Original poster: Pat Masterson <bat-at-grumman-dot-com> I was tuning my small coil (15/30 NST) and noticed little sparks dancing around the windings of my variac. Is there something fundamentally wrong with the setup, or do I need an RFI filter between the variac and the NST? The variac is an older model, and has no 3rd wire (ground) on its AC line. -pat