NEW YORK, July 7 (Reuters) - Calpine Corp. (CPN.N: Quote, Profile, Research) on Thursday said its subsidiary Calpine Construction Finance Co. launched a tender offer for some of its 9.75 percent second priority senior secured floating rate notes due 2011. Calpine said it was offering to buy the notes at par plus accrued interest through the purchase date, using expected net proceeds of about $225 million from the prospective sale of the Ontelaunee Energy Center. However, Calpine said it can only buy the notes after offering to repay debt under its term loans, which currently have $379.2 million outstanding. If...