Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 22uf on September 15, 2022, 04:20:19 am

Title: Preamp voltage AB763 (tweaking dropping resistor value with a pot)
Post by: 22uf on September 15, 2022, 04:20:19 am

I have a blackface AB763 twin.
I was going to see what lowering the pre-amp voltage does. I don't have a ton of spare 3w caps. I do have a 3w 10k pot.

I'm OK to just wire in that 10k 3w wire wound potentiometer (designed for high loads) in place of the current 4.7k 3w preamp dropping resistor, yes?

I figure I can then turn that from 10k (Deluxe ~280v) down about 50% of its rotation to 5k (Twin ~400v) and hopefully find a sweet spot somewhere in between that affords just the right amount of "sweet" and then measure that value and order and hard wire in the corresponding cap value to fix the deal.

Sorry, haven't attempted death by amp for some time, so I thought I better check that this isn't insane or some such.  :icon_biggrin:

Title: Re: Preamp voltage AB763 (tweaking dropping resistor value with a pot)
Post by: sluckey on September 15, 2022, 05:14:54 am

Quote from: 22uf on September 15, 2022, 04:20:19 am

I'm OK to just wire in that 10k 3w wire wound potentiometer (designed for high loads) in place of the current 4.7k 3w preamp dropping resistor, yes?

That's fine. I would rather put the 10K pot in series with the 4.7K.

Title: Re: Preamp voltage AB763 (tweaking dropping resistor value with a pot)
Post by: 22uf on September 15, 2022, 05:55:10 am

Great idea! Thanks mate.  :worthy1: