I use a ballast from Ballastwise for my 70W mh nano light fixture. They are electronic, so they are silent and don't get too hot.
Here's a link....
http://www.ballastwise.com/item.asp?...FID=17&level=1
Hope that helps. One thing to note, they are not fantastic shippers across the border...I had to put all the paperwork together myself, pre-pay the shipping company and then they shipped it.