Vacuum tube hearing aid use 1933

Forfatter/Opretter:

UkendtUnknown author

Kredit:

Retrieved July 9, 2014 from Radio News magazine, Tek Publications, Inc., New York, Vol. 15, No. 6, December 1933, cover archived on American Radio History website

Shortlink:

https://dkwiki.dk/b/3ba26

kilde:

Wikimedia Commons

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1194 x 788 Pixel (194263 Bytes)

beskrivelse:

Illustration on the cover of an electronics magazine of use of the first mass market vacuum tube hearing aids in 1933. Amplifying hearing aids, made possible by the invention of the triode vacuum tube by Lee De Forest in 1906, had just come on the market a few years before, and were a great improvement over previous crude electric hearing aids that used the amplifying ability of a carbon microphone. The hearing aid consisted of a box about the size of a loaf of bread, with a built-in microphone, that the user directed toward the speaking person, with a plug-in headphone. The illustration shows two hearing-impaired men using the hearing aids on a train. Alterations to image: Cropped out extraneous text on the cover.

Licens:

Public domain

Kommentar på licensen:

This 1933 issue of Radio News magazine would have the copyright renewed in 1961. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. [1] Search of the Renewals for Periodicals for 1960, 1961 and 1962 show no renewal entries for Radio News. Therefore the copyright was not renewed and it is in the public domain.