Radio station group Chancellor Broadcasting Co. increased its loss 26% in the first quarter to $15.4 million, it said Tuesday in New York, on 118% higher revenue of $55.8 million. Chancellor announced in February plans to merge with Evergreen Media Corp.Polygram Holdings promoted Helen Murphy to chief financial officer from her previous position as senior VP of mergers and acquisitions, it said Tuesday. Murphy will report to Polygram Music Group CEO Roger Ames. Silicon Graphics, whose computers created the special effects in such movies as “Jurassic Park” and “Twister,” announced the departure of two key execs. Chief financial officer Stanley Meresman and senior VP Michael Ramsay departed “to pursue outside opportunities,” the firm said.