1969 Fender Bassman Circuit

Discussion in 'Amp Tech Center' started by kramazeek, Feb 26, 2020.

  1. kramazeek

    kramazeek TDPRI Member

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    Hey all, I recently picked up a 1969 Fender Bassman with an ac568 circuit with the intent of having the biassing modded to the aa864 circuit spec. When it arrived and I peaked at the circuit (I know very little) it looks like the telltale tan resisters of the ac568 circuit are already gone. I had read in a different post those resisters can’t be removed without altering the biassing in some fashion, either to the ab165 or aa864 spec? Any chance a circuit guru would be able to tell a nontechnical fool like me what may have been done based on the pics below? Much appreciated!
     

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    Last edited: Feb 26, 2020
  2. kramazeek

    kramazeek TDPRI Member

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    Better lighting :
     

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  3. Paul G.

    Paul G. Friend of Leo's

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    Something has been done to the bias balance. You definitely still have bias balance, not true bias. There have been changes, but it doesn't look like AB165 or AA864.
     
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  4. kramazeek

    kramazeek TDPRI Member

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    Thanks for the info, Paul. Drag though, was hoping someone had done the work I would have paid to have done.:)
     
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