The Varidrive 600W is a good quality dimmable, digital ballast from Maxigrow.
It will power 250W, 400W or 600W lamps (be sure to match the correct lamp to the wattage) and includes a boost option to 660W - very beneficial during the flowering/fruiting stage to help increase yields. Soft-start technology extends the life of your lamps by offering protection from power surges and eliminating flicker.
1 year guarantee as standard.