[DaveWM]

ok I am going to go ahead and take a leap of faith here with Timmy and GUESS what we are talking about.

I am currently uploading a video of a set that exhibits what I think Timmy is talking about ( I don't recall seeing any pictures or video). it will be done in a few..
One thing for sure if I reduce the brigthness control I can eliminate them.

IF its what I think it MAY be some kind of vertical retrace issue. Note the issue I see does not seem related to the color lever setting on the front of the set. It does seem related to the brightness and contrast settings. This would point to the luma signal from the video out where the vert retrace pulse is fed for vertical blanking during the retrace interval.

a wild guess could be assuming the level and duration of the pulse is correct, would be maybe an issue with the video out tube (poor gain)? I have no 1st hand experience with this being a cause but I have noticed it before, generally shows up on tube that are not it the best shape, hence I just assumed it was related to the condition of the picture tube. Perhaps a cut off issue. I do know that at least in the CTC-17 there was a transistor inserted into the vert blanking. I have never tried to increase the amplitude or duration of the pulse to see if this was indeed the issue.

Now that I have reversed myself and gone ahead and speculated, I will see if that video is done and will link it here.
I just checked the schematic, the vert blanking pulse is fed in at the plate of the video out (cathode of the CRT) so guess the gain of the vert out tube is not an issue, that leaves either not enough of a pulse or not enough cut off control of the CRT.


Timmy get that HV fixed.