Retrace Blanking

[DaveWM]

while trying to help timmy I was doing some research. thought I would start a new thread with a better title for search on.

here is the video of a problem that I have seen on some of my sets where the CRT is getting a bit weak.

https://www.youtube.com/watch?v=39Dl...CVtyRrqXVtll-g

and here is something that looks like a possible fix (I guess this problem was worth looking into back in the day).

http://www.google.com/patents/US3247418

the above circuit adds a neg going pulse to the G2 grids in addition to the reg positive pulse added to the plate of the video out (cathode of CRT). Effectively increasing the bias to further cut of the CRT during the retrace

[DaveWM]

there is an RCA patent out there as well looks like what is used by the CTC-17 (single NPN transistor) except the B+ is listed as 405v while the CTC-17 uses the voltage drop across the supressor resistor on the horz out to supply 27v.

http://www.google.com/patents/US3436475

I wonder if this would help with some of the Macro vison lines seen on some early RCA and clones.

[old_coot88]

Hah. Always wondered what that transistor in the CTC-17 did specifically, but never had occasion to find out.

[DaveWM]

a little more digging, it was ONLY on the CTC-17X (I checked my sams for the CTC-17 I had which was not an X and could not find it).

My plan it to try at least the 1st blanking (two pulse method) since the CTC-12 I have does not have a nice 27v supply (the supressor grid is connected to the cathode inside the tube, both to ground) on the CTC-12. Besides it looks a lot easier. My Sylvania RCA clone roundie may have used a 6JE6, and would be a good candidate for the transistor, esp to see if it could clear the macro vision (seen clearly in one of my early videos on You tube).

[miniman82]

Get a TBC to get rid of macrovision, all the blanking in the world won't cure that AFAIK.

[DaveWM]

well we shall see, its on my to do list.