The CV6 was developed by M-OV from their E1148 experimental prototype. Like all CV valves the spread of operating parameters is smaller than the commercial versions. Commercially the CV6 is known as the DET20, the two are similar but not identical. DET stands for Dull Emitter Transmitting.
To reduce lead length and thus inductance and to raise the frequency of operation the control grid and anode connections are taken to top caps.
The small front to back dimension is about 4 mm.
A closer view.
The wide glass tube envelope is 30 mm in diameter and, excluding the IO base pins, is 75 mm tall.