I have ownedand serviced ctc4 television for years. I have one receiver,
The Director. My specialty was alignment. Many set ups are needed.
RCA printed many books about the set and how to service it. They are a
sleeper. Restoredand corrected, they are quite nice.

Hello Len:
I have one also, a Haviland, and I spent about 6 months restoring it, as time permitted. I agree that they are capable of remarkable color, if not in full detail. I am blessed to have an early 21AX, which has a dark green screen, as opposed to the grayish colored later tubes. The blues are spectacular on this tube.
I have yet to go through a complete alignment, prefering to use it as it is, with no major problems. The luminence channel produces crisp video when fed with a good source, and the chroma only needed a slight touch up as to oscillator frequency adjustment. "If it ain't broke, Don't fix it!".
I have a large binder with all the RCA service bulletins, ad SAMS PF's, as well as picture documentation of the restoration, before and after. One thing left is to re-do the veneer on the top, which is flaking, but I am more of a person who cares more about performance than cosmetics. Perhaps the next "custodian" will restore the cabinet. Thank you for your post. Please post more!
All the best to you,
Kevin G.

Please enlighten me about the "early 21AX" with a dark green screen. I was under the impression that the only dark green screens came in with the sulfide phosphors in the early 60s.

The early dark green screens on the early production 21axp22 crt's are believed to be of the same full gamut formulation phosphors as the 15gp22 used in the ct100.

I have 2 sets with this dark green phosphor 21axp22. I have one in my 21ct55 and also one in my ctc4 Haviland.

Sometime during the production of the ctc4, (or perhaps at the beginning of the ctc5 production) the phosphor formulation was changed to that which is common in the later tubes with the light gray screen.

The early production 21axp22 has vivid Blue and Green phosphors. I love to watch The Wizard of Oz with the saturation control cranked up. The colors are very vivid.

Well, that is peculiar, since the 15GP22 screen is gray - scratching my head on this.

It's funny that this discussion came up. I was messing with my CTC4 Haviland and the 5 the other night and started comparing the phosphors of the early 21AXP in the 4 to the 21AXP22A in the 5. The early one does have a slightly greenish look to it, not like a sulfide 21FBP22 but green compared to the grey of the 21AXP22A.

I hadn't realized that there was a change in the production of the 21AX... I had been under the impression that the change came after the 21CYP22. I haven't done any research myself, nor compared them, but I'm now curious! If anyone had said this in the past, I'd have said it was a result of the CTC-2 & 2B having the I & Q demod, and the CTC-4 & newer (except for the CTC-121, I believe), are R-y etc demod. Now that I think about it, I haven't ever worked on a 4... Are those I & Q?

Charles

...

Ok

The Sylvania data sheet makes no distinction between phosphors in the 21AXP22 and 21AXP22A. I suppose they would have not have used an early formulation in either one.

http://tubedata.itchurch.org/sheets/137/2/21AXP22.pdf

... quite right

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.