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 rectangular anode mounted vertically. Note the small mica strip at the top.
The front to back dimension is approximately 5 mm, whereas the width is 22 mm.
The helical filament tension springs are mounted on the mica top strip.
A closer view of the mica strip with the tops of the electrodes held within it. The white specs on the glass are the remains of the gettering.
The balloon envelope is 40 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.
