RCA CTC-11D Restoration

[IsthmusTV]

Hi all,

I'm starting a thread for the restoration of the RCA CTC-11D that I picked up last week. Thanks to Phil Nelson, I have the SAMS info for it. I pulled the chassis and gave it the once-over. For the most part, it's clean and unmolested (aside from missing six tubes).



When I went to check the condition of the thermistor, it fell right off its leads. I'm starting to think that these failing thermistors were a good thing because they got people to just push these sets aside decades ago.


I opened the HV compartment and found that the 6BK4 regulator tube had separated from its base. When I tried to remove it, it broke. I think it had already gone to air.


I removed the HV cage to investigate and there is evidence that the 6BK4 got seriously hot-- hot enough to melt the HV cup. Fortunately, the flyback looks OK.



Is the HV cup usable like this? Could I try to heat it up and bend it back? What would cause the regulator tube to get so seriously overheated?

This restoration will probably take a while because I have so many other irons in the fire right now.

-Clark

[DaveWM]

seen that before, don't think its a problem. I would not worry about it, just leave it be.

[IsthmusTV]

Thanks, Dave. That's what I was hoping to hear. I'll leave it be, at least for the initial power up.

[DaveWM]

you will know if the shunt tube is working by checking the current thru it with the screen darkened. IIRC they want it to be about 1.4ma. With that much you will see the tube glowing pretty brightly figure its disapating nearly 30 watts. Of course the real test is does the HV hold constant regards of scene brightness.

[Tom S]

I have a CTC 10 and 11. Both great performers. I have my 10 in my living room. Use it on a regular basis. Love to watch the old early color shows on it. I also have Schematics too. Let's see a pic on the set soon.

[IsthmusTV]

I have the chassis all cleaned up and the missing tubes replaced. I just got my order from Mouser, so now I just need to find the time to change out the electrolytics. After that, I'll do a first power-up to see what else I'll need to do. I got a CL-90 thermistor to install, but I think it's underrated at 2 Amps. I'll use it for initial testing. I will definitely measure the shunt regulator current (along with the HOT cathode current). They make it easy with a little jumper to remove.

[Phil Nelson]

Originally Posted by IsthmusTV

I got a CL-90 thermistor to install, but I think it's underrated at 2 Amps. I'll use it for initial testing.

Yes, a CL-60 (5-amp rating) might be a better choice. I used CL-90s in a couple of TVs because I happened to have them on hand for radio projects. They have held up under occasional use, but since this is a known weak point of the set, there's no reason to skimp.

Phil Nelson

[bandersen]

Keep in mind the cold resistance for a CL-60 is only 10 ohms while a CL-90 is 120 ohms. So the CL-60 doesn't provide much of a soft start.

[DaveWM]

I have used the CL-90 on 60's era tube color sets with no problems.

[IsthmusTV]

I had the day off work yesterday, and it was drizzly and cool so it was a perfect day to work on vintage TV's! I recapped the power supply and the EC on the vertical output board. I also installed a new CL-90 thermistor. It took quite a while just to remove the cardboard cover on C1: No wonder, I've never seen so much tar used just to hold on the cardboard!


The new caps are so much smaller, I could fit them all in the cans.



I triple checked all my work, and powered up the set with a metered variac. All the filaments lit, but the set was drawing only 1 Amp and there were no other signs of life. A quick checked confirmed no B plus. Although I had checked it, I suspected the circuit breaker. Sure enough, that was the issue. On next power up, I had B plus and the set was drawing about 2.5 Amps. I got a raster and a wild blue light show from the chassis which tuned out to be a defective NOS 12BY7A video output tube. After replacing that, I was able to get stable horizontal and vertical lock and a decent color image.


After a very quick set up, things looked considerably better.


There is clearly a vertical issue and the focus control seemed to have little effect. The set is still full of leaky brown drops and even a couple of paper caps, including one across the AC line After about 30 minutes I shut it down. The HV cage was much warmer than I would have expected. I think there is still an issue with the HV. Next time I power it up, I'll measure and adjust the HV. Then I'll recap the horizontal and vertical boards and reassess.

[IsthmusTV]

The HV was a bit low at 22KV and it was easily adjusted to the specified 24KV. I got the first look at it playing in daylight, and the image was certainly bright enough. I was able to adjust the focus, too. Here it is playing a few minutes ago:


I'm pretty happy with how this is turning out!

[Retspin]

Great work!

[DaveWM]

looking good. those chassis really are easy to work on.

[wiseguy]

Did you have a Bad breaker? if so I have a couple of n,o.s ones you can come and get

[BigDavesTV]

Great looking pictures! I really like my two CTC-11 sets, they are easy to work on, and can provide nice looking video, especially with a good CRT. Good job on your restoration, enjoy seeing your progress in pictures!