Here’s how the Gray Tube works

The power supply charges BOTH the HV cap on the front side directly AND the cap behind the inductor by jumping from the HV Rod to Grids through inductor to cap. This charging through the inductor will not make the effect of the coil pulsing for mechanical work. When you close the switch at the LV side, the cap on the backside of the inductor discharges and smashes into the HV potential at the HV only place to ground is the LV diode placement as shown causes the cap behind inductor to