WNET has promoted David Horn from series producer to e.p. of Great Performances, the station announced today as the PBS Showcase Conference wrapped up in California. Horn has led four Primetime Emmy-winning productions and won two ASCAP Deems Taylor Awards for music programming. He came to Thirteen as a production assistant in 1979 and later created In the Spotlight and was e.p. of Sessions at West 54th, both pop music series.