ResonantLive Sound Archive

Equipment file · Triode vacuum-tube gain stage

Audion amplifier

De Forest / later developers · 1906 patent; amplification demonstrated later

Evidence status · verified

Claims in this file are tied to item-specific sources.

A control grid modulates plate current, allowing a small signal to control a larger one.

Introduced
1906 patent; amplification demonstrated later
Category
Triode vacuum-tube gain stage
Intended use
Detection, oscillation, and electrical signal amplification
Production
1907 onward in successive forms

Equipment photographs · 1

First Audion amplifier 1914

1 / 1 · First Audion amplifier 1914

First Audion amplifier 1914·Lee De Forest·Public domain

Why it mattered

  1. 01

    Added an active gain element between microphone and loudspeaker.

  2. 02

    Made cascaded electrical amplification possible, completing the conceptual architecture of a modern sound-reinforcement chain.

Engineering record

Control element
A grid placed between filament and plate controls a larger plate current with a smaller input signal.[1][2]
Historical caution
De Forest patented the three-electrode device, while later researchers established and refined its practical amplifier circuits.[2]

Original pricing

No reliable launch price located

2026 equivalent

Not calculated without a reliable original price.

Surviving records describe patents and licenses more consistently than a single public list price.

Use in the field

The Audion itself was not concert equipment; its importance is enabling the tube amplifiers used by the first complete public-address systems.[2]

Manuals & original documents

Sources

  1. 1Space TelegraphyUnited States Patent Office · patent · 1908
  2. 2Lee de ForestEngineering and Technology History Wiki · reference

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