Cold-cathode gas-filled tubes as circuit elements

SINCE the discovery by Hull¹ that oxide-coated cathodes could be used as commercially practical thermionic emitters in gas-filled tubes, these tubes have found extensive use. For high-voltage d-c power supplies two-element mercury-vapor rectifiers have almost entirely replaced rotating machines and the earlier high-vacuum tube rectifiers. The addition of a grid to the gas-filled thermionic rectifier yields the thyratron which is used in regulated rectifiers, for the inversion of direct current to alternating current, and as a sensitive relay in numerous industrial control circuits. The discovery by Slepian and Ludwig² of the ignitor principle in initiating the arc spot on a mercury-pool cathode provided a ready means for controlling current flow in tubes with mercury-pool cathodes and the ignitron has now shown itself to have a large field of application.