A Rheostat is used here for convenience, and because I found these for $6 bucks apiece at Excess Solutions, in Downtown San Jose. The Rheostat had a waxy smell when it got hot, so I baked it in my toaster oven for a while, to out-gas that. The Rheostat could be replaced by a Variac (Variable Voltage Transformer), but this application demands high peak current capability. A rather large Variac would be helpful. Current reads ~12 Amps for 4 seconds, then it goes to zero for 11 seconds (27% duty cycle). Non sinusoidal peak current can exceed ~40 Amps, while pulsing full power. The Rheostat has a metallic wiper which appears more rugged than graphite brushes commonly found on Variacs. The rheostat could be replaced by a jumper: distance from the the scalp could be adjusted to vary applied field strength. Eventually Arduino-based phase control might adjust power level using the primary power Triac.