John's given you a good start.  You can also plug the VSL into the Strothers String Gauge Calculator along with the desired open note to determine reasonable gauges.   Tom & Missy Strothers | String Choice

One reason that that instrument might not be so great sounding is that the square area the soundholes seems a bit less than would be common, and there are no holes in the upper bout

I have not heard of Mr Johnson, but I would go by the VSL (distance between the inside of nut and inside of bridge) to make a determination, at least to start out, anyway.  My dulcimers usually have long VSLs (27"- 28"), and I use .012" plain steel for the first and second strings, and .022" wound for the drone.  Nice looking dulcimer.

Hi there!  Have any of you had a Geoffrey R. Johnson dulcimer?  If so, what string gauges did you use?  The one I recently acquired is oak and spruce, gold plated tuners, extended "foot" that I know is common in his instruments.  Not a particularly great sounding dulcimer, but well crafted and pretty good looking!

updated by @jerry-posner: 04/07/24 11:43:13AM