I have an esoteric question I probably should know the answer to

[old_tv_nut]

By the way, a correction to what I posted, from another thread :

the older type sets with a regulator tube measure the boost voltage as a substitute for the actual high voltage, rather than measuring the beam current. The result is the same - the HV stays constant when beam current varies.

As you know, the '76 vintage solid state set works entirely differently. Any variation in HV would be: higher voltage on dark or black scene. I don't remember what the overvoltage circuit is actually measuring in these sets.

These sets often also have an beam current limiting circuit. again, I can't remember what is actually measured. The control effect would be made by adjusting brightness or contrast. In discrete transistor sets this was usually done by turning down the "brightness" (black level) to prevent excessive current. In some later models with analog ICs, the "picture" level (what used to be called "contrast") could be controlled to limit beam current. The beam limit is what would limit the picture brightness for photography.

I don't think there is a real need to boost sets of this vintage for film photography. You need an exposure time no faster than 1/30 in order to capture a full frame, and with modern film speed of 400 or so, you can get there with a reasonable lens aperture. Even film speed of 200 is probably quite workable.

For best image quality, you do want more HV, but it's risky to push a set. The other way to improve the spot size is to keep the beam current low by turning down the contrast and brightness.

One more comment: using film for this seems like something you would do just for the reason of wanting to play with film. Digital cameras can give better results these days, if your purpose is simply to document the picture on the set.