So far only the CTC 121 and CTC136B were suspected to have used WB IQ chroma demodulators. Wayne states he evaluated the performance of a RCA CTC13X that had WB IQ demodulators but gave no details of its implementation; did it use a NEC IC? A whole bunch of guys say they have or had either CTC 136Bs or the CTC121s which also is claimed to have WB IQ processing:
CTC136B stromberg67 Kevin
CTC121 zenithfan1 Mark, waltchan, zenith2134, wa2ise, nrx37, blast
Surely at least one of these has a schematic or other documentation that definitely proves the CTC136B or CTC121 used WB IQ and how it was implemented. Since I have a CTC2B open on the bench I would appreciate any information why RCA tried WB IQ on only a couple of CTVs and quickly dropped it. Thanks, Tom

I have the service manual for my CTC-121, I'll look into what it says. I know for a fact it's IQ but it's been a while since I read the details. It was just too complicated and they thought in the '80s that they had the technology to try it again but it just wasn't cost effective IIRC. Like I said, I'll look in the book and see later or tomorrow.

Hey, that's '2134 to you! :D sorry, I don't have the schematic

Hi Folks: I have the SAMS for my CTC-133B open in front of me, and the chip designated "U 700" , a 42-pin DIP, shows I and Q demodulators and amps, and the integration of luma and chroma signals on the chip. I haven't had the chassis out for service for a number of years, as it still performs amazingly well for a 24 year old, but I do believe the chip(s) are marked NEC. The color detail in the picture is very sharp, and many different shades of red are visible, and very distinct from red/orange hues. A very enjoyable TV to watch.
The RCA part number for the chip is 176225, and no sub numbers are listed, so maybe the chip was proprietary.
The only repairs to this set have been a resistor open on the CRT board, and a blown audio output IC. Looking for parts chassis' now.
Thanks to all for YOUR postings.
Kevin

[QUOTE]Hi Folks: I have the SAMS for my CTC-133B open in front of me, and the chip designated "U 700" , a 42-pin DIP, shows I and Q demodulators and amps, and the integration of luma and chroma signals on the chip.[QUOTE

Kevin.........That CTC133B schematic is a great find! The RCA number 176225 crosses with Hitachi, maybe its the same chip? The fact that it combines luma and chroma at low levels instead of at the CRT is great. It's probably why you get such great color detail. I bet there's a lot of inductors and caps around the chip to do all the required filtering in analog. Is there any way you can scan or photo the small schematic portion around the chroma demod chip? Can you PM me for my email address. If the chip is available ($5.00), it would be fun to attempt to build up the circuitry and try it out. Thanks, Tom

My interest is peaked now, I'll dig that stuff out tonight and have a look at the CTC-121 as well. We should take some pics so we can compare chassis too.

Hi Tomcomm I scanned a few pages from the SAMS, which is #2513, and hope they can offer some insight. It looks like the logos on the chips have been covered or removed, why I don't know, so U700 could be Hitachi.
Let me know if you want more scans.
Kevin

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Good suggestion, thanks. I wasn't sure that they would look right. I'll try to make them bigger later, but maybe not tonight. Much to do with family today. I'll email them to myself until they seem OK for the forum.
Kevin

Make your pictures bigger. They can be up to 900x900.

Sorry Kevin, I couldn't read any of the chip block diagram lettering, which is probably the most revealing info. I think 900 X 900 pix should read fine. Thanks, Tom

Originally, the I signal was 1.5 MHz bandwidth and the Q signal was 0.5 MHz bandwidth. A television that made use of both bandwidths would have both a luminance delay line and an "I" signal delay line to ensure the signals arrived at the same time at the CRT. Otherwise, I and Q demod is just like R-Y, B-Y but with different matrix values.

CTC-2 forever!

Modern CTV to me is when they went solid state. That's when I lost TV interest and knowledge. Perhaps WB IQ didn't work so well after the CTC2/B was due to the fact the later CTV had fewer IF stages than the original six. When they got down to three stages they couldn't get the flat responce and precise uniform phase delay required for WB IQ without artifacts, so they stuck with NB R-Y B-Y? Rediscovering WB IQ really fascinates me and others. Sort of cultish,eh?......Tom

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There were several I & Q sets made in the 80s, including that CTC-121 (or 120?). Also isn't the Sony Indextron I & Q?

Charles

Trying again to send readable pics. Kevin

Thanks Kevin. They look good on my end.:thmbsp:

Here are some shots I took out of the manual for the CTC-121. I'll post one of the board from the manual too If I can make it turn out legible. I buried the set last time I rearranged. I'll try to dig it out today and take some pics since my OT got cancelled due to no snow like we thought.
http://i262.photobucket.com/albums/ii90/zenithfan1/000_0538.jpg
http://i262.photobucket.com/albums/ii90/zenithfan1/000_0537.jpg
These pages explain how the chroma is processed. Let me know if they suck, my scanner is broken (darn kids)

Well we’re starting to get some schematics of the CTC133B from Kevin and some description pages of the CTC121 from Zenithfan1. The photos from the CTC121 are 1023 X 769 and are perfectly readable. However the CTC133 schematics at 600 X 424 are still unreadable. The chip block diagram at 800 X 567 is ok but fuzzy. Sorry Kevin. It seems VA will let you do 900, even 1023! I and those really interested in WB IQ would like to see you go for another try at 900 or 1023 this next time, please? I gotta see how they implement the critical LP filtering and the necessary compensation delays. The CTC121 description doesn't mention this consideration at all! Thanks for you guys interest in my silly WB IQ exercise………Tom

It would be nice to get larger schematics, but I can read them well enough to tell you that this does show wideband I (and narrowband Q). The RCA trick to getting a delay line or filter with one pin is applied to pins 8 and 9, which in the chip block diagram go to stages called "Q-phase filter" and "I-phase filter."

If you look at the schematic of the parts attached to these pins, you see an external buffer transistor on each. This buffer (an emitter follower) drives what would normally be the ground point of a delay line (for I) or a filter (for Q).

Normally, a delay line or filter requires one IC pin to drive its input and another pin to sense the voltage on the output. However, with the clever circuit trick, you need only one pin to drive the delay line or filter input with voltage (via an internal emitter follower). Then, with the ground also driven by the external buffer, the output current of the delay line or filter cannot go anywhere except through the pin and the internal emitter follower. So, the internal emitter follower has the delay line input voltage, but the delay line output current! This current, being in the emitter, is also in the collector (minus a little base current) and is taken off the collector of the internal transistor and goes to the matrix for R-Y, B-Y and G-Y, having been subject to delay or filtering as desired.

Wayne…….I recalled you mentioning this when you described ”how clever” these RCA guys were with the one pin delay-line when you were comparing RCA’s WB IQ with Zenith’s NB R-Y B-Y color systems. I traced out the pins 8 & 9 of the demod and found the tiny DLxxx and buffer xistors on Kevin’s 600 X 424 schematics. I hope he has no problems with re posting at 900 X 638 or larger. Then we can get part numbers and everything! Hitachi has a 176225 listed for $6. I wonder where I can get the delay line? Everything else seems generic, would be fun to build this WB IQ demod up…..Tom

I'll try taking some pics of my schematic and see if they are legible, if so I'll post 'em up. Sorry it takes me so dang long but I'm pretty busy these days....still gotta dig that set out too....

For what it's worth, Hoffman had a wideband system which used R-Y and B-Y detectors but after a chrominance channel where the high bandwidth chroma signal was delayed while the narrowband was not. This is a bizarre method and was used briefly (around 1955, I think), but I would prefer I, Q demod. The NTSC spent a lot of effort to determine the resolution and criticality of the eye for various colours and I think I, Q demod would be as good as HDTV because the eye does not see large bandwidth in blue or yellow.

I wonder where I can get the delay line? Everything else seems generic, would be fun to build this WB IQ demod up…..Tom

There may be a problem finding out the coil specs for the Q filter also. I believe the values on the schematic are probably resistance readings for troubleshooting, not the inductances. I suspect they may also be wound for specific self-resonant frequencies.

For what it's worth, Hoffman had a wideband system which used R-Y and B-Y detectors but after a chrominance channel where the high bandwidth chroma signal was delayed while the narrowband was not. This is a bizarre method and was used briefly (around 1955, I think), but I would prefer I, Q demod. The NTSC spent a lot of effort to determine the resolution and criticality of the eye for various colours and I think I, Q demod would be as good as HDTV because the eye does not see large bandwidth in blue or yellow.

It is usually stated that the I axis was chosen to match the axis of maximum color resolution of the eye. But if that is true, the eye can't see if the small details are somewhat off in hue, so the axes chosen by NTSC actually could have been R-Y (wideband) and B-Y (narrowband). Actually, it is probable that using B-Y as the narrow axis would be better in terms of color detail than using Q, that is choosing the axes so the narrowband one falls on the lowest color resolution axis and not worrying if the high res one is slightly off. However, there are other more important reasons to use I and Q. One is that I is very close to flesh tones, so if there is a transient effect on the edge of a face, it doesn't look the wrong hue. This is probably the most important practical result of using the I axis in particular. Another is that the roll-off in color resolution is not abrupt, and you can't force people to sit far enough away to guarantee they won't see edge effects. A further reason is that pictures made of I axis colors often look plausible, while pictures made of only Q axis colors often do not. Most of the automatic tint circuits developed later were based on this. Another reason is that much of the test material was color slides scanned by unmatrixed cameras, both facts which tended to suppress greens, so the test material was notably lacking in strong Q axis colors. So, if you picked the axes to provide the best overall results with a random selection of color transitions, you might have ended up with something different; but the choice of I and Q actually catered to the statistics of the color palette of common source materials and important image elements (faces), which meant it was well suited for general use.

Summary: the choice of I and Q was optimum, but not purely for the reason of resolution that is usually stated.