The Russian guitar is an acoustic seven-string guitar that was developed in Russia toward the end of the 18th century: it shares most of its organological features with the Spanish guitar, although so
A seven-string Russian guitar
The Russian Guitar by Ivan Krasnoshchekov
"Sister" (Deutsche Guitarre) by Johann Wilhelm Bindernagel, circa 1800
"The Guitar Player" by V.A. Tropinin (1823)
The seven-string guitar adds one additional string to the more common six-string guitar, commonly used to extend the bass range or also to extend the treble range.
A Brazilian seven-string guitar
Seven-string electric guitar Ibanez RG7321