I currently have a 3 lamp F32T8 ballast in the fixture with 2 of the wires being used for the F24T12, I just want something that is magnetic. Unfortunately for me however the channel won't fit a standard sized slimline ballast and will only take something as big as a standard F40T12 rapid start ballast. The 539 would fit I just do not know if it would run right with a 2 foot lamp.