The CV848 is a low power amplifier beam tetrode that features a low anode to cathode capacitance and has two small anode plates at a wide separation from the cathode. It can operate as an RF or IF amplifier with a maximum operating frequency of 400 MHz. The commercial Type designation is 6AG5.
The /J identifies the maker as Radar Electronic Equipment.
The reverse carries the commercial Type designation of 6AG5.
The gap in the internal coating gives little detail whereas the commercial versions offer a view of the insides.
The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins the valve is 46 mm long.
