I have an Oscar Schmidt Festival diatonic autoharp. It is signed by the builder and is dated 2/2/83. I used to play this instrument when I purchased it in the 80's brand new. It has a most lovely sound, unlike other autoharps. I would like to start playing it again, but am trying to restring, and re-felt it first. I am looking for someone who is familiar with its use and how to use the key change levers...I don't really remember. Anyone familiar with this?