The CV1931 is the glass GT version of the commercial 6H6 valve family. This valve has pinch construction that adds to the length of the envelope and has space above the electrode assembly making it twice the length of the metal version.
This exhibit is a double diode. The diodes are low voltage low current signal rectifiers and not suitable for power supply service. The low current is reflected in the low heater power.
The two diode sections are mounted close together with an electrostatic screen in between.
The two diodes seen end on.
The wide glass tube envelope is 29 mm in diameter and excluding the IO base pins the valve is 60 mm tall.