There is no need to use a step down transformer with Atari machines, you can set-it for 240V by exchanging (if included, not very likely on a US machine) the "loops" plug on the power brick. Else, you can simply rewire the loops on the connector but make sure to MARK it clearly for which voltage it is, because the color of the wires normally indicates for what voltage the plug is. See the manual...
I've worked on a Gravitar that was originally imported from the US to the UK (so also 230V) and now to Holland.
@Wolfeel, 230 (240) is for normal stuff, 360V (or three-phase 230V) is what we use for serious stuff....
Our higher voltage is more energy efficient.The higher the voltage, the lower the current, the less loss in the power lines....but hey....nobody's gonna switch now anymore
Besides, "all" modern stuff can accept anything between 100 and 250V today...
By the way, I envy you for getting a Gravitar.....what a brilliant game it is....I think I made the most time on Gravitar during my last Funspot visits