The 220B is a double triode audio output valve from the early 1930s. Like similar valves this was designed to offer reasonable volume at minimum consumption from dry cell HT batteries by being operated as a Class B push-pull stage. Pure Class B suffers from cross-over distortion as the initial conduction region of the valves operating slope is non linear.
Our other 220B has the Cossor paper label as the Type identifier. Here is a later version with lettering on the glass.
The reverse side is opaque and so no internal structure can be seen. The other lettering visible is a UK military old stores code. 10E/9141 equated to Types CV1032 and VR32.
The dome has a top mica fitting into the shoulder of the envelope and above the mica can be seen one of the triode sections. Note the spring that tensions the filament.
The classic envelope is 44 mm in diameter, and excluding the B7 base pins, is 93 mm tall.
References: Datasheet & 1043. Type 220B was first introduced in 1933.