Welcome To the Hoffman Amplifiers Forum

September 06, 2025, 06:55:18 am
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: Cathodyne bias problem  (Read 119 times)

0 Members and 1 Guest are viewing this topic.

Offline scstill

  • Level 3
  • ***
  • Posts: 884
  • https://stillampd.com
    • Still Amp'd
Hoffman Amps Forum image
Cathodyne bias problem
« on: August 28, 2025, 03:46:24 pm »
The 12ax7 PI grid is reading 20v while the cathode reads 40v
It seems the grid should be at about 38.5v.
Have replaced the .01 coupling cap and the .00015 cap.
All resistors measure correct value.
Have tried another tube same issue.





Offline tubeswell

  • Level 4
  • *****
  • Posts: 4201
  • He who dies with the most tubes... wins
Hoffman Amps Forum image
Re: Cathodyne bias problem
« Reply #1 on: August 28, 2025, 04:43:31 pm »
The issue is your meter.
A bus stops at a bus station. A train stops at a train station. On my desk, I have a work station.

Offline scstill

  • Level 3
  • ***
  • Posts: 884
  • https://stillampd.com
    • Still Amp'd
Hoffman Amps Forum image
Re: Cathodyne bias problem
« Reply #2 on: August 28, 2025, 05:04:06 pm »
yep that stupid "meter"; measures 20v between grid and ground
but after slapping it a few times, it measures -2.5v between grid and cathode
Thank you for pointing me correctly
« Last Edit: August 29, 2025, 02:31:19 pm by scstill »

 


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