The 68506 is a Tungar half wave rectifier designed for low voltage battery chargers. Tungar comes from the Tungsten filament and the Argon gas filling. The anode is graphite. The gas makes possible a low voltage drop across the rectifier, typically 10 Volts, but also limits the anode voltage.
See also The general Electric Tungar booklet.
The Tungar name and the makers identification - Edison Swan.
The logo and etched lettering on the silvered glass.
The construction of this exhibit. Some Tungar rectifiers had a clear envelope but with this gettered design the internal structure is obscured. With a very strong backlight and a long exposure this image was formed.
The anode connection and ceramic insulators.
The balloon envelope is 81 mm in diameter, and including the GES base is 157 mm tall.
References: Datasheet. Type 68506 was first introduced in 1948.