Prince’s album “Purple Rain” turned 40 on Tuesday. The man behind the beat of the album, record producer and musician Bobby Rivkin “Bobby Z” joined Minnesota Now. Rivkin played in Prince’s band, The Revolution, from 1978 to 1976. After Prince’s death in 2016, he and other members of the band reunited and kept performing.The band played two anniversary shows on Friday and Saturday to commemorate Purple Rain. Some fans who took part in the weekend’s celebrations got a preview of an upcoming musical based on Purple Rain, the film, where Rivkin is serving as a musical advisor for the project.