Today's Mystery Guest (RCA CTC-4)

[ChrisW6ATV]

Yes, I await the results of your always-informative tests and comments, Phil. Good luck with the set.

[Phil Nelson]

Back to the CTC-4. Here are comparisons of the signal at the video amp input. The first photo shows the CTC-11, which makes a nice picture with accurate colors. On the bottom is the video output direct from the generator. Above it is the output from the CTC-11's IF section, where it enters the video amp.



The CTC-11 IF output isn't perfect, but it resembles the color-bar signal and it seems to have a healthy burst signal. My reason for looking at this is to understand what the video amp input should look like in a similar color TV that works normally.

Next is the CTC-4's IF output where it enters the video amp. Here, the direct color-bar signal from the generator is on the top and the CTC-4's signal is on the bottom.



The CTC-4 signal is attenuated, to say the least.

I have a bad socket on the IF board, the 3rd video IF amp. I have cleaned the devil out of that socket, swapped tubes, etc., but the socket is very intermittent. Only by nudging the tube into exactly the right position will it pass a signal at all. In the wrong position the screen goes completely dark.

I did scope some of the CTC-4's color tubes (chroma bandpass amp and chroma phase detector), but the photos aren't worth including. Those waveforms look like no usable color signal is present.

There's obviously something wrong with the IF socket, so I guess I'll address that, either by ordering a replacement socket or trying to transplant new pins into this one (a trick I haven't tried before).

Phil Nelson