Steve Conner's PLL SSTC: the HEF4046 Tesla coil driver

Weekend two: “I had heard of many people trying to run a PLL and failing. So that made me all the more eager to try it.” He used a single HEF4046 (sixty pence) with its VCO always running, so the coil starts like an oscillator and tracks like antenna feedback, with a smooth changeover. The phase angle is adjustable, so the MOSFETs can switch exactly on the primary current zeros or a little before them, which plain antenna feedback cannot do. Once set, the phase holds as corona loading detunes the resonator. The page has three scope traces: early, in tune, late. He got arcs of 9 or 10 in at 190 V half-wave rectified, doubled by a toroid. Audio modulation came from varying a 50 V supply, with an arc pulled to ground to prove the sound comes from the discharge. At the Derby Teslathon in May 2004 it gave 12 to 14 in, until the secondary toppled and burned through. The parts went into the Dirty DRSSTC. Conner's PLL driver starts on this hand-drawn sheet. His 2005 DRSSTC driver grew from it, and Uzzors2k built from it in 2007.

Schematics and photos

schematic: DWSSTC II, the PLL driver, in his hand
scope: tuned for exact resonance
photo: 9 to 10 in on the PLL, 190 V half-wave
photo: the audio modulation demonstration, arc to ground
photo: with a toroid, twice the spark
photo: 240 V half-wave, toroid on
photo: an arc to ground on the PLL

Sources

This is the card from the driver tree, written from what the builder published. Send corrections through the forum.