Homemade Color Wheel TV

[wa2ise]

If it comes to that, I'd just install a modern small screen color set rather than throw it out.

If he were to do that, I'd have him build a circuit that would sequentially blank 2 of the 3 guns in the color CRT so as to rotate thru RGBRGBRGB. Take the vertical sync pulse from the vertical circuits and build a divide by 3 digital circuit using TTL chips. Use a digital decode chip to convert from the binary divide down count to 3 outputs, only one enabled at a time. This vertical scan output 1 is enabled, 2 and 3 disabled. Next vertical scan 2 is enabled and 1 and 3 disabled. then next scan 3 is enabled and 1 and 2 disabled. Lines 1, 2, and 3 control blanker circuits tied to the R, G and B signal lines going to the video CRT driver amps that in turn drive the CRT. You will need to turn up the contrast to make up for the fact that each color phosper is "on" for 1/3 the original time.

This should give you a good simulation of what a color wheel sequential set would have looked like.

[ceebee23]

with a field sequential set (or for that matter a B/W set using a a color wheel adaptor)....how do you adjust color saturation ?? brightness and contrast are obvious...phase ..well that too ..but saturation ....or is that effectively fixed?

chris

[Steve McVoy]

This issue is white balance rather than saturation. In the CBS system a color balance device was instaled with each camera. The three colors were extracted. Level controls allowed the operator to achieve white balance, then the colors were put back in sequential order.

Since all receivers used the same color filters and the same CRT phosphor, white balance on the receiver was automatic. However, we noticed a noticable difference in balance on the two CBS sets we demonstrated last year. This was due to ageing of the filter material. In fact, the filters on both sets had been replaced, and the colors were different from each other. Darryl adjusted the saturation of the colors within his converter to acheive the best white balance on one of the sets (the other, the Gray monitor, had a yellowish tint when this was done). Eventually we will use the same filter material for both wheels.

[ceebee23]

having read so much about the CBS system ...and the infamous spinning wheels....I have always wondered just how good or ...if you prefer, bad was the system in operation....

having seen the stills of the field sequential sets on the ETF site...which are in themselves amazing ...the question remains what is a real moving image really like on this system ...was the flicker as bad as you would expect ....and what about fast moving objects???

mmmmm...one day I will have take myself to OH. and find out...(may I will bring Troy ...the other Aussie on this board with me ..!)

[Steve McVoy]

The picture is amazingly good, especially when compared to the RCA sets of 1954-65. Colors are very sharp, no fuzzy reds, good flesh tones. And, I haven't seen any flicker. I think the flicker problem was with the early CBS systems which used 20 fps rather than 24.

[Dave A]

I have my Col-R-Tel up and running on a Philco 12" although the CRT is not great. The picture is a very rich CT100-like color and can be saturated right off the dial. And full hue control to boot.

There is a noticable flicker that dulls down the more you watch it, but the most objectionable thing is the artifacts in the picture from the conversion process. Crawling stuff everywhere. And the resolution drops like a stone. Small graphics are tough to read.

Now if anyone has a spare 12KP4, I would like to buy it and be able to get a better picture so I could post some photos.

Dave

[wa2ise]

Below is a simulation of what I think a sequential color image would look like with a color wheel. The animated GIF is supposed to cycle from color to color in 1/100 sec, but may be slower on old computers.

Picture is a tiger in the green grass.

[Steve D.]

Here's a British site for you color wheel do it your selfers.




http://www.sptv.demon.co.uk/

[Chad Hauris]

On the picture of the tiger it is really pulsating on my computer. The real color wheel TV looks better...the color is pretty steady.

Originally posted by ceebee23
with a field sequential set (or for that matter a B/W set using a a color wheel adaptor)....how do you adjust color saturation ?? brightness and contrast are obvious...phase ..well that too ..but saturation ....or is that effectively fixed?

chris

Chris,

With a colour wheel converter on a monochrome set, saturation is adjusted by varying the gain of the chroma amplifier (i.e. the "Colour" control), exactly the same as a conventional tri-colour CRT set. If you turn the gain of the chroma amplifier all the way down, the colour-difference signals disappear and only the luminance modulates the CRT (the same for all three filter colours), so a black and white image results.

[tubesrule]

As John pointed out, you could adjust the saturation and hue on an adapter like the Col-R-Tel since it was receiving a standard composite NTSC signal which you could adjust before matrixing it into the R,G and B fields, but for the true field sequential standards like the CBS, there is no way to adjust either. Since there is no composite color information being sent, and each color field is received sequentially as a monochrome image containing only the appropriate color for that field, the color information is in effect embedded in the fields, and can not be modified easily. The saturation and hue are set entirely by the filters in the camera and the montior. (some correction would be done at the camera end)

While it would be possible to at least provide hue control at the monitor end, it would have required a seprate brightness/contrast controls for each color field that would be switched in at the appropriate time. I think this would have been to cost prohibative at the time to be worth while.
From the fading we have seen of the original filters, it appears that they would need to be replaced periodically to keep the set performing properly, although it's hard to say how often this would need to be.

Darryl

[ceebee23]

thanks guys ...it is sort of what I thought ....that with CBS field sequential sets you don't get a colour control ....and don't actually need a tint control.

(But then we in the PAL world simply don't get phase error anyway ...most of our sets don't have a tint control of any sort).

It certainly would be odd ....color tv with no color control!

[domfjbrown]

Originally posted by ceebee23
It certainly would be odd ....color tv with no color control!

Hey - at least it would stop some div coming in and messing up your picture settings though

Hey - that reminds me of that Buggs Bunny cartoon with the TV sets with ever-more-complicated controls, when one of them has a built in device that shoots the guy who's fiddling with his mate's TV - IIRC

BTW - my Sony TV (UK standard KVM25F2U) is NTSC compatible AND has tint - quite odd, since the tint even works on the RGB input when watching NTSC R1 DVDs - quite cool!

I bought the schematic from Colordaptor in 1960 or so. It looked good enough for me to collect all the parts, wind a delay line on a lathe, and build the 11-tube NTSC-to-RGB converter. The TV was a 10" Crosley 9-403M. I glued wooden blocks inside to support a 3/8" shaft to belt-drive the wheel from a 1947 Plymouth heater motor powered from my Heathkit Battery Eliminator (since I didn't have a 117vac motor). I drilled vertical counter-sunk holes in the hardwood blocks and kept them saturated with machine oil. The wheel was cut from 1/16" aluminum, 24" in diameter, and ran at 600rpm. Two pieces of colored celluloid (R, G, B) were held to the wheel with laquer and the wheel was sprayed black to eliminate reflections from the metal. The shape of the color cutouts in the aluminum resembled that of a bowling pin -- this shape was the result of graphically plotting the intersection of a rotating radial line against a downward scanning horizontal line, then allowing +/-20 degrees rotational phase error (the wheel position must be phase-locked to the vertical sweep in the TV) in the wheel position. The results were thrilling (after much work in getting it all together). And although the flickering mentioned by others was annoying, especially on a bright red object, the picture was good enough that we watched it for 4 years before I, too, bought a "real color TV" kit from Heathkit. The best color at the time seemed to be during the Kraft commercials and the Tonight Show. I did not see any significant smearing of color as mentioned in some articles; this problem might have something to do with the delay line needed to slow down the black & white video to meet the delayed color-demodulated video. I still have all of the above, and will very soon spend some time to make it all operational once more -- "for old times sake" and for the challenge. The subject of Colordaptor's design brings back many wonderful memories of a fun project.

[kx250rider]

Great job Steve K!!!!

But the photos aren't showing for me...

I guess that means I'll have to come out and admire it in person sometime soon!

Can you eMail me your phone #? I had it in my old cellphone and somehow didn't copy it over...

Charles
[email protected]