Reverend Hellhound Bias problem

Discussion in 'Shock Brother's DIY Amps' started by OahuClay, Sep 14, 2021.

  1. OahuClay

    OahuClay TDPRI Member

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    Working on a Reverend Hellhound with way too cool bias 20 ma for 6L6's. It is supposed to be per manual 46ma. That asside the manual states that you should ask for 46ma tubes from vendor. Ok I'm not going there for a variety of reasons, here's the circuit. Drawn by someone not Reverend and I'm ready to try something. I have tested bias with different 6L6's new russian NOS american and I have about the same idle 20 ma. I have seen other posts by people with the same problem but no solutions that I've seen from peoples posts anywhere. I need the Bias Voodoo guys on this one. reverend_hellhound_partial.jpg
     

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  2. Wally

    Wally Telefied Ad Free Member

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    So….this is a non-adjustable fixed bias with a switch that throws in a bit of cathode Biasing to lower output??
    Have you considered adding a trim pot to adjust that fixed bias voltage? That -54.4vdc or even the schematics -52 is not going to allow much current draw, ime. and..what is the plate voltage at that 20ma of current draw? If it is around 495vdc, then at 20ma of current draw, you are somewhere near 33% of max plate dissipation…pretty cool. At 46ma of current draw and 495Pv, it would be approx. 76%. However, without real life measurements of the plate voltage at any one bias setting, everything is merely hypothetical.
    What does that 40/60 switch that takes that cathode resistor in or out of the bias picture do to things?
    It is odd, ime, that all of your power tubes are exhibiting such ‘matched performance’.
    We need to know the plate voltage.
    And….I don’t know that one can order ‘46ma’ power tubes. Some distributors do have insight as to what tube parameters put a certain amp circuit into the range of plate dissipation for which the amp manufacturer designed the circuit, though.
     
    Last edited: Sep 14, 2021
  3. Ten Over

    Ten Over Tele-Holic

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    Reduce the value of the 68K resistor that is closest to the 220K resistors. Try 56K first and see what happens.

    Or, replace that 68K resistor with a 47K resistor in series with a 25KL pot that is wired as a variable resistor.
     
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  4. OahuClay

    OahuClay TDPRI Member

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    thats what I did, thanks, useda 56k and a 10 k pot instead of that 68 k, it got me where I need to be.
     
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  5. Wally

    Wally Telefied Ad Free Member

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    If you don’t mind sharing, for our edification, where did your bias numbers end up? PV and current draw?? Ten Over’s suggestion of a static 47K resistor with a 25K pot to give a swing from 47K to 74K would give one a wider range and therefor widen the selection of tube parameters that one could use….But…if a 56-66K sweep got it done, that is fine,too.
     
  6. OahuClay

    OahuClay TDPRI Member

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    Yes this 46ma thing sounded stupid to me, I just go by the bias tables and thats way to hot, installed a variable bias and set it much lower
     
  7. Wally

    Wally Telefied Ad Free Member

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    I suppose this is banging my head against the sky; but having spent whatever time I have spent giving whatever insight I could here on this problem and not having any experience with this amp, I have a curiosity as to the plate voltage at whatever bias point one arrives. It would be of use to know what plate voltage at what current draw a Rev Hellhound operates in case one comes down the pike, and since there is no schematic available that I f8nd, your personal insight would/could be of value.
    I have no idea if the voltages on that drawn schematic have a lot to do with your actual amp. I figure ere is something over 425pv there, but I don’t know. As I noted, 46ma at 495Pv is around 76%of MPD. That is not a bias point which would bother me IF the user liked what they were hearing and feeling while playing the amp. At 425Pv, 46ma gives one about 65% of MPD. At 375Pv, 46 ma gives a figure of 57.5%.
    No matter….if one comes around, I’ll manage.
     
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