DuMont RA-102 vertical transformer bad?

[Phil Nelson]

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

[Phil Nelson]

Well, the doorknob cap was bad, after all. When I played the set to check another issue, a faint tick-tick returned in the HV section and then the cap failed, causing hash in the video and loud static in the audio. When I swapped in a doorknob borrowed from my National TV-7W (which has four to choose from), the picture stabilized.



I don't have a cap checker that can test at such high voltage, but out of curiosity I temporarily clipped the old doorknob cap in parallel with the good one. It immediately started hissing, so I guess it really is a goner.



There's more work to do on this set, but I'm counting this problem resolved. Thanks again for the good advice.

Regards,

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

[EdKozk2]

Phil,
How did you get that chassis so clean looking, it almost looks new.
Ed

[Phil Nelson]

Both chassis on this set had bad rust. After using Naval Jelly & the usual tomfoolery, this chassis still looked rotten, so I painted it (not my usual practice).

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

[EdKozk2]

Better than having rust.

[Penthode]

Nice job