Today's Mystery Guest (RCA CTC-4)

[Phil Nelson]

Originally Posted by dtvmcdonald

Try viewing 50% or 25% saturated color bars, they won't show as much problem with the magenta bar. In any case, I would do really careful, really full IF and RF alignment next.

Doing a full alignment ain't gonna happen soon, at least not by me, but you were right, simply turning down the chroma level on my pattern generator made the magenta more obvious in my crummy photos.



I plunked down 71 cents at the local store and installed a 1N60 diode in place of the 1N34A. Can't say that I noticed much difference. This scope trace from pin 2 of the 1st video amp looked identical before and after the diode transplant. (The top trace is the output from my video detector and the bottom trace shows the color bar pattern direct from the generator).



'That still looks more like a luma stairstep signal than a color signal," I thought, but as Username1 recently pointed out, there is more than one output path from the video detector (forehead slap). I put the scope on pin 4 (cathode) of the 1st video amp, and finally saw the kind of signal I had been expecting to see way back when:



That looks like a burst signal as well as chroma info. When you fine-tune the signal in and out on the tuner, the upper trace gets fatter & skinnier and the screen colors come and go.

I still haven't done the ground-up color setup procedures, but simply trying different sources and exercising the controls (including AGC) makes me think that I can eventually make this a watchable television.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html