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 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

Contribute to the record

Know more about Three-electrode Audion?

Corrections, firsthand information, original documents, and credited photograph sources are welcome.

Your email is private and will not appear in the archive. Contributions are not published automatically.

Back to all equipment Back to Origins of electrical sound

Help build the archive

A missing piece? A correction?

Contribute to Resonant
Support the archiveVenmo@mercer-aplinCash App$MercerAplinHow it’s used