Built one when I was in high school. Power was a neon-sign Xformer, the main coil was 5 ft tall. This unit could generate close to 1M volts according to the article in Popular Electronics (where I got the plans). All I know is it generated sparks almost a foot long.
One needs to be VERY careful with that much electricity. Yes, the amps are so low it is not that dangerous... however: Just one minor wrong issue... and that ZAP will go across your heart and it will stop ticking (death).
There are lots of videos about Nicola Tesla at U-tube... some are quite interesting!
Your comfort, Your way, Everyday!