The VT-139 is the US Government procurement specification for the commercial 0D3.
The design is of a neon discharge tube whose geometry allows for a nominal stabilised voltage of 150 Volts at around 30 mA. The regulation is 150 plus or minus 5.5 Volts over the range 5 to 40 mA through the tube.
Internally pins 3 and 7 are linked. This shorting link is designed to protect the connected equipment from overload, as when the stabiliser is removed the supplied circuit is disconnected.
The side of the base cap has the alternate Type designation of VR150. The cathode cylinder is closed with mica sheets the hold the rod anode centrally.
The SC966A code. Is this an inspection office?
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 87 mm tall.