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  #46  
Old 05-07-2011, 08:43 AM
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15GP22 demo @ ETF 2007
 
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Quote:
Originally Posted by old_tv_nut View Post
By the way, when you measure a tube, you get the operational color, not the pure phosphor color, because any imperfections in the color purity settings, light scattering, electron scattering, etc. are all included.
Armed with old instrumentation experience [as a kid I worked for an instrument manufacturer for some years doing initial power-up, troubleshooting, test, and calibration] and when the Spyder calorimeter became known a few years ago, I made some measurements of a near-pristine 15GP22. I particularly considered purity, ambient light, and repeatability when making the 'operational color' measurements.

For example, I took measurements at screen locations that exhibited the best purity. All readings were made with a dark cloth over the set.

Results did support the 15GP22's reputation for gamut. Only the green fell a bit short of the 0.21, 0.71 1953 NTSC standard. But not by much.

At the time, John Folsom platted the results on a graphic that included the 1951 CBS and 1953 NTSC, and I believe the sRGB standards. As I am in SC visiting relatives after the ETF convention, I unfortunately do not have access to the graphic at this time.

For me, this was one step in the quest to reproduce what one would have seen in the early days of color television. Wayne Bretl has demonstrated mathematically that the TK-41 was capable of generating a 1953 NTSC compliant image. Now if we can only get Mrs. Astaire to allow us a DVD of her husband's restored October '58 special, we could demo the real thing at the next ETF convention...

Pete
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  #47  
Old 05-07-2011, 11:24 AM
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Quote:
Originally Posted by miniman82 View Post
Wow, outstanding work!

Looks like they are pretty close, for the most part. I'd bet the later tubes are farther apart than the early ones, have you tested any of them?
The 1931 CIE chart shown exaggerates the difference in green and minimizes it in blue. The difference between the CBS blue and others is as significant as the difference in green between the SMPTE and others. There is an alternate plot developed in 1976 that is closer to uniform variation.

Here are the two versions of the plot (1931, x,y; 1976 u',v') comparing several color gamuts:


Technicolor at three different dye concentrations
(Many thanks to Ed Reitan for supplying the dye spectral curves used to calculate these colors);

NTSC;
sRGB (digital still cameras and HDTV);
Fujichrome test target;
Kodachrome test target;
Pointer's surface colors (a survey of the range of natural, paint, and printed colors).

Note the more significant differences in the blue and magenta region shown on the u', v' diagram.
Attached Images
File Type: jpg assorted gamuts xy.jpg (117.2 KB, 32 views)
File Type: jpg assorted gamuts uv.jpg (117.3 KB, 37 views)
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  #48  
Old 05-07-2011, 11:36 AM
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Quote:
Originally Posted by cbenham View Post
Here are the spectrum charts for the 15GP22 and a rare earth Mitsubishi tube at the ETF Museum. Please note that the vertical scale for the 15GP22 is different than that of the 21AXP22 and the rare earth tube. That's why it appears to be very low when in fact it is close to the 21AXP22.
The spectrum from the Eye-one has 10 nm resolution, which is good enough for color calculations, but does not show how spiky the rare earth red is.

This page has a finer resolution plot of the individual phosphors in a modern tube, about 20% down the page:
http://www.websters-online-dictionar...&sa=Search#922
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  #49  
Old 05-07-2011, 11:58 AM
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Pete Deksnis Pete Deksnis is offline
15GP22 demo @ ETF 2007
 
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Quote:
Originally Posted by old_tv_nut View Post
By the way, when you measure a tube, you get the operational color, not the pure phosphor color, because any imperfections in the color purity settings, light scattering, electron scattering, etc. are all included.
Armed with old instrumentation experience [as a kid I worked for an instrument manufacturer doing initial power-up, troubleshooting, test, and calibration] and when the Spyder calorimeter became known a few years ago, I made some measurements of a near-pristine 15GP22. I particularly considered purity, ambient light, and repeatability when making the 'operational color' measurements.

For example, I took measurements at screen locations that exhibited the best purity. All readings were made with a large dark cloth over the set.

Results did support the 15GP22's reputation for gamut. nly the green fell a bit short of the 0.21, 0.71 1953 NTSC standard. But not by much.

At the time, John Folsom plotted the results on a graphic that included the 1951 CBS and 1953 NTSC and I believe the sRGB standards. As I am in SC visiting relatives after the ETF convention, I unfortunately do not have access to the graphic at this time.

For me, this was one step in the quest to reproduce what one would have seen in the early days of color television. Wayne Bretl has demonstrated mathematically that the TK-41 was capable of generating a 1953 NTSC compliant image. Now if we can only get Mrs. Astaire to allow us a DVD of her husband's restored October '58 special, we could demo the real thing at the next ETF convention...

Pete
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  #50  
Old 05-07-2011, 09:05 PM
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miniman82 miniman82 is offline
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Double post?
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  #51  
Old 05-07-2011, 11:48 PM
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Quote:
Originally Posted by Pete Deksnis View Post
I took measurements at screen locations that exhibited the best purity. All readings were made with a large dark cloth over the set.

Results did support the 15GP22's reputation for gamut. nly the green fell a bit short of the 0.21, 0.71 1953 NTSC standard. But not by much. Pete
One other set of data that should be helpful in visualizing the gamut of P22 phosphors is from the RCA HB-3 Tube manual, 1964.
Cliff
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File Type: pdf HB-3 P22 Group Phosphors .PDF (887.7 KB, 50 views)
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  #52  
Old 05-08-2011, 10:12 PM
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Quote:
Originally Posted by cbenham View Post
One other set of data that should be helpful in visualizing the gamut of P22 phosphors is from the RCA HB-3 Tube manual, 1964.
Cliff
Wow - thanks, Cliff - I never saw that combined comparison data sheet before.
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  #53  
Old 05-11-2011, 12:14 AM
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cbenham cbenham is offline
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Quote:
Originally Posted by old_tv_nut View Post
Wow - thanks, Cliff - I never saw that combined comparison data sheet before.
That material came out of an HB-3 manual I got at Kutztown from John Timinsky. It came from RCA Labs and was the property of Al C. Schroeder.
I'm kind of proud to own it. #;^) Cliff
Attached Files
File Type: pdf Al C. Schroeder HB-3 Manual.PDF (159.3 KB, 32 views)
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  #54  
Old 05-13-2011, 12:51 AM
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Sweet info, Cliff! We'll have to get back into this once I have the thing up and running, which it surely has not done recently...


because now...


The peaking coil replacement odyssey begins.


Lots of bad ones, and my attempt at repair was not met with success. There's just too much damage done by the corrosion intrusion, and though I was able to peel the plaster shell off one, it also peeled some fine copper wires along with it.
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  #55  
Old 05-13-2011, 01:23 AM
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miniman82 miniman82 is offline
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BTW- I don't follow the notation of inductance in the schematic. MH is obvious- millihenries. I am assuming mu-h is literally μ spelled out- microhenries in other words.
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  #56  
Old 05-13-2011, 08:16 AM
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Hu- You know there's some funny stuff in yer graphs...... In the "15gp22-21axp22.pdf" that includes "RX43" in the on screen title. The 15gp22 actually has a narrower color spectrum than the 21axp22, and much narrower than p22 phosporous. Smaller triangles on the graph do actually indicate narrower color spectrum. And on the measured graphs both the 15gp, and the 21axp seem to have a very similar shape, except for the brightness level. (You notice in the old RCA p22 graphs also put up on this thread RCA correctly uses the term "relative" in its brightness scale, the vertical left scale. Relative in this case is kind or normalizing with refrence to brightness.) For actual more acurate comparison you are going to have to measure both, or all tubes you compare at very similar brightness levels. (or beam currents, Something I took exception to when this discussion took place many years ago on Pete's private site.) You will get very hard to distinguish readings using those scales with such wide differences in light levels. Think about reading 2V acurately on an analog meter when you chose to use the 400V full scale deflection setting. And you also have to first establish that your instrument has a flat response across the full spectrum. And in addition, that the instrument is accurate across all light intensity levels. And as for the overall screen face color, it may just be the difference in the material between the phosphorous pigment, or in the material used to hold the phosphorous in suspension when deposited on the screen. Anyway just a squirrels thought on the presented data.
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  #57  
Old 05-13-2011, 08:50 AM
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And while were on the subject, I was also wondering just what it would be like to set tube purity adjustments using live readings and that fancy color measuring device. After all its been proven in the design of color sets, and in VCR design that our eyes are very very easy to fool. So howbout it you guys ever think of setting purity with that fancy color thing and then doing color spectrum measurement? It sure would be cool if a computer set purity and not our eye..... (Dam that squirrel)
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  #58  
Old 05-13-2011, 10:50 PM
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Originally Posted by Username1 View Post
And while were on the subject, I was also wondering just what it would be like to set tube purity adjustments using live readings and that fancy color measuring device. After all its been proven in the design of color sets, and in VCR design that our eyes are very very easy to fool. So howbout it you guys ever think of setting purity with that fancy color thing and then doing color spectrum measurement? It sure would be cool if a computer set purity and not our eye..... (Dam that squirrel)
Those "fancy devices" are much too slow to use for adjusting purity. For that you would need a fast-responding (though less accurate) device. Plus, you would need a multi-headed device that reads center, edge, and corner areas simultaneously. Only the production factory could afford such special instrumentation. In the home, the eye is the best instrumetn for adjusting purity.
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  #59  
Old 05-13-2011, 11:18 PM
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Quote:
Originally Posted by Username1 View Post
Hu- You know there's some funny stuff in yer graphs...... In the "15gp22-21axp22.pdf" that includes "RX43" in the on screen title. The 15gp22 actually has a narrower color spectrum than the 21axp22, and much narrower than p22 phosporous. Smaller triangles on the graph do actually indicate narrower color spectrum. And on the measured graphs both the 15gp, and the 21axp seem to have a very similar shape, except for the brightness level. (You notice in the old RCA p22 graphs also put up on this thread RCA correctly uses the term "relative" in its brightness scale, the vertical left scale. Relative in this case is kind or normalizing with refrence to brightness.) For actual more acurate comparison you are going to have to measure both, or all tubes you compare at very similar brightness levels. (or beam currents, Something I took exception to when this discussion took place many years ago on Pete's private site.) You will get very hard to distinguish readings using those scales with such wide differences in light levels. Think about reading 2V acurately on an analog meter when you chose to use the 400V full scale deflection setting. And you also have to first establish that your instrument has a flat response across the full spectrum. And in addition, that the instrument is accurate across all light intensity levels. And as for the overall screen face color, it may just be the difference in the material between the phosphorous pigment, or in the material used to hold the phosphorous in suspension when deposited on the screen. Anyway just a squirrels thought on the presented data.
P22 refers to any RGB color tube. The points shown are some particular set of phosphors, which appears to have the later non-NTSC blue. Cliff maybe can tell us the source of the numbers, which may be ideal phosphor numbers or measurements with a colorimeter rather than a spectroradiometer.
The reduced purity in the 15GP22 tube is to be expected. Later techniques for reducing electron scatter, etc. had not been invented yet. Specifically, the green is very close to where it should be, the blue is close to NTSC blue, which is not as violet as later blue phosphors. The only real degradation is in the red, indicating the red purity was not ideal. Also, maybe Cliff can comment on whether these numbers came from a spectroradiometer, or a colorimeter. If a colorimeter, errors are also to be expected.

I talked with the president of Spectracal at the Hollywood Post Alliance in February, and he said that the I-1 spectroradiometer is much more accurate than colorimeters, and is reasonably comparable to much more expensive spectroradiometers. Of course, this non-lab model, costing about 1/10 of the top ones, is only calibrated once, at the factory, whereas a lab instrument would be calibrated yearly or more often to a NIST-traceable standard. The important thing is that it can correctly handle the red primary spectrum that trails off into the infrared. Back when we first measured Cliff's field-sequential color wheels on a CRT with the Spyder II colorimeter, we got wildly wrong results due to the deviation of the deep red response from the standard observer curves. The Spyder III improved that considerably, but only the I-1 gives results that are really close to eyeball color.
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  #60  
Old 05-18-2011, 12:31 PM
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21FBP22A red Accuracy

On the good color bars displayed on my reactivated 21CT55, yellow is best ever while the red is much truer red then the '97 27in Sony which is distinctly orange/red! My two 21FBP22's have differently unenergized phosphor screens. The one in the 21CT55 has a light gray tone while my spare has a greenish tone. My Sony pro monitor has SMPTE-C spec'ed phosphors. Its red is more accurate, not as pure red as the 21CT55, but close. I read somewhere the modern SMPTE phosphors are more orange/red since they produce better "flesh tones" with less accurate chroma demodulators. So anyway, I designate the gray screen CRT as a "rare-earth" 21FBP22A and the green screen CRT as a sulfide 21FBP22. It would be very interesting to see real-time side by side displays of the color bars produced by the NTSC 15GP22 / 21AXP22 and the gray and green screen 21FBP22's.
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