Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: scstill on August 28, 2025, 03:46:24 pm

Title: Cathodyne bias problem
Post by: scstill 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.

Title: Re: Cathodyne bias problem
Post by: tubeswell on August 28, 2025, 04:43:31 pm

The issue is your meter.

Title: Re: Cathodyne bias problem
Post by: scstill 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