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Summary
DescriptionThree GE amplidynes 1951.jpg
English: Three amplidynes made by General Electric Co., from an advertisement in a 1951 magazine.
Top left - 1 kW amplidyne motor-generator
Bottom left - 3 kW amplidyne motor-generator
Right - 5 kW amplidyne generator
An amplidyne is a rotating machine that functions as an amplifier. It consists of an electric motor turning a DC generator. The electric signal to be amplified is applied to the generator's field windings. The output voltage is proportional to the field current. Amplidynes are used in power industrial servo and control systems.
This image is from an advertisement without a copyright notice published in a 1951 US magazine. In the United States, advertisements published in collective works (magazines and newspapers) are not covered by the copyright notice for the entire collective work. (See U.S. Copyright Office Circular 3, "Copyright Notice", page 3, "Contributions to Collective Works".) Since the advertisement was published before 1978 without a copyright notice, it falls into the public domain.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.