The PP4 audio output pentode is directly heated and designed for mains based receivers, it is also essentially identical to the Mullard PM24M and of similar vintage.
These valves were marketed as pentode versions of the PX4 (and equivalents) and were designed for AC filament heating. The 4.0 Volt heater was the standard in the late 1930s. The anode load impedance for the rated output has to be 7,500 Ohms.
Seen from the top of the envelope the makers name and type identifier are visible.
Tungsram was a Continental valve maker in which Philips had some sort of interest.
The classic envelope is 48 mm in diameter and, excluding the B5 base pins, is 107 mm tall.
References: 1040 & 1043. Type PP4 was first introduced in 1936.
Absolute Maximum Operating Conditions¶
Updated January 04, 2013.