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How do I check the bias on an SVTII

Discussion in 'Amps and Cabs [BG]' started by Martizmo, Apr 20, 2009.


  1. Martizmo

    Martizmo

    Mar 26, 2009
    Metro Detroit
    Or any SVT, but I have a 92-93 SVTII.

    Also, mv or ma What is the idle voltage or current.

    And what type of 6550's do you prefer and why?:bassist:
     
  2. Steveaux

    Steveaux Supporting Member

    Jul 1, 2008
    The Wilds of NW Pa.
    Start by asking in the "Amps" section.
     
  3. wvbass

    wvbass Supporting Member

    Mar 1, 2004
    West Virginia
    ...and finish by taking it to a qualified tech. Past that, PM Jerrold Tiers and see if he can help.
     
  4. Directions inside [the amp] if I recall.
     
  5. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    With your lack of electrical skills, "What is idle voltage or current?", this is not something that you should be attempting! Take the advice of WvBass and take the amp to a tech.

    Paul
     
  6. Martizmo

    Martizmo

    Mar 26, 2009
    Metro Detroit
    TalkBass Forums > Bass Guitar Forums > Bass Guitar Forums > Amps [BG] > How do I check the bias on an SVTII

    READ IT AND WEAP:crying:
     
  7. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Despite your ignorant reply to what was a response concerned for your safety, ask yourself this. If an experience tech refuses to work on an SLM era Ampeg, WHY??? If it's so easy why won't HE do it? Working on amplifiers is how he makes his living. Now ask yourself what gives you the skill set he lacks?

    Setting bias correctly is not just about mA through a tube or mV across a resistor. It's about removing crossover distortion and about the compromise between running "hot" and shortened tube life or running cold for a longer life. Warmth and sterility. Do you even own a dummy load rated at 300W or a scope? Needed items for a proper bias setting.

    In your original post, which I quoted, you asked "What is idle voltage or current." you missed out the "the" from the question thus asking a different question than the one you intended.

    Ok, that said, I'm done. I will not be a party to what I consider unsafe practice. Please endeavour not to harm yourself!

    Paul
     
  8. Martizmo

    Martizmo

    Mar 26, 2009
    Metro Detroit
    I guess it does sound a bit more complicated then I anticipated. I was just reading the SVT CL manual and they make it sound much easier with the whole LED blikin g thing. I just wanted to be sure I had the proper Voltage is all. If I need a dummy load and a scope Im SOL.

    I'm no Rocket Scientist, otherwise I would be working for NASA.
     
  9. Steveaux

    Steveaux Supporting Member

    Jul 1, 2008
    The Wilds of NW Pa.
  10. The requirements are printed on the back of the chassis.

    Can't check mine, it's taking up space at my folks house right now. But from memory it's something like 74 or 76 mA (or is it 0.74 or 0.76mA, meh, dont think it would be as low as the latter, a couple orders of magnitude shouldnt hurt :bag: ).

    I've got Svetlana 6550Bs in my SVT-II at the moment. Sadly I was new to tube amps when I got mine retubed (when bought, the Philips ECG (Sylvania) 6550A's that were in it were on the way out). I soon afterwards found out these tubes were pretty poor. Sonically they are perfectly fine and not too far from the original tubes that were in there, more the build quality was an issue. But mine has run for years with whats in there, so I guess I was lucky.

    If having a choice now, I'd probably go for JJ KT-88s or TAD 6550 (or KT88) or possibly the new reproduction Mullards (though I will admit I dont know if they are doing KT-88s/6550s)

    Take it to a tech who isn't so stupidly fussy about amps :)
     
  11. Martizmo

    Martizmo

    Mar 26, 2009
    Metro Detroit
    Paul,

    My tech is not an authorized out of warranty dealer for Ampeg. He gets little support from them starting in the SLM error. He feels pretty comfortable working on the older models but will not work on new Ampegs, Crown, Hartke and a few others (sign posted at front counter).

    If someone was to set my bias using the scope method, would in not be better to use the actual speaker cab Im going to play through rather then a dummy load?

    My friend has a tube biasing kit(for current draw method) and an extensive manual. He has biased class A A/B amps in the past. Im not having any major problems, I just want to make sure nothing is too far out of wack. How long would it take for a tech to bias an amp?

    If I were to bias the amp I would use only one hand while the amp is hot.
     

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