Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: nateflanigan on July 12, 2010, 08:39:23 pm

Title: reusing fender bias pot on hoffman board (pinout)
Post by: nateflanigan on July 12, 2010, 08:39:23 pm

I'm not totally sure on this so I thought I should ask.  I'm reusing the bias pot from a DRRI on my ab763 build, I can't find much in the way of pinout info.  So I'm assuming...

Looking at the back of the pot, with the pins facing down...

pin 1 to 22k resistor
wiper to bias cap
pin 3 to the diode

Does that sound right?

Title: Re: reusing fender bias pot on hoffman board (pinout)
Post by: nateflanigan on July 13, 2010, 09:22:11 pm

hmmm, how bout can anyone verify which pin on the hoffman bias pot is the wiper?

Studying the schematics it seems like the hoffman bias/tremelo combines aspects of the brown face and black face, I just can't seem to sort it out.  Melting my brain.

Title: Re: reusing fender bias pot on hoffman board (pinout)
Post by: sluckey on July 13, 2010, 10:30:46 pm

Quote

pin 1 to 22k resistor
wiper to bias cap
pin 3 to the diode

Does that sound right?

That's fine.

Quote

which pin on the hoffman bias pot is the wiper?

Follow the pots/knobs link at the top of this page for a pic of the bias pot. In this pic, pot on the left, wiper is on the bottom, just like in the layout.

Quote

the hoffman bias/tremelo combines aspects of the brown face and black face, I just can't seem to sort it out.

That's right. Maybe this schematic will help.
http://home.comcast.net/~seluckey/Hoffman_AB763.pdf

Title: Re: reusing fender bias pot on hoffman board (pinout)
Post by: nateflanigan on July 14, 2010, 07:22:36 am

Thanks so much, that schematic definitely cleared things up.  It gets kind of hard squinting at those old fender schematics and toggling between different windows.