I've just fired up my latest coil, with a 1" x 5" secondary (only about 1/4 the size of my last couple). Interesting thing is that it produces sparks that are fractionally longer, for the same power input! By the way it uses a flyback circuit to give about 10kV for the primary with a 4gap RQSG, scaled down, and a primary capacitor made from fibreglass pcb. Steve