This N30 carries the Osram badge, it is a Catkin external anode audio output valve. All Catkins were made by M-OV.
It was designed to be used as the audio output stage of an all-mains receiver. The design is dated to 1934 and is a series 2 Catkin. The N30 was a version of the MPT4 but with a 13 Volt 0.3 Amp heater for use in AC/DC sets without mains transformers.
The thin metal tube envelope is 18 mm in diameter, with the metal base 28 mm in diameter and, excluding the B7 base pins, is 103 mm tall.
References: Datasheet & 1005. Type N30 was first introduced in 1934.