String gauges are totally dependent on the notes of the Open tuning -- DAA, DAd, CGG, CGc, EBB, EBe -- and the VSL of the instrument. 

A "normal" set of strings will tune DAA, DAd, DAC, DAG, on up to EBB, EBe, etc and maybe up to the key of F.  But The bass string will probably break if your try to tune to GDD, GDg etc.  To tune up to G you need another set of strings.  Those "normal" string will also tune down to key of C -- CGG, CGc etc.; and maybe to B.  But below that they will be too floppy and again you would need different strings.

There are people who play fretless dulcimers, or it could have been built to be bowed.

In her collection was one interesting old dulcimer, same builder.  Beautiful dark wood, possibly walnut, but NO frets! That one was already sold.

Thank you both Kens.  I know she will have no idea of string gauge but that can be figured out with a micrometer.  Still have Dad’s old antique...or let local music shop figure it out.  Good reminder about the peg dope etc. for cantankerous fiddles.  A little goes a long way. I would be surprised if this one has 6.5 fret but that is something I use frequently.  

What I have never understood is what gauge to use.  Is it dependent upon the tuning or?

Sorry I missed that you mentioned the 28" VSL. KenH's suggestion for strings is good. A 6.5 fret can be added if you don't have one and really want one.

Ken

"The dulcimer sings a sweet song."

Wooden tuning pegs may indicate that the instrument does not have a 6+ fret. Do you actually USE the 6+ fret (like every other time you sit down and play), or is it just there because everyone around you has it?  Yes it can be added, sometimes even at a festival; it's not usually very expensive (less than $50).

KenWL gave you a great list of things to look at and for and report back to us.  If it were me, I'd purchase a bottle of "peg dope", which may help with those tuners. 

Ask your friend to show you how to tune using those tuners; you don't just turn, but sorta turn-and-push.

With an "approximate 28" VSL, I would just go buy a set of dulcimer strings with gauges around .010, .012. .020. 

I guess I need to see whether it has the 6.5 fret.  Duh!  If not, is that something that can be added?  I think the price will be reasonable - likely around $100 or maybe less.

Hi Janis. Here a few things to look for: no separation of joints, a flat fret board, and length between the nut and bridge (VSL). Tuning pegs can be replaced if they don't work. My guess is that the ones on this dulcimer may need a little adjustment after 30 years. If those are the original strings on the dulcimer, they will need to be replaced. If your friend does not know the gauge of the strings a stringed instrument repair person should be able to use a micrometer to measure them for you. There may need to be an adjustment in the action (height of strings above the fret board if they are too high or low. The reason I mentioned VSL above is how far you need to stretch to make chords. If you do not play chord/melody style VSL is not a problem. Smaller hands work better with a shorter VSL.

Ken

"The dulcimer sings a sweet song."

A long-time friend has been downsizing her collection of mountain dulcimers - the usual, thought it would be good thing to play but never happened.  She has probably had it at least 30 years and is down to one and knows I have been contemplating purchase of a second MD.  I've not yet seen it, but would like to have 'gut reactions', or things to consider or watch for.  Check it out, 'run', look for something newer like McSpadden or  Folkcraft, etc.?  Thanks for any advice.

Wood: cherry. Pegs: 'old' style; she said they are not geared tuners.  Maker: a local builder, now deceased.  Name is likely marked inside. VSL: approximately 28". Strings: "look old".  Case: none, apparently been sitting out (who knows where) but has a case from another dulcimer that should fit.  The other dulcimer was sold but she kept the case and thinks it might fit.  I have my old Bill Taylor, usually playing in DAD or DAC.  Since we sometimes play in DAG or DAA, thought was that a second dulcimer would avoid having to retune during gigs.  Any advice appreciated.