21-CT-55 power supply failure

[miniman82]

Originally Posted by Penthode

120Hz is ripple from the B+ supply. With 120Hz you will see two distinct bars floating up the screen.

60Hz will originate from the mains directly and you will see a single bar.

How many bars are there? Can you post a photo of the screen with the bars present?

And have you substituted the tuner tubes?

To me it looks like a pair of bars on screen at one time travelling up through the pisture, but the power supply has no ripple so I'm not sure what to think. I've already subbed every tube in the tuner/IF and even the first video (6CL6), nothing made an improvement. If I had to pick a word, I'm flummoxed.

Originally Posted by Penthode

If the grid bias is too high, then the grid current must be too low [OR] the tube is being over-driven. I need to get my diagram; is there a cathode resistor in the deflection output; if so, is it by-passed?

I think the tube is being overdriven, because it's DC grid bias is not what it should be. As I said before, I'm going on the assumtipn that the cause of the flat topped waveform at the grid is being caused because the tube cannot be driven any harder than it already is. Result: power comes from the only place it can, in the form of grid current.