Elvin Bishop wasn’t fooling around when he fell in love with the blues. Growing up in Tulsa on his family’s farm, the blues came to him in the night on radio stations from such far-flung locales as Nashville, Mexico, and Coffeeville, KS. “Out on the prairie, in those days, the local stations would shut down at midnight, and then you could pick up the 50,000-watt stations,” Bishop told Ravinia in a phone interview in anticipation of his festival debut with virtuoso harp player Charlie Musselwhite.