There were a few old blues guys who used 9-string guitars in the 1930s---maybe Lonnie Johnson.

I followed Big Joe around Chicago for a few years when he was recording for Bob Koester's Delmar Records (later Delmark). Big Joe took a 3-tuner metal strip of tuners (like you would find on one side of the tuning stock on a cheap six string guitar) and stuck it on the end of his tuning stock wood. (Hope that makes sense.) One of the 3 extra tuners didn't fit on the wood so it just hung out there in space. Somehow, it still worked for him though.

The 9-string guitar I made when my hands started getting numb was accomplished by putting 3 straight-through-the-wood banjo tuners down the middle of the head stock of my Martin D-76 guitar. I doubled up on the trble strings---like a mandolin. As was said here already, the 3 bass strings were single. To my ear that made for more clarity than a 12-string guitar could achieve. (12-strings always sounded muddy to my ear.) I wanted to really "hear" the picking clearly---at least as clearly as I could achieve. I thought the fuller sound when strumming I would get might make up for some of the problems I was having picking from the MS. Then I had to go back to 6 strings anyhow as my abilities deterriorated further.

You would play a 9-string guitar the same way a 6-string guitar would be played. It's just that 3 of them were doubled. The paired strings (2 at a time) are played as if they were one string.

Alvarez-Yairi guitar company made a commercially available 9-string guitar for some years not too long ago---but come to think of it, that was 20 years ago.

Art Thieme