File:Tuning a TRF radio 1925.jpg
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[edit]DescriptionTuning a TRF radio 1925.jpg |
English: A man tuning a Grebe Synchrophase vacuum tube radio receiver in 1925, made by the A. H. Grebe Co. This type of radio, called a tuned radio frequency (TRF) receiver, was popular during the 1920s. It had several stages of amplification, each with a tuned circuit which had to be tuned to the desired radio station with a knob on the front panel connected to a variable capacitor inside. Tuning a TRF receiver to a new station was difficult because all the knobs had to be tuned to the correct point before the station could be heard. The knobs were not marked with frequency, due to large frequency drift of tube receiver. So all the knobs had to be rotated in unison to keep the receiver in tune. This receiver had 3 tuned stages. In order to make the process easier, the controls are thumbwheels instead of ordinary knobs, which can each be rotated with a finger. This picture shows the tuning technique; the operator is turning all 3 thumbwheels simultaneously, Once a station is found, the index numbers on the dials above the wheels are written down so that henceforth the dials can individually be turned directly to the station without this elaborate procedure. The radio's speaker (right) is a large horn loudspeaker as modern cone speakers were not prevalent. The radio is powered by a square 45 V "B" battery, visible behind the cabinet. |
Date | |
Source | Retrieved September 24, 2014 from S. Gordon Taylor, "How to get the most out of your ready-made receiver" in Popular Radio magazine, published by Popular Radio, Inc., New York, Vol. 8, No. 2, August 1925, p. 123 on American Radio History website |
Author | S. Gordon Taylor |
Permission (Reusing this file) |
This 1925 issue of Popular Radio magazine would have the copyright renewed in 1953. 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 1952, 1953, and 1954 show no renewal entries for Popular Radio. Therefore the magazine's copyright was not renewed and it is in the public domain. |
Licensing
[edit]Public domainPublic domainfalsefalse |
This work is in the public domain because it was published in the United States between 1929 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs.
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 (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties. العربية ∙ Deutsch ∙ English ∙ español ∙ français ∙ galego ∙ italiano ∙ 日本語 ∙ 한국어 ∙ македонски ∙ português ∙ português do Brasil ∙ русский ∙ sicilianu ∙ slovenščina ∙ українська ∙ 简体中文 ∙ 繁體中文 ∙ +/− |
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