Six-string Banjos
The 6-string banjo (note, these still have the short thumb string with re-entrant tuning) began as a British innovation by William Temlet, one of England's earliest banjo makers. He opened a shop in London in 1846, and sold banjos with closed backs and up to 7 strings. He marketed these as "zither" Banjos from his 1869 patent. American Alfred Davis Cammeyer (1862–1949), a young violinist-turned banjo concert player, devised the 5/6-string Zither banjo around 1880. It had a wood resonator and metal "wire" strings (the 1st and 2nd melody strings and 5th "thumb" string. The 3rd melody string was gut and the 4th was silk covered) as well as frets and guitar-style tuning machines.
A Zither banjo usually has a closed back and sides with the drum body (usually metal) and skin tensioning system suspended inside the wooden rim/back, the neck and string tailpiece was mounted on the wooden outer rim, the short string usually led through a tube in the neck so that the tuning peg could be mounted on the peg head. They were often made by builders who used guitar tuners that came in banks of three and so if 5 stringed had a redundant tuner. The banjos could also be somewhat easily converted over to a six string banjo. British opera diva Adelina Patti advised Cammeyer that the zither-banjo might be popular with English audiences (which was certainly true, as it was invented there), and Cammeyer went to London in 1888. Due to his virtuoso playing he helped show that banjos could be used for more sophisticated music than was normally played by blackface minstrels, he was soon performing for London society, where he met Sir Arthur Sullivan, who recommended that Cammeyer progress from writing banjo arrangements of music to composing his own music. (Interesting to note that, supposedly unbeknownst to Cammeyer, William Temlett had patented a 7-string closed back banjo in 1869, and was already marketing it as a "zither-banjo.")
In the late 1890s Banjo maker F.C Wilkes developed a 6-string version of the banjo with the 6th string "tunnelled" through the neck. It is arguable that Arthur O. Windsor had much influence in creating and perfecting the Zither banjo and creating the open-back banjo along with other modifications to the banjo type instruments, such as the non-solid attached resonator that banjos' today have (Gibson lays claim to this modification on the American Continent). Windsor claims to be the first in creating the hollow neck banjo with a truss rod, and he buried the 5th string in the neck after the 5th fret so to put the tuning peg on the peg-head rather than in the neck. Gibson lays claim to perfecting the banjo with the tone rings.
The six-string or banjitar was the instrument of the early jazz great Johnny St. Cyr, as well as of jazzmen Django Reinhardt, Danny Barker, Papa Charlie Jackson and Clancy Hayes, as well as the blues and gospel singer The Reverend Gary Davis. Nowadays, it sometimes appears under such names as guitanjo, guitjo, ganjo, banjitar, or bantar. Today, musicians as diverse as Keith Urban, Rod Stewart, Taj Mahal, Joe Satriani, David Hidalgo and Doc Watson play the 6-String guitar banjo.
Rhythm guitarist Dave Day of 1960's proto-punks The Monks replaced his guitar with a six-string, gut-strung guitar banjo on which he played guitar chords. This instrument sounds much more metallic, scratchy and wiry than a standard electric guitar, due to its amplification via a small microphone stuck inside the banjo's body.
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