Old 6 string dulcimer
Instruments- discuss specific features, luthiers, instrument problems & questions
That seems unusual for a dulcimer. Usually if a dulcimer has six strings, they are arranged in 3 pairs on the fretboard. Each string pair (or "course") have a distance of about 1/8" between them, so they can be played as one string.
Tuning is generally in the DAA or CGG range (Ionian or Major mode) if it's a conventional length dulcimer. Each pair is tuned alike. Do you have any photos of it?