How did Lee de Forest’s Audion amplify radio signals?

Developed by Lee De Forest in 1906, the Audion was the first vacuum tube to function as an electronic amplifier. It improved upon earlier two-electrode valves by introducing a third element: a control grid made of bent wire, positioned between the cathode filament and the anode plate.12

In operation, the anode is maintained at a positive potential relative to the cathode, while the grid is negatively biased. Because the grid is composed of open space, it acts as a gate for the flow of electrons emitted from the hot filament. When the grid is highly negative, it blocks electrons from reaching the anode; however, by applying a less negative bias, the grid allows electrons to pass through to the plate.2

Consequently, small fluctuations in the grid's potential can control much larger currents flowing to the anode. This ability to modulate the anode current allowed the Audion to amplify weak radio signals, a process further enhanced by "cascading" multiple tubes together.32