RCA 21CT55 #8802897 is Dead

[Pete Deksnis]

Originally Posted by John Folsom

The resistor elimination in the 21CT55 matrix from the CT100 design was a patent dodge. RCA did not want to pay royalties on I/Q demodulation. Well, thats the story I heard. RCA was known to do almost anything to avoid paying royalties.

John. I came to the same conclusion recently. The quadrature transformers for the CTC2 and CTC2B chassis have different part numbers. They would have to be since the demodulation angle is different for R-Y demodulation than it is for I demodulation,

I do not have a CTC2B chassis to test my theory, but one must rule
out the possibility that the CTC2B chassis does not properly decode the color signal transmitted by an NTSC broadcast transmitter. The two color signals, I and Q, that are trasnmitted by NTSC standards are in quadrature. In the CTC2B the decoded chroma, Q and R-Y, are not. When a quadrature signal is encoded, it must be deconded in quadrature if crosstalk is to be minimized.

If I am right, the CTC2B chassis is inferior to the CTC2 chassis when decoding an NTSC broadcast.

Now, it is always possible that some stone has been left unturned by me. Perhaps eliminating the one insignificant-in-cost resistor in the CTC2B matrix somehow negates the not-in-quadrature problem. I don't know.

BTW: I believe it was probably Philco that RCA was dodging.

Pete

[Tomcomm]

Here are preliminary comparisons of the original FBX vs the replacement FBX installed in my 21CT55. The screen is still too wide, must be the original yoke is more sensitive then the newer yokes intended to be driven by the replacement FBX. No, I wont try to find a newer yoke………..Tom