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Svt classic Bias when not playing

Discussion in 'Amps and Cabs [BG]' started by Auslaender, Jul 20, 2012.

  1. Auslaender


    Jul 14, 2012
    Hello and greetings from Italy, fellow bassplayers, new to the forum and new to the svt classic and already I have a question for you, but first of all a brief summary of what happened so far: I was playing a Fender Preci hot rodded through an SVT Pro 3 and a SVT 610 HLF cab and decided to change to the SVT classic. When it came first, I had to play with the master at 10 (gain at 6 or more), without basically hearing myself playing. Returned the backbreaker to the shop and got it back yesterday. "Wrong bias settings" said the tec. Now everything sounds fine, I'm playing with the master at 5 and I'm very very happy with my sound (the guitar players aren't...they always want me to lower the volume :)
    But here's what I've noticed: when the amp is on and not in standby, one of the bias leds (the left one, seen from behind) shines bright, but there's no light on the other one. As soon as I start playing, the right bias led shines up in a bright green. Is this the way it's supposed to be? Thanks for your help! Cheers and rock on!
  2. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    You may have either a bad bias light or the tech didn't bias that set correctly. The user manual available in pdf form on the ampeg website gives you detailed explanations of the bias light system.
  3. I'm not a tech, but from what I remember reading in my SVT's manual (my SVT as a 1994 SVT Classic, but it should work the same way that yours), the user bias should be set so that both green leds are lighting up when you don't play, and they can turn red when you play. Following that logic, the right side of your amp might not be set high enough. Check your manual to see how to do that and to make sure your amp works exactly like mine.
  4. Auslaender


    Jul 14, 2012
    thanks to both the users above, will look again today and try to set the bias according to the manual.
  5. jarrydee


    Oct 22, 2011
    use your fingernail and turn the bias knob to the until the green led kicks on, then turn it the other way until the red led comes on, then back it off a little until the red led goes out
  6. I have a vintage SVT, so I don't have the bias lights. But I recall reading about this in another thread, apparently those bias lights can lie! If it sounds good now, trust your ears and your tech, not those lying lights.
  7. Auslaender


    Jul 14, 2012
    the problem is: my ears may say "everything is allright boy" but my brain insists: "if one is green, what happens to the other three valves?" Worst case: I'll have to change "only" three valves. Guess I have to do it anyway, bought an used one...
  8. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Bah, just play it till you can't. If it sounds good, that's what's important, not the bias lights. SVT's aren't as fussy as those bias lights might make you think sometimes.
  9. mrkreuzschlitz


    Jun 30, 2008
    Dacula, GA

    If you're really worried, get the tools (multimeter etc) to check it yourself.
  10. hello, needed some confedence about this head today so i am here before i spend money to find out if my classic is broke. its a 2004 made in the usa model. the back bias lights dont seem to be working as a team to me because they both dont show green for [go] right. the number one shows green right away and when turned clockwise turns red like you mentioned then i backed it down until it became green again. number 2 however is blank until i turn it clocjwise and then it turns red and wheni i back it down it becomes blank no color but according to the first bias light i should be into the bias green zone if that makes any sense. but nothing i dont feel like the sound is crackling or anything i cant turn it up pass 3 in the house and i play thru a 4003 ric. i dont get any hum once i turn my bass and treble controls on from my bass. i always turn them off when i stop playing/practice. anyway am i in trouble without this green light or can i or better yet would you use it without the second side bias light on. green. thanks, mark. appreciate any and all assistance please.
  11. 4StringShooter

    4StringShooter Inactive

    Jun 26, 2011
    London, Ontario, Canada
    GBX Member #1
    Take it to a tech, and have the Bias set. After that..IGNORE those dam lights!!!!!! They were the WORST thing Ampeg EVER put on an SVT !!!
    I owned one, and can attest to that.:ninja:
  12. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I have to agree. Most of the time, they just drive people crazy. I know enough to ignore them so they don't bother me, but they sure drive folks on here crazy sometimes.
  13. Auslaender


    Jul 14, 2012
    yes they do, but there's areason for that: when someone tells you (maybe the user's manual) that both lights should be green and on, and you don't have them both on, then you may have some doubts like...do I get everything I can get out of that monster or not? Like in my case the bias setting lead to a volume improvement of I would like to say +50%. What could a proper setting give me? And btw: I' sure no look-all-the-time-at-the-leds-trembling guy, I'm more the I leave everything as it is and play the hell out of it...:bassist:
  14. doomloop


    Mar 1, 2011
    Portland, OR
    I have a similar issue where the right light works as in the manual and the left light would be off until I played then green and into the red, as the manual.

    I adjusted it so the left green light was on-ish with no appreciable difference in tone.

    I recently had the bias checked and it was all good. Now I'm thinking about setting it back to where it was, with the left light off, just because it was the proper, tech checked bias setting, but also am thinking why bother...it was maybe a turn of 1/12th if that on the little screw...

    Learning not to be too uptight about this stuff as the posts go on...:cool:
  15. skychief


    Apr 27, 2011
    South Bay
    Not to complicate matters..but know that underbiasing causes too much current flow in the tubes. Thick 'n fat tone, but the tube life is drastically shortened. That could get expensive ($240 for six 6550's) to be replacing output tubes every 6 or 7 months.

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