Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: coreysan on April 02, 2015, 05:38:32 pm

Title: Question about the Hoffman 1 channel AB763
Post by: coreysan on April 02, 2015, 05:38:32 pm

I'm working on a AB763 for the Fender Super Reverb kit, and also comparing it to the Hoffman AB763 one and two channel
designs (which are really really nice, I might add!).

So far the one thing I don't understand is that on the Hoffman schematic, the
preamp signal going to the PI has a 47k resistor (r30) going to ground.

What does that do?

Title: Re: Question about the Hoffman 1 channel AB763
Post by: sluckey on April 02, 2015, 07:11:48 pm

It simulates the loading of the AB763 Intensity pot.

Hoffman's AB763 is not a true AB763. It uses an earlier version bias modulating tremolo. Look at the schematics to compare.

Title: Re: Question about the Hoffman 1 channel AB763
Post by: EL34 on April 03, 2015, 07:36:12 pm

What Sluckey said

If you look at the original AB763 there is a 50kra intentsity pot connected to that same point and the bottom end of the pot is connected to ground
I am replacing the 50kra post with a 47k resistor

Title: Re: Question about the Hoffman 1 channel AB763
Post by: coreysan on April 06, 2015, 03:29:56 pm

Ah yes - makes perfect sense. If I had read through the entire schematic...
I'm sorry!