The string calculator referenced suggested a string diameter of .005".

27.5

I have to admit that I was getting dizzy trying to make sense of all those tunings.    I don't think we can fully answer your question without knowing the VSL of your dulcimer.  You might consult the Strothers String Gauge Calculator to determine the ideal string gauges.  

A string should be able to tune one whole note up or down, so I would suggest establishing the ideal string gauge for G#3 for the bass, D4 for the middle, and C#4 for the melody.  With gauges established for each of those, you should be able to tune to the other tunings.  With one exception.  That c5 may indeed need a different string.  I don't believe a string can be adjusted for a whole octave.

And it's always a good idea to have extra strings on hand and to wear protective goggles when you retune .

--
Dusty T., Northern California
Site Moderator

As a musician, you have to keep one foot back in the past and one foot forward into the future.
-- Dizzy Gillespie
updated by @dusty: 03/16/26 04:01:01PM

I recently picked up a copy of Lorraine Lee Hammond's Barley Break: An Elizabethan Songbook with Arrangements for Appalachian Dulcimer.

In this book (and The Magic Dulcimer) she uses four different tunings. I will list them in order from bass to treble using the scientific notation (as in D4 A3 d3):

Tuning I

G3

D4

d4

Tuning II

G3

D4

c4

Tuning III

A3

D4

c5

Tuning IIII

A3

D4

c4

The question: In order to not repeat the first mistake I made, tuning up from D3A3d4 to  D3A3a4 (instead of tuning correctly to D3A3a3) and breaking the thinnest string, what would be the best way to actually tune these? It doesn't have to be in a specific key- they would be tuned to each other. 

The bass strings in all tunings go down, so not an issue.

The middle strings all go up from A3 to D4, which is only 3 notes.

The treble strings stay the same or go down except for Tuning III, where it goes up to C5, which is a 6-note increase.

Can the middle strings handles going up 3 notes?

Tuning III scares me...