For a Jacob's ladder you will need a high voltage supply that is capable of at least 5000V. This is normally a neon sign transformer or an oil burner transformer. If you don't have either of these you can build a very easy inverter type high voltage power supply. This can be the flyback driver that uses the 555 or the flyback driver that uses the two 2N3055s. You will also need two solid metal rods or metal strips that are strong enough stand up themselves. This can be two pieces of coat hanger or two metal strips bought from a hardware store. Don't use aluminum strips, use copper or steel. Aluminum is will melt if it is left to run for a long time. If you use coat hangers be sure to strip of any paint and to straigten them out well. Next you will need some sort of insulating base to mount the rods or strips to. You should also remember that arc length isn't dependent on voltage, it is dependent on power. A couple of microwave oven transformers will produce a very long and large flame even though it is only at around 4kV as where a flyback will produce a short arc even though it may have a potential of 20kV. Voltage will determine at what distance the arc will start at. At 4kV an arc will start at about 4-5mm as where with 20kV an arc will start around 20mm. With your design there should be some room to adjust the rods a bit so you can set the breakdown distance. So, mount the rods to your insulating base which should preferably be plastic or ceramic and should always be non-burnable. Make sure the gap at the bottom is adjustable. If you are using a 10kV power supply the distance should be about 3/16". As with any Jacob's ladder the rods should not be perfectly vertical, rather they should be bent into a vee shape. The arc will break out at the shortest spot (the bottom) and since ionized air is very hot it will rise until the rods become too far apart and will extinguish and start over again. I will have a picture of a few different types of Jacob's ladders soon. One will be a picture of one that uses a microwave transformer and another will be of one that uses a flyback. I have also used the single ignition coil circuit with good results, so a picture of this will soon be here. Pictures of running Jacob's ladders can be found in the pictures section.