Chicago Symphony Player To Be Soloist WithNorthwest SymphonySoloist with Northwest Symphony orchestra December 5 at Maine township high school will be William Hector of the Chicago Symphony playing the Mendelssohn violin concerto.Mr. Hector made his first appearance with orchestra in 1935 in San Diego playing the Jules Conns concerto with the Seattle Symphony orchestra. This was a rare honor for a 17-year-old boy, for he was the only outside musician engaged to play solo during the 3-month stay of the orchestra.A series of recitals in the Los Angeles area and continued study with Gregor Ogranovitch, cousin of Pratigorsky, followed, after wrhich he returned east and studied with Max Bendix, concert-master of the Theodore Thomas orchestra. Hector appeared as concertmaster and soloist with the Illinois Symphony ensemble under Leo Kopp and in recitals in this area. He went to Indianapolis with the symphony, returning to Chicago and a post with its orchestra 12 years ago. Mr. Hector formerly lived on the northwest side of Chicago and now makes his home in Wilmette. (B4