12850 is the serial number. You could call Lyon & Healy at their toll-free number and they could tell you when it was made and the model. Looks like an 85 series semi-grand. The 85s have come in several different sizes and some minor redesign since they first appeared; originally there was the concert grand (47 strings) and the semi-grand (46). Then appeared the petite (40 strings) and the grand petite (44).
In the photo it looks like you have a couple of plug in connections on the right side of the base. Your harp may be electric. Some close up pictures of the base, the soundboard and the kneeblock (that tight curve above the shortest strings where the neck joins the body) would be helpful.
By the way, put the pedals in the highest notch if possible when not in use. Takes pressure off the strings. A certified harp technician could tell you what repairs it needs to make it playable and/or salable, should you wish to sell it.