The CV686 is a voltage stabiliser. The prototypes were the 0C3 and VR105/30.
Internally pins 3 and 7 are linked. This shorting link is designed to protect the connected equipment from overload, as when the stabiliser is removed the supplied circuit is disconnected.
The reverse carries the Type designations 0C3 and VR105 thus proving a direct equivalence to the CV686.
Construction of this gas filled stabiliser follows the normal pattern of closed cylinder with the second electrode as a central vertical rod.
References: Data-sheet & 1040. Type CV686 was first introduced in 1939. See also1939 adverts.