File:Woman tuning radio 1923.jpg
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English: Woman tuning early radio, from 1923 radio magazine. Broadcasting had just begun in 1920 and vacuum tube radio receivers like this had just come on the market.. They ran off batteries, usually a 3-6V storage battery to power the vacuum tubes' filaments and a 30-90V "B" battery to provide the plate voltage. This woman kept forgetting to turn off the set, running the battery down, so she has wired a small indicator lamp (on top of radio) in the filament circuit to remind her. The early vacuum tubes could not produce much audio power, so early radios used horn loudspeakers, like the one on top of the set. The horn coupled sound from the speaker's diaphragm to the outside air better, and so could produce 10 times (10 dB) more sound power from a given audio signal than a cone speaker.
Caption: A fair fan's idea that saves a lot of worry when she shuts off for the evening. Miss Margie O'Neil found that she sometimes went to her downy and forgot to turn the current off her Magnavox, with the result that her battery was run down the next morning. So she placed a small 6V lamp in series with the battery line, which warns her to "turn off".
|Source||Retrieved March 1, 2014 from Radio World, Hennessey Radio Publications Corp., New York, Vol. 2, No. 26, March 24, 1923, p. 17 on Google Books|
|Author||Credited to Kadel and Herbert|
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This 1923 issue of Radio World magazine would have the copyright renewed in 1951. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here.  Search of the Renewals for Periodicals for 1950, 1951 and 1952 show no renewal entries for Radio World. Therefore the magazine's copyright was not renewed and it is in the public domain.
This work is in the public domain because it was published in the United States between 1923 and 1963 and although there may or may not have been a copyright notice, the copyright was not renewed. Unless its author has been dead for the required period, it is copyrighted in the countries or areas that do not apply the rule of the shorter term for US works, such as Canada (50 pma), Mainland China (50 pma, not Hong Kong or Macao), Germany (70 pma), Mexico (100 pma), Switzerland (70 pma), and other countries with individual treaties. See Commons:Hirtle chart for further explanation.
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