The PP225 is a battery audio output pentode from the mid 1930s.
Side view of the bright anode.
The filament is formed into an M. The control grid wires have been pinched together on the inside of the supports and pass flat across the filament. Grid three seems to just consist of the two vertical supports.
The classic envelope is 38 mm in diameter and, excluding the B5 base pins, is 91 mm tall.
Reference: 1043. Type PP225 was first introduced in 1936.