|
Man, that is a brain teaser. From the FWIW department regarding the 'ringing', here's what I would try at the present stage:
Get a disc ceramic cap rated at at least 4KV, around 82pf (anywhere from 68 to 100pf will do). put it directly across the damper, plate to cathode. This will increase the width just a smidgin*. It may (or may not) have some noticable effect on the 'ringing'. Now connect the cap from the cathode (pin 3) to the other side of L39 and see if there's any effect (other than the increased width). If nada, try the cap directly across L39.
If any of those three arrangements had any effect on the ringing, either increasing or decreasing it, it will have at least localized the problem area.
*Besides increasing width, this will also reduce H.output tube cathode current slightly, and reduce HV slightly. Thus you can't go much higher than 100pf with the cap.
oc
|