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Circuit diagram two-stage ("2 step") vacuum-tube amplifier used

circa 1921 in conjunction with the w:Ambrose Channel pilot cable. Date February 1921 Source https://books.google.com/books?id=eugxAQAAMAAJ&pg=PA36 Author A. Crossley

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Public domain	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.	United States
	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.