Experiments with double resonance and a new output transformer

I got some large I Cores from ebay and these were the starting point for some new experiments with an output transformer. The cores are about one inch square by four inches long.

The idea is to resonate a series capacitor with the leakage induction at the resonant frequency of the coil.

The primary and secondary are placed on seperate legs to minimise inter winding capacitance which was a major source of trouble and to maximise the leakage inductance as this will be working to advantage in this situation. Note the high tech frame which clamps it all together.

The hope is that instead of the transformer creating all kinds of spurious ringing, it will now ring happily at just the right frequency to give output voltage rise, zero current switching and free jelly babies for all. 

I made a simple current probe  for these experiments. The line is fed through a very small toroidal core with 50 turns of 0.2mm wire.

The output is placed accross a 1 ohm resistor.  The voltage across the resistor is 1/50 of the current value.

The initial setup was with the output going directly to a soloniod primary. Clearly the current rises to a maximum at the switching point, this causes a lot of spurious ringing.

One fairly standard sstc set up.

Its my very first coil, 1500 turns of 0.4mm enamelled copper wire close wound around a 4" PVC pipe. Small toriod. Resonating at 230kHz according to the generator.

The primary is 11 turns, 3" high, 7inch diameter.

Feeding the numbers into a culculator suggests a 0.077 cap to resonate witth this.

The half bridge and driver electronics unfortunately it still plays God save the queen.

The lash up, the current probe is in place.

a bit of calculation suggested 0.077uf as a suitable resonance cap. It proved to be too much and I reduced the cap to 0.06uF.

The free jelly babies have not materialised. Yes the current can be made to zero switch and this corresponds to maximum current draw but still a lot of hash at switching. The other thing which was apparent was just how critical the tuning was - if I waved my arm it went from zero current to max current switching. (Same amount of hash though)
This shows the voltage across the primary - there is a five times voltage rise. But there is a lot of rubbish that just shouldn't be there.....