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SVT 2Pro Biasing

Discussion in 'Amps and Cabs [BG]' started by Alexander, Apr 16, 2010.

  1. Alexander


    Aug 13, 2001
    Seattle, WA
    How often does this amp need to be biased and is it possible to affect the biasing during (careful) transport? I had my amp serviced shortly after I got it and have now had to bias it again a couple of times since (maybe 3 times in a month or so). Is this normal or is it possible something is going wrong with the amp? When the tech changed the tubes, he mentioned they looked like they had been overheated\overbiased, causing them to fail and I want to be sure there isn't a fault somewhere that may cause the same issue to happen again (I bought this amp used).

    If it is normal or tubes require some sort of "settling in" period, then cool - maybe I'm just being paranoid...

    Thanks for the help.
  2. Once the bias has been correctly set it should need no more attention for a good long time. Three times a month is just ridiculous!

  3. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Why does it need to be repeated? How do you know?

    It's not normal, not for a decent quality tube.

    Possibly the first bias job was done wrong. Maybe the tubes have been overstressed the whole time... that can make them change.

    or there COULD be a problem with the amp parts, not the tubes...... impossible to tell, my ESP is affected by that volcano and I am not gettin the vibes.......
  4. No need to be an ash about it :D Just kidding JT, kind of asked for it, left an open door ;)
  5. Hi.

    IMLE the CP tubes needs close attention for the first 20 or so hours of operation, but after that an annual check is sufficient.

    I tend to check mine a bit more frequently, but then again I have trimmers and test points for every single tube on my Fame.

    I hate to disagree with You on this Paul, but my experience has been almost totally opposite when it comes down to CP tubes and busy techs/DIYers.

    However, if the tech is a good one (or the DIYer an informed one) and he/she lets the amp work for a longer period of time checking the bias along the way, I do agree with You. Sadly that doesn't seem to be the case nowadays.

  6. Alexander


    Aug 13, 2001
    Seattle, WA
    Thanks - I've not had a full 20 hours on these new tubes and have maybe played the amp 12-15 hours if I had to guess.

    The SVT 2Pro has two lights on the back of the amp that are supposed to glow green when the amp is properly biased. When it isn't, one or both of the lights are not lit or the red lights are lit. The tech biased it the first time and I did it the other two. After playing it for a rehearsal and one gig, both lights were out in the back, so I adjusted the bias back to where both showed green. After another rehearsal and gig, I checked and only one lamp was green. So I biased it again.

    In addition to the lights, you can tell by increased hum. If it doesn't settle down quick, I may have it looked at again.

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