and played thru it...he was able to fix the problem and the amp played fine after that...however, i'm running glocklenklang heads now and they are great!!
    :bassist:
     
  17. Willem

    Willem

    Dec 26, 2005
    Belgium
    Why do people always assume it's the tubes?
     
  18. Easiest (granted, not cheapest) thing to replace.

    They are made of glass, they must be fragile :rolleyes:
     
  19. Mandril

    Mandril

    May 10, 2006
    Madrid
    Yeah, anything but cheap... I spent 400 € in tubes!!! Bought best tubes available, when it stops making this thing, sounds awesome, but hey, didn't solve the problem!!! :crying:
     
  20. Well each tube produces a certain wattage, Everytime I saw volume dropping issues (often in guitar amps), one or more tubes needed to be changed.

    Often tubes and volume drops are related.
     

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