This was an attempt to rectify high voltage, high frequency AC to DC. It didn’t really work.
“Continue reading” for further explanations and experiments.
A Tesla coil has an output of typically 200 kV AC at 100 kHz. To convert this to DC would allow charging of objects and capacitors. The problem is that vacuum tubes (valves) to do this are not readily available, nor are high voltage diodes that can handle the high frequency and voltage together.
It is known that ionic flow in air will be greatest from a positively charged point than from a negatively charged flat surface. To utilize this I have made a set-up using soda cans with the ring-pull twisted and cut to a point. This gives a point to concave surface from the underside of the previous can. Not only are cans convenient, but they are rounded and don’t have a lot of corona generating surfaces. To record DC charge, I used an electrometer which is an ancient device using foil leaflets which separate when charged (with DC only).

The photo above shows the set-up with two “diodes” in series and shows a spark between 2 of the cans. The left can is earthed and the right can is attached to the output of my mini TC which has an output of about 2 inch sparks at probably 500 kHz. The middle can has a wire supporting the electrometer leaflets which are not separating. Note that sparking will short circuit any diode effect so no DC is expected.

The top photo above shows the electrometer on the left ground terminal. No charge here as expected.
The second photo shows the electrometer on the right terminal from the TC. This is AC, so no deflection.
The last photo shows the electrometer on the centre terminal. This should be at a DC potential and indeed with the right combination of input voltages to avoid sparking, there is a DC indicated by the electrometer.

So is this attempt at rectifying a Tesla coil a success or failure? One problem with this set-up is that the TC frequency of my mini TC is so high (~ 500 kHz) that capacitance effects of the cans between each other and in free space may dominate and give spurious results and low output. It was not possible to use this DC to charge another sphere for example. Still the concept is simple, cheap and scalable to higher voltages and bigger TC’s with lower frequencies. The cans can be placed in series in large numbers so for a large TC it might just work.

Bear in mind that a TC giving a 6 foot spark would need perhaps 100 cans which would still be a significant capacitance and much larger than the toroid. Also a TC with a 6 foot spark of 300 kV peak when rectified would only be a 1 foot spark when rectified to DC 300 kV as there is no spark growth with DC (at these domestic scales).

Generally speaking it is simpler to use another method to generate high DC voltages like the van der Graaff generator or voltage multiplier.

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Photo Date: 2007