Merry CTC-5 Christmas 2020

[Penthode]

Been spending a number of hours working on my CTC-5N.

I gave my 21AXP22A a rejuvinate. A few years ago I attempted to with no apparent effect. The tube did not look like it had many hours and the set had sat unused for at least 35 years before I got my hands on it. I was more aggressive as I had nothing to lose and the red gun came back and it stills appears to be running fine after six hours.

I fixed the purity with the edge magnets. The biggest problem was the black and white tracking. Found that a number of resistors have driffted upward 100% to 300% around the color difference amplfiers.

I made a chassis mod in the RCA latest chassis itteration (1957) to the color difference grid bias/ clamp input reduced the color difference amplifier temperature (tube envelope not color) because of the lower plate current with a slight raise in plate voltage.

Went through the setup with special attention to the black and white tracking. I found there was too much Green gain as I could not get rid of a gren cast in the whites. I cheated by moving the green cathode down the 2nd video amp plate load divider to the same point as the Blue cathode. The tracking is very good now and it maintains a good black and white irrespective of brightness and contrast setting.

I attached the original and revised diagrams and some screenshots of my resulting efforts.