The VR105/30 is a cold cathode voltage stabiliser. The details of its operation are given in the type designation. This tube will stabilise the voltage across it to 105 Volts for output currents between 5 mA and 30 mA. To strike the tube the voltage must exceed 135 V.
As with all such stabilisers the voltage will vary slightly with the current drawn. For this tube the stabilisation is 4 Volts across the current range.
If used as a reference within a stabilised power supply the stabiliser tube would be run as close as possible in constant current mode, i.e. with a fixed load and controlling the voltage on the control grid of the amplifier within the power supply.
The construction is as a cylindrical anode with a central rod cathode. The low pressure gas filling is probably neon.
The envelope is also marked with the Type of CV686 indicating direct equivalence.
The top mica disc has fingers to grip the inside of the envelope. The central electrode can be seen as a plain rod.
The wide glass tube envelope is 38 mm in diameter and, excluding the IO base pins, is 89 mm tall.
References: Data-sheet & 1040. Type VR105/30 was first introduced in 1939. See also1939 adverts.