I have many doner chassis at my disposal, I would never deprive another collector of the opportunity to restore something like a projection set in the process of getting this thing to work. I'd much rather use a common chassis, like a Maggie 6V6 amp or something that no one will miss.

Is there a chance that some markings are hidden and would be visible if the subchassis is removed?

You haven't been around long enough;-). There are way too many
of those projection sets around and I bet there are few collectors
that have just the chassis to use for flybacks and hard to find parts.
It is very unlikely that any have used the power supply chassis. I think
would be a very good fit.

I guess if one fell into my lap I'd use it, but it would have to be pretty much free. I can't justify much more expense with this chassis, the last thing that will be bought for it is a nice cabinet to house it when it's finished.

While I didn't take under-chassis photos, from what I recall, your idea could probably be tested without completely removing that assembly; there seem to be only four screws in the photo associated with the chassis.

I thought perhaps the separate chassis was for flexibility during engineering design and testing.

I'd of course love to work on the chassis, but there are no current plans to do so at this time.

Pete

I doubt there are any markings under the panel, for all intents and purposes it's just another subchassis.

Found a patent online which may be of some use to us:
http://www.freepatentsonline.com/2736859.pdf

It is a patent filed by Dalton H. Pritchard and Alfred C. Schroeder (assignors at RCA) on July 25, 1952, which details a 'Color Phase Alternation Control System'. It outlines a system whereby the phase of the red syncronous detector is flipped by 180 degrees at field rate by a transformer with windings arranged to accomodate this change in phase. According to the patent, this would eliminate any reflective errors induced in a system incorporating a double ended delay line, while at the same time reducing cost.

"Previously, color phase alternation has been brought about in the following manner. Each of the synchronous detectors in a receiver were coupled to a different tap point on a delay line having a total delay of 360 degrees of the color carrier frquency. During one field a wave of color carrier frequency was applied to one end of the delay line so that different phases of the wave were available at the different tap points. During the next field the wave of color carrier frequency was applied to the opposite end of the delay line. As is well known, the closer the tap point to the energized end of the delay line, the nearer it is to the phase of the wave applied to that end. Therefore by energizing opposite ends of the line during successive fields the phases of the wave at the different tap points are interchanged. Some difficulties have been experinced in that reflections from the non-energized ends of the line interfere with the apparent phase of the wave at the various tap points. In addition, the delay line attenuates the wave applied to it so that as the wave progresses from one of the line to the other its amplitude is reduced. Because the line is energized from one end during one field and from the other end during a succeeding field, the amplitude of the wave at any tap other than the one located at the exact center of the line changes from field to field. At the center the attenuation of the wave is the same irrespective of the end energized. Such an arrangement is useful where 2 or more synchronous detectors are employed.

In accordance with one of the objects of this invention, the necessity for using a delay line is completely eliminated and the attendant difficulties are entirely avoided in arrangements requiring only 2 different phases of the wave of color carrier frequency during any one field."


Sheet 2 of the patent outlines the actual phase alternating circuit; if Wayne's supposition that the 'CPA' transformer in this chassis has something to do with phase switching:

Then I would assume that the 'CPA' transformer in this chassis is wired in much the same way as the patent outlines, we'll know for sure later on tonight when Tim and I trace the circuit out and compare it to the ones found here and in some of the other literature forwarded to me over the past few weeks. Additionally, the text of this patent may also explain why there is also a blank hole in the chassis marked 'delay'. It's possible that the 'delay' on this chassis has more to do with the type of delay described by the patent, and not any sort of later delay (such as the common luma delay lines) that might have been associated with later NTSC standards.

I attached a Hazeltine article on Friday but upon looking for it this evening it is gone!? Don't know what happened but I will see if I can repost it tomorrow.

In the Hazeltine diagram, R-Y phase inversion is accomplished by simply using a field rate multivibrator (12AT7) locked to a field recognizer detector (another 12AT7) to the correct field. The CPA transformer secondary is center tapped so that either end (180 degrees apart) is selected field by field to supply R-Y or -(R-Y) as required.

Note that the Hazeltine implementation at that time did not include a crystal controlled subcarrier oscillator.

Did anyone of you have a chance to see the article/diagram I posted on Friday while it was there?

is this the one? I downloaded a copy... :-)

If you're referring to post 177, it's still there.

It was a paper by Hazeltine, I assumed it was removed on purpose, not by the author... If there are no objections I will repost it.

You posted at 12:35 and I copied it at 1:55, but when I went to view it on my better monitor at home at 5:30PM it was gone. I assumed that you had canceled it to correct the upside down drawings.

One question.
The underside of this chassis does not show chassis mounting screws or mounting holes.

Is this common on prototypes?

Jas.

.

Quote:

Originally Posted by earlyfilm (Post 3007310) You posted at 12:35 and I copied it at 1:55, but when I went to view it on my better monitor at home at 5:30PM it was gone. I assumed that you had canceled it to correct the upside down drawings. If I've done this reply correctly, it is attached. Jas.

That's the one, thanks. Yes, I did correct the upsidedown drawing and posted it. But later it was gone. Very odd.

I suspect their were many variations to the CPA demodulator. Note from the time this article was written, it appeared that CPA support was dying. I believe it was just too difficult to implement effectively in 1952.

Note the upside of IQ and a lower subcarrier frequency was elimination of the crosstalk and the bothersome flicker. The downside was reduced Q resolution and the lower subcarrier frequency reduced the luma bandwidth hence luma resolution.

Engineering is all about trade offs.

A sidenote: the BBC was planning to adopt a modified NTSC as late as 1966. The UK 625 line channel is 8MHz wide with the sound carrier 6.0MHz away from the video carrier. This means that the bandwidth was available for full double sideband chroma (4.43MHz +/- 1.4MHz). Hence IQ working in the UK would not have been necessary. The UK could have had wide matching bandwidth for B-Y and R-Y. The dropping of NTSC in favor of PAL in the UK was very late. Proof of this were the rubidium frequency standards used at Television Centre and Lime Grove in London: the standards were cut for NTSC and augmented equipment was required to provide the PAL subcarrier frequency (1/4 line offset plus 25Hz).

I think NTSC for the wide channel UK 625 would have looked terrific and better than PAL.

Some may refer to NTSC as "Never Twice the Same Color"

But in a similar vein, PAL may be referred to as "Problems are Lurking"

Spent this whole weekend doing a combination of things- a little woodworking to get closer to finishing a decorative shadow box for the ground breaking shovel at work, and Tim did some circuit tracing on the chassis. He started at the tuner and worked through the IF strip, at the end of the day he got as far as the first video amp tube (6AG7). Next weekend we will be getting close to the demod and CPA sections, so I'm hoping by then that we will finally be able to get a feel for how this set operates. Circuit tracing is labor intensive though, many breaks are required to avoid getting burned out and to avoid making mistakes. Right now, everything is on paper. When he is finished, it will be drawn out with MS Paint or a schematic program so it's easier to read. One thing is clear: it will be a very large schematic indeed. We both had the idea of breaking this up into sections: tuner/IF, luma channel, chroma, matrix, and finally deflection. That should make it easier to understand.

I have heard of a signal called "NTSC 4.43", and I think it is basically NTSC color encoding but using the frequencies common to most PAL signals (625 lines, 50 fields/25 frames, and a 4.43 MHz color subcarrier. One or more models of Sony monitors I have worked with had this as one of the signals they could accept. An online search should turn up more about it, or maybe others here already have details to share.

There are also several variations of PAL color signals (B, G, M, and several more), and one of them is 525 lines, 60 fields, and a 3.58 MHz color subcarrier if I remember right.