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Using Y R B with Plumbicons makes mroe sense than with Vidicons, because the Plumbicons are linear, making the chroma matrixing work better. However, all cameras with a separate Y tube used only for Y tend to have too much luma on saturated colors, and things have to be fiddled to get acceptable reproduction on a TV set or monitor. Mathematically, this is because the single luma channel outputs (0.3R +0.59G + 0.11B) raised to the (1/gamma) power, whereas in a RGB camera, each of the R,G,B is gamma corrected BEFORE the indicated fractions are added to make the luma. If you run through the two different calculations, you find the same results for gray colors, but very different results for pure reds and pure blues and less so for other pure colors. RCA produced papers calculating that the errors were not too great to be objectionable. It is also conceivable to matrix the Y,R,B to R,G,B and process only low frequencies the original way, while using the direct Y tube signal only for high frequecy detail.
RCA couldn't practically eliminate the G Vidicon, because the image orthicon is linear, and the Vidicons are non-linear. They had to use three Vidicons so the gray scale tracking would be acceptable.
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