Type CV717 is a high voltage power full wave rectifier and was designed for providing HT in low power transmitters particularly in aircraft. This valve is also marked with the commercial equivalent of 5R4GY.
The output rating is 180 Watts with a maximum reservoir capacitor of 4 µF. The rectifier needs a series resistance of 250 Ω to limit peak-current.
This type of rectifier has proved popular for modern audio amplifier construction.
The 5R4GY commercial Type designation.
One anode. The ribs add to the mechanical stability of the thin sheet nickel.
The lower end of one anode. The filament ribbon is welded to the support indicating that the metal is not tungsten. It is probably molybdenum or nickel.
The top of one anode. The loop is held in a tension spring arm that is anchored to a support in the centre of the mica disc.
The classic envelope is 51 mm diameter at its maximum and excluding the IO base pins the length is 116 mm.