[maxhifi]

Read videokarma long enough, and one recurrent theme is the VDR.

My favourite subject, the CTC38 uses about four of them (don't have the manual with me), but the two I am most interested in are in the vertical and horizontal sweep circuits.

I have noticed two things, which I am starting to suspect are related.

1. Vertical size must be turned all the way down to get the correct size, with linearity adjusted properly.

2. Line voltage fluctuations/transients (electric space heater coming on, furnace starting, etc) seem to affect the vertical size.

My Theory: the VDR is supposed to keep the vertical size constant with line voltage fluctuations. Since this isn't happening as well as could be expected, is it also possible that a bad VDR could be causing the vertical size control to be adjusted at the bottom of its range, rather than in the middle?

Now another and related question, is how to test a VDR out of circuit?

Digikey and Mouser have tons of MOVs available, but it will take some doing to find a substitution, because the way they are specified appears different. I think some more homework on my behalf is needed, I am posting my thoughts so far though for a reality check to see if I am staying on the rails or not.

I also ordered two interesting documents which may have some answers for me

1. Field Service Guide RCA Color TV Receivers 1969 1970 CTC-22 Through CTC-40

2. 1969 RCA PRODUCT TECHNICAL MANUAL TV RADIO TELEVISION PHONOGRAPH TAPE ORIGINAL

I am hoping I can get answers from either or both of these, to some of the mysteries of the CTC38 chassis which Sams has not revealed to me.