ResonantLive Sound Archive

Equipment file · Vacuum tube (triode)

Three-electrode Audion

De Forest Wireless · 1906–1907

Evidence status · documented

Identity and core specifications are documented; some historical fields remain unavailable.

Lee de Forest added a third electrode, the grid, to a two-electrode vacuum tube in 1906, creating the Audion, the first device able to amplify as well as detect electrical signals. Early Audions used a lamp-style glass envelope built by incandescent-lamp maker H. W. McCandless.

Introduced
1906–1907
Category
Vacuum tube (triode)
Intended use
Wireless telegraph/telephone signal detection and amplification
Production
Hand-built by De Forest and licensees; commercialised by De Forest Radio Telephone Co. from 1907

Equipment photographs · 2

Audion tube

1 / 2 · Audion tube

Audion tube·Paul Thompson·Public domain

Why it mattered

  1. 01

    The Audion was the first practical electronic amplifying device; earlier detectors could only sense a signal, not boost it.

  2. 02

    It is the ancestor of every valve and transistor amplifier used in telephone repeaters, radio and sound reinforcement, beginning with the [[western-electric-101b|Western Electric repeater tubes]].

Engineering record

Third electrode
A grid between filament and plate let a small grid signal control a much larger plate current[1]
Early construction
The 1906 Key West Audion used a lamp-style envelope built by H. W. McCandless[2]

Original pricing

No reliable period price located

2026 equivalent

Not calculated without a reliable original price.

Public price evidence was not sufficient to publish a defensible original figure.

Use in the field

No named deployment could be tied to this exact item by a checked source yet. Know of one? Suggest it on the contribute page.

Manuals & original documents

Sources

  1. 1Lee DeForestLemelson-MIT Program · reference
  2. 2deForest's Early Audions, Electronics World, September 1965RF Cafe (reprint) · technical paper · 1965-09

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