A fourth way, and the cheapest, is not to make a ramp at all. The coil is gated in sync with the rising half-cycle of the rectified mains, so the envelope the arc sees is the mains waveform itself. There is no buck stage, no phase-shifted bridge and no modulator capacitor. A staccato interrupter reads the line and fires the bridge only while the voltage is climbing. The cost is that the shape and length of the ramp are fixed by the supply, not chosen. For that reason the serious long-arc records sit under the other three techniques. In return, an ordinary builder can finish a QCW this way.
Sources
This is the card from the driver tree, written from what the builder published. Send corrections through the forum.