These are Ford automobile ignition coils. I paid 5.00 UK Pounds ($8) for the pair at a used auto parts junkyard in Beck Row, England. They are available at US auto salvage yards for nearly nothing. Beside them is a 3uF/370V motor start capacitor which cost about $1 from a surplus dealer. I wired the capacitor, one spark coil primary, and an ordinary 600W dimmer switch all in series and plugged it in to 120VAC. I placed the dimmer and capacitor in the black (hot) mains line to the positive primary terminal. By adjusting the dimmer setting, I got a very hot continuous spark about 1/2" long between the center tower terminal and the negative primary terminal (white/neutral mains connection). The coil can run like this continuously without even getting warm. A power supply like this powered my first-ever tabletop coil when I was a kid, and it worked fine. Warning! Don't try this without the series capacitor, or the coil will quickly overheat and possibly burst!