Westinghouse K840CK15 Restoration

[consoleguy67]

I still think the color rendition on the roundie crts was much better, and closer to the NTSC specifications than any time after.

[Tom9589]

The first color TVs were made to be the best they could be and closest to the NTSC standard so they would sell. After that the bean counters stepped in and started reducing costs and quality. Muntz would have been proud. Speaking about Muntz, did he ever make his own color TVs or did he just use RCA clones?

[Electronic M]

Originally Posted by Tom9589

The first color TVs were made to be the best they could be and closest to the NTSC standard so they would sell. After that the bean counters stepped in and started reducing costs and quality. Muntz would have been proud. Speaking about Muntz, did he ever make his own color TVs or did he just use RCA clones?

You're wrong about the reason for phosphor changes. The original color phosphors used in the 15GP22 and 21AXP22 were VERY dim and the amount of light output per unit of gun current was badly imbalanced. The blue phosphor would produce 3x the light as the red for the same gun current (surviving CRTs tend to have worn out red gun cathodes because of this). They simply used existing primary color phosphors when they designed the 15GP22 so they left HUGE room for improvement.
Because the NTSC correct phosphors we're horribly dim and terribly unbalanced once the early adopter boom ended they started trying to solve those problems. The 21CYP22 had a different blend that improved gun balance and brightness, and the 21FBP22 improved on it further. Those improvements did shrink the color space and change color accuracy a bit but in exchange for brightness that was competitive with monochrome TVs and improved longevity.

The oldest surviving Muntz color I'm aware of is a CTC-5 chassis in a Muntz made cabinet...It makes sense since the CTC-5 was the most Muntz-like color chassis RCA designed.

[etype2]

Thank you, Wayne, Tom, consoleguy67, Electronic M.

“ They simply used existing primary color phosphors when they designed the 15GP22”… My understanding was the phosphors were designed to come as close to NTSC color specifications, after all the 15GP22 was the first color CRT introduced to the public.

“ Because the NTSC correct phosphors we're horribly dim and terribly unbalanced … “ I believe it was more of a problem of the shadow mask design. The first shadow mask blocked 86% of the electron light. RCA could have designed a more efficient shadow mask without changing the color phosphors, but I’m not sure it was technically possible at the time. It is true that later RCA CRT designs were brighter, but at the expense of color accuracy. As Wayne has explained many times, the reds became more orange and greens became more yellow. Precisely why the Chromatron and beam index tubes were developed, to overcome the inefficiency of the shadow mask.

Edit. Sidenote. Muntz tried marketing a Chromatron television.

[Tom9589]

Tom C. I just re-read my post and I didn't make any reference to phosphors at all. I don't know where you got that idea.

I was referring to circuitry. RCA took its CT-100 and then started to see what circuitry could be eliminated without causing a noticeable perception of degradation to decrease the cost of color TVs. In just a few years the parts count dropped in color TVs. Demods changed from the the I and Q demods to something else. Some service controls disappeared. DC restoration disappeared altogether.

[etype2]

Hello all. Remainder of screenshots from “Cover Girl” in the dark shot with the Sony A6300. Shot in RAW, processed IN TIFF, RGB 16 bit, P3 color gamut, reduced to JPEG.

https://visions4netjournal.com/wp-co...595EFEAF3.jpeg

https://visions4netjournal.com/wp-co...C71A5D92A.jpeg

https://visions4netjournal.com/wp-co...6D7CAAB12.jpeg

https://visions4netjournal.com/wp-co...B7F823B7E.jpeg

https://visions4netjournal.com/wp-co...420E30954.jpeg

https://visions4netjournal.com/wp-co...B046BFE0C.jpeg

[old_tv_nut]

Originally Posted by etype2

Thank you, Wayne, Tom, consoleguy67, Electronic M.

“ They simply used existing primary color phosphors when they designed the 15GP22”… My understanding was the phosphors were designed to come as close to NTSC color specifications, after all the 15GP22 was the first color CRT introduced to the public.

“ Because the NTSC correct phosphors we're horribly dim and terribly unbalanced … “ I believe it was more of a problem of the shadow mask design. The first shadow mask blocked 86% of the electron light. RCA could have designed a more efficient shadow mask without changing the color phosphors, but I’m not sure it was technically possible at the time. It is true that later RCA CRT designs were brighter, but at the expense of color accuracy. As Wayne has explained many times, the reds became more orange and greens became more yellow. Precisely why the Chromatron and beam index tubes were developed, to overcome the inefficiency of the shadow mask.

Edit. Sidenote. Muntz tried marketing a Chromatron television.

It wasn't quite as you have stated.

The NTSC primaries were chosen to match available phosphors, not the other way around. RCA would have preferred to use an even wider color gamut as achieved with the trinescope prototypes, but the original phosphors were quite good. There was some confusion with the blue. They had to abandon the deeper blue sulfide phosphor that is used today, due to copper contamination turning it green, plus there seems to have been a typo in documents somewhere that didn't even get the blue coordinates exactly right for the FCC specs.

Also, it is correct that the original phosphors have horribly unbalanced efficacy. It was tolerable in the 15GP22 mainly because the small screen size meant a reasonably bright picture at reasonable gun currents. You are correct that shadow mask transparency was improved with the 21 inch tubes, but this was more than countered by the need for increased gun current to get reasonable brightness. The current ratios gradually improved but were still nowhere near unity until rare-earth reds came along. In the meantime, the ratio problem was reduced by going to a very cyan white point ("9300K + 27MPCD") which simply meant that the red gun was driven harder but not enough to make a 6500K daylight white.

There is also a psychophysical effect of increased "colorfulness" with increased brightness, which tipped all consumer preference toward brighter pictures instead of measured color gamut.

Also, the main change in gamut was from the yellower sulfide green and to some extent the deeper blue sulfide blue (more saturated purples and magentas). The reds through the years were all close to NTSC with the exception of the sulfide red in the early 60s. Original NTSC red is slightly orange to begin with; it can reproduce tail-light red but not traffic signal red.

[etype2]

Wayne, thank you for the updated information. Did color television phosphors exist prior to the 15GP22? Prototypes only right or no? We’re they used by the military prior to color television? I did not dispute the inefficiency of the three primary color phosphors used in the 15GP22, but I believe the design of the original shadow mask used in the 15GP22 was largely responsible for the brightness issue. From RCA’s own technical published paper, the 15GP22 blocked 86% of the electron light and was only 14% efficient. The original shadow mask was horribly inefficient.

[Steve D.]

Marshall,

The Cover Girl screen photos are fantastic. Much more viewable than the previous photos w/the somewhat distracting lighting reflections. This, IMO, is the way to showcase the Westy. Thanks for sharing.

-Steve D.

[old_tv_nut]

15GP22 mask transmission 14%
Later tubes (of any type including Trinitron) mask transmission ~ 25%
Ratio 1:1.8

15GP22 area: 88.5 in^2
21 inch round tube area: 255 in^2
Current per unit area ratio: 2.88:1

Brightness ratio (15G 14% / 21 inch 25%), all else equal including beam current: 1.6

So the larger tube had a 38% deficit compared to the 15G, operated at the same beam current.

[etype2]

Coming from you Steve, a real compliment.

Wayne, point taken. Thanks.

15GP22

Shadow mask apertures: 195000, dots: 525000
Aperture diameter: Unknown, assume 0.010 inch.
Filtered glass faceplate light transmission: 70%
195000 / 15 = 13000
Phosphors: P22

21AXP22

Shadow mask apertures: 357000, dots: 1071000
Aperture diameter: 0.010 inch.
Filtered glass faceplate light transmission: 77%.
357000 / 21 = 17000
Phosphors: P22, red 30% more efficient, improved manufacture/assembly, citation RCA.

[jhalphen]

Hi to all,
Hi Wayne,

Re: shadow mask vs other (Trinitron) Mask/Aperture Grid electron transparency.
Read this excerpt from UK "Practical Television Magazine" which published a 3 month series on progress of Color CRT developments (June to Sept 1986)

https://worldradiohistory.com/Practi...n_Magazine.htm

Technically sound or Marketing BS ?

Best Regards
jhalphen
Paris/france

[old_tv_nut]

Very interesting. There are a number of things there I never heard about before.
I think it will be necessary to read the entire articles.

I never heard of hexagonal holes.

The transparency of the mask per se is not the limiting factor in black matrix (negative guardband) tubes, it's the percent coverage of the black matrix. This excerpt doesn't make a distinction, so i wonder if it is referring only to older tubes in the case of very low transparency and strong gradient.

I do recall discussion of the noticeability of the gradient in transparency from center to edge in tubes that had a strong gradient. This was of concern if a manufacturer bought tubes from different sources that had different gradients. A strong gradient is not very noticeable by itself, but two different ones displayed side by side might be.

[old_tv_nut]

Judging from the abundant detail (much of which I only knew in general terms), I have to think that the excerpt is accurate, although as I said it does not distinguish between positive and negative guard band tubes in terms of relative transparency. I note the author does discuss negative guard band, but does not say if the later tubes had greater transparency than the figures in the excerpt.

As noted in the articles, the exact numbers varied from manufacturer to manufacturer and over time as innovations improved the performance incrementally. All this disappearing knowledge illustrates why we can't practically build color CRTs any more, just as we can't practically build a Saturn V rocket now that the dedicated factories are gone.

[jhalphen]

Hi to all,
Hi Wayne,

Thanks! for your interest.

CRTs: a dying art & lost knowledge, so sad.
So much work, ingenuity, cleverness and sometimes sheer genius to make the device better and better over nearly a century.
Will we ever be able to properly re-seal a 15GP22, rebuild the guns and get a new lease on life...

The UK magazine had a fourth & very interesting final article (Oct 1986) about Beam-Index tubes but the issue scanned is missing all the relevant pages.
Really a shame !

Best Regards
jhalphen