21-CT-55 Acquisition

[ohohyodafarted]

Interesting stuff from you Eberts. Thanks you!.

In answer to bgadow...

The phosphor aplicaton process is a photo optical process. Each of the color phosphors is applied one color at a time. First one color of phosphor is applied to the glass front of the tube. Then the shadow mask is set in place. The phosphor is then subjected to a beam of light that is focused at the same angle of the corresponding electron gun for that color. Where ever the light penetrates through the holes in the mask, the phosphor, which is photosensitive, addheres to the glass. The mask is removed and the unexposed phosphor is rinsed off, leaving only dots of the color phosphor behind.

Then the next color phosphor is applied over the entire inside of the faceplate of the crt. The mask is again installed. But this time the light source is moved to corespond with the position of the electron gun for this color of phosphor. Because the light is comming from a different angle, it shines through the holes in the mask and strikes the phosphor on the faceplate in a different spot, then it did in the first exposure. The mask is removed again and the unexposed phosphors are washed off. Now there are 2 colors of dots next to each other.

The inside of the faceplate is now coated with the third phosphor color and the mask is installed again. The light source is moved to the position of the angle of the third electron gun and the last color of phosphor is exposed. The mask is removed again and the unexposed phosphor is again washed off and now (if everything was done properly) you have triads of phosphor dots all over the inside of the faceplate.

Then the tube gets aluminized as discribed by Eberts.



AFter the aluminizing the mask is installed for the last time and the front faceplate is mated with the glass funnel and neck assembly using a glass FRIT that when heated, fuses the front and rear into one unit.

AFter that the electron gun assembly is installed and the tube is run throiugh the evacuation oven at between 650 and 700 degrees F.

There may be some technical aspects that Eberts may wish to elaborate on but this is basically how the phosphor dots are applied.

BTW: the process above was patented by CBS Hytron Division, and Sarnoff had to buy the rights to use this process. It must have realy frosted him good that CBS had a better way of doing things. The first tube to use the application of the phosphors directly onto the inside of the faceplate was the 19vp22 built by CBS and used in the set on John Folsoms avitar. Prior to the developement of the photo process above, RCA did the manufacture of the 15gp22 crt using a silk screen process which required the making of several negatives to expose silk screens to silk screen the phosphors onto the flat glass phosphor plate that was suspended inside the glass envelope. It was very inefficient and expensive. It is rumored that RCA lost lots of money on each tube made.

Bob G.