RCA 21CT55 #8802897 is Dead

[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