[Reece]

The 25Z5 and 43 are 25 volt tubes, and the 6 volt ones and probably the missing one all add up to 68 heater volts. The tube in your picture must be a ballast tube, which is a wire wound resistor in a glass envelope, used to drop line voltage to 68 volts. Look carefully and see if it looks like that's what it is. Try measuring resistance across all the tube pins and see what you get. Ballast tubes get very very hot in operation.

Is there any writing on the tube base? Try putting the tube in the freezer for a few minutes and then take it out and breathe on it and look around on the glass for a number.


Edit: I can't think of another 4 pin tube that would make sense here. The radio could function with the rectifier, output, and the two 6 volt tubes you have. Perhaps the two four-pin sockets are for TWO ballast tubes. Some manufacturers in the thirties inflated their tube count to make folks think they were getting more radio for the money, where in fact the extra tube or tubes were not needed. Inspecting the way that the sockets are wired would tell you. If the two four pin sockets are wired in series some way it could indicate that they are both for ballast tube impressivity. If that's so there are ways around having to use ballast tubes, which can be hard to find. Time to flip the chassis over and start drawing the actual back into the schematic diagram. I've had to do that on several orphan sets and it's good practice in tracing circuits and in patience! As you go you'll see how the circuits come together. Then you can compare your set with the schematics of sets using similar tubes. There's a lookup table for that at grillecloth.com