The iron core transformer will be changed with an air core transformer and its ground will be connected to earth ground for it to be a tesla coil.The 1uf cap is attached to one end of an audio source and other end is to ground.The frequency of the circuit when pot is set to 10kohm is about 70khz and at 100ohm is about 1Mhz according to this website: www.daycounter.com/Calculators/NE555-Calculator.phtml
