2.) what is going on: Removing DC (tube plate voltage) from the transformer to prevent DC core saturation in the transformer, then giving the tube a new plate B+ DC source (the two resistors and lytic) to replace the now cap blocked path through the transformer.

Well, the screen image is definitely unstable, although I'm not sure if I would ascribe it only to the vertical. The whole image seems to expand and contract in both dimensions -- horizontal and vertical -- slightly and rapidly. I can also see faint "retrace"-like horizontal lines, both light and dark. It's hard to capture with cellphone video, but these brief clips give an idea what's happening:

http://antiqueradio.org/art/DuMontRA...ngScreen01.mp4

http://antiqueradio.org/art/DuMontRA...ringScreen.mp4

Edit: I just noticed that the "retrace"-like lines are light in the top half of the screen and dark in the lower half. ????

I wonder if instability in the high voltage supply could cause the fluttering in screen size? Adjusting the Regulator Control and Voltage Control on the power supply chassis doesn't affect this problem. My high voltage meter shows a steady 10KV output, although that meter may not be sensitive enough to show such small, rapid fluctuations.

Ideas? The RA-102 service manual with schematic is at:

http://www.earlytelevision.org/pdf/d...-rider-tv1.pdf

The HV section in this set needed repair beyond the usual caps & resistors. The previous owner tore up the HV output transformer and did other odd kludges, but Andy Cuffe was able to repair the transformer and it seems to function normally. I have done extensive work on the rest of the TV. In the vertical & horizontal sweep sections, I have replaced nearly every cap and resistor.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Is there by chance a faint 'ticking' coming from the CRT socket/base, in step with the fluctuating raster size? Sometimes a pin-to-lug connection is open, creating a tiny spark gap that the CRT beam current is jumping across, resulting in the bloomy raster.

No ticking at the CRT socket, and those connections are clean & bright.

Where I do hear a wee ticking, however, is near the base of the 1B3GT HV rectifier tube. Corona inside the HV cage was a common problem with these sets, the subject of a Dumont service note. I thought I had solved that with multiple applications of corona dope, but perhaps more is needed.

I took another video with a test pattern instead of broadcast video from my agile modulator:

http://antiqueradio.org/art/DuMontRA...ngScreen02.mp4

I don't know if that tells us anything new, but at least I know I'm not watching interference from the home broadcasting setup.

Phil Nelson

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?)

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

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

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.

Hi - I believe your problem is some kind of spike in the Horiz. Osc. Signal
that is then sent to the Horiz. Output. While doing a freeze-frame on yer
video, I can see what looks like a a spike or reduction in amplitude of
the horiz. Scan line. Making a few scan lines run long or short. You can
also see the Damper circuit faithfully reproduces the effect over on the left
side of the screen. That makes me think it's source is Before the Horiz Output
tube, and Damper circuit. I would look over in the Horiz. Osc. area as being the
cause. Effects of the spike, well, larger, or shorter scan for that instant,
possibly raise or lowering of B+ Boost? Raise or lowering of HV? Anyway, to me
it looks like a Horiz Osc. Origin - I did not look at the schematic, but you know
it's so short in duration, and intermittent, you may just need to change
parts to get it..... Of course it's possible for some type of discharge somewhere
else to be causing a spike to give you this display, you will have to figure out
if you have a HV arc somewhere.... It would be really neat to get this problem
figured out down to a single part, and post it's location on a schematic because
the effect is just so different.....

Good Luck.

.

Hi Phil. In answer to your question #1....My Clifton had rock solid vertical locking and no vertical jitter at all after I recapped it. The vertical jitter modification had not been done on my RA-102 chassis, it was still the original configuration.

My RA-102-B3 Club 15 does that, on occasion. I also could not measure any fluctuations in power from the 2nd Anode.:smoke:

Thanks to Ampico-kid and M3-SRT8 for that useful info. I have been laid low with the flu, but in a day or two I should be able to quit whining and get back to work.

My RA-103 has rock steady vertical & horizontal sweep, so given the similarity, that's what I was expecting from this RA-102, as well. I'll start by applying more corona dope, since that issue must be addressed in any case. If I eliminate the corona but the jitter remains, then I guess the doorknob cap would be an easy and logical thing to swap next.

Happy 2017 to all !

Phil Nelson
Phil's Old Radios

I know I am repeating myself on this. But the similarity of what you depict to the problem I had on my 1948 RCA striking. I was in a similar dilemma trying to determine the twitching in the video when I found the 500pf hi-voltage filter with a crack. The were tiny sparks in the crack which I could not see but heard and located them by using a listening tube around the hi-voltage cage. The ticks coincided with the twitching in the video.

The hi-voltage capacitors generally have a clip which you can remove. (The aquadag provides ample filtering anyway). You may wish to disconnect the capacitor just to see if the twitching disappears.

I ended up replacing the DoorKnob Cap as well. It was fried. Put in a 20kV one. It screws in place IIRC.

I also replaced the four micas under the high voltage chassis around the 807. They all failed in quick succession.

Thanks. I did replace the micas under the power chassis, along with resistors in that area.

On this set, the previous owner eliminated the doorknob HV filter cap, possibly because he was using a substitute CRT that had an aquadag coating (the 12JP4 that I'm using has no aquadag). I got a new doorknob from Surplus Sales of Nebraska and installed it as shown in the schematic. I suppose it's possible that the new doorknob is bad; I can pull one from another restored TV and try substituting that, to rule it out.

Meanwhile, I removed the HV transformer and coated the whole thing with thin corona dope, along with the likely connections on the HV line and 1B3GT HV rectifier socket. This seems to have quieted any corona noise.

If subbing the doorknob has no effect, I'll look into the horizontal circuits as suggested by username1.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html