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.
The marking on the side is EEVC 214 - possibly this was made be English Electric.
The this mark is an 8 in a circle. The construction of the neon stabiliser is as a bright cylinder with central second electrode.
The classic envelope is 37 mm in diameter and, excluding the IO base pins, is 87 mm tall.
References: Data-sheet, 1040 & 3002. Type CV3798 was first introduced in 1943. See also1943 adverts.