“This is probably the most fun I’ve had in show business,” a sweat-soaked O’Brien told a crowd of about 300 before launching into a fiery finale of Eddie Cochran’s “Twenty Flight Rock” with White.

O’Brien has been riding a bus around the country with his band on “The Legally Prohibited From Being Funny On Television Tour,” a music- and comedy-filled variety show, while waiting for his new hosting gig at TBS to start. He left “The Tonight Show” earlier this year after NBC reinstalled former host Jay Leno.

O’Brien ripped through a rockin’ set with his ace band behind him and The Cocettes singing backup. White, the leader of The White Stripes, The Raconteurs and The Dead Weather, introduced O’Brien as “a rockabilly legend in the making.” White’s Third Man Records has a concert space as well as reel-to-reel recording equipment.

O’Brien wore all black, his unemployment beard and a light blue Fender electric guitar. He was comfortable and confident, using the kind of salty language you can’t get away with on TV as he joked about himself, White and members of his band.

He told the audience that in six months he’s gone from hosting “the greatest franchise in television history” to touring the country in a bus to making a vinyl record.

“I’m going back in time,” he joked. “Next week I’ll be playing Vaudeville and then I’m going to be a steamboat captain.”