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:
Quote:
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The air-core coil that Nick found looks suspiciously like it was built to reduce variations with temperature, spacing to the shield can, etc., etc., but we won't know until we discover whether there is a phase switching circuit.
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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.