The Cossor P2 is a bright emitter valve and first went into production in 1922. Cossor launched the valve as for HF use.
This exhibit came in an original box and the valve in the box is shown below.
The picture on the box shows a clear top to the valve that matches the picture of the valve in the box. However close examination of the etched writing on the valve shows that it is in fact a P1. The P2 was distinguished from the P1 by having the envelope dome and pip painted red as can be seen from the main picture.
The box is also interesting in that the maker prints an apology that the valve has been shipped in old stock and not the new box. Even so the box is sturdy and the valve was originally packed in horse hair.
The P1 was designated for detector and AF amplifier use. It is possible that the valves were made on a single production line and selected on test for the best HF response to carry the P2 designation.
The early production valves had a metal shell base as our exhibit. Later production moved over to Bakelite moulded bases.
The wide glass tube envelope is 27 mm in diameter, and excluding the B4 base pins, is 80 mm tall.
References: 1003. Type P2 was first introduced in 1922.