RA103-D has strange issue(s)

[David Roper]

I recapped this set a year ago and it's still not back in the cabinet. When horizontal hold is adjusted for greatest stability, the two fields are misaligned at the top of the picture and wave madly. If horiz hold is adjusted far enough toward the left, the waving can be made to stop entirely, but the sweep cannot sync by itself at that setting. In other words, if adjusted for best picture, the horizontal will be torn from either a cold startup or just momentarily tuning away and then must be manually re-synced.

The set is also extraordinarily prone to drift of the gain, showing excessive contrast when first turned on that fades quite a bit over the course of a half hour or more.

I'm also curious about others' experience with similar Du Monts as to their DC restoration. I would rate this one as quite poor, about on par with that of a GE locomotive. It's an almost impossible thing to quantify, but I know good DC resto when I see it and I don't see it in this set.

Any help appreciated.

[DavidGoncalv]

How does it measure up when you do resistance/voltage checks against the service notes?

[zeno]

I dont have much experience pre 1960 BUT
it sounds like you have an AGC problem causing it all.
Too much gain will clip the hoz sync pulse & tear up the pix.
Also causes sometime audio buzz, jittters, over contrast,
negative pix........
Start with adusting AGC then tube then any caps not changed
in the AGC area. Also high ohm resistors working your way down..

73 Zeno

[Phil Nelson]

I believe the RA-103D is like RA-103 in not having AGC. On the 103, the contrast control varies the gain on the 1st and 2nd video IFs. As I understand it, the contrast acts as a manual gain control, like the "picture" control on an RCA 630TS.

Re your main question, the instability and drifting of the gain doesn't sound typical for this model. My RA-103 is one of the most stable early TVs in this house. The whole set seems rather over-engineered, apart from the Focus pot, which is a notorious weak spot.

Phil Nelson
http://antiqueradio.org/index.html

[kramden66]

Perhaps a leaky mica cap or two ? a tube or two that tests good but isn't operating properly when in actualy use ?

mike