Quote:
|
Originally Posted by andy
They're from the mid to late 80's and they use a single gun color CRT. Instead of a shadow mask, the single gun rapidly switches between red green and blue as the spot passes over the phosphor stripes. There's a 4th "index" stripe on the inside of the screen that's used to sync the switching to the RGB stripes. There's a light sensor behind the CRT that picks this up. This is the same idea as the Philco "Apple" CRT from the 50's.
.
|
Not exactly the same as the apple.
The indextron is guided by a SEPERATE, GREEN phospor, which is BEHIND the main one. The index phospor is laid out so that it will tell the optical sensors on each side of the tube bell where the beam is at any given instant. Ther eis(in my vidimagic projector, anyway) a LARGE ckt. (proably about 5x7")board with a bunch of SSI ic's, that takes this information and then uses it to control the switching of the one single large gun on the tube.
In the original Apple, I do NOT think they used a phospor for guidance. IIRC, there were two anode potentials and an index "stripe" of aluminum behind each trio of phospors that would deflect back to the read anode and then be used to guide the main beam. A second beam was used for the index stripe.
In fact, on the indextron, you can SEE the green index phospor glowing behind the bell, whenever the tube is on.