Found a notation & one pix in an old Airco book from the 1950's
I asked Google to scan the magazine, and even though it took 6 months,
I think it was well worth it.
I think the magazine is called "Electronics", and dated July 1945?
There is a very detailed description of how the vacuum-tube ( valve ) amplifier for the photo-detectors works.
I like this part:
"Operation under mill conditions has proved the advantage of plug-in components, not only in reducing outage time but in the ability of plant men, unskilled in electronics or electrical controls, to make replacements themselves. It is no more difficult for them to replace a defective amplifier or relay than to change tubes in a radio."