The VS68 is a four in one voltage stabiliser that GEC marketed as the Stabilovolt. The commercial designation is STV280/40 and has a maximum current draw of 40 mA. Also made was the STV280/80 with higher current rating.
It has four anodes, and thus four outputs with gaps of 70 volts each. These output voltages are 70, 140, 210 & 280.
The striking voltage is above 420 Volts and the tube current is 5 - 35 mA. The tube voltage regulation is about a couple of Volts for each 70 Volt step.
The VS indicates it is a Voltage Stabiliser specified for the Royal Air Force. The AM and Crown is the Air Ministry stamp. The 280/40 refers to the commercial designation.
The outer can is not connected to the base pins. All the leads from the pinch upwards are shielded in glass tubes in this gas filled envelope.
The wide glass tube envelope is 46 mm in diameter and, excluding the B5 base pins, is 115 mm tall.
References: Data-sheet & R J Sutherland.