This object is a mercury half-wave rectifier within a glass envelope with a large-metal-shell super-jumbo four-pin bayonet base and a cap for the plate at the opposite end. The circumference of the base is metal, with a ceramic bottom through which the pins project. There is a small protrusion on the side of the base positioned between pins 2 and 3. At a mercury vapor temperature of 20 to 60 degrees C, the tube is rated at 5000 V forward voltage at 5 A maximum peak current. A circle made with yellow ink surrounds the cap at the top of the tube.
Printed in silver ink around the glass envelope.
Written vertically in green ink on the glass envelope.
Printed in tiny black ink toward the bottom of the metal base.