The NSP2 strobotron is a neon flash tube. The flash is produced when the trigger voltage initiates a discharge between the cathode and caesium coated anode at the top of the envelope. The bright column of light can be directed by a polished parabolic mirror to form a stroboscope.
For different flash rates up to the maximum of 250 per second the capacitors used are: 6-35 Hz 4 μF, 30-50 Hz 3 μF, 45-80 Hz 2 μF, 80-150 Hz 1 μF & 140-250 Hz 0.5 μF.
The evacuation hole in the pinch stem.
Made in England.
Trying to see into the well in the cathode and trigger electrode.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 86 mm tall.