The 6X5GT is a standard HT rectifier for low power AC mains driven equipment. It was of a type made by several manufacturers, in this case Sylvania.
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.
The picture shows the two anodes stacked vertically on the common cathode tube.
The active area is a small cylindrical space and so the radiating fins have only a narrow profile.
The construction uses support rods for the anodes on either side of the mica and both are full height. By using identical anode pressings but one facing forward and the other backwards the full wave design is achieved with good stability and an economy of different parts.
The wide glass tube envelope of the top valve is 29 mm in diameter and excluding the IO base pins the valve is 66 mm tall.
References: Datasheet, 1040 & 1043. Type 6X5GT was first introduced in 1936.