Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Misc Schematics and Layouts => Topic started by: mwickham on October 31, 2017, 01:42:40 pm

Title: AB763 schematic - Hoffman and Fender difference
Post by: mwickham on October 31, 2017, 01:42:40 pm

Hi All,

I'm a newbie to tube amps and am on my second build - my current project is a Deluxe Reverb using a Hoffman turret board. Great quality and love working with this board as opposed to an eyelet board!

My question is around the schematic for the 2-channel AB763 and the bias supply. There appears to be a difference between how this part of the circuit is wired in regards to the Intensity pot on the Hoffman Amps schematic:

http://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf (http://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf)

vs. the Fender schematic:

http://el34world.com/charts/Schematics/files/fender/Fender_deluxe_reverb_ab763_schem.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_deluxe_reverb_ab763_schem.pdf)

I'm curious if anyone knows why the difference or if I'm simply misinterpreting things. I've read the Hoffman AB763 circuit information page and searched the forum, but have found nothing to clear-up my confusion.

Thanks for any input!
Mark

Title: Re: AB763 schematic - Hoffman and Fender difference
Post by: sluckey on October 31, 2017, 03:31:55 pm

Hoffman's AB763 is not a true AB763. Hoffman uses a bias vary tremolo circuit from the older 6G16 amplifier. That accounts for the difference. Compare the two schematics to see the circuit differences.

Title: Re: AB763 schematic - Hoffman and Fender difference
Post by: mwickham on October 31, 2017, 04:45:49 pm

Thank you, Sluckey! I appreciate the quick reply.

(...and there it was on the AB763 circuit information page...as I said I read it, but I didn't understand what I read until you clarified)

Thanks again!
Mark