The 210VPT is a variable-mu amplifier HF pentode dating from the early 1930s. The design use is as an HF or IF voltage amplifier in AGC controlled battery superhet radio receivers.
Our other 210VPT is earlier and has a screw top cap and the identification is by a stick-on paper label.
The classic envelope is 44 mm in diameter and, excluding the B7 base pins, is 109 mm tall.
References: Data-sheet & 1043. Type 210VPT was first introduced in 1934.