The 12CN5 is a car radio amplifier pentode designed to operate from 12 Volt vehicle supplies. The intended use was as an IF amplifier. It is a straight design and not designed for the stage gain to be controlled by an AGC line.
The anode is a flattened cylinder and reveals little of the internal structure. The made in USA is clearly visible.
The end elevation of the anode.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 56 mm tall.
Reference: Data-sheet. Type 12CN5 was first introduced in 1958.