ctc4 owners

[old_tv_nut]

Some info from several sources:

A1955 RCA Review article, describing the 21AXP22 fot the first time says that the red phosphor efficiency was improved from "previous tubes" (meaning, I beleive, the 15GP22) by using an excess of zinc phosphate to prevent hydrolyzing of the phosphor, and by improved techniques in its manufacture. The net result was a 80% increase in red efficiency compared to "previous tubes." So, perhaps these early 21AXP22's had a different color to the red phosphor due to "excess zinc phosphate" or other details of the process.

An article on color TV phosphor screens from July 1965 indicates that the first red phosphor was cadmium borate silicate, which was, I believe, only used in the first experimental shadow mask tubes and needed a filter to make it more red because it was too orangish. The 15GP22, 21AXP22, and 21CYP22 are all listed as using sulfide blue, silicate green (P1) and phosphate red; but improvements in the phosphors and the tube electron optics resulted in efficiencies increasing from 0.6 to 1.0 to 1.4 lumens per watt. The next big jump was to 2.6 lumens/watt using the all-sulfide phosphors in the 21FBP22.

So, the colro of the screen in the first three tubes may have differed as improvements were made in efficiency, but it appears all three would have similar color rendition IF set to the same white color temperature, especially since they all used the NTSC P1 green. I would note, however, that somewhere along the way, the blue phosphor moved from the somewhat cyan NTSC blue to the modern violet blue, which would have noticeably changed the yellows toward green to compensate. Thsi change, hoiwever, should not have changed the screen color as far as I know.