Brown Fender Princeton Question

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Brown Fender Princeton Question

Postby Crisp on Wed Feb 10, 2016 2:22 am

I am looking to get another Brownface Princeton before they get too expensive. The last three I have checked out have this odd blue trimpot by the power supply section. Any idea what this is all about? I do not think it is original.

Any advice as to what and why this exists is greatly appreciated.

-Crisp
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Re: Brown Fender Princeton Question

Postby Unit_1 on Wed Feb 10, 2016 3:18 am

It's a mod to allow you to adjust the bias when adding new tubes. Setting bias simply means setting the voltage so the tubes don't run too hot, or too cold.

Without this mod, you really need to only use old NOS tubes, which were all preselected to run 'in spec'. This way you can buy new tubes, set the bias, and be assured your tubes won't burn up, and that your amps performance will be up to par...
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Re: Brown Fender Princeton Question

Postby Crisp on Wed Feb 10, 2016 3:40 am

Hey!

Thanks a lot for the response. I always thought the bias pots where stuffed around the power tubes somewhere and usually made accessible through the back of the chassis for easier adjustment. Learned something new.

The rock gods are smiling upon you today. Thanks again.

:jam:
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Re: Brown Fender Princeton Question

Postby Smolder on Mon Mar 21, 2016 7:24 pm

Princetons did not come stock with a bias adjust in the brown/black/silver face eras. But it's a great mod.
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Re: Brown Fender Princeton Question

Postby stratele52 on Tue Mar 22, 2016 9:08 am

Smolder wrote:Princetons did not come stock with a bias adjust in the brown/black/silver face eras. But it's a great mod.



+1

Crisp,
Bias blue filter caps is cheap, I'll put F&T or Sprague Atom.
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Re: Brown Fender Princeton Question

Postby Unit_1 on Tue Mar 22, 2016 7:11 pm

Crisp wrote:Hey!

Thanks a lot for the response. I always thought the bias pots where stuffed around the power tubes somewhere and usually made accessible through the back of the chassis for easier adjustment. Learned something new.

The rock gods are smiling upon you today. Thanks again.

:jam:


That's where Fender was putting them back at that time. Later they starting making them more accessable so the chassis didn't need to be removed from the cab to adjust the bias.

+1 on Stratele's suggestion to add a higher quality capacitor in that area. F&T's look great. Black with gold writing. Perhaps the best looking, and one of the best quality you can get.
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Re: Brown Fender Princeton Question

Postby Smolder on Wed Apr 13, 2016 12:16 am

Unit_1 wrote:
Crisp wrote:Hey!

Thanks a lot for the response. I always thought the bias pots where stuffed around the power tubes somewhere and usually made accessible through the back of the chassis for easier adjustment. Learned something new.

The rock gods are smiling upon you today. Thanks again.

:jam:


That's where Fender was putting them back at that time. Later they starting making them more accessable so the chassis didn't need to be removed from the cab to adjust the bias.

+1 on Stratele's suggestion to add a higher quality capacitor in that area. F&T's look great. Black with gold writing. Perhaps the best looking, and one of the best quality you can get.


Not buying it. Why would Fender put a bias pot in a Brown and the later not in the blackface or silverface? That is a board mount 50k that is standard in Marshall amps. If you go to Hoffmanamps.com you'll find instruction regarding how to add one in that exact configuration. It was likely done when that bias cap was changed.
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