15GP22 Manufacturers

[Tom9589]

Do we know who manufactured the 15GP22 used in the Westinghouse H840CK15?

Who were the other CRT manufacturers in 1954 who manufactured 15GP22s?

Likewise, who made the 15HP22s?

[etype2]

I’m not 100% on this, but I believe Westinghouse had manufacturing capabilities to assemble the 15GP22. Ive seen H840CK15 production line photos and read articles indicating they were manufacturing this tube. RCA shared technical information with all the manufacturers to promote color television.

I know Westinghouse manufactured a prototype one gun color CRT in 1954. This prototype was independent of the work being done at Autometric.

I think Admiral may be another, not sure. I have focused on Admiral and Westinghouse in my research, not sure about the others.

[ohohyodafarted]

15Hp22 was made by CBS Hytron. CBS owned the patent on the photographic deposition method of putting the phosphor dots directly onto the inside face of the screen.

RCA used a silk screening method to deposit phosphor dots onto a flat glass plate which was mounted inside the crt bulb.

IIRC RCA did some patent exchanges with CBS in order to be able to deposit phosphor dots directly onto the inside face of the 21AXP22. One of the rare instances that RCA had to grovel to another competitor to obtain the rights to a patent that RCA could not get around. Sarnoff was a real SOB and vowed that if RCA did not invent something they would not use it. But in this case Sarnoff had to eat crow.

[colorfixer]

I think the 15" Philco set at the ETF has a Sylvania tube. Rauland apparently claims to have made them as well.

[Tom9589]

Did any of these other manufacturers have a better record than RCA with regard to leaks with the 15GP22?

[Electronic M]

All color CRTs had to have the large metal-metal and sometimes metal-glass seal around the face plate (until the 21CYP22 came out in the CTC-7 a few years later) which is a seal failure point...one possibly for minor reliability improvement is if some makers used a glass evacuation stem. Most early color CRTs and some later all glass types (ie 21FBP22) had a pinched copper evacuation stem...of the later all glass types I've had ~20 in my ownership and 2 were gassy...Those 2 both had copper stems. I think the copper stems are a failure point. Using a glass stem on a 15G wouldn't fix the glass-metal-metal-glass face ultor ring failure point, but it would remove the neck evacuation seal as a failure point, and might have increased the survival rate some percentage.

Originally Posted by colorfixer

I think the 15" Philco set at the ETF has a Sylvania tube. Rauland apparently claims to have made them as well.

I've read that too. I wonder if Zenith/rauland sold it as a replacement or in any of the field sequential medical closed circuit color sets they sold or if it was for prototypes only. Zenith also had a prototype rectangular color CRT in 1954...It is rather fascinating with how much development the did that they waited till late 1961 to market their first consumer NTSC set.

[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!!

[old_tv_nut]

CBS argued that the color wheel was not a forever limitation on their field sequential system, as a three-color CRT could be used too. Of course, they didn't mention that it would be only 1/3 as bright, due to each gun being on only 1/3 of the time.

[etype2]

I read that the 15GP22 blocked 86% of the electron energy by its shadow mask, hence the Chromatron and beam index development. I don’t think the color filters blocked that much light. If it’s true that the filters caused a 33% reduction in light, it’s still much better than the 86% light reduction.

The field sequential system could have been viable and had advantages. Simple tube, less parts, no convergence requirements, brighter images, higher resolution, no dot or stripe deposits required, no moire effects.

But the General and his suits made sure the competition would never prevail. Just litigate, litigate and litigate until they broke the will or the financial ability of the competition.

[old_tv_nut]

Originally Posted by etype2

The field sequential system could have been viable and had advantages. Simple tube, less parts, no convergence requirements, brighter images, higher resolution, no dot or stripe deposits required, no moire effects.

The field sequential system had advantages as originally demo'd vs. simultaneous sustems as originally demo'd, but it had disadvantages too that weren't often mentioned.

It could have convergence problems if the high voltage wasn't well filtered, or the B+ had a little hum that modulated the scan differently in each field.

The camera had hue shift due to partial image retention from one field to the next. The color filters in the camera and receiver could be chosen to compensate this, but if the characteristics of either were changed in the future (maybe for optical efficiency) there might be hue shifts with no customer hue control to fix it. CBS did tests with non-expert viewers to determine which way the hue error was likely to be least noticeable (RGB sequence or RBG - they chose the latter).

On the face of it, you would think the simpler camera optics would make it more sensitive than a three-tube TK-41, but the less than ideal filters combined with a shorter field exposure time took away that advantage.

The basic flicker rate in the display was the same as double-shuttered movies - 48 Hz. While the maximum flicker modulation only occured for pure green, this was still approaching the 50 Hz flicker rate of European systems, and was a step backwards for 60 Hz countries in terms of the picture brightness that ultimately could be used. Note that much later sequential displays (single chip DLPs) for HD projectors always use much higher field/frame rates. Looking at the 10-inch SD monitors at the Early Television Museum, you can verify that the color breakup is practically unnoticeable and flicker is not visible, but this is not the case for a large, bright high-definition display.

The bottom line is, you don't get something for nothing - physics and psychophysics both giveth and taketh away.