The CV3798 is a 75 volt voltage stabiliser tube. The prototypes for this stabiliser were the OA3 and the VR75-30.
The striking voltage is 100 but a supply of 105 volts is suggested to take into account tolerances. The minimum current is 5 mA and in the working range of 5 - 40 mA the voltage regulation is 5 Volts over this working range.
The base is International Octal but in this case only four pins are fitted 2, 3, 5 and 7.
In the glass tubular format the outer cylinder almost fills the diameter.
The mica disc prevents a view inside the cylinder.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 77 mm tall.
References: Data-sheet, 1040 & 3002. Type CV3798 was first introduced in 1943.