How is a tetrode different from a triode vacuum tube?

A triode is a three-electrode electron tube consisting of a cathode, an anode, and a control grid. A tetrode differs by incorporating a fourth electrode, known as the screen grid, which is positioned between the control grid and the anode.123

The addition of the screen grid provides two primary functional differences:

• Electrostatic Shielding: The screen grid acts as a shield, protecting the control grid from the influence of the plate when its potential changes.2
• Increased Gain: By reducing the effect of plate voltage on electron flow, the screen grid increases the tube’s amplifying property compared to that of a triode.23

While the pentode has largely replaced the tetrode in many applications, specialized versions such as the beam-power tube and radial-beam tetrodes remain in use for high-power amplification and radio frequency applications.12