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In page Electric guitar:

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The feedback associated with amplified hollow-bodied electric guitars was understood long before Paul's "log" was created in 1940; Gage Brewer's Ro-Pat-In of 1932 had a top so heavily reinforced that it essentially functioned as a solid-body instrument.[1] In 1945, Richard D. Bourgerie made an electric guitar pickup and amplifier for professional guitar player George Barnes. Bourgerie worked through World War II at Howard Radio Company, making electronic equipment for the American military. Barnes showed the result to Les Paul, who then arranged for Bourgerie to have one made for him.