The 4316A is a UHF power output valve triode, made by STC in the UK. The design is the Western Electric 316A but when made by STC the prefix 4 is added to the Type designation.
It is a wonderful doorknob shape, and is a famous type of valve in that it was used for the first successful radar transmitter to be operated whilst airborne. In this application it was operated in pulse mode and the individual pulses were of a few hundred watts.
The maximum grid current for its native Class C mode of operation is 12 mA.
The getter holder is mounted on the support that carries the filament tension spring.
The triode is small but the envelope size is determined by the tension spring and dissipation requirements.
The balloon envelope is 63 mm in diameter and, excluding the special base pins, is 58 mm tall.