A Confession

[dtvmcdonald]

"You may find the tripler actually works a little better than a real flyback supply. HV stability may be a bit better, for better focus stability, etc. "

For those who would accept a bit of non-originality, tucked away, there
is a simple cheap, effective panacea for focus instability: Zener diodes.
Just install a long chain of 200V Zeners from the focus pot down to ground.
I did this and it works great. I measured the correct focus voltage and
set the total Zener voltage so that the focus control was about 1/4 or 1/3 of
the way up from the bottom.