Today's Mystery Guest (RCA CTC-4)

[Phil Nelson]

After a detour to restore yet another CTC-11 (which needed very little work), I'm preparing to tackle the color issue again. In the meantime I got a new pattern generator with variable chroma output, which should be ideal for following up on Nick's suggestion to vary the chroma while looking at a tube such as the chroma bandpass amp.

While I have the CTC-11 on the workbench, it seemed a good time to try this method and see what the results look like on a similar TV that displays color very well. Here's an animated GIF showing pin 1 of the CTC-11's chroma bandpass amp (6AU6A) at 0%, 50%, and 100% of chroma output from the generator:



Pin 1 of the chroma phase detector (6AL5) also has a waveform that changes obviously in response to varying chroma input:



My idea is to get the CTC-4 back on the bench and scope the bandpass amp and phase detector and watch for change when I vary the generator's chroma output. I hope this will answer the question whether a usable color signal is making its way through the TV's video IF section.

We're leaving tonight for a mini-vacation, so I may not be able to try this until this weekend.

Phil Nelson