Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:I would expect you'd need separate controls for each CRT for focus and brightness.
The internal construction of the electrodes should be the same but there are mechanical tolerances that will affect deflection sensitivity, grid bias and best focus voltage as a minimum. These are shown in the datasheets.
However, the tolerances are much better than semiconductor devices where hfe for example (basically current gain) can vary from 125-700 for one particular type of device. This also then varies with temperature, current and quite a few other factors - in fact a lot of other factors!
[/quote]In both cases there will also be differences between production batches and manufacturers.
Steve A.
Klaas Robers wrote:Why is your video signal on the left screen upside down?
I see sync pulses peaking up in stead of down.
And then I have the feeling that if you make the brightness of the left screen less, much less, that you get a sharper image.
Success!
Klaas Robers wrote:In the video demo with the dual grey-scale I see on the picture display (right) far too much contrast. You should see a black bar and bars in 7 shades of grey. I see only 2 or may be 3.
Flipping the vertical plates of the wave form monitor (left) is the good idea. Then you get a standard video wave form with the sync peaking downwards.
By the way this dual grey scale is a perfect (test)picture to align the contrast and brightness of the picture display (right). Then mark the video amplitude on the left screen and for future NBTV-video the amplitude between black and white should be equal to your marks. Then automatically the grey rendering (contrast and brightness) of the picture will be optimal.
Good luck!
Steve Anderson wrote:Another suggestion...reduce the amount of light in the room, it appears quite bright in the photos. This will allow you to reduce the CRT brightness and thereby achieve a better focus. The rendition of the grey-scale should be improved too, even so, it may still not be perfect yet.
We're used to being able to watch TV in a sunlit living room, even from CRT TVs, but these little (and old) devices were not capable of that. Just like a mechanical disc NBTV monitor they're best viewed in subdued light. When used in an oscilloscope application mostly there's only one line, whether it be a sine-wave, square-wave, whatever. Here we're spreading out that same amount of light over 32 lines. Something has to give.
Going back a few eons, if you look at the snapshots of my 3" DG7/32 display you'll see that the ambient light is very low yielding a much better focus and overall picture quality.
Steve A.
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