Simple cascade
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A 25-stage cascade on PCB.
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A very simple and comparatively harmless method to generate moderately high voltages (say, 10kV) is a, say, 20-stage cascade with 100-200V AC input. This method only requires components that should be available in any electronics store. Suitable are e.g. diodes 1N4007 (1000V, 1A, very common) and caps with at least 630V rated DC voltage (e.g. WIMA MKS-4 630) and capacitance as high as affordable (e.g. 47nF). Cheap caps tend to fail in this application, so buy some more than needed. The cascade can be soldered together freely or on a PCB, see exmple layout below. For safety (yours as well as the caps) you should put some resistors in the Megohm range in series at the output to limit output current and damp any unwanted oscillations, which could occur when discharging the caps rapidly.
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Example PCB layout for the cascade. Extend to the number of stages you need. The light grey symbols only indicate the position of diodes and caps, the do not belong the PCB of course.
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The input can be connected directly to the mains (in fact, this is done in some electrostatic dust filters and negative ion sources). To avoid messing with mains voltage, take a AC mains adaptor with, say, 12V output and connect another mains transformer "back to back" as in the circuit diagram below.
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To make this a safer method than mains directly, the second transformer must be a very low power unit (e.g. 5VA)! Alternatively, use an input voltage below 50V which should be safe under reasonable cirumstances.
In any case, the double transformer arrangement does not act as an isolations transformer, as the input of the cascade must always be grounded. Grounding, in turn, is necessary, as otherwise the transformers may be damaged when you discharge the cascade output to ground.
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A way of producing 170V while avoiding direct mains voltage. Note warnings above!
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The output current of the cascade is relatively low, especially if you use many stages to compensate for a (safe) low input voltage. This can be avoided by using a higher frequency than mains frequency. For example use a function generator and audio amplifier instead of the AC adaptor. Even better results should be possible by using a special 100V audio transformer together with the amplifier.
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Remember that although the average output current of the cascade is low for any reasonable capacitor value, the energy stored in them might still be dangerous. Also, of course, if you´re very ambitious and use e.g. 10uF caps, the current might no longer be harmless!
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