CTC5 Drooping HV

[Penthode]

Hi All,

My Whitby suffers from a poor HV supply. I believe all CTC5's have this problem. The DC voltage measures at about 21kV at minimum brightness (no load and with the shunt HV regulator disconnected. Increasing brightness causes the supply to droop to 15kV.

I have gone through the flyback supply. I can find no problem. I can minimize the Horizontal output tube current to 190mA with the efficiency coil. (I ended up slightly misadjusting to see if I could raise the HV a bit.

Today, I tried substituting a solid state rectifier substitute for the 3A3: it is an ECG508 (depicted). The results are promising: I can now adjust the brightness to a level for a reasonable picture and good focus without blooming. There is a noticeable improvement. The photo below is of the set taken with the new rectifier. (Note the color bars are the last remnant of analog TV from our cable provider).

Any thoughts or comments?