This PM2HL looks to be a replacement type. It was found in its original box and was priced at 4/9 (four shillings and nine pence). This battery triode is a small signal amplifier of low impedance and gain.
Flat on to the bright anode the grid, and notched support rods, can be seen to extend beyond the 22 x 12 x 5 mm anode. Note the coil springs above the top mica to tension the hot filament.
The anode in close-up shows the spacial relationship between the twin inverted V (coated?) filament and the grid. The wide spacing makes for a low mutual conductance.
The balloon envelope is 40 mm in diameter and, excluding the B4 base pins, is 83 mm tall.
References: Data-sheet & 1043. Type PM2HL was first introduced in 1938. See also1938 adverts.
