Strangely, the schematic doesn't show how the lamp is wired into the chassis. So, measure the voltage across the lamp socket. Probably 6V or so?
Is the lamp a screw-type or bayonet? Pick one out from the lamp data sheet here under "References."
Often, there will be two lamps with the same voltage rating and base, but with different amp ratings - e.g., a #40 and a #46. The one with a higher amperage will run brighter and hotter.
Thanks Doug & David for your replies. Found info on the great Philco Repair Bench web site. Bulb Type F, 6-8v, 200ma., bayonet. May be replaced with Type 44.