NEW YORK — Bob Reichblum, CNBC’s head of current primetime programming, has ankled the financial news cabler, sources said Friday.Reichblum will become CEO of a Chicago-based convergent broadband service, said a source. “It’s a great opportunity for Bob. We wish him well,” said a CNBC spokeswoman. Reichblum, who joined CNBC three years ago, was previously exec producer of ABC News’ “Good Morning America.” During his tenure at CNBC, the net expanded its flagship nightly newscast “Business Center,” which began taping live from the trading floor of the New York Stock Exchange in August. CNBC was down 29% in primetime ratings in cable homes from 1998 to 1999, according to Nielsen Media Research. Reichblum was unavailable for comment.