The Seven string guitar reference article from the English Wikipedia on 24-Apr-2004
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Seven string guitar

A guitar (classical, acoustic or electric) with seven strings instead of six.

The Russian Guitar

The classical and acoustic seven string guitars originated in 19th century Russia. Its invention is attributed to Andreas Sichra who also wrote the method for the guitar and seventy-five compositions. It has been then proclaimed to be a Russian guitar and has been primarily played in Russia and later the Soviet Union. While it did not replace the regular six string guitar in Russia, many of the more "patriotic" musicians such as Simeon Aksenov and Yuri Vizbor chose to play it as it is a part of Russian herritage.

The Electric Guitar

The electric version of the seven string guitar was introduced in the late 1930s by George Van Eps. The guitar was basically a regular electric guitar with an additional bass string. This feature allows playing bass, chords and solos simultaneously. Van Eps referred to this style of playing as "lap piano". While still considered a rare novelty, seven string electric guitars are occasionally used by popular rock and metal bands.