What is a Marx generator – essentially, a device that lets you charge a set of capacitors in parallel (say, to 24 kV), and then discharge they in series, say, at 240 kV, if you have 10 capacitors. There is much more theory to it, all has been very well described elsewhere since the times of Mr. Marx, who first deviced such circuits, arguably, in 1923. If you need more explanation – please ask, I will be glad to explain it to you.
To build a nice Marx generator, you need a few parts:
(1) High voltage resistors – don’t assume this is the easy part – the resistors need to be able to withstand quite some voltage, several kV, and high discharge energy-changes in potential. Carbon composite resistors are best for such applications, but rate to find nowadays. You can get away with series connection of some high-value metal oxide layer transistors. I used some Vitrohm 1 M (Megaohm), 7.5 kV rated resistors obtained as NOS (now-old-stock; series 176 – could not find any data, but seem reasonably robust), some current/more widely available types that may be suitable: Vishay 0207 High Pulse Load Resistors (2 in series), or similar, successfully used for similar projects of more serious nature.
(2) Capacitors – also these must be not only be designed for high voltage, but also pulse rated. Best are especially made pulse discharge capacitors – but these often are oil-filled, rare, and too big for the given purpose. Best alternatives are PP type film capacitors, like the Wima FKP-1 or FKP-4. I used Vishay MKP1841, 0.1 µF 1.6 kV capacitors, metallized PP. The spec to look for is the maximal pulse rise time – the 1841s are not too bad, at least, good enough for this project, and a large bag could be sourced at low cost.
(3) Spark gaps – these need to trigger precisely, otherwise, the apparatus won’t work at full performance, or constantly misfire. Best use polished stainless steel spheres, about 15-20 mm diameter, readly available, already threaded, and easy to attach to the stages.
(4) Some hardware – isolating stand-offs, and some isolating sheet material for the stags – I used some FR4 glass fibre-epoxy boards (leftovers from failed printed circuits, with the copper fully stripped).
(5) A high voltage supply and a feed resistor (about 3-10 M, capable to withstanding at least 50 kV). A series of resistors, item 1, mounted along a plastic rod (Plexiglass, or the like) will do. For the supply, this needs to provide about 20-25 kV (make sure it doesn’t provide more, otherwise the capacitors will suffer!), about 0.5 mA. A fly-back transformer based supply. I’m use a regulated supply (TL494 switchmode regulator, flyback transformer), so the stage charge voltage can be adjusted precisely, and no risk to damage anything.
(6) A good ground connection (earth conductor). Never use plain mains ground, if you don’t want to damage your home electronics! Anything will do, like a water pipe (if fully metallic down to the inlet), or a heating pipe).
(7) Plenty of ground wires around that you can use to safely discharge the apparatus and to keep it shorted to ground if not in use. RISK OF ELECTRIC SHOCK! ALWAYS SHORT THIS APPARATUS WHEN NOT IN USE!
