The Cossor P1 is a bright emitter valve and went into production in 1922. Cossor launched the valve as designed for detector and AF amplifier use. A sister valve the P2 was designed for HF use.
The early production valves had a metal shell base. Later production moved over to Bakelite moulded bases.
Marconi held a patent for cylindrical anodes and grids and we believe that the electrode shape used by Cossor was a way to get round the patent.
Cossor was not known to use phosphorus gettering but this exhibit clearly has such gettering. It also lacks any Cossor markings or Type designation. A close look revealed some inverted lettering etched into the glass.
The lettering reads 'Repaired by Radions Ltd' and the advert listed above shows the service available. Bright emitter filaments had rather short lives and new valves were expensive. Repairing receiving valves was a business model that existed for a short time. However, Repairing large silica transmitting valves remained economic.
The wide glass tube envelope is 27 mm in diameter and, excluding the B4 base pins, is 83 mm tall.
References: 1003 & 1004 Type P1 was first introduced in 1922. See also1922 adverts.