The VR135 is a military receiving valve that became reclassified as the CV6 when the common valve listings were drawn-up to remove the problems of a lack of interchange between the UK Armed Forces.
The VT135 is a service version of the commercial DET20 from M-OV. DET stands for Dull Emitter Transmitting. The VR135 is a low voltage high frequency triode with both anode and control grid taken to top caps for maximum isolation. Its intended use was as a modulator valve.See also the American version type 7193.
As is normal the triode has a small front to back distance. The side rods are mica supports.
A closer view of the electrodes. The anode and grid connect to top caps with tape. The anode is blackened for better heat radiating performance.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 73 mm tall.