Which vacuum tube has five active electrodes, including a cathode, control grid, screen grid, suspension grid, and plate?

• A. Diode
• B. Triode
• C. Pentode
• D. Tetrode

Answer: (C)

In vacuum tubes, the number of active electrodes defines the tube type and how it controls and amplifies current. Each added grid helps steer the electron flow more precisely and often reduces unwanted effects like capacitance or secondary emission.

Five active elements described—cathode, control grid, screen grid, a grid between the plate and control grid (the suppressor or suspension grid), and the plate—fit the structure of a pentode. The suppressor grid is placed between the control grid and the plate and is typically tied to the cathode to suppress secondary electrons, improving gain and linearity. The plate (anode) collects the electrons.

So this arrangement corresponds to a pentode, the tube with five active electrodes.