This is the fourth episode of my Spark Gap Tesla Coil series. I show how to calculate and build the secondary coil and how to measure its resonant frequency. The first episode: https://www.youtube.com/watch?v=wSp1IzmRUk8 The next episode: https://www.youtube.com/watch?v=hfEde2j-8yY Please support this channel on Patreon: https://www.patreon.com/DiodeGoneWild