The 1P11 is identical to the 3V4 and is an audio output pentode from Mazda. The 1P11 was designed for use in battery portable radio receivers. The filament is centre tapped.
The bright, low power, anode is circular.
The reverse of the envelope carries the Made in England lettering.The fine filament wires can be seen at the top of the image.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 47 mm tall.
References: Data-sheet & 1040. Type 1P11 was first introduced in 1946. See also1946 adverts.