The E2174 is an M-OV experimental laboratory sample. The serial number is 28. Visually it looks like one of the 6AT6 family. The pin connections also match. Testing the heater revealed that it is 12.6 Volts at 0.15 Amp the same as the 12AT6. The 12AT6 dates to 1946 and probably this valve does as well.
The rest of the paper label and serial number.
We have another example that is missing part of the label and clearly shows the electrode structure.
The black triode anode in the centre and the two diode anodes seen end on. The diode cathode is obscured by the gettering.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 47 mm tall.
Reference: Observation. Type E2174 was first introduced in 1946.