Vacuum Tube Sandbox · Introduction to Information Technology

Vacuum tube (triode)Thermionic emission · amplification & switching

Anatomy

FFilamentHeated cathode

CCathodeEmits electrons

GGridControl electrode

AAnode / plateCollects electrons

The filament glows like a light-bulb element and heats the cathode so hot that electrons boil off its surface — thermionic emission. The grid, a thin wire spiral between cathode and anode, acts like a valve: a tiny change in grid voltage lets a much larger anode current through. That is how one tube amplifies a weak radio or audio signal, and how the giant ENIAC of 1945 switched with thousands of them.

Emission

thermionicheat

Electrodes

3triode

Grid

controltiny signal

Life

hotbulky · fragile

Watch the orange filaments glow, the blue electrons stream from the cathode toward the plate, and the grid strands woven between them. Tubes made first-generation computers possible — and their heat, size and unreliability made the transistor necessary.

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