The CV686 (commercially the 0C3) is a cold cathode voltage stabiliser. This valve 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.
Pins 3 and 7 are linked internally and can be used to allow voltage to the controlled circuit only when the stabiliser is in place.
The KB/F identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the F identifies the maker as STC, Paignton.
The reverse carries the commercial Type designation and the old RAF Type code of VR105/30.
The cathode cylinder has the rod anode at the centre.
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 CV686 was first introduced in 1939. See also1939 adverts.
