In order to purchase the right variable transformer, it is critical that you know the amp usage by your electronic device. It is always best to be conservative otherwise you risk destroying the variac and it can be very dangerous. For example, if your device requires 5 amp, buy the variac with up to 10 amp. A rating of 500VA means that at 100volt, the unit can sustain at maximum 5amp.
Using it for Guitar Amp ("Brown-Sound") and for controlling a transformer for Lichtenberg wood burning