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[email protected] jurb6006@gmail.com is offline
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Default Reactive Overscanning

"Reducing B+ reduces EHT too, which is derived from B+, so picture size doesn't change."

In my experience it does get smaller with less B+. Apparently the pulse to the yoke had a greater effect than the deflectiion sensitivity of the CRT.

Here's an interesting thing maybe. (because this is all academic, I'll get this one any which way once I get the thing on the bench)It was an NAP PTV 310 I think, it was the one with the flyack on the power board on the right and the deflection board on the left, viewed from the rear.

It used a regulation scheme somewhat like IRC a C3 chassis. The H drive comes from the filter choke off the chopper regulator which is locked to the horizontal sync. This means the H output duty cycle increases with increased load on the PS. I guess it was a way to tighten up the H and HV regulation..

So this thing uses about the same circuit but there is a sub regulator for the B+ going only to the flyback. Looking at the circuit I could tell that the regulation was not rock solid, and I mean by design. Well one time I had one that was shorted and since it only drops a few volts the set did not shutdown, or there was something not right in the shutdown circuit. But the B+ nto the flyback was rock solid then. This does NOT feed the yoke, that is a separate transformer and output all together on the other board.

Well when the beam current increased, the raster size shrunk. +This must have had to do with the actual density of the electron beam. There could be no other reason. I saw the effect one other time only and thar was on a high ed Soy direct view moitor, I think a Profeel. It had separate hV and H as well. A few other models had it as well.

But this NAP apparently they had to let the B+ and therefore the HV drop slightly to keep the raster size constant. But so much for that.

This little **** is nothing like that, the only thing the same is the name. It is an elcheapo, model KV1396R and I am surprised it even has video in. That is good because the IF strip is whacked out and since my convertor box is defective and doesn't put out sound on video, only on RF, I have to use a VCR to tune it in. I'll probably fix that IF when I have it apart, but it works for now the way it is. The RF probably doesn't put out stereo so it picks off the mono signal before it becomes stereo in the box. I am NOT fixing the box. I refuse.

"Don't increase B+ on failing tubes, it increases xray output. "


Don't worry.

1. I am old and I don't care if I glow in the dark.
2. The CRT is nice and strong.
3. Increasing B+ would not do what I want at all.

So I am safe.