[Penthode]

I would like to share a few of my thoughts.

The design of the CTC2 is interesting from the perspective of the state of the art in the early 50's. I suppose the extra wide IF response of the CTC2was to help ensure a relatively flat I IF response (3.58 MHz +0.5/ -1.5MHz) and Q IF response (3.58 MHz +0.5/ -0.5 MHz). However, the extra luma response was more or less lost due to the need to employ a 3.58MHz notch filter in the luma channel.

The balance between a marginal increase in quality vs cost of implementation weighed heavily against continuance of the I Q demodulator approach. Also it was found that a narrower video IF together with chroma channel which compensates for the sloping response at the video IF at 3.58 MHz made sense with the savings in manufacturing cost. Not until the introduction of proper 3 line comb filtering in the late 80's did the wide band demodulator approach fully make sense.

It is interesting to note that pre1953 Black and White sets with 10" screens or larger often had full 4MHz video IF. After the introduction of color, most Black and White sets IF bandwidth was limited to 2.5MHz to 3MHz. Wider IF bandwidths were pointless because all you would get is a heavy NTSC dot crawl. The heavy color subcarrier on wideband B&W sets would be rectified by the gama curve of the CRT and tend to darken the image hence distort the gama.

The second NTSC which was responsible for color knew that there was going to be a tradeoff: I recall reading that the NTSC thought that the loss in luma resolution would be more than offset by the addition of color. (I may of read this in Donald Fink's book on the NTSC?)

I agree that the increase in tube transconductance would yield the need for fewer tubes. The 6EH7/6EJ7 tubes later used in TV IF amplifiers, have a transconductance of about 15000 micromhos. Hence two tubes could be used where three once were. However the transconductance alone I do not feel is responsible for the change in design philosophy of color TV receivers.

Sensitivity was mainly determined by the front end S/N and to a lesser extent overall gain. Cascode amplifiers and later the neutralized nuvistor amplifier (both with triodes) generated less noise hence improved the S/N.