Twenty-eighth operational CT-100 screen shots...

[old_tv_nut]

Bobgary, I believe the waveforms you posted correspond to an old Hickok generator, which had full field bars, but not in the modern order according to luma level. Also, once things are reasonably close, it's much easier to check if these color difference signals are exactly correct by looking at the R,G,B waveforms (if available) or looking at the picture through colored filters, or turning off two guns at a time. (Professional monitors will send the blue-only signal to all three guns so you can see blue as monochrome.)

Pete, I don't have a schematic in front of me, but you said the matrix is all fixed resistors. I thought I recalled an "I gain" adjustment in there somewhere?

[Pete Deksnis]

Originally Posted by old_tv_nut

Pete, I don't have a schematic in front of me, but you said the matrix is all fixed resistors. I thought I recalled an "I gain" adjustment in there somewhere?

You're right about the I gain of course, it was set weeks ago and has never seemed to require further tweeking. And I probably shouldn't have thought of the matrix as only the nine discrete 1/2-watters that combine the +/-IQ and Y.

I wish you could all experience the actual video: 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 similiar 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. Now I'm wondering what the DVD image would look like on the Merrill. Na. Not worth the fifteen bucks to find out.

[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.

[old_tv_nut]

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?

[andy]

---

[Pete Deksnis]

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?

[old_tv_nut]

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].

[Pete Deksnis]

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

[Pete Deksnis]

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.