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Tube techs AD200 Bias Question?

Discussion in 'Amps and Cabs [BG]' started by demon666, May 11, 2010.

  1. demon666


    Jul 16, 2005
    Providence RI
    Looking for a little help with this. Recently retubed my Orange AD200B. Now biasing the amp I'm getting some strange (to me) readings.
    The output tubes are in pairs 1+3, 2+4. I can bias tubes 3 and 4 to Orange specs 18-20ma but tubes 1+2 show only 5ma. Swapped around the tubes, swapped out the PI tube(12AU7) doesn't make any difference. Is this normal on this amp? Checked under the hood for burnt resistors bad solder joints, etc.. Can you guys give me some insight.
  2. bluesrx

    bluesrx Supporting Member

    Mar 31, 2006
    Lakeland, Fl.
    I'm not familiar with this amp at all... but I would check the coupling caps. I cap leaking DC will throw the bias off.
  3. demon666


    Jul 16, 2005
    Providence RI
    Thanks I'll check 'em. Found a bad resistor (47K) coming off the tube failure fuse/leds

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