PK German presents Richie Havens in concert Friday at 8 p.m. at University Hall. With the release of his first album in 1966, "Mixed Bag," and his second album, "Something Else Again," Mr. Havens has become a significant contemporary singer, taking his themes from a variety of experiences but always with a hopeful outlook. Tickets are on sale at Mincer's and Newcomb Hall. They cost $3 in advance for students and $3.50 at the door and for non-students.