Audion fidelity audio equipment. Audion The Audion was an electronic detecting or amplifying vacuum tube invented by American electrical engineer Lee de Forest in 1906. It was the first triode, consisting of an evacuated glass tube containing three electrodes: a heated filament, a grid, and a plate. It is important in the history of technology because it was the first widely used electronic device which could amplify; a small electrical signal applied to the grid could control a larger current flowing from the filament to plate. The original triode Audion had more residual gas in the tube than later versions and
Zone valve spring but can be opened by the force of the wax motor. Removal of electrical power re-closes the valve. This style of zone valve operates with a perfectly ordinary SPST thermostat. For vacuum- or pneumatically operated zone valves, the thermostat usually switches the pressure or vacuum on or off, causing a spring-loaded rubber diaphragm to move and actuate the valve. Unlike the electrical zone valves, these valves automatically return to the default position without the application of any power, and the default position is usually "open", allowing heat to flow. Highly sophisticated systems may use some form of building automation