Part 5/7:
Beyond switching and rectification, vacuum tubes serve as amplifiers. The addition of a control grid between the cathode and anode enables small input signals to control a much larger current flow in the circuit. When a weak voltage is applied to the grid—such as a faint radio signal—it modulates electron flow from the cathode to the anode.
A negative voltage on the grid reduces electron flow, diminishing the current.
A positive voltage on the grid increases electron flow, amplifying the current.
This modulation allows a small input signal to produce a large output—a principle fundamental to radio, audio, and other electronic amplification systems.
Core Principle: