The CV589 is also contains the etched designation 6Q7GT in an RCA octagon and the 6Q7GT was the prototype for the CV589. It is a double diode triode and was designed for receiver audio use.
The diodes would be for signal and AGC rectification and the triode would act as AGC amplifier or first audio amplifier.
The RCA etched 6Q7GT with the rough overprint of the CV number to the right.
The anodes seen end on.
At the top is the triode section with the carbonised anode to radiate heat. The two part anode is stitched together. The connection from the control grid to the top cap is visible. The lower bright box section forms the two diode anodes, one either side of the common cathode tube.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 71 mm tall.