Dick Clark Prods. will produce ABC’s fall preview special, “How I Spent My Summer Vacation,”featuring stars of new ABC series.The show will air at 8 p.m. Sept. 8 and 9:45-11 p.m. Sept. 12, following the preem of “Lois & Clark: The New Adventures of Superman” (Daily Variety, Aug. 12). Next July 16, Jose Carreras, Placido Domingo and Luciano Pavarotti will perform at Dodger Stadium. Ticket range for “Encore — The Three Tenors” is $ 15 to $ 1,000. Information: (800) 552-6168, (213) 224-1448 The Hollywood Radio and Television Society will co-host a daylong seminar Sept. 14 around its annual fall preview luncheon featuring the heads of the four network entertainment divisions.