That observation leads us to a third important point:Making the primary resonant at the same frequency as the secondary is important for efficient generation of the one spectral component that matters.

Let’s take a look at these one at a time.First, a Tesla coil’s primary needs to be driven by a signal with spectral components at the same frequency as the resonance of the secondary. Since it sounds as if you are not using any tuning capacitors in the primary circuit of the Tesla coil, you’re relying on adjusting the spark gap spacing to hit the resonant frequency of your fixed secondary. A bit of light oil is floated on top of the water to eliminate evaporation, and insulate the conductive water from the varying amount of water vapor in the air, which affects overall capacitance.I’ll talk more about my designs, if anyone asks for it; do not hesitate to do so! jocularEdit: (red) There is essentially no resonant circuit in the primary, as no significant capacity exists in it, only inter-electrode capacitance of the transformer used as a voltage source. » Read more