Isn't that the same chassis as the T-100? I seem to recall having the same issue with the width on my T-100.

Eventually, I decided it was time to stop, as Mr. Detrola suggests. I think some early sets might have been designed with a healthy amount of overscan. That way, the picture is guaranteed to fill the mask, and customers won't know whether they're missing 5% of the image vs. 2%. I'm just making up those numbers, but you get the idea.

Phil Nelson

yes I can see how a complaint of under scan would show up much more so than overscan which would most likely go unnoticed.

It odd how when I put it all back in the cabinet I get more buzz and the sync becomes more critical. Perhaps its just the heat (at least with the sync). and maybe the location on the buzz, as its def effected by antenna rotation. I will try it again with a cable hookup vs OTA.

argh, it will run all day out of the cabinet, but after 20min or so in the cabinet the horz gets messed up.

the pic looks as if the top slug (the one used to adj the waveform so the two peaks are of equal height on the scope) is changing. Of course if I pull it from the cabinet I am pretty sure it will be fine.

I replaced the cap that goes across that coil and the resistor also. The pic is staying locked on freq, just the the phasing and bad horz fold over taking place. The vert is locked well. I tried the AGC, no effect so I am pretty sure its in the horz osc circuit and not the sync.

I did NOT replace the 100pf a 390pf or the 180pf as they tested ok, but who knows when get goes up.

I suppose I could try heating with hot air when the chassis is out, since cooling is not reall an option (cant get the spray pin pointed with the chassis in place. So I wil go ahead an place my order for those few remaining caps.

Well, it is certainly something that only gets hot with the set in the cabinet. The tubes will get fully hot in either case. There is not much other than the capacitors and resistors, and I think that the capacitors are the more likely.

I had a 48 or 49 RCA with the exact problem you are describing a couple of years ago and it turned out to be a mica cap way over in the sync separator or video area that had about 500 or 1000 megs of leakage on the Sprague TO-4 when it was hot. I didn't want to believe that was enough to cause the problem until I replaced it and no more drift. IIRC it was either 100pf or 180pf and not in a place in the circuit that you would think could cause horiz drift.

I had another RCA that did the same thing but it wasn't the same cap, however after changing all the mica caps in that chassis it worked.

Some of the high value resistors in the horiz circuit have been found to drift with temperature, and so do some 6SN7's, you will never find it in a tube tester but might be able to hand pick one that drifts less than others.

Also readjust the phasing so the rounded peak is very slightly lower than the point of the other peak. Just about the width of the scope trace lower, not much more than that.

This was a well-known trick of the old timers to cure horiz problems in that circuit. It does make the circuit stability a little better under certain conditions. May not be your problem, but something I always make sure to do.

well it got to the point where it would act up even cold. So pulled the chassis, one of those 100pf caps in the sync circuits acts very odd. it will test ok for value and ok for leakage, (eye opens almost instantly as you would expect for such a low value) BUT if you hold the voltage on it for a few seconds the eye closes up and stays closed all the way down to 25v.

anyway I only have a N750 disc cap that is a 100pf and I did not like the idea of using that, so ordered the right caps from mouser today.

spent a couple hours on it tonite. there was a 390pf that tested fine, but I figured may as well get it out. It was in a very hard to get at place, near the back of the chassis, under a power resistor, both of which were attached to a tube socket (a tie point). then both those went to a single term strip. It was a big cluster mess (some of which I had done in a hurry to get it going). So I took the time and carefully so as not to tear off the socket tab, used solder wick and lots of patience to clean everything out and do it all over, with a new 390pf and new resistor. It just looked like too hacked for me.

I decided to tack in that100pf disc since I wanted to make sure of the clean up job not doing any damage.
came right up with perfect sync. I will still replace the with the correct caps when they come in (the 100pf and the 180pf off the osc coil that test fine), but for now its looking good.

been running all day OUT of the chassis not a hint of horz issues. I am tempted to put it in the chassis, no knobs or screws, just set it in and see if it still works after cooking. Just waiting for those correct caps. Geez this thing make a nice B&W pic, really puts to shame my late 50's-early 60's stuff (GE and magnavox's).

Those sets did have a great picture and fair to good sound. Not quite as great a picture as the earlier 630, but close. But a Magnavox from the late 50's or early 60's ought to work every bit as good as the RCA, with a great picture and far better sound.

its prob a function of the CRT, most of my BW sets had pretty weak CRTs to start with. The 12LP4 tested very good.
It just seems sharper on the RCA. I was fooling around with my 27ZP4 maggie last nite, the focus pot does NOTHING to focus the screen, but the voltage does vary from around 200 to over 500v (electrostatic of course). I don't get that.

The sound on the maggie is great, the sound on the RCA is pretty good, but it has a pretty narrow "sweet spot".

Exactly.

Some electrostatic focus CRT's show almost no perceptible difference in focus regardless of the voltage applied to the CRT's focus element. I have seen them left floating by technicians who left the little focus link off the base of the CRT on sets that used it, and they still looked just fine.

It's just the nature of the beast. Once in a while you will find one that adjusting the focus voltage actually does make a difference.

Something new to report. whilst fooling about with the variac I tried reducing the ac voltage, if I go below 122v the sound COMPLETELY drops out, just a slight hum is left. Its very abrupt, almost like an osc tube stopping. However the pic remains fine and all else is fine. the sound takeoff is after the 2nd pic IF, so I will have to start there. I will try some new tubes in the sound section, but if that does not do it I figure a a signal trace will be the way to go. Very odd the way it completely cuts off, exactly at 121v one volt plus or minus make it work or not at all.