Here is a complete protocol of how to make a cheap and simple high voltage diode capable of handling voltages up to 50 kV. In pulse mode it should stand 30 A peak, because it is based on the 1N4007 diode. These small diodes can be bought very cheaply and I have tested them in pretty hard high voltage discharges.
Because of the simple construction with no balancing resistors or capacitors it is vital that all the diodes have identical specifications. The diodes should be of the same batch and not a collection of random diodes from e-bay. If one diode gets more than its share of voltage it might fail short circuit and increase the voltage over the remaining diodes, this will likely cause all diodes to rapidly fail short circuit.
This means that this design is a compromise between reliability and complexity, with well-matched diodes of modern design it should still be a very useful project.
The required tools and supplies.
Solder the diodes together. Try to make each joint as a "pearl" to avoid corona
70 diodes soldered together. A lot of work but with experience you can make it in 30 minutes. Therotically it should be able to handle 70 kV. It has been tested with 50 kV AC.
Use a small piece of a silicon tube which has little bit smaller diameter then the final PVC
tube which will be filled by the sunflower-seed oil. The silicon as material is very important in this case.
Fill the tube with hot-glue and let it cool down.
Remove the silicon tube from the filling (silicon will never adhere to the hot glue, that’s why it should come off quite easily).
Cut a piece of clear PVC tube (available from aquarium suppliers) 8-10 cm longer than the string of diodes.
Place the string of diodes carefully inside the PVC tube. Use cooking oil as a lubricant to make this process easier.
Put the string of diodes completely inside the PVC tube.
Suck the vegetable oil through the PVC tube so it is completely filled (in case of using mineral oil be extremely careful – it can be toxic).
Double the PVC tube over and use a rubber band to block back leakage of the oil.
Use the rubber band to squeeze the PVC tube around the filling made by the hot-glue before. This will hermetically seal the oil inside the tube. Repeat at the other end.
Use more of the hot-glue. This will fix the rubber band in place and also improve the squeezing by heating up the filling.
Final product is string of diodes inside an oil bath. It can be carefully coiled (not more then three turns) to make it more compact.
Testing the diodes by connecting it as a two stage CW
multiplier powered by the 50 kV ignition coil