The 6AS7G is a double triode with a very low AC anode resistance. The value is 280 Ohms. The literature gives a single ended audio amplifier as its use. But a more likely original design purpose is as a series pass element for stabilised power supplies. This M-OV valve is branded GEC which was the imprint of their industrial and professional valves.
With a pair of U channel anodes for each triode, one per side of the flat cathode, the construction closely mirrors other series pass valves.
See6080 as an example from Mazda with similar ratings.
The classic envelope is 46 mm in diameter and, excluding the IO base pins, is 105 mm tall.
Reference: Data-sheet. Type 6AS7G was first introduced in 1946.