The PM24M is a directly heated output pentode. The valve would have been designed for the audio stages in AC mains broadcast receivers. It has an output of 2.8 Watts and was aimed at single ended use. This PM24M was a replacement type made after WWII.
The dome has the identification etched into the glass.
The three inverted V's of oxide coated filament are each held in springs. The springs are held in a glass rod by the side of the anode.
This image shows the grids within the anode.
The grids are bright wire wound with rounded ends.
The balloon envelope is 44 mm in diameter and, excluding the B5 base pins, is 118 mm tall.
References: Data-sheet & 1043. Type PM24M was first introduced in 1932.