Time to get this site upgraded, so we are passing the hat around. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html
We appreciate your help
in keeping this site going.
Barkhausen oscillation? Perhaps try holding a strong magnet close to the horizontal output tube to see if the pattern changes. Just a WAG, I have never observed BO.
Threaded Mode