A triode is an electrical circuit component that uses a small voltage to control a relatively large flow of current. A triode contains three electrodes, a cathode, an anode, and a control grid. The name triode is derived from the term tri-electrode (i.e., three electrodes).

The triode is actually a variation on the diode, a device that has just two electrodes sealed in vacuum. One electrode, the cathode, is attached to a negative electric potential, the other electrode, the anode, is attached to a positive potential. This device allows current to pass through it in one direction only.

Under normal operating conditions, the cathode is heated to high temperature and the anode remain cooler. Current flow through the device can be increased by a further increase in the temperature of the cathode, by increasing the potential difference between the cathode and anode, or by shortening the physical...