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Thread: Need advice RE Hammond E100 bias

  1. #1
    ppp Pianississmo mwhca@iafrica.com's Avatar
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    Need advice RE Hammond E100 bias

    I am measuring the negative bias voltage which is supposed to -22vdc. I am measuring around -38vdc. This was before a cap replacement. All caps replaced. Zener diode replaced. No difference. What could this be and is it a problem. Organ playing perfectly but I don't want to kill any tubes!

  2. #2
    mp Mezzo-Piano KC9UDX's Avatar
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    Well you certainly won't damage a tube of it's grid voltage is too far negative. I suspect you may be measuring this wrong, but I could surely be wrong about that. Are you measuring control grid to cathode? Or grid to ground? How is the tube biased? Of course, I'm not familiar with the E100 at all, so someone who is may have a better off-the-cuff idea of what's going on here.

  3. #3
    ppp Pianississmo mwhca@iafrica.com's Avatar
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    Thanks for your response. I measured the voltage from the 3 pin plug on top of the amp that I believe is there to measure the bias for the pot to set to zero and the -22vdc reference

  4. #4
    mp Mezzo-Piano Jyvoipabo's Avatar
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    Hello,

    Refer to the service manual.

    There are 2 amplifiers.

    A reverb amp with a fixed bias of + 22 Volts. Here is the zener.

    A main amp with a fixed negative bias circuit of - 22 Volts and a balance adjustment. No zener in this circuit.
    If you find -38 Volts instead of -22, i think you made a wiring error.
    Check the -22 Volt filter cell wiring on the power supply and in particular the load R364 5600 Ohm.

    JP
    Last edited by Jyvoipabo; 11-08-2018 at 10:26 AM.

  5. #5
    ppp Pianississmo mwhca@iafrica.com's Avatar
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    Thanks JP

    Sorry yes I got the 22v Zener mixed up I the equation!

    The fixed negative bias is where I am getting the wrong voltage. I have not changed any wiring. Please can you assist with volt filter cell wiring location etc..
    Thanks.

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