Today's Mystery Guest (RCA CTC-4)

[Phil Nelson]

Originally Posted by DaveWM

seem like you can confrim that if you feed it a ntsc signal to the video amp (if correct and strong enough anyway).

Yes, I have tried injecting video at various spots on and around the video amp grid and cathode. Injecting at the grid seems to work best, but you never get that magical result where the video is suddenly much clearer than when coming through the RF & IF sections.

I suspect my injected signal is not strong enough. The 1st video amp calls for +2.7v at the grid and +4.1v at the cathode, both of which are connected to the video detector output through different paths. This part of the schematic shows the paths between the video detector and the video amp and bandpass amp:

http://antiqueradio.org/art/RCACTC-4SchematicPart2.jpg

I tried disconnecting the detector diode, or grounding the grid of the 3rd IF tube, to make sure there is not a competing signal coming through the IF. That doesn't seem to matter, as long as you don't have a strong signal at the antenna. (You can't just pull the 3rd IF tube, since half of it operates as the 1st sync amp.)

Learning to do a full alignment is on my "someday" to-do list, but I will need to collect the right equipment and then practice on a simpler B/W set that already has good alignment.

Perhaps the CTC-4 is similar to the CT-100/CTC-2B, where injecting video requires that you add a little video preamp. This article describes the preamp that I built following Pete Deksnis's design:

http://antiqueradio.org/VideoAdapter...Television.htm

Possibly something similar would work on the CTC-4, but note that the CT-100 has only one path between the video detector and the 1st video amp.

Phil Nelson