Svt 2 pro help needed.

Discussion in 'Amps and Cabs [BG]' started by jdubbass38, Jun 17, 2019.

  1. jdubbass38


    Mar 20, 2009
    long story short... I brought my used amp of about a year... svt 2 pro into the tech to have a once over along with fixing an issue where after playing for 10 minutes or so I would get a slight power drop in volume level. If I put it on standby the issue would correct itself and again 10 or so minutes it would drop in volume.

    My tech was convinced it was power tubes so he replaced them and one pre amp tube. $300+ later my amp is worse off then before. My v4b at half volume is louder then my svt 2 pro at half volume. The pre amp seems to distort very quick as well. I had to run the master at 3/4 and gain at 3/4 to get somewhat usable volume... I believe it should be ripping my face off thru my 810.

    Any thoughts appreciated.

  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Did your tech run any diagnostics to determine AND CONFIRM what the actual problem was with your amp before replacing tubes?
  3. Warpeg


    Jun 20, 2005
    The first thing to do is get back in contact with that technician.
  4. jdubbass38


    Mar 20, 2009

    I don’t believe so, I’m hopeful meeting with him tonight to review what he did or “did not do”! This is the second time the amp has gone back. When I picked up the amp the first time I plugged in and got no sound at all. The peak light was flickering on and off sometimes staying on like it was getting a signal but nothing (bass/ instrument cable) was plugged in yet.
  5. Wasnex


    Dec 25, 2011
    Ultimately the problem may be as simple as a tube, or there may be faulty components that a competent tech needs to identify and replace. Unfortunately replacing a preamp tube and a sextet of 6550s costs about $300 (or more).

    Your tech may be in over his/her head, or it could be one of the new tubes suffered from infant mortality. This is not unusual and if one of the new tubes failed it should be covered by a warranty. However, when an output tube fails in an SVT it's common for it to take out a screen resistor. The screen resistors are low wattage so they act like fuses to protect the amp from major damage when the tube fails. The tube warranty does not cover collateral damage to the amp.

    You could try to narrow down where the problem is. You can plug another preamp into the power amp on the back of the 2-Pro and it will bypass the preamp. If you use the preamp out from your V4B make sure you have speakers attached to both amps. You could also run the preamp from your 2-Pro into your V4B. This is assuming your V4B is a reissue.

    Good luck!
    jdubbass38 likes this.
  6. jdubbass38


    Mar 20, 2009

    Great idea with the pre amp / power amp testing each part. Yes I have a v4b reissue so I could do that
  7. get a new tech. seems like he's just guessing and not actually diagnosing.
    hbabels and jdubbass38 like this.
  8. jdubbass38


    Mar 20, 2009
    I figured I should close this thread on a good note. It ended up needing new driver tubes, (3) 12au7’s causing the reduced power I was seeing after replacing the power tubes. Amp is home and running strong, no power dips as it was doing before. Couldn’t be happier having this monster running again! Should last me a long time now with new power and driver tubes in place.

  9. Wasnex


    Dec 25, 2011
    SVTs are a bit unusual in that the bias of the output tubes is actually controlled by the driver tubes, so this makes perfect sense. Glad the beast is healthy again :thumbsup:.
    jdubbass38 likes this.
  10. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Ya, some will replace driver tubes along with the power tubes as a matter of course. Not me, of course...but I will have them tested if I think they're weak.
    jdubbass38 and Wasnex like this.