The Marconi P240 is an battery audio output triode with a two Volt filament. In 1929 it was regarded as a 'Small Super' for offering a reasonable output power for the time.
A special valve - the E147 - was a P240 with a coated filament.
The P240 Type designation on the dome. The lettering will have been printed onto the glass and then baked to give an etched appearance.
The B4 Base pins.
Thanks to Mark Mallison for sending the images.
The balloon envelope is mm in diameter, and excluding the base pins is mm tall.
Reference: Data Type P240 was first introduced in 1929. See also1929 adverts.
