The 1P11 is identical to the 3V4 and is an audio output pentode. The 1P11 was designed for use in battery portable radio receivers. The filament is centre tapped allowing for 1.4 or 2.8 V working.
All the original printed identification has been rubbed off. Checking the pin connections verified that this was correctly marked.
The end of the oval anode.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 46 mm tall.
References: Data-sheet & 1040. Type 1P11 was first introduced in 1946. See also1946 adverts.