This exhibit has only the BTH logo on the base but the long supports and a small triode high up in the envelope only matches one BTH valve. The filament is intact and measures the same as the B23.
The B23 is a low power battery audio output triode from 1927.
The A for anode marks the base pin and the 3 on the glass looks to be a later addition.
The BTH logo on the underside of the base cap.
The triode: the filament is a single V strand with the point within the hook on the left of the picture. The grid wires can be seen wound on supports at either side.
A better image of the grid shape from the filament connection side.
The balloon envelope is 50 mm in diameter, and excluding the B4 base pins is 99 mm tall.
Reference: 1043. Type B23 was first introduced in 1927. See also1927 adverts.