Fender Bias Circuit Wiring

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by daveyajd, Jan 23, 2012.

  1. daveyajd

    daveyajd Member

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    Hey guys and gals. I have a 1970 Fender Bantam Bass that I use as a guitar amp. Works great. I am in the process of upgrading a few parts and checking the circuit changes that were performed by a previous tech I worked with. When comparing schematics of bias adjustable Fenders of the day I notice a few differences. My bias pot seems to be wired backwards on the two outer lugs. The previous tech said the original was bad and replaced with what you see.[​IMG]

    [​IMG]

    Does this matter or will it just change the directions for increasing/decreasing m/A? Also do I need to change these resistors to blackface spec'd 220k and 100k/82k? What difference would that make?

    http://i422.photobucket.com/albums/pp301/drivenbyastronauts/Amp Pictures/th_Resistorchange.jpg
    Thanks for any help.
     
    Last edited: Jan 23, 2012
  2. daveyajd

    daveyajd Member

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    Sorry, I can't get the pictures to show up like they should. Any info you can give while I work that out is appreciated.
     
  3. Blue Strat

    Blue Strat Member

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    I can't see the photos but if connections to the outer two lugs of the pot are reversed and the middle lug is the same the direction of the pot rotation will be opposite, that's it.
     
  4. jbltwin1

    jbltwin1 Member

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    Like Mike said, it's just backwards. Down is up and left is right. It just adjusts backwards, no big deal.
     
  5. daveyajd

    daveyajd Member

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    Last edited: Jan 23, 2012
  6. TweeDLX

    TweeDLX Member

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    Your pics are way small. Can you get them bigger?
     
  7. daveyajd

    daveyajd Member

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    Ok, the bias pot wiring is not critical. Any experience with swapping out the resistors for more blackface era accurate ones?
     
  8. Blue Strat

    Blue Strat Member

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    Yes, lots. In some amps it sounds good, in others, it can make the amp mushy. In the end, the only thing that matters is what works for you. It literally take 2 minutes to find out. Less time than it takes to get an opinion here that may not match your own.

    Tip: Before being unduly influenced by opinions on a forum, just try different things. Opinions be damned (except your own)!
     

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