Welcome To the Hoffman Amplifiers Forum

September 07, 2025, 05:46:13 pm
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: Power supply for Sunn Model T standalone preamp  (Read 1802 times)

0 Members and 1 Guest are viewing this topic.

Offline JFlo

  • Level 1
  • *
  • Posts: 2
  • I love Tube amps
Hoffman Amps Forum image
Power supply for Sunn Model T standalone preamp
« on: January 12, 2022, 06:29:17 pm »
   I am building a Sunn Model T (first gen) standalone preamp and have some questions about the power supply. How important are the chokes if there is no power section? Any reason to use the chokes over a pi filter? I am using a 50VA 280V toroidal transformer from Antek (AS-05T280) and a bridge rectifier.
   This is my first post here and I appreciate the wisdom of this forum. I have previously built a Champ and Orange OR120 from kits, then Rob Robinette's SLO-Nakid Micro. I thoroughly enjoyed building these and was able to troubleshoot my mistakes but this is my first attempt at building from just a schematic.

Offline sluckey

  • Level 5
  • *******
  • Posts: 5075
    • Sluckey Amps
Hoffman Amps Forum image
Re: Power supply for Sunn Model T standalone preamp
« Reply #1 on: January 12, 2022, 07:41:40 pm »
I would not use any chokes. 3 caps and 2 resistors will give a very smooth dcv for that very light load.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline PRR

  • Level 5
  • *******
  • Posts: 17082
  • Maine USA
Hoffman Amps Forum image
Re: Power supply for Sunn Model T standalone preamp
« Reply #2 on: January 12, 2022, 11:38:07 pm »
Chokes are for high current with low voltage drop. Here you actually want some voltage drop at low current. About 6.2mA at 330V. 330V/6.2mA is like 54k of resistance. You could fool with numbers but this is the late 20th century (or beyond?).

... caps and 2 resistors will give a very smooth dcv for that very light load.

Oddly, SUNN's values are really conservative. Smaller caps will still get B+ buzz far below tube self-hiss. Since we are starting well below 500V we want to reduce the resistors, and the filtering is still excellent. Any commercial amp factory would cut the caps in half again and still have a 'perfectly' quiet B+ rail. In DIY we can spend the dimes to be generous, 47uFd.

(More stages of small parts is a lot better than one or two soup-cans.)

Offline JFlo

  • Level 1
  • *
  • Posts: 2
  • I love Tube amps
Hoffman Amps Forum image
Re: Power supply for Sunn Model T standalone preamp
« Reply #3 on: January 13, 2022, 10:07:58 am »
Thanks, guys! That's a big help.

 


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