RCA 21CT55 #8802897 is Dead

[holmesuser01]

All I have to add is:

I hope the set will be running again. The picture you provided of it was beautiful.

I love old electronics. I want to keep it all going for as long as I can.

Someone here said that the minute we expire, someone will let it all go for the price of copper. Maybe. In the meantime, its still mine and I am the caretaker.

Best of luck rewinding the flyback, Mr Folsom. That's one beautiful coil winder!

Bruce

[Giulio Maiocco]

Hi everybody!

I'm sorry to hear about this mishap with the flyback transformer, I think it's one of the worst "oh no!" moments.

I don't know the color flybacks, but I rewound some B&W ones without problems, and from what I saw, they are less critical than one may be led to believe. I even rewound a couple that were wave-wound in a more conventional "layer" winding, these still work flawlessly. In my Bush TV22 I rewound both the primary (bad enamel on the magnet wire crumbling away, so I decided to fix it) and the EHT winding (this one was wave wound and covered in tar, but the acid in the tar corroded the copper). As a result the TV works very good, I'm 600-700 volts short on the EHT, unfortunately I ran out of wire while rewinding. Using a test pattern, I cannot detect image distortion or ringing, so I'm really happy with the results!

A question for John Folsom, if I may ask: what kind of substance do you use to keep together the winding when you pi-wind? Now I have a wave winding machine too and experimented with some shellac, it works, but it's quite slow to set.

Thanks

Giulio Maiocco

P.S.: Sorry about my so-so English...

[old_tv_nut]

Giulio, thanks for posting this information. Your work looks good - I know handling the fine wire is very difficult. Also, your English seems fine to me.

I wonder if you have an oscilloscope and high-voltage probe, and can check the shape of the flyback pulse?

[Zenith26kc20]

I'm curious (again)and was looking at the schematic of a TS-905 Motorola regulator. These are shunt regulated high voltage supplies that, in the case of the Motorola, sample boost and that gives the 6BK4 grid bias thru dropping resistors. It seems to me a balancing act between the CRT beam current and the Shunt regulator tube to keep high voltage near constant voltage. Since high voltage was 34 KV, It makes me wonder if the higher than normal RCA HOT current came mainly from too much B+. Having no regulation would lessen the load on the high voltage as the shunt regulator would be biased to cut-off. I read the drive was OK to the tube (waveform voltage) but was the negative voltage on the HOT normal or too low. Higher RF voltage on the output would be expected but this would tend to break down the high voltage winding. The primary failed from what I read but these generally have around 6 to 8 KV RF on them so breakdown is usually rare.
Since the picture was wonderfully linear, I don't think the flyback had any shorted turns until failure.
When running before the failure, was the flyback running hot? I don't have a schematic on the CT2 series but the shunt regulators seem to be similar in the older sets.
Any opinions?

[Giulio Maiocco]

Hi again

To old_tv_nut: I'm happy you liked my work rewinding this FBT, just to let you know how boring it is, it counts 2045 turns of 31awg wire on the primary, and close to 3000 turns, 2960 to be exact, of 36awg wire on the the EHT winding, all done by hand, so not an easy task.

Yes, I do have 2 oscilloscopes, a Tek 545B and a Solartron CD1400, but at the moment I don't have the needed high voltage probe, I should indeed buy one if I can find one at a good price. As soon as I succeed at locating this probe at a fair price, I'll check the flyback waveshape, no problem!

Cheers

Giulio