I think I'm getting there. And I suspect I have a partially shorted flyback
I have read that a lower frequency horz signal being fed into the flyback drives it harder, due to longer on times from the plate of the HOT. So that may explain why I get reasonable B+ and boost voltages when I run the horz frequency too high.
As I lower the frequency to the correct value, things go haywire as voltages start to drop. If I disconnect the yoke and the 15 ohm resistor that connects between pins 4 and 5 of the flyback, B+ jumps to 280V. I'd expect an increase because there's no load. But the damper and deflection systems seem OK with this resistor in circuit, they're just being underpowered. So I've either got a shorted flyback (my guess) or a poorly regulated power supply. Given the simplicity of this supply, and the fact that the diodes and all electros have been replaced, I doubt this is the culprit.
Thoughts?