Question

Describe the action of a diode valve

The diode valve contains an anode and a cathode, the latter being heated either directly by passing a current through it or indirectly by means of a heating element adjacent to it.

The cathode thus emits electrons which form what is known as the "space charge" in the evacuated glass container.

By making the anode positive with respect to the cathode, these electrons will be attracted to the anode and as more electrons are emitted from the cathode a current will flow through the valve.

Since electrons are emitted from the hot cathode, current can flow in one direction only and this property enables a diode valve to be used as a rectifier. It should be remembered that the conventional direction of current through a valve is from anode to cathode, i.e. opposite to the flow of electrons.