How do electron tubes control the movement of electrons in electronic circuits?

Electron tubes control the movement of electrons through a combination of heat, electric fields, and physical structures within a vacuum or low-pressure gas environment.1

The Process of Control

• Emission: The process begins at the cathode, which releases electrons—most commonly through thermionic emission, where the cathode is heated until electrons gain enough energy to escape its surface.23
• Acceleration: An anode (or plate) is maintained at a positive voltage, creating an electric field that attracts and accelerates the emitted electrons toward it, establishing an electric current.14
• Modulation: To control this flow, a control grid is placed between the cathode and anode. By applying a negative bias to this grid, the tube can modulate or block the stream of electrons. Because the grid is an open mesh, small variations in its voltage can effectively control large amounts of current flowing to the anode, allowing the tube to function as an amplifier.5674

Additional grids, such as screen grids or suppressor grids, may be used to further refine electron movement and improve performance.45