Here is the most easiest way to build high voltage power supply.Notice that is very dangerous to taste it. It can cause you dead. Let's see how to make the simple way. First you must buy the TV tuner substitute card from local electronic store. Second, get the positive voltage terminal from the fly back transformer and the negative voltage terminal from the Ground(GND). That's all. As in my case, by spark length, air discharge 1cm need 10000V, it take spark length 2cm. So it's about 20000 or 20KV. See the photos that I've tested.
TV Tuner Card
Here is my first attempt to High voltage. I used motor car ignition coil. The driver circuit is simple. It used 555 timer IC to produce pulse. Variable resistors could easily control the out put frequency. I used two separate battery to avoid the damage of this circuit and power transistor. 9V battery is to drive the circuit and 12V motorbike battery is for Ignition coil. This device is quite nice. I like it very much. It produce about 15kV by the spark length. I do not have any device to measure the high voltage.
This is circuit diagram