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  #31  
Old 09-06-2005, 01:20 PM
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old_tv_nut old_tv_nut is offline
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Quote:
Originally Posted by Chad Hauris
Isn't this how the modern sets do...the chroma and luminance signals are mixed before they get to the CRT? Seems like in most of the tube type sets the mixing actually occurs in the crt itself with the chroma at the grids and the luminance at the cathodes.
Yep - Several things combined to make solid-state sets go back to RGB cathode drive:
1) CRT's with unitized guns, where only the cathodes were separate for the three colors;
2) cheaper to have only 3 high-voltage video output transistors instead of 4
3) with ICs: definitely cheaper to do all matrixing to RGB in the IC - also, at this point, the chroma and luma gain controls could be electonically ganged so they go up and down together without changing color saturation when the "picture" control is turned.

I can't remember if I ever saw a design implementing a "picture" control with mechanically ganged "contrast" and "color" controls - anybody remember such a thing?
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  #32  
Old 09-06-2005, 02:54 PM
andy andy is offline
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Last edited by andy; 12-07-2021 at 02:33 PM.
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  #33  
Old 09-06-2005, 04:19 PM
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Pete Deksnis Pete Deksnis is offline
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Quote:
Originally Posted by old_tv_nut
I can't remember if I ever saw a design implementing a "picture" control with mechanically ganged "contrast" and "color" controls - anybody remember such a thing?
The CT-100 and the 21-CT-55 (basically a 21-in. CT-100) both used a ganged pot assembly to control luma and chroma simultaneously. For some reason however a production change to the 21-CT-55 bypassed the chroma pot, leaving only the luma pot functional. The user color was a separate pot in all cases, of course.

Back to the drawing board. I located the vintage matrix alignment procedure that includes adjusting L141, the inductor in the hue control circuit. This is where a course adjustment to the hue control takes place.

These main and alternate procedures seem to use the old non-luma-progression color bars Old_TV_Nut referred to earlier, who must also be the one to ask this question: ten years ago I worked on military stuff that used multiplying DAC's to contol what amounted to audio-frequency-range levels; is that how the function is or was implemented in TV for audio gain, contrast, and whatever? Is it even a good question?

Last edited by Pete Deksnis; 09-07-2005 at 06:05 AM.
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  #34  
Old 09-06-2005, 04:31 PM
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John Folsom John Folsom is offline
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Pete,

Did I miss it in your description? There is one tweak in the demod, the I gain control, which will modify the amount of +/- I signal used by the matrix adders to generate R, G, and B signals. Just one more independant varable in the equation.
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  #35  
Old 09-06-2005, 05:22 PM
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Quote:
Originally Posted by Pete Deksnis
....ten years ago I worked on military stuff that used multiplying DAC's to contol what amounted to audio-frequency range levels; is that how the function is or was implemented in TV for audio gain, contrast, and whatever? Is it even a good question?
It's a good question. There were no such things as multiplying DACs until much later. The first ICs for the color and video sections [and audio] were all analog, and did gain control using Gilbert-cell analog multipliers, which could be controlled by a common DC voltage. By the way, this was easier to implement cleanly, since the video and chroma signals did not have to be wired all the way to the customer controls and back, and the DC voltage could be filtered to get rid of noise pickup.

[Start of brag] One of my favorite inventions is a three-way I did with two other guys at Zenith (for monochrome chassis), where we stacked Gilbert cells, and using a simple external RLC filter as a simultaneous lowpass filter, differentiator, and second differentiator, did contrast control, switchable gated noise reduction, and video peaking control, in one swell foop [end of brag].
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  #36  
Old 09-07-2005, 01:20 AM
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Pete Deksnis Pete Deksnis is offline
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Quote:
Originally Posted by old_tv_nut
...we stacked Gilbert cells, and using a simple external RLC filter as a simultaneous lowpass filter, differentiator, and second differentiator, did contrast control, switchable gated noise reduction, and video peaking control, in one swell foop.
The more you think about it the cooler it gets
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  #37  
Old 10-30-2005, 01:26 AM
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Pete Deksnis Pete Deksnis is offline
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CT-100 Update from my site's Restoration Page

Have been working on the restored CT-100 recently to prep it for display in my living room. After extensive tuning and testing, got it buttoned up a few days ago, including the screen under the chassis, a small fan near the back to aid in dispelling heat, and wood screws in the back cover.

I cleaned and polished the mahogany veneer, tightened four wing nuts that lock the cabinet lid, and then turned it on and damn, three minutes later the screen went dim.

Remove the back, then troubleshoot to find the second video amplifier (a 6AN8) causing the headache. Pitch it in the trash. Put in a replacement. Button it all up again. Get out the NOS fine tuning knob I’ve been saving for this occasion and, after first testing the installation procedure on a spare CTC2 chassis, crack the plastic on the new knob trying to install it on the restored chassis. Cuss. Mix some epoxy. Stick it back together, and use a worn knob for now.

Okay, all this sets the stage for what I’ve been working for since 1999, but intensely since last April: eyeball 1953 NTSC color!

I think it happened. After mocking the WB earlier on AudioKarma, WPIX channel 11 came through with (pun intended of course) flying colors! South Park. Never watched it. Some of my thirty-something acquaintances love to quote it. Don’t care about it. But what color!

Chrominance charts indicate the extended green capability of the 1953 standard. My eyes believe the green on the character’s hat is in that extended area of the 1953 spec. A simultaneous display of the program on a high-definition direct-view CRT receiver in the NTSC mode was strikingly less vibrant.

The HDTV serves as a standard — a stable source of color used in the initial alignment of the color AFC circuits of the CT-100 for example. During the past several weeks, I would adjust the CT-100 to match the colors of the HD set. Not the brightness of course, but particularly subtle pastels and varying hues of violet. It’s a darn fine HD television set. But for this experience, which reproduces a program on two different sets driven from the same antenna, the HD set displayed completely lackluster green hues for that character’s hat compared to the CT-100.

Yellow was also visually different. A suggestion of which appears as this guy’s mittens.
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  #38  
Old 10-30-2005, 03:47 AM
frenchy frenchy is offline
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The color resolution of hdtv is supposed to be more than twice that of NTSC, so next time you should crank up a true HDTV signal on that hdtv set if you want to see the CT-100 get even more green... with envy ; )
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  #39  
Old 10-30-2005, 06:20 AM
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Pete Deksnis Pete Deksnis is offline
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Quote:
Originally Posted by frenchy
...next time you should crank up a true HDTV signal on that hdtv set if you want to see the CT-100 get even more green... with envy ; )
The color resolution, screen acreage, widescreen 16x9, luma resolution, six-channel sound, brightness, and just plain digital stability of HDTV produces an awesome video experience. One I never want to miss.

Books and charts say the color gamut is greater with 1953 NTSC, as I interpret them anyway. My gnawing itch wonders if WB11 actually transmitted the video with wide-enough gamut to make the effect I saw on the CT-100 vs. the HDTV. I wonder if the cartoon makers had their software set to 1953 NTSC. I wonder if the NTSC generator in my VCR is spitting out a color bar signal good enough to calibrate the CT-100. I wonder, as I wander…!

Oh well, only 63 more days to the next Rose Bowl.

Last edited by Pete Deksnis; 10-30-2005 at 09:02 AM.
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  #40  
Old 10-30-2005, 12:00 PM
Jonathan Jonathan is offline
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Everyone uses VCR's for the RF modulation on channel 3 or 4! I can't remember the last time I used a VCR. Both my 630TS and CTC9 Felton has VHF tuners, and there are no VHF stations in my area. I was honestly going to buy one of those RF modulator boxes, but use my satellite receiver for the time being. Most newer model RCA directv boxes output full feild color bar by pressing the menu and info bottons on the receiver at the same time, and it has RF output too. I'd use my UHF to VHF converter for off air reception, but I guess the only way to use it is if I connect an amplified antenna to it's input since it has no RF amp?

Jonathan
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  #41  
Old 10-30-2005, 03:41 PM
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Gorgeous, Pete!
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  #42  
Old 10-30-2005, 05:34 PM
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Hey Pete,

Very nice set up on your CT-100. The color looks great and the convergence looks spot on. Congratulations.

-Steve D.
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  #43  
Old 10-30-2005, 10:44 PM
frenchy frenchy is offline
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<<My gnawing itch wonders if WB11 actually transmitted the video with wide-enough gamut to make the effect I saw on the CT-100 vs. the HDTV. I wonder if the cartoon makers had their software set to 1953 NTSC. I wonder if the NTSC generator in my VCR is spitting out a color bar signal good enough to calibrate the CT-100. I wonder, as I wander…!>>

yup unless it is calibrated pretty good as far as color, you could always be seeing just more green due to off-value resistors, coil adjsutment issues, variations in drive of the guns etc. in the color section of the set. The potential for that old tube to display true NTSC is one thing... how accurately that old chassis is going to present it as it currently sits is another. All my old sets seem to have tendency to play up certain colors over others (mainly red) but not enough for me to go in and perfectly realign the color section, plus I don't really have the equipment necessary.
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  #44  
Old 10-31-2005, 12:10 AM
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kx250rider kx250rider is offline
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On the subject of pictures on working CT-100s... Steve D. demonstrated his CT-100 for me one day back in '84 or '85, and that was the first time I ever saw a CT-100 turned on. Well, the show that we happend to get was a live news feed from the McMassacre (in progress at that moment) in Chula Vista, CA. A rather macabre way to remember my first CT-100 viewing, but it is a sad and real part of history in California. We sat glued to the little vivid image, maybe for a moment overlooking the fact that it was a CT-100 at all. The CT-100 was, for an instant, restored to its original purpose as a medium of communication of sorts. I wonder if Steve remembers that day??? Deep thoughts

Charles
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  #45  
Old 10-31-2005, 07:31 AM
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Pete Deksnis Pete Deksnis is offline
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Quote:
Originally Posted by frenchy
...old sets seem to have tendency to play up certain colors over others....
What finally made me go public… ‘er, AudioKarma, was (1) achieving ‘standard’ HDTV-hues that are eyeball-duplicate on the CT-100 and (2) finally accepting the modified chroma-AFC alignment-procedure as okay (where final tweaking of L41 is needed because the circuit needs it, not because a component has drifted).

It should be remembered that all other hues on the CT-100 screen eyeball-matched those on the ‘standard’ HDTV screen. Only the green stood out and only on that character’s hat.

Here’s another CT-100 screen shot taken the same night. There are three different areas of green; two on the hat and one weird snow-capped mountain whose base is green seen through the now-open door. That green matches the HDTV green.

So, I’m speculating for now that the striking green on the character’s hat is a result of wider gamut and not some unusual peaking or weird spurious oscillation somewhere in the CTC2 chassis.

But I could be wrong. And so my next step is to rearrange my living room over the next couple of days, time permitting, with the CT-100 to the right of the HDTV. Then develop some photographic evidence supporting or debunking current speculation.

Was chatting with John Folsom yesterday and recalled that in September I reported the same effect as here. That time it was the eyes of a cartoon character that were vivid on the CT-100 but not in control images.

Here it is: “There's a commercial playing for a Lilo&StitchII (sp?) DVD. The bug-eyed character in the commercial on the CT-100 has bright, intense, large lime-green eyes that pop off the screen at you. Interestingly, in an A-B comparison between the CT-100 and my 38-in. widescreen CRT HD set, there's no similar effect on the HD set, although there may be setup issues to consider. Just came back from seeing the DVD at Target. The eyes in the print version were pale blue and didn't even appear to have been designed to draw attention --nothing like the TV ad to my eyes anyway.”
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