Today's Mystery Guest (RCA CTC-4)

[Penthode]

Phil,

Are you connecting the Sencore from terminal J to ground? The detector circuit output is across J and L. I looked at the CTC4 schematic and the connection of the generator from J to ground may not work because L is floating. Note that L is the sync separator feed. L also attaches to the cathode of the first video stage. V110 is a cathode follower.
The first cathode follower video stage does not invert the signal nor does it provide any voltage gain. It only provides an impedance match to the delay line.
So why not try and attach the generator from L to ground and see if that works? (You might want to DC isolate the connection to L with a 2uF 50v electrolytic with "+" to the cathode of v110).

Cheers,

Terry

[Phil Nelson]

Originally Posted by Penthode

So why not try and attach the generator from L to ground and see if that works?

I tried connecting the generator from L to ground and the picture became completely unstable: horizontal wouldn't really lock, and I couldn't tell whether vertical locked or not. When I connect to J, the image is stable apart from rolling colors.

Originally Posted by Penthode

(You might want to DC isolate the connection to L with a 2uF 50v electrolytic with "+" to the cathode of v110).

Not sure what this means. Can you explain what is connected to what?

Phil Nelson

[ChrisW6ATV]

Originally Posted by Phil Nelson

And thanks again to Chris for this bit of advice.

Phil, after all of the great advice and tips I have learned from many of your restoration pages, I am glad to be able to offer even a little tidbit back in return.

Originally Posted by Penthode

Phil, Are you connecting the Sencore from terminal J to ground?

Terry, I also connected my VA62's video between point J on the RCA CTC-4 schematic and ground, and in my case, I got near-perfect video right from the start. The signal was, if I remember right, inverted video at about 3 volts peak-to-peak. Feeding it at point J seems to also put the needed signal to point L, through the nearby components. I also tried between point L and ground and did not get a usable signal; I did not try between points J and L (but did not need to, as noted above).