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 wide glass tube envelope is 44 mm in diameter and, excluding the B5 base pins, is 120 mm tall.
References: Datasheet & R J Sutherland.