Welcome To the Hoffman Amplifiers Forum

September 07, 2025, 01:46:31 am
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: Preamp voltage AB763 (tweaking dropping resistor value with a pot)  (Read 1851 times)

0 Members and 1 Guest are viewing this topic.

Offline 22uf

  • Level 1
  • *
  • Posts: 66
  • I love Tube amps
Hoffman Amps Forum image
Preamp voltage AB763 (tweaking dropping resistor value with a pot)
« 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:

Offline sluckey

  • Level 5
  • *******
  • Posts: 5075
    • Sluckey Amps
Hoffman Amps Forum image
Re: Preamp voltage AB763 (tweaking dropping resistor value with a pot)
« Reply #1 on: September 15, 2022, 05:14:54 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.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline 22uf

  • Level 1
  • *
  • Posts: 66
  • I love Tube amps
Hoffman Amps Forum image
Re: Preamp voltage AB763 (tweaking dropping resistor value with a pot)
« Reply #2 on: September 15, 2022, 05:55:10 am »
Great idea! Thanks mate.  :worthy1:

 


Choose a link from the
Hoffman Amplifiers parts catalog
Mobile Device
Catalog Link
Yard Sale
Discontinued
Misc. Hardware
What's New Board Building
 Parts
Amp trim
Handles
Lamps
Diodes
Hoffman Turret
 Boards
Channel
Switching
Resistors Fender Eyelet
 Boards
Screws/Nuts
Washers
Jacks/Plugs
Connectors
Misc Eyelet
Boards
Tools
Capacitors Custom Boards
Tubes
Valves
Pots
Knobs
Fuses/Cords Chassis
Tube
Sockets
Switches Wire
Cable


Handy Links
Tube Amp Library
Tube Amp
Schematics library
Design a custom Eyelet or
Turret Board
DIY Layout Creator
File analyzer program
DIY Layout Creator
File library
Transformer Wiring
Diagrams
Hoffmanamps
Facebook page
Hoffman Amplifiers
Discount Program


password