Electronics · Vol. II|Vacuum tube|1904 (Fleming valve); 1906 (De Forest triode)

Vacuum tube

1904 (Fleming valve); 1906 (De Forest triode)

A heated filament in a vacuum emits electrons. Fleming used that as a one-way valve to detect radio. De Forest added a grid and made an amplifier: a small voltage on the grid controlling a larger current. For fifty years the tube was the transistor. Radios, radars, and the first digital computers are rooms full of glowing glass.

John Ambrose Fleming; Lee de Forest · Britain and the United States

Vacuum tube — Original plate drawn for this atlas. Not a photograph of a museum object or a copyrighted portrait.

How the mechanism is arranged

A triode: electrons boil off a cathode, a grid voltage steers them, a plate collects them. The first electronic amplifier.

How it works

Heat a cathode so it emits electrons into a vacuum.
A positive plate collects them — current in one direction (diode).
A grid between them, charged slightly, throttles the flow (triode amplifier or switch).

Why it mattered

Made weak radio signals loud enough to hear.
Gave computing an electronic switch before semiconductors.
Set the performance bar the transistor had to beat: smaller, cooler, tougher.

What it unlocked

For further study

IEEE History Center. Fleming and De Forest.
Okamura, History of Electron Tubes. Technical survey.

Check

What extra part turns a diode valve into an amplifier?