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. As is the top cap from the other PM16 and PM14.
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 number 16 in large bold numerals. The BVA logo sits below.
The gettering obscures the internal structure. The metal cylinder that can be seen is part of the screen. The electrodes are mounted vertically. The filament is a single inverted V and the two wire grids can just bee seen with a glass.
The balloon envelope is 46 mm in diameter, and excluding the B4 base pins is 104 mm tall.
References: Data-sheet & 1043. Type PM16 was first introduced in 1927. See also1927 adverts.