First I want to say that the only reason to even do it would be for sentimental reasons. To just play the autoharp, the money is better spent on a different instrument, something newer generation. As an interesting project, it would be okay if you didn't expect too much and could still buy a better autoharp to seriously play.
I am not actually aware of step by step stringing instructions but recall good essential line drawings in the Autoharp Owner's Manual and in the front part of Bonnie Phipps' book for beginners. Others may offer knowledge of other sources.
Key points would be
1. Backing the tuning pins out where strings had broken, so they can take up a new string without sinking too deep.
2. Removing the chord bars, so they will be out of the way.
3. Not tuning to full tension until all the strings are on, then tuning in octaves. That spreads the tension gradually. Those old glue joints are pretty tender, so this is important.
The key to felting is having a template for placing felt on each bar. I provide that at
Chord pattern for chromatic 36 stringBe sure to print it to full scale, so the spacing is 1/4".
You can take note of evidence on the bottom of the bars where felt was formerly placed, but you really need to sand that perfectly flat, possibly removing the marks. Be creative.
Felt can be cut in chunks like the originals or felt can be run all the way across and then notched in V shaped cuts over the strings for the chord.
Felt is peel and stick, so all you have to do is clean and flatten the bar.
New felt will be unbleached white wool. The old black felt or green is not available to my knowledge. If someone was doing an authentic restoration just to put in a glass case, I would part with some black felt chunks I saved from old used autoharps.
To cut felt, I use a single edge razor blade held in a special handle, bought in a paint store for a couple bucks. You will like the work better if you use really sharp blades. Don't be stingy. You might use two or three.
Let the felt extend slightly beyond each end of a bar. Then you can use precise sliver cutting to fit the bar end to end, better that it not slop around. Each felt position then stays more aligned with the string and either its seating in the felt or the opening to vibrate freely as part of the chord. Whatever adhesive is exposed should be carefully cut away, leaving just the felt below. Then the adhesive won't cause the bar to stick.
That should get you well on your way, still able to post specific questions or even call as you go along.