The BA2 is a class B audio output double triode for battery operation and the design dates from 1933. The operating mode is quiescent push-pull. In use the given anode to anode load is 10,000Ω and the output can be up to 1.5 Watts.
The side elevation shows the two triodes and the supports originating at the pinch.
Looking under the gettering from the base one of the triodes can be seen. The filament is a single inverted V and is oxide coated.
The data-sheet enclosed in the box with the valve.
The balloon envelope is 45 mm in diameter, and excluding the B7 base pins is 94 mm tall.
References: Data-sheet & 1043. Type BA2 was first introduced in 1933.