On Tue, 21 Jul 2009 18:51:47 +0100, Arfa Daily wrote:

The arcade game "Tank Battle" used a monochrome stroke writer, so no
convergence issues with that. Around 27 years ago, I worked with some
very high end graphics systems from a U.S. company called Vector
General. They used a colour stroke writer (vector display) from a
company whose name I can't remember now, but they were in San Jose.
There was not any convergence issues, because they employed a special
CRT type known as a Beam Penetration Display. It worked by having
different colour phosphors layed on top of each other at the faceplate.
Individual colours were 'selected' by modulating the high voltage supply
to the final anode, which in turn modulated the 'intensity' of the
electron beam, and determined how far into the layers of phosphor it
penetrated, and hence which ones it excited. Obviously, its pallette was
very limited - just the basic primaries and a couple of complimentaries
as I recall, but still quite impressive.

The exact details might not be quite right, but good enough to give you
the idea. It's been a long time since I did the factory course on it,
and they were never very popular with our customers this side of the
pond. I'm sure there must be references on the 'net that you could look
at.

Interesting! I'm just about positive that Tektronix made 'scopes using
peam-penetration CRTs for a limited color palette. Those CRTs can't
change color quickly without a heck of a lot of fuss, because the
accelerating voltage has to change by several kV, and that take a little
while, maybe milliseconds. Afaik, the 'scope changed color to display a
different category of data, perhaps alphanumerics, possibly a ground ref.
line, multiplexed with the waveform display.

Furthermore, the CRT's sensitivity changes a lot, just about sure, so the
gain of the deflection amps needs to change when color changes.

Thanks much, and best regards!

--
Nicabod =+= Waltham, Mass.
who once owned a Western Electric
224-B gas focused CRT (burned out).