tuning my guitar into a three string dulcimer
General mountain dulcimer or music discussions
As I think was mentioned before you started this thread, you will not have a doubled melody string unless you want to rework the nut and bridge on your guitar. If you choose to do a three string configuration, take off the 4th, 5th, and 6th strings. You will need to restring your 1st, 2nd, and 3rd strings. The bass D string (in either DAA or DAd) should be a wound 0.022 or 0.023. The middle string would be a plain steel 0.014. If tuning to DAA, the middle and first string (melody) are the same gauge. The first (melody) string for DAd tuning is a plain steel could be 0.011 or 0.012. You may need to modify the slots in the guitar nut to fit the these string sizes. Another possibility would be to buy and inexpensive guitar nut, slot it yourself, and run your strings down the center of the fretboard. Also, you will not be playing a traditional diatonic dulcimer by doing the this. The guitar fretboard is fretted for chromatic playing.
You did not say what style of dulcimer playing you want to do, but if you are going to play a traditional diatonic dulcimer, trying to learn on the chromatic fretboard may cause you fits when moving to the diatonic fretboard.
Best wishes for your project. Let us know if you have more questions.
"The dulcimer sings a sweet song."