SVT II Pro Premiere Edition with problems

Discussion in 'Amps and Cabs [BG]' started by Mik75, Dec 15, 2014.

  1. Mik75


    Sep 21, 2013
    Frankfurt, Germany
    Hi there!
    I just made a nice deal (that's at least what I've thought yet) that got me an Ampeg SVT-II Pro Premiere Edition (071/250).
    This thing has been played a lot and it has dings and dongs all over it, but I got it as "technically in perfect condition", with tubes that have "some 20 hrs".
    I already played the amp on a gig and it sounded really sweet. That SVT crunch I've missed so badly, I got it back! ;-)
    However, when testing it once again at home, I recognised the following 2 problems:
    - the mid tone control doesn't work at all (no matter which frequency is dialed in on the 5 position selector). Even turned all the way to the right (maximum boost) or to the left (maximum cut), there is absolutely no change to the sound.
    - the bias of the power tubes can't be set the way it's intended (green LEDs on). No. 2 is either red or red and green and No.1 is always red or red and green when turned all the way to the right.
    What could cause these problems? I would love to keep this sweet sounding head. but bringing it to a technician who repairs it for 6-700$ isn't an acceptable option for me.
    Thanks in advance for your input!
    Last edited: Dec 15, 2014
  2. The bias issue could be just miss-matched output tubes (hope for this over a bias circuit problem). The mids problem not likely not a "plug and play" fix, more likely a trip to a good tech. $600 to $700 for repair is not a good tech, just an overpriced one with no guarantee of quality.
  3. Mik75


    Sep 21, 2013
    Frankfurt, Germany
    Thanks for your answer. The guy I've got the amp from, already offered to take it back. But I love its sound and I'd love to keep it. I'll have to look for a good tech who's able to find the problems to estimate the cost of fixing them. I've found some information on the web that the mid tone control circuit uses one 12AX7 in the preamp circuit. Could a faulty tube cause the non functional tone control?
  4. Yes, as well as a bad ground, open inductor, open pot. Tube being the least likely on the list. An amp you really enjoy is much more valuable than one you settle on because of "cost". Most diagnostic bench fees run between $50 and $85 and at least a portion of that may apply to repair costs. If recently shipped the chances of a damaged pot or failed ground go up and neither is very expensive, as in less than $100.
  5. Bass 45

    Bass 45

    Jun 23, 2011
    Tempe, Arizona
    I had the same model - the pot for the mids failed on mine - so that would be my guess from here.

    Great sounding amp. I hope you get it right.
  6. Mik75


    Sep 21, 2013
    Frankfurt, Germany
    Thanks a lot for your answers. I already contacted a technician, I really want to keep the amp. it sounds so good! I hope it's only a defective pot...
    B-string likes this.