Dan there is more to it than just a capacitance value. Voltage plays a big role in this. If you look at this photo of Stan's, the first level is the polarization process. You want this process to take place with around 2 volts on the primary. If you tune to resonance at 2 volts and you see no gas being produced at all then you know there is something wrong. By leaving it at resonance at 2 volts, raise the voltage from 2 volts 4,6,8,10,12 somewhere in that voltage range you should see some gas being made. What ever that voltage is that you see the gas being made let's say 6 volts. That should tell you, the turn ratio is off on the secondary, because you want it to take place at 2 volts to the primary not 6 volts. This is where everything gets tricky to adjust. In order to keep the impedance match, what you have to do is take turns off the chokes and add them to the secondary to increase the voltage. By doing this you change the inductance which will change the resonate frequency. So it's a balancing act that your shooting for. Again if the polarization process takes place at 6 volts and it's suppose to start at 2 then you've lost 4 volts in the process that you can no longer do anything with.