I did a little more work before installing a new 16GP4. The old candohm was replaced with an aluminum housed chassis mount power resistor. A beefy Panasonic high-ripple current 105C electrolytic main filter cap replaced the Nichicon I had tacked in earlier.
I then installed a vertical retrace suppression circuit as described in
Rider TV Manufacturers' Receiver Trouble Cures - Volume 1
Next I popped open the focus rheostat and bridged a break in the resistance wire. It's working very well now
It sure looks strange with that dinky 5" CRT installed.
A strong, rebuilt 16GP4 will take it's place.
Ah, that's better
Time for some tweaks with a test pattern generator before installing back in the cabinet.
