Setting bias question

Discussion in 'Fisher' started by walyfd, Oct 10, 2013.

  1. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,714
    Location:
    Glen Burnie Md.
    Thanks Dave. That works for the Normal 800-C. So what do I do for the Executive 800-C. Way different circuit there. Do I measure the 120K out of circuit and the 68K and do the calc the same way?
     

     

    Please register to disable this ad.

  2. walyfd

    walyfd Well-Known Member

    Messages:
    715
    Location:
    Northeastern PA
    I tried this method on the 500B. Each resistor read 32.8 so I started fiddling with the pots. The highest the pots will go is 24.2! What's the workaround for that?!?!?!
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,565
    Location:
    Ball Ground, GA
    Larry -- Sorry I missed your post. The process would be the same with both models of the 800C.

    In one version, it is a 120K resistor that needs to be lifted and measured, and the cathode (pin #3) measured to ground, and then the combined resistance can be determined by the formula.

    In the other, it is a 180K resistor that is lifted, but the process is exactly the same.

    Walyfd -- in the 500B, the process is exactly the same as with the 800C as well, except that it is a 150K resistor that needs to be lifted and measured out of circuit. Then, with this resistor still out of the circuit, the resistance from the cathode of the phase inverter (pin #3) to ground can be measured, and this value, combined with the actual value of the 150K, plugged into the formula to determine the effective value. The effective value is then the value that is used to set the phase inverter plate load value by way of the Phase Inverter control, and the procedure given.

    Dave
     
  4. walyfd

    walyfd Well-Known Member

    Messages:
    715
    Location:
    Northeastern PA
    AHHHH... I failed to follow "THE FORMULA" and went about it like I did with the 202! This makes far more sense.
     
  5. Regnal

    Regnal New Member

    Messages:
    1
    Location:
    Australia
    Hello Dave,

    Reading through that procedure of adjusting the phase inverter - which is a lot more complex according to the SM of my Fisher x-101-d amplifier - I wondered if it would work in a similar way on my Fisher x-101-d model ?

    Regards
    regnal
     
  6. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,565
    Location:
    Ball Ground, GA
    Hi Regnal -- It will in fact work. In your case, and with the unit unplugged and turned off:

    1. Temporarily ground point A on the Fisher schematic for your unit. It can also be identified as the two terminals that are connected together on either of the two Phase Inverter controls.

    2. Measure the resistance from pin 3 to ground on each phase inverter tube, and record the resistance measured.

    3. Now measure the resistance from pin 1 to ground on each phase inverter tube, and adjust the relevant phase inverter adjustment so the reading is equal to the reading recorded for pin 3 of of the tube being adjusted.

    4. Remove the temporary ground connected in step #1 above.

    And that's it -- I hope that helps!

    Dave
     

     

    Please register to disable this ad.

Share This Page