The KD24 is a cold cathode voltage stabiliser. The details of its operation are given in the type designation. This tube will stabilise the voltage across it to 105 Volts for output currents between 5 mA and 40 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 stabiliser the figure is 4 Volts across the current range. For making a stabilised power supply the reference tube would be run at as close as possible to a constant current.
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 central rod is the anode.
The seam in the cylindrical cathode showing that the metal is very thin.
The classic envelope is 37 mm in diameter and, excluding the IO base pins, is 90 mm tall.
References: Data-sheet. Type KD24 was first introduced in 1939. See also1939 adverts.
