Horror author Stephen King has converted his Bangor, Maine, radio station to a non-profit operation. King, a Bangor resident, bought WZON-AM five years ago and changed the format to top 40. The station continued losing money and he tried to sell it last year but couldn't find a buyer. Now that he's eliminated commercials, WZON will play old rock and blues, which King prefers, but it will no longer broadcast the Boston Celtics games, which disappoints many listeners.