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Klaas Robers wrote:I expect the black ring to be a plastic box around the connection of the wires, and not a magnet? I have there a magnet, but the 5AHP7 should not have a magnet there.
If the deflection coil fits around the neck of the tube, it will be a 70 degree deflection coil, and that is what you need. It looks promising to me.
The two thin turnable rings at the very back are two magnetised rings, that are used to place the picture in the centre.
- When the tabs are on each other the magnetic field is zero.
- When you turn them in opposite directions the magnetic field is increasing and
- the picture centre moves in a certain direction.
- When you turn both rings together the direction of displacement rotates accordingly.
Klaas Robers wrote:As you have seen, I have a square with rounded corners. The picture is slightly smaller, it just touches the inner sides of the rounded corners. Any way the picture is not always at the same position, I think the magnetic field of the earth deflects it slightly. So a real sharp square is not a good thing.
But I should make the hole in the front plate circular any way. Then you may make a cadre with the squarish aperture before it. Look at the pictures that you have found. As well the wooden chassis with the 7BP7 (7 inch) as the "Heathkit" casing of the SB500 has this.
AncientBrit wrote:Has anyone tried directing a scanning laser beam onto the external face of an unpowered CRT?
This would of course need both X and Y deflection of the laser beam.
Would the phosphor glow or does it only get excited by an electron beam?
EDIT.
For a quick test just use the existing polygon line scan and holding the CRT (in lieu of the phosphor drum) move it sideways and see if a raster is left behind.
Graham
AncientBrit wrote:Hi Harry,
Two great demos.
Not sure I'd care to hold those two wires though!!
Cheers,
Graham
AncientBrit wrote:Hi Harry,
A couple of things to watch out for on those cheaper models is that they don't recommend continuous opearion and the output current is fairly small and probably would be insufficient for use as a HV supply for a CRT.
Cheers,
Graham
Klaas Robers wrote:The current that a CRT needs from the HV is very low. I guess for a 7BP7 and the like 100 uA. These generators can easily supply that. A colour CRT has a beam current of 0.5 mA per colour, so 1.5 mA in total for a white screen. However this is at 25 kV. But then the amount of light that it gives is enormeous. And you should take in account that the shadow mask absorbs at least 75%. So an SSTV picture tube will need no more than 0.1 mA.
In my 7BP7 / 5FP7 monitor the 5 kV is generated by a fly back converter, made from a 88mH ring core with two extra windings. It runs from about 15 volts. The advantage is that it supplies too +250 volt for the focussing and +100 volt for the video driver stage.
An important thing is, Harry, that the HV should be stabilised. The drawn current changes between black and white, and then the voltage should be stable. If not, the picture size breathes between black and white areas. That will be very well visible.
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