This is a bit of radio/electronics test equipment that I just recently got and started to work on. It dates from 1939 according to the schematics.
it uses 4 vacuum tubes. A 5W4 (full wave rect) a 83 (murcury vapor full wave rect) and 2 6H6's (Twin diode/voltage doubler as according to the RCA receiving tube manual that I have) all tubes check good exept for an odd variance in electron emissions in one half of the 83 tube which registers close to "?" on my other tube tester but still in the green. to begin with The meter had an open wire wound resistor inside it. Causing the needle not to deflect at all. I tried some unorthodox things to repair the resistor but wound up unraveling the whole thing. so I found on some vague source that iw was a 450 Ohm resistor so I replaced it with a 400 Ohm resistor and 5 10 Ohm resistors connected in series. since my replacement part was too big for the inside of the meter I attached it to the outside of the thing by means of one of its connections and just soldered th two internal wires where the old resistor was together. the meter now registers but the device has other issues still. I cannot bring the meter to line voltage during a tube test. So the readings are to inacurate to use. The ohm meter only seems to work on the X100 scale although I have not made any resistance measurements with it yet to tell weather or not it's acurate. The capacitor tester has yet to be tried as well as the AC volt meter. the low resisntance scale does not work at all and has been tried with low resistance components. The DC volt meter seems to work but may be off by anywhere from a volt to half a volt. So that might need looking at too but then again I havent tried a DC source that i know is what it says it really is. The neon short indicator is good as is the "fuse bulb" which is not really a fuse at all but a light bulb attached as a fuse in the primary circuit. and this is original to its design. I may post more about this as things progress. I just dont know when that will be as of now.