The 220P battery triode was designed as an audio output valve. With a maximum output of 190 mW it would be used with headphones and not a loudspeaker.
This exhibit carries the diamond shaped paper label and proudly displays the New Process of production. This exhibit dates to the late 1920s.
The Cossor 220P was initially called the Stentor Two when introduced in 1927. The Stentor Two features the 'Tin Hat' anode construction of the early Cossor valves, whereas the 220P has a rectangular anode and probably used the Cossor multi point filament fixing.
The gettering covers almost all of the bulb. Here the outer anode supports give a a clue to the electrode width. It looks to be around 21 or 22mm.
The small part of the envelope that is clearer gives a view of the bright box anode.
A closer look reveals the four strands of oxide coated filament and the shaped grid wires.
The balloon envelope is 41 mm in diameter and, excluding the B4 base pins, is 82 mm tall.
References: Data-sheet & 1043. Type 220P was first introduced in 1929. See also1929 adverts.
