The G400/1K from STV is a high stability, high voltage, low current voltage stabiliser that is directly equivalent to CV2194. The priming anode and actual anode are to be connected together in the external circuit.
The plain card box that this exhibit came in is dated 15 August 1961.
The rear has the CV Type designation.
The two main electrodes look to be solid pieces of metal backed by mica sheets. This mica backing would confine the discharge to the region between the main electrodes.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 46 mm tall.
Reference: Datasheet. Type G400/1K was first introduced in 1958.