where is the bias resistor on a DRRI?

Discussion in 'Amp Tech Center' started by tedro, Feb 24, 2015.

  1. tedro

    tedro Tele-Afflicted

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    where is the bias resistor on a DRRI?

    thanks in advance.


    edit: i mean the resistor which value can be changed--so the adjustment pot's range can be altered..
     
    Last edited: Feb 24, 2015
  2. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    If you lay the the amp down on its face, on the chassis there is a 1/4" jack looking thing with the pot inside, I think a flat head screwdriver operates it. Things are tight, I used one of those sets of plastic screwdrivers that are about 5" long.

    Hopefully someone will correct me if I'm wrong, I remember clockwise cooling down the bias and counter-clockwise heating it up.

    [​IMG]
     
  3. tedro

    tedro Tele-Afflicted

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    sorry, waparker, i didn't mean the adjustment pot, i meant the resistor that can be changed--to change the pots range. ?

    you're correct on the over/under direction, ;-)
     
  4. BobbyZ

    BobbyZ Doctor of Teleocity

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    You know I can never rember which way to turn the bias pot ! What I do is hook the voltage meter with no tubes in the socket and check the bias voltage while slowly turning the pot. That way if there's dirt in the pot or a bad spot you'll see it on the voltmeter instead of on the red plates of the tubes. (that pot doesn't get turned often so dust or whatever can build up inside)
    More negitive voltage is cold like -40 and less is hot like -10. I set it all the way cold then put the tubes in and bias them.
     
  5. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    R59
     
  6. BobbyZ

    BobbyZ Doctor of Teleocity

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    Whoops your after the range resister. I'm not sure on the reissuies.
     
  7. tedro

    tedro Tele-Afflicted

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    and is that a typical resistor sitting on there, that can be changed? although, i have UNsoldered from the board...i was unable to resolder to it. :( any advice, i need a lower value?...to under bias further (hotter). thanks.

    btw, you that cage they put in now, behind the power tubes, mounted on the standard back board?

    it's ok to remove those, right? they only did that so ppl won't stick their hands up there when hot, right?
     
  8. Wally

    Wally Telefied Ad Free Member

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    Editted due to lack of mental engagement on my part in that post.
     
    Last edited: Feb 25, 2015
  9. Jack Hester

    Jack Hester TDPRI Member

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    Is there a schematic handy? I'd like to see the Bias supply.

    Jack
     
  10. Wally

    Wally Telefied Ad Free Member

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    Google Schematic heaven...go to Fender...go to Deluxe Rever Reissue..under the Reissue heading on down the page.
     
  11. Johnny Cache

    Johnny Cache Former Member

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    +1 This ^^^^^

    If I remember it's 22K if you replace it with a 10K the vari-pot resistor works better. You could just piggyback another 22K on it in parallel which comes out to 11K, that's what I did on my DRRI when I upgraded the PT to a Hammond.
     
  12. tedro

    tedro Tele-Afflicted

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    thanks a lot guys.
     
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