Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fenderguy81 on November 21, 2022, 05:18:07 pm
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I am working on a 70s Fender Bassman 100 that has a 4 lug (additional center tap) 10K linear balance pot in the bias circuit. The pot is broken and beyond repair. Unfortunately, I have not been able to find a suitable replacement so I think I will need to substitute it for a traditional 3 lug 10K linear pot. There is an updated 100uf/100v capacitor and 3.3k resistor attached to the center tap of the original pot. How would I rewire this to work with a standard 3 lug 10k linear pot? Any help would be appreciated!
Thanks!
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If you want a bias balance circuit, rewire following this schematic...
https://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_ab568.pdf
If you want the old style bias adjust circuit, rewire following this schematic...
https://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_ab763_schematic.pdf
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If you want a bias balance circuit, rewire following this schematic...
https://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_ab568.pdf
If you want the old style bias adjust circuit, rewire following this schematic...
https://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_ab763_schematic.pdf
Thanks sluckey! I think I’m going to go with the first schematic (balance pot) and add a trim pot with the bias resistor to make the bias adjustable.
My only question is related to the extra 3.3k resistor and 80uf/75v electrolytic cap that had been tied to the previous 10KL pot’s CT. Should I remove the resistor and cap completely like the Fender Twin Reverb AB568 schematic or tie it in on the lug of the new 10KL pot and attach them to the 470R & diode?
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Just follow the schematic.