The 6X5GT is a standard HT rectifier for low power AC mains driven equipment. The output of a centre tapped transformer would be applied to the anodes, the rating given is 325-0-325, the common cathode would be the output for the rectified voltage. A effective series resistance of 350 Ohms was required to limit surges and the reservoir capacitor had to be restricted to 16 µF. Nothing special and soon replaced by miniature valves of higher specification.
The picture shows the two anodes stacked vertically on the common cathode tube. The 6X5GT is also marked with the American service code of VT-126B.
National Union Made in USA is written on the base.
The wide glass tube envelope is 29 mm in diameter and excluding the IO base pins the valve is 69 mm tall.
References: Datasheet, 1040 & 1043. Type 6X5GT was first introduced in 1936.