SVT CL Volume Drop, all Bias lights on

Discussion in 'Amps and Cabs [BG]' started by mr_goodbomb, Oct 15, 2011.

  1. mr_goodbomb


    Oct 10, 2009
    I dunno what is up with my SVT. I came in for practice one day, and the volume was just incredibly low. I checked the bias lights, and when I play, they all flicker, all three (or is it two? red and green?). I've had to practice with it a few times because it's all I've had, but sometimes it's a little louder, but not by much. I have to crank it pretty high to be heard at practice... which was never an issue before. I realize I'll probably have to take it to a tech, but they're so expensive around here, and far away... any ideas what the issue could be?
  2. jmattbassplaya


    Jan 13, 2008
    Sounds like tubes to me. Make sure they're all snug in their sockets.
  3. Indeed.
  4. B-string

    B-string Supporting Member

    First) Download the manual, this is the information age and readily available as a download at Ampeg (sorry if it sounds grumpy but you found your way here). The bias lights are covered in the user manual and will "flicker" while playing.

    Second) It could be a relatively cheap preamp tube, could be a bad output tube(s), could be an instrument cable used for speaker cable that is shorting. You could spend $400 for a tube set, with the downloaded manual get a close bias adjustment then still have to spend the money on a tech to find a cold solder joint. Which is cheaper?

    Make sure you are using a Speaker cable, not an instument cable to connect your amp to your speaker cab. Try the amp with a different speaker cab, try a different instrument cable from your bass and finally does your bass have a battery that needs to be changed? These things will at least make sure you don't make a trip to an amp tech with the amp not being at fault. :)
  5. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    +1 on B-string's advice.

    One more thing to try: connect a patch cord from the "preamp out" to the "power amp in" and see if it solves the problem. The power amp in jack has a switch in it, sometimes the contacts get corroded. Sometimes just putting a plug in the jack and pulling it out again is enough to get good contact again.
  6. mr_goodbomb


    Oct 10, 2009
    I appreciate that. Is there any way to test if the tubes are bad?

    I have checked the cables many times just to be certain, but next time I go over, I'll bring the instrument and speaker cables from my guitar amp just to be sure.

    No battery, I used Gibson Grabbers.

    Funny, though, when I mentioned the flickering bias lights on another forum, they all overwhelmingly said "IT'S GOING TO EXPLODE TAKE IT TO A TECH."
  7. 4StringShooter

    4StringShooter Inactive

    Jun 26, 2011
    London, Ontario, Canada
    GBX Member #1
    DO have the Tech check the GROUND WIRES to the power tubes as well. Mine were ALL bad when I had it torn down, and benched. After that, with ALL new Power tubes, a biasing AND a new Pre-Amp Tube, it sounded NEW. Never been happier with it.

    Oh, ...those lights on the back are ****. DO NOT trust them. Get it biased by A Tech !!!!!!!!:ninja:
  8. 4StringShooter

    4StringShooter Inactive

    Jun 26, 2011
    London, Ontario, Canada
    GBX Member #1
    << You could spend $400 for a tube set,>>

    Just where the hell do you guys shop? A totally NEW ...FULL set of 6550s cost me 90 per PAIR....$270.00 Canadian. A new 12 AX7 was $27.00.:ninja:
  9. B-string

    B-string Supporting Member

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