This CV12 is a mercury vapour thyratron developed by GEC as experimental Type E1191 for use as a pulse modulator in the type 277 radar in service from 1943. BTH also made the CV12 and modified their Type BT49 and this exhibit is believed to be of BTH origin. Our other example of the CV12 is believed to be from GEC.
The Type 277 radar used cavity magnetron Type CV76 as RF generator. This magnetron operated at 9 cm and peak power output was up to 500 kW, well within the rating of this modulator thyratron.
The pulses generated for the magnetron were 2 μs long and repeated 500 times a second.
The Type designation is etched into the envelope. The number 976 also appears. The visible structure is the anode. Looking through a hole in the ceramic base one can see that the grid connection is insulated with a glass sleeve.
This unused valve has the filament leads - with large brass spade connectors - colour coded yellow and black. The smaller spade connector connects to the grid and is insulated with all white ceramic beads.
The wide glass tube envelope is 69 mm in diameter, and excluding the base pins is 300 mm tall.
References: Data-sheet, Jeremy Harmer & 3002. Type CV12 was first introduced in 1941.