RCA CTC4B "Gainsborough" picked up in San Francisco

[Electronic M]

Originally Posted by Tom9589

Think of the CRT and the shunt regulator as two variable loads on the flyback. When the CRT has a bright scene, it becomes a greater load while the shunt regulator becomes a lessor load. Conversely, a dark scene causes the CRT to become a lessor load while the shunt regulator becomes a greater load. The whole idea here is to present a more or less constant load on the flyback and the circuitry upstream of it. The real question is whether the designers specified the flyback so that it can withstand this combined load (CRT plus shunt regulator) on a continuous basis without having too much of a temperature rise.

That is a good explanation (and a good part of the point I was going to make before reading it). I'd like to add that the regulator is also an "emergency limiter"....if say the CRT heater goes out for some reason without the regulator in place there is no load on the HV winding of the flyback, and it then can easily shoot up to 30-40kV in a CTC-4....Once it hits that range the factory insulation on and INSIDE the HV winding is near to beyond it's design rating, and prolonged operation under those conditions is likely to cause external and INTERNAL arc over and all the damage that goes along with that.

Most late 60's sets with a pulse regulator also get their focus from a resistor divider fed from the CRT's HV lead, and probably also serve as an emergency minimum HV load.

Chris, one thing that now comes to mind is that you are calibrating the horizontal and HV system with that set on a test jig (right?), the jig likely is not providing the exact yoke (and, as mentioned, CRT) characteristics the chassis will see with it's own CRT and yoke that are in the cabinet. I doubt all those adjustments will still be correct once the chassis is back in it's cabinet, and I'd be inclined to redo them when the chassis is ready to be mounted. My cabinet acted as it's own test jig when I was servicing my set (cables have enough reach to allow the back of the chassis to face the cabinet and reach), and upon reflection I'm glad I did it that way.