Such tools may be either gas filled, or partially or fully evacuated; such as,vacuums.

Common tubes include vacuum tubes, cathode-ray tubes, phototubes, mercury vapor tubes, thyratrons, and microwave tubes.

Thyratrons are gas-filled hot-cathode tubes which are used as electronic switches or relays in which signals applied to the control grids initiates anode currents but does not limit them and cannot interrupt, the flow of electrons.