15GP22 Manufacturers

[Tom9589]

A field sequential medical closed circuit monitor would not have used a -P22 CRT. It would have used a -P4 CRT.

[Electronic M]

Originally Posted by Tom9589

A field sequential medical closed circuit monitor would not have used a -P22 CRT. It would have used a -P4 CRT.

IIRC CBS themselves made atleast one field sequential set with one of the prototype Shadow mask tubes that eventually became the 15G.

It was absolutely possible to make field sequential on a shadow mask tube and the converse was also done...Col-R-Tel made a color wheel converter for monochrome NTSC sets. http://earlytelevision.org/col-r-tel.html

Prior to CBS color becoming standardized Zenith was one of the big players in the medical closed circuit color market. Before CBS color was on air there was a sizable closed circuit field sequential network between hospitals and medical schools to make surgical procedure education easier. I don't remember reading much about the replacement of that equipment with NTSC, but I would assume since it was costly and had a decent install base that it persisted into the NTSC era and that if any new recievers were needed after the 15G came on the market that engineers would have been tempted to use it. I'd bet you a cookie the last field sequential recievers receiving actual program material in the 50s were medical CC monitors.

Wayne/Old TV nut you are right the shadow mask implementation would be dimmer than NTSC on a shadow mask, but I think you overlooked the fact that the color filters in color wheel converters also significantly attenuate the light passing through them...I don't have the figures on hand, but I suspect the difference in brightness would not have been quite as substantial as one might think.

[old_tv_nut]

Originally Posted by Electronic M

...
Wayne/Old TV nut you are right the shadow mask implementation would be dimmer than NTSC on a shadow mask, but I think you overlooked the fact that the color filters in color wheel converters also significantly attenuate the light passing through them...I don't have the figures on hand, but I suspect the difference in brightness would not have been quite as substantial as one might think.

The monochrome tube + wheel was probably about the same efficiency overall as the shadow mask, since the filters were not ideal and probably resulted in white brightness 20% or less of the bare monochrome tube. But - using the shadow mask for field sequential would mean both the shadow mask attenuation down to 15% of a monochrome tube, AND the 33% factor of each gun being on only one third of the time, so about 5% overall - roughly 1/3 to 1/4 the brightness of a color wheel set for the same beam current and high voltage. And then there are other factors such as the poor efficiency of the P22 red phosphor, compared to the poor output of P4 filtered through the red filter, etc., etc.

[old_tv_nut]

Originally Posted by Electronic M

...Col-R-Tel made a color wheel converter for monochrome NTSC sets. http://earlytelevision.org/col-r-tel.html
...

Did you ever stop to think how this could possibly work? It depended on the temporal characteristics of the human visual system. The field rate was so low that the pictures were guaranteed to flicker, yet you could see good color.

The reason is that the color temporal (flicker) response of the human visual system is much slower than the luminance temporal (flicker) response - that is, you could see that the luminance was changing due to the red to green to blue sequence, but you could not see that the color was changing in sequence, only the brightness variation. You only saw the blended color. So, the pictures were deemed viewable even though flickering strongly.

Some early advanced TV systems (leading up to HD) attempted to reduce the frame rate of the color component compared to the luma component. There were problems in fast moving objects with the color information jumping behind and/or ahead of the luma on sequential fields, which would have required some sort of motion compensation. Edit - but it was mostly unnoticeable.

[old_tv_nut]

Originally Posted by Electronic M

...

Prior to CBS color becoming standardized Zenith was one of the big players in the medical closed circuit color market. Before CBS color was on air there was a sizable closed circuit field sequential network between hospitals and medical schools to make surgical procedure education easier. I don't remember reading much about the replacement of that equipment with NTSC, but I would assume since it was costly and had a decent install base that it persisted into the NTSC era and that if any new recievers were needed after the 15G came on the market that engineers would have been tempted to use it. I'd bet you a cookie the last field sequential recievers receiving actual program material in the 50s were medical CC monitors...

SKF converted to NTSC in 1956:
https://www.earlytelevision.org/skf_mackenzie.html

More:
https://www.earlytelevision.org/skf_color.html

[wkand]

It's really neat reading all the comments on this post. So much knowledge packed into this group!!