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  #1  
Old 01-13-2010, 06:29 AM
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Colour TV with the Aurora World Converter on Nipkow disk

Hi folks,

currently I am experimenting with color tv on a mechanical television set. You find more informations on the UK Vintage Radio Repair and Restoration Discussion Forum, see

http://www.vintage-radio.net/forum/s...ad.php?t=49520

Perhaps this topic might also be of interest for American readers.

Kind regards,
Eckhard
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  #2  
Old 01-13-2010, 09:10 PM
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Definitely of interest! Is it possible to see the stills without signing up for the vintage radio net forum?

Edit - I am signed up, just asking if the links can be made to work without signing in, perhaps by posting directly here?
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  #3  
Old 01-14-2010, 03:37 AM
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I will make a web page about this project in the next days. Currently, I am working on a better method to video and to photograph pictures and footage from the Npkow disk.

Here is a photo of the set:

http://fernsehmuseum.net/mechanical/scanningdisc.htm

and attached some stills.

- Eckhard
Attached Images
File Type: jpg Unbenannt-Echtfarben-01.jpg (77.0 KB, 99 views)
File Type: jpg Unbenannt-Echtfarben-02.jpg (89.6 KB, 72 views)
File Type: jpg Unbenannt-Echtfarben-03.jpg (103.1 KB, 61 views)
File Type: jpg Unbenannt-Echtfarben-04.jpg (76.8 KB, 87 views)
File Type: jpg Unbenannt-Echtfarben-05.jpg (94.3 KB, 89 views)
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Old 01-14-2010, 09:59 PM
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I like the NBC Peacock and the test card in Unbenannt-Echtfarben-04.jpg. That latter one I haven't seen for some years. What is the source of the original images, especially 04?
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Old 01-15-2010, 02:31 AM
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The test card in [Unbenannt-Echtfarben-04.jpg] is an early PAL test card which was used in the 1960s only for a short time. It has a human face at the bottom for checking the correct fleshtones similar to the British testcard F.

This early test card was soon replaced by the FUBK test card, see photo in the attachment, which was broadcast until the closing of analog television over here in the last years. See also

http://upload.wikimedia.org/wikipedi...K-Testbild.png

- Eckhard
Attached Images
File Type: jpg Unbenannt-Echtfarben-06.jpg (89.1 KB, 54 views)
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  #6  
Old 01-15-2010, 10:20 AM
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thanks
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Old 02-02-2010, 04:11 AM
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Some more remarks regarding mechanical colour tv which might be of interest: I have compared the colors of Darryl's RGB LED array picture on the Nipkow disk with the colors on a screen of a PAL color tv set, both feed with the same test patterns.

Green of the LEDs seems to be much "deeper" and saturated than the green on the CRT screen, and also red of the LEDs seems to be much "deeper" and saturated than the red on the CRT screen. The LEDs seems to provide a wider gamut than the colors of the CRT.

This obeservation was confirmed by the actual values for the wavelengths of the RGB LEDs of mechanical television:

632nm (red)
523nm (green)
465nm (blue)

This seems to be more similar to the wavelengths of the early NTSC color picture tubes than with PAL (except of blue)

636 to 658nm (red)
523 to 532nm (green)
442 to 452nm (blue)

For comparison PAL/SECAM dominant wavelength (these values are estimated from the color space triangle):

607nm (red)
552nm (green)
466nm (blue)

In the attachment are the wavelengths for the early wide gamut NTSC tubes 15GP22 and 21AXP22. Note that 1 Angstrom is 0.1 nm.

Eckhard
Attached Images
File Type: jpg US_15GP22_21AXP22_phosphors.jpg (53.0 KB, 29 views)
File Type: jpg Parot.jpg (84.7 KB, 48 views)
File Type: jpg Testcard.jpg (98.3 KB, 47 views)

Last edited by yagosaga; 02-02-2010 at 07:36 AM. Reason: photos added
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  #8  
Old 02-04-2010, 04:16 PM
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This is the first time I've compared the spectra on that CRT spec to the NTSC standard - I always asumed it matched - but it appears that the red and blue are both more extreme than the NTSC standard says they should be. This needs further study.

LED red and traffic signal red made with an incandescent lamp and red filter are both outside the NTSC standard gamut and outside every color TV gamut proposed since. Auto tail lights, however, are quite orangy and are inside the gamut.

The NTSC standard blue is much less violet than modern tubes' blue or SECAM or HDTV blue. The reason is that they had trouble at first making the modern sort of blue because even a small amount of contamination would turn the blue phosphor to green. Therefore, they went to a less-violet blue formulation that did not suffer from contamination. Once the contamination problem was solved, it was possible to build the all-sulfide tubes, which moved blue towards the modern deep blue, but also moved the green forever towards yellow.

Regarding the parrot and color bars images: the mechanical TV pictures (at least as photographed) have a very strong highlight white balance towards purple. No attempt should be made to judge the colors relative to the CRT until this problem is fixed.
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  #9  
Old 02-05-2010, 02:16 AM
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Thanks very much for your remarks.

Quote:
Originally Posted by old_tv_nut View Post
Regarding the parrot and color bars images: the mechanical TV pictures (at least as photographed) have a very strong highlight white balance towards purple. No attempt should be made to judge the colors relative to the CRT until this problem is fixed.
I will check it. It is not easy to adjust a correct white balance only with the eye due to tints in the surrounding light.
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  #10  
Old 02-10-2010, 08:26 PM
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Quote:
Originally Posted by old_tv_nut View Post
This is the first time I've compared the spectra on that CRT spec to the NTSC standard - I always asumed it matched - but it appears that the red and blue are both more extreme than the NTSC standard says they should be. This needs further study.
I just looked up a paper on the shadow mask CRT from the January 1954 IRE Proceedings (the NTSC issue). The phosphors there are very slightly different from the graph posted here, but the notable thing is that the dominant wavelength plotted on the chromaticity chart is not the same as the peak wavelength for red and blue. This apparently is because both of them are on the edge of the visible spectrum, and therefore, the wavelengths more toward the center are more effective.
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  #11  
Old 02-18-2010, 06:15 AM
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I have tried to take photos with a correct white reference for both kinds of display, but it was nearly impossible. Every time I got a different tint due to daylight or artifical light properties, so I gave up.

Here are some more attempts to make good photos of the Nipkow disk screen:

http://fernsehmuseum.net/mechanical/...MitFarbe15.jpg
http://fernsehmuseum.net/mechanical/...MitFarbe14.jpg
http://fernsehmuseum.net/mechanical/...MitFarbe13.jpg
http://fernsehmuseum.net/mechanical/...MitFarbe12.jpg

- Eckhard
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