If you use a dalight MH it works good for flowering from what I have read, but I have never heard of a 750 watt bulb, as far as I know they come in 70w, 100w, 175w, 250w, 400w, 600w, 1000w.

call 888-990-9933 (buylighting.com)if you are in the US, they claim to carry ballasts for all wattages of MH from 50 to 1500, their business hours are 8:00am-4:30pm US central time (gmt -6 hours)