The PM24M was a replacement type made after WWII and is a directly heated output pentode. The valve would have been designed for the single ended audio stages in AC mains broadcast receivers and can produce 2.8 Watts.
The glass is coated internally as well as the getter residue above the base.
The three loops of oxide coated filament is held taught by the curved tension springs.
Looking up from the base some grid wires and the box anode can be seen.
The classic envelope is 45 mm in diameter and, excluding the B5 base pins, is 108 mm tall.
References: Data-sheet, 1040 & 1043. Type PM24M was first introduced in 1932. See also1932 adverts.
