The PM1LF is a classic battery valve. Designed to operate at low frequencies and operate from a 2 Volt accumulator and a 125 Volt HT battery. This would be used as an audio amplifier.
The label gives the operating conditions and guarantee.
The balloon envelope is 40 mm in diameter and, excluding the B4 base pins, is 85 mm tall.
References: 1931 datasheet & 1043. Type PM1LF was first introduced in 1926.