I recently got a 15 chord Oscar Schmidt autoharp model number OS-15BB.The inside label says serial number 880086, 1879-1979. Outside it has a little gold sticker saying made in Korea. What year do you think this was made and what part was made in Korea? Also, if I tighten the black bar screws over the lower sounding strings it does deaden/block the last two strings from ringing. Should I leave the screws (the ones holding the chord bars in)a little untightened? It plays well this way but it is loose!! Thanks