The PM16 is a screen grid (tetrode) valve and the design dates from 1928-9. It is on a B4 base and the anode connection is taken to a top cap. In our exhibit the top cap is missing.
The valve has both etched lettering in the glass and a paper label around the base.
During the 1920s battery valves had various filament voltages and the Mullard PM12, PM14 and PM16 were all the same basic valve with two, four and six Volt filaments respectively. The Mazda 215SG shows an equivalent of the PM12 but with the top cap in place.
The BVA logo and a clear 16 on the envelope.
The envelope is marked in many places, here is the Mullard logo and the words protected by patents.
An echo of earlier times, the aerial, coil an earth logo of the early valves.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 101 mm tall.
Reference: 1043. Type PM16 was first introduced in 1927.