The SS501 is a cold cathode flash tube. The tube is filled with low pressure argon. The main body is a 16 mm diameter U shaped tube. It is believed that the design purpose was in marine buoys. The anode voltage was 1,900 volts ± 100 V and the flash rate was up to 12 flashes per second. The energy for the flash was stored in a 2 μF capacitor. Giving a value of 4 Joules per flash.
Like professional photographic flash heads the trigger pulse would be applied to a thin wire wrapped around the length of the main tube.
The sources found give the gas as argon and this produces a violet to lavender colour discharge. For a white flash xenon would be used.
The connecting pins.
The overall shape. The long tube ends in a reduced diameter tube that covers the right hand side connection. This small diameter tube is open at the base to the gas reservoir.
The SS501 came in a box measuring 102 mm square and 190 mm long. The tube was wrapped in wood pulp packaging.
The wide glass tube envelope is 28 mm in diameter, and including the base pins is 150 mm tall.