Checking bias of my Mark III

Discussion in 'Amps and Cabs' started by cisspcism, Feb 18, 2009.

  1. cisspcism

    cisspcism Member

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    I have the 60 watt non graphic eq purple stripe with 2 6l6 power tubes.
    I have the Weber bias rite.

    Plate voltage measured 438 and the mA measured 36.9 to about 37

    so according to eurotubes 6l6, el34, 5881, all are 25 watts
    where on webers site they have 6l6 at 30 watts and el34s at 25 watts

    so when I do my caculation

    25 / 438 plate voltage = .057 (total dissapation(not sure if that is right word) and 37 mA is about 65% of that.

    now if I use the ted weber wattage for 6l6s
    30 / 438 plate voltage = .068(Total Dissapation) and 37 mA is about 55% of that.

    so my conclusion is if I rate the 6L6 at 30 watts my amp must be very, very cold, and if use the 25 watt measuring for 6L6 the my ampo is biased about right.

    Am I right?
     
  2. Blue Strat

    Blue Strat Member

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    55% is not VERY VERY Cold. Biasing is not an exact science. % dissipation numbers are only guidelines. NEVER exceed 70%. Don't exceed 65% if tube life means anything to you (particularly with new production tubes), the bias control is not an overdrive control, etc.

    Stay under 65% and use your ears. Better yet, let someone else to the adjusting and reading so your ears aren't influenced by the numbers you're seeing with your eyes.
     
  3. kludge

    kludge The droid you're looking for

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    Are you using MESA branded tubes?

    They took the bias control away to keep you from doing what you're trying to do. For better or worse, the bias setting is what MESA/Boogie thinks is appropriate for tone and reliability.
     
  4. cisspcism

    cisspcism Member

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    I am not trying to bias thye amp, I just replaced the tubes with TAD 6L6 power tubes and I was just checking the bias to make sure the tubes werent to hot
     
  5. cisspcism

    cisspcism Member

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    but most important, do I use the 30 watt or 25 watt for the 6L6? I would like to know if I am at 55% or 65% of total dissipation. I just want to make sure as i saw conflicting information.
     

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