Definition
A vacuum tube containing five active electrodes: a cathode, a control grid, a screen grid, a suppressor grid, and a plate (anode). The added grids reduce unwanted internal effects found in simpler tubes, allowing the pentode to amplify weak signals more efficiently and at higher frequencies than a triode or tetrode.
Plain English
An old-style electronic tube with five working parts inside it. It was used to make weak electrical signals stronger, such as in early radios and radio receivers in aircraft.
Context Anchor
Seen in older aircraft radio, communication, navigation, and electronic equipment descriptions, especially in maintenance or historical systems.
Derivation
From the Greek 'pente' meaning 'five' and '-ode' from 'electrode.' The name simply tells you how many electrodes are inside: five.
Why Pilots Care
Most modern pilots will not operate a pentode directly, but the term can appear in older avionics manuals or maintenance references. Knowing it identifies an electronic tube helps keep the discussion from being confused with a switch, wire, or modern solid-state part.
Intuition Check
Do not read “pentode” as simply any device with five outside terminals. In this context, it specifically means a vacuum tube with five internal working electrodes.
Example Sentence 1
The pentode in the old aircraft receiver had to be replaced when the radio's reception became weak and noisy.
Example Sentence 2
Early navigation receivers used a pentode stage to boost incoming signals.