File:Magneto wall telephone 1917 open.jpg
![File:Magneto wall telephone 1917 open.jpg](https://upload.wikimedia.org/wikipedia/commons/thumb/2/27/Magneto_wall_telephone_1917_open.jpg/660px-Magneto_wall_telephone_1917_open.jpg?20141021153811)
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Summary
[edit]DescriptionMagneto wall telephone 1917 open.jpg |
English: Early magneto wall telephone manufactured in 1917 by Julius Andrae and Sons Co., Milwaukee, Wisconsin, USA from an advertisement in a telephone trade magazine. Shown with case open revealing internal parts. Magneto for ringer is seen above the cylindrical batteries. Magneto telephones were "local battery" instruments; power for the transmitter was provided by dry cell batteries in each telephone, which had to be replaced periodically. These were superseded by modern "central battery" systems, in which all the power for the phone was provided by the local switching office. Alterations to image: Cropped out surrounding advertising copy and partially removed aliasing artifacts (crosshatched lines) added by scanning of halftone photo, using Gimp FFT filter. |
Date | |
Source | Retrieved October 20, 2014 from Telephony magazine, Telephony Publishing Co., Chicago, Vol. 73, No. 10, September 8, 1917, p. 33 on Google Books |
Author | Unknown authorUnknown author |
Licensing
[edit]Public domainPublic domainfalsefalse |
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This media file is in the public domain in the United States. This applies to U.S. works where the copyright has expired, often because its first publication occurred prior to January 1, 1929, and if not then due to lack of notice or renewal. See this page for further explanation.
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This image might not be in the public domain outside of the United States; this especially applies in the countries and areas that do not apply the rule of the shorter term for US works, such as Canada, Mainland China (not Hong Kong or Macao), Germany, Mexico, and Switzerland. The creator and year of publication are essential information and must be provided. See Wikipedia:Public domain and Wikipedia:Copyrights for more details.
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Annotations InfoField | This image is annotated: View the annotations at Commons |
Carbon granule microphone (transmitter)
Hand-cranked magneto (electric generator) generates ~ 100 V ringing current to ring remote phone's bell when initiating call.
Moving iron diaphragm earphone (receiver)
Electric bell ringer alerts owner to incoming calls. The bells themselves are on the outside of the front panel
1.5 V dry cell batteries power the calling circuit
"Hook switch" turns on the audio circuit when the receiver is lifted
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