Re: G08's and inductive kick

At 09:52 AM 9/1/97 -0700, John Lee wrote:
>Zonn wrote:
>>
>> At 04:26 PM 8/29/97 -0700, you wrote:
>> >I'll bet removing those resistors and replacing the
>> >voltage with regulated voltages could possibly give a nice solid display
>> >without having to have, high power, low voltage, regulation.
>> >
>> >yup.. that's what they did in the ampliphone.
>> >
>> >We also just figured out what the two multipliers do in the WG vector
>> >generator design; they multiply the square of the opposite channel's
>> >deflection value, scaled down by a voltage divider to the channel's
>> >value prior to it being scaled by the pot/VDR linearity circuit.
>>
>> I posted somewhere what those things were doing, if I wasn't so lazy I'd
>> have written a FAQ or something.
>>
>> >From reading a lot of different sources I found that in some yoke/CRT shape
>> combinations (especially the older tubes/yokes) there is an affect where the
>> farther from the center of your CRT the beam is, the more affect the yoke
>> has on moving it. I never really was able to find out why, maybe something
>> to do with the inverse square law and the distance from the gun and the high
>> voltage <plate> attracting the electrons. The farther the distance the less
>> attractive force, leading to more "blooming".
>
>Blooming is usually caused by low high voltage. Lower the voltage, and
>the electrons are
>less attracted to the plate. The picture will look expanded.

That's useful information but I was simply describing the effect all picture
tubes have of enlarging things when they are drawn toward edges of their
screens, not a symptom of a badly operating monitor. Call it what you like,
the bloom effect is always present and must be compensated for, and
depending upon the design of the tube/yoke it can also lead to pincussioning.

As for the edge expansion, to correct for this effect Atari used VDRs, Sega
used their custom IC, Cinematronics used an array of diodes and resistors in
the feedback loop of an op-amp. Raster displays must also compensate for
this and I'm sure there's as many ways as there are monitors for doing this.

-Zonn
Received on Tue Sep 2 10:26:54 1997