This exhibit is a mystery, it is clearly identified as a K3 but no K3 exists in the published lists of Ferranti valves that we have as yet found.
A current flows between pins 3 and 4 but at over one Amp at less than half a Volt this is outside the ratings of any published Ferranti valve.
The reverse is plain except for the code GI.
The wide metal tube envelope is 32 mm in diameter, and excluding the B4 base pins is 63 mm tall.
Updated October 11, 2018. shape:wide.metal.tube base:b4 pins:4 pin: