A friend of mine built one with a Model T ignition coil and a 1 foot metal plate and some wire. He measured voltage on it, but very small. He said there was something about the Model T coil that was different from other coils. Don't remember what.
That guy was very eccentric. He had antique radiology (healing) equipment. He cured me of minor intestinal illness from 100 miles away in 10 minutes. Like a light switch.
Tesla wrote that it was possible to extract energy from the natural ethers. He said he did it but never wrote much about the details. He may have patented it, look for his patent.
I've read everything there is about Tesla, and designed and built a tiny working version of his bladeless turbine.