Ct-100

[Tom Albrecht]

I picked up a CT-100 earlier this year from a local collector, and after finishing off a bunch of other projects over the past few months, I've now turned to this wonderful RCA.

This set has seen a bit of work over the years. Many of the original paper caps have already been replaced, sometime between the 1960s and 1980s, based on the appearance of the replacement capacitors. The main power supply electrolytics were replaced with nice GE FP electrolytics that are still doing fine. The selenium rectifiers were replaced with diodes, and the ballast has been removed and replaced with fixed power resistors mounted in the area where the seleniums were.

Cosmetically, the set is not bad, with a cabinet that could use refinishing, but with the wood in pretty good shape except perhaps for a couple of the feet. Unfortunately the main front panel knobs are gone, so I'll be eager to find a possible source for replacements.

Everything else is there, and the good news is that the original 15GP22 tests good on all three guns.

I recapped a number of the already recapped paper caps (the replacement caps were a mixture of paper and polymer dielectric caps). I haven't done a full recap yet, but tried to cover the sweep circuits and video output stages.

Powering up briefly, I got sound immediately, as well as anemic high voltage (12 kV) and some semblance of a dim picture (bad sync, quite dark, but some video information making it to the screen).

I then recapped the HV cage, hoping that would bring the HV up to normal, but it didn't. I replaced some resistors in the focus section, putting original values in place of various jury-rigged components, and now notice that if the focus rectifier is connected, I get no HV. With the focus rectifier disconnected, I get 10 kV. There may be a (possibly brand new) short in the vertical dynamic convergence transformer, but we'll get to that later. For now, I'm leaving the focus rectifier disconnected.

Unfortunately, the flyback gets hot. I have a nice horizontal drive waverform on the horizontal output tube, and about -40V bias on the HO grid. Running the set briefly and then feeling the warmth on the flyback seems to indicate clearly that the source of the heat is the HV outer winding on the flyback, and most likely not the primary windings. It heats up pretty quickly, so I'm running much less than a minute. No nasty damage, but it is clearly getting too hot too fast. I gather this indicates a shorted turn in the HV winding; any other diagnosis possible? That would certainly be consistent with my anemic HV. The heating is the same whether the HV rectifier is connector or not, so that seems to rule out something loading down the HV as the cause of the heating.

Moyer does not have a replacement flyback available. Any junker chassis out there for a possible replacement?

Otherwise, I may try some surgery on the flyback. However, I don't want to do that prematurely. The original *looks* very nice and clean, and whatever surgery I do will irreversibly change that, and also has a fairly low chance of success. I've saved one flyback on a different set in the past by removing some outer turns on the HV winding, where the short happened to be. No guarantee by any means that would be the case here.

Open to advice on how to proceed.

P.S.: Moderator, I suppose this really belongs in the COLOR section! I'm so used to posting in the black and white section that I forgot about that...