Working on my CTC9

[Unimatic1140]

Hey Guys, happy holidays to everyone in Audio Karma! I've starting working on restoration of my CTC9 and I've gone from nothing but a loud buzz to a full color picture by replacing all the tubes and all the electrolytics as well as a few black beauties. At first the picture didn't have enough height, but after I found the hidden height control I was able to bring the vertical sweep all the way from top to bottom. I do need to go and recap the vertical board and I'm sure I'll find other problems too. My most perplexing problem right now is that after the set is on for about five minutes I start to hear a static sound coming from inside the high voltage cage. I checked the flyback for a pinhole opening where it might be leaking HV but the tire looks like its in great shape, with no burned areas. I tried coating the entire inside walls of the metal cage with several coats of aerosol corona dope and still I have this problem. I have been running the chassis outside of the cabinet with the lights off and I cannot see any signs of arcing, but even with the cage door open its not wide enough for me to see the Flyback so I don't know exactly where the arcing is coming from. Is it safe to power up the chassis with the HV cage removed (of course without touching anything near there)? Might the sound be coming from deep inside the flyback and its on its last leg? Any suggestions you guys might have about what to check will be very appreciated.

[Rob]

Uni,

Congrats on your success so far. It is perfectly fine to operate the set with the HV cage cover removed as long as the circuitry is intact (i.e. the HV rectifier isn't disconnected fom the yoke) and you don't have cats that might investigate while your back is turned.

[Unimatic1140]

Thanks Rob, well I removed the HV cage and powered up the TV, even after turning off all the lights I cannot find any sign of external arcing or anything else unusual, at least visually. After about five minutes I hear a sort of static-sizzling sound coming from the area around the flyback, I'm assuming this sound isn't normal, does this normally indicate that the Flyback is in its final stages, or might there be some bad caps that are driving it too hard? How would you guys investigate a situation like this?

[Rob]

Uni,

I guess I'd measure the cathode current of the H. output tube to make sure it was within spec (not too high) and if not adjust the H, drive control to set it properly. Too much current here will overheat the flyback. Then I would ry to determine if there are any portions of the flyback that are getting locally over warm after a bit of a run. You will have to be careful to be sure the CRT ultor path is shorted/discharged to chassis ground before placing your hand in there as soon as possible after shutting down and unplugging from the mains.

BTW, leakage corona from the 15 KHz AC high voltage output of the flyback makes a hissing/sizzle sound. Once it is converted to DC (after the 3A3) it will make a soft crackling sound, or a loud bang if it actually jumps to ground.

Just be careful. These circuits bite hard if you don't take measures to discharge the high voltage DC stored in the picture tube. Charge will be present at the socket of then 3A3 rectifier, the plate cap of the 6BK4 shunt regulator and on the red wire running to the ultor connection on the CRT bell. There's 25 kVDC on this path when the set is operating.

Make sure that the spring loaded wire that connects the outer aquadag of the CRT to the chassis ground is present and connected properly. If that ground strap is missing the set will bite you.

[Unimatic1140]

Rob, thanks for the great information. I had no idea about the sound difference between AC high voltage and DC high voltage. Unfortunately I can't decide whether the sound is a soft sizzling or a soft crackling type sound. It would help if I could just see any sign of a blue light or arc flash but everything visually looks fine, both underneath and above the chassis. I'm hoping that the sound isn't coming from underneath the rubber tire on the flyback, but I can't tell. I'll have to keep a look out for a new CTC9 Flyback just in case, which won't be easy to find. I have more caps on order and when they arrive I will keep recaping in hopes of solving this and a few other problems. The color and clarity is just beautiful on the picture tube though so at least I know I have a good tube.

Good safety points as well, I'm extremely careful when working on these old sets, big rubber yellow dishwashing are a must as well as shorting the high voltage lead to the chassis before touching anything.

[rcaman]

i have a nos flyback for my ctc9 set and my ctc10 and ctc16.
i got them from moyer electronics. www.moyerelectronics.com
they are great to do business with.

[Unimatic1140]

Hi RCAMan, thanks for the info, I tried Moyer and unfortunately they do not have any more Flybacks for the CTC9. All I have is the original RCA part #106359. Do you guys know any other cross reference #'s for this Flyback that I can be on the lookout for?

[merrylander]

Have you tried MCMElectronics?

Rob

[kc8adu]

i doubt mcm has anything that old.
if you can get a thordarson number i will check my stash

[Unimatic1140]

Thanks Kc8adu, I appreciate you help. I need to see if I can find a cross-reference book to look up the after-market part numbers for RCA#106359.