DuMont RA-102 vertical transformer bad?

[old_coot88]

Phil,
None of those linkys will play on my (Linux) rig for some reason. But a coupla questions.. Is the tick you're hearing in sync with the raster-size fluctuation? And does the period of the fluctuation vary with the brightness setting? (e.g., speed up with hi brigntness, slow down with low brigntness?)

[Penthode]

There is probably a one megohm resistor in series with the HV lead. It often breaks down and offers the symptoms described.

[Phil Nelson]

Thanks. There is a 47K resistor (R12) in series with the HV lead. It has been replaced with a new 1-watt 47K resistor. Those solder joints have been coated with corona dope, but they are candidates for corona, along with several other spots in the HV cage, and I'll probably go over them again when I get around to it.

It's hard to observe whether the image jitters coincide with ticking sounds, since the screen is at the other end of my workbench from the power chassis, where I need to hold my ear close to the HV section to hear any ticking. Maybe I can rig up something with a mirror and a long listening tube. That might be in a day or two.

Regards,

Phil Nelson

[Penthode]

The intermittent picture expansion would result from the HV dropping. It appears that the high voltage regulation is bad due to the insulation breaking down.

I would also suggest paying close scrutiny to the HV capacitors. I had the same intermittent problem because the 500mmfd HV cap was breaking down.