This is actually in a small photographer’s light table, used to view transparency film.
Most of this discussion is academic at this point. Unless you want to retain the old style preheat start magnetic ballast arrangement to keep a vintage item original, just replace the ballasts with a modern multi-lamp electronic ballast. The type is not even all that critical, T12 tubes all run at about the same current (ignoring HO and VHO types which you'll rarely run into at home) and most electronic ballasts will work with a fairly wide range of lamp types. All you need is a ballast that lists F20T12 as a supported lamp type and you are good to go.
For reference, F20T12-KB decodes to Fluorescent, 20 Watts, Tubular, 12/8" (1.5") diameter, "Kitchen & Bath" which is one of the old halophosphate phosphor blends, IIRC it was a bit warmer than "Cool White", but not as warm as "Warm White". Electrically speaking, all F20T12 lamps are identical.