Questions on brightness of old colour TVs

[Dan Starnes]

Guys,, you are a wealth of knowledge. Love this place.
Dan

[vintagecollect]

see color CRT question other other thread


for brightness info

[old_tv_nut]

Eckhard, I think you exchanged the x and y values for blue on your plot (numerical values in your text are correct)

- Wayne

EDIT: I meant the x,y plot for >>>PAL<<< blue

[ceebee23]

Without going into deep discussion about colour it is interesting to note that even the best colour film stocks have to battle the same issues of gamut etc. Perhaps the most famous colour film of all time "Kodachrome" cannot handle magenta correctly...even after 70 years. (Kodachrome was introduced in 1935).

So even if your television system is capable of creating marvellously accurate colour the source material is just as important!

[yagosaga]

Originally Posted by old_tv_nut

Eckhard, I think you exchanged the x and y values for blue on your plot (numerical values in your text are correct)
- Wayne
EDIT: I meant the x,y plot for >>>PAL<<< blue

Yes, you are alright. I will update the plot in the next hours.

Already done. See

http://audiokarma.org/forums/attachm...9&d=1197198353

- Eckhard

[old_tv_nut]

Here is an RCA add titled "Luminescence" from 1967. The thing that is amazing to me is that they included a chromaticity diagram of the picture tube phosphors, including tolerance boxes. This kind of thing was usually proprietary for TV makers - but maybe they were OK with it because they were trying to sell the phosphors themselves.

[yagosaga]

In the last days, I got an old Kodak digital camera (DC3400) with 2 Megapixel. It is an older one, very heavy. And I did some screenshots from the 21AXP22A. The colors looks more original on the photos than the colors on my Canon A70.

These experiments show again the potentials of NTSC. Our European propaganda perpetuated always the deficits of NTSC, but these demonstrations show that NTSC is superior than PAL in many disciplines.

And these experiments show that the problems of NTSC were not on the receivers side but mostly on the early studio recordings and camera's side. It is a pity that we did not introduced NTSC.

- Eckhard

[vintagecollect]

...

[yagosaga]

A table of brightness results for different crt's with the same cathode beam power consumption would be a very interesting thing. I have driven the 21AXP22A at it's upper limit when I took the photos. Due to the different color sensitivity, an overdrive effect is first visible on the red color.

A comparison of brightness effectivity might be possible with an A63-11X (your 25AXP22) and the 21AXP22A on the same photo, both adjusted with 0.8 mA for the A63-11X and 1.0 mA for the 21AXP22A which is the same power consumption.

[old_tv_nut]

There are several factors that affect the over-all result for brightness obtained with a given phosphor change. It depends not only on the power output of the phosphor, but also on its exact color, which affects the amount needed to get white. Therefore it also depends on what white color is chosen. A paper by A. Hardy in 1968 indicated that at a 9300K white, the vanadate rare earth red provided 8% greater brightness than the all-sulfide tube, and the oxysulfide tube provided 30% greater brightness. Also, the red/blue current ratio was improved from 2.2:1 in the 15GP22 and 221AXP22 to 1.5:1 in the all-sulphide tube, then about the same in the vanadate tube (1.6:1), and finally 1.1 in the oxysulfide tube.

Individual samples of vanadate phosphors from 6 suppliers showed variations in birghtness of +9% to -10% compared to a reference. The average oxysulfide from RCA measured +46% compared to the reference vanadate in these tests.

The brightness of a phosphor depends on its physical preparation as well as its chemical composition. In the 70's (if I recall correctly) Sylvania discovered that a very thick phosphor slurry would increase the brightness. I recall at Motorola the tube engineers studied how to duplicate this without getting swirl marks due to uneven deposition,

[ChrisW6ATV]

Regarding that paper, I am fascinated to learn that they were already using 9300 degrees Kelvin as a "white" reference in 1968. 6500K is proper/daylight white as used in TV studios; 9300 is that bluish, brighter tint, what I call "TV white", that was and is still very common on consumer TV sets, since being brighter helps to sell them.