This exhibit is clearly marked VT141 - an RAF transmitting valve. However, we can find no details of a VT141. Observation and heater testing shows that it matches the commercial 220DD double diode.
The Cossor 220DD is an indirectly heated double signal diode with a common cathode. It was designed for battery sets using automatic volume control (AVC) now known as AGC (automatic gain control).
Slightly enhanced to show the etched lettering.
The gettering makes the internal structure difficult to see clearly.
The dome carries the Cossor name and the maker code V9. Within can be seen the top mica and tops of the electrodes.
Here the construction is clearer. The heater is a single hairpin within the cathode tube. The two anodes wrap around the cathode with small gaps to prevent shorting.
The balloon envelope is 30 mm in diameter, and excluding the B5 base pins is 72 mm tall.
References: Data-sheet, 4010 & 1043. Type VT141 was first introduced in 1934. See also1934 adverts.
