Equipment file · Thermionic diode

Fleming valve

Marconi / J. A. Fleming · 1904

Evidence status · documented

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

John Ambrose Fleming built the first oscillation valves in October 1904 and patented them that November (US equivalent 803,684): an evacuated bulb with a heated filament and a separate plate that conducted current one way only. Marconi used it as a radio detector.

Introduced
1904
Category
Thermionic diode
Intended use
Detecting radio signals in wireless receivers
Production
Developed for the Marconi company

Equipment photographs · 1

Fleming valve

1 / 1 · Fleming valve

Fleming valve·Gerald F. J. Tyne·Public domain

Why it mattered

  1. 01

    It was the first practical vacuum tube.

  2. 02

    Adding a control grid to it produced the Audion triode, the first device that could amplify sound electrically.

    Pictured in this passage

Engineering record

Construction
Evacuated bulb with heated filament cathode and plate anode, conducting in one direction only[1]
Patent
British patent 24,850 of 1904; US equivalent 803,684 issued 1905[1]

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

No authoritative manual or original document has been located for this profile.

Sources

  1. 1In the Matter of Fleming's PatentReports of Patent, Design, and Trade Mark Cases · reference · 1919

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