The CV3929 (5840) is the special quality version of the EF732 pentode. It appears to be an updated version of the EF72.
The 5840 CV3929 was designed for wide band HF amplification under adverse conditions where good reliability was required. These applications include military equipment and industrial applications. As it will maintain its emission when used with long periods operating at cut-off, application in computer circuits are a possible use.
Another application area is as a microphone pre-amplifier built into condenser microphones.
The open pitch of the suppressor grid can be seen at the top of the image and the closer wound screen grid is clearer at the bottom. The control grid supports can be seen but not the wires.
Looking along the grid axis, all three grids can be seen.
Here the white oxide coated cathode can be seen. and below the lower mica the the cathode can be seen to have a slight curve. One can only marvel at the dexterity required to hand assemble such a small valve.
The thin glass tube envelope is 9 mm in diameter and, excluding the B8D base wires, is 33 mm tall.
References: Data-sheet & 3002. Type CV3929 was first introduced in 1956.