Probably a neon sign transformer. The tube won't ionize until tens of thousands of KV but when it does light off, the resistance of the plasma drops to practic

Probably a neon sign transformer. The tube won't ionize until tens of thousands of KV but when it does light off, the resistance of the plasma drops to practically nothing compared to the excellent insulator it is when not ignited. Neon tubes are negative resistance devices, 25KV at zero current vs maybe 10 mA at 300 V after it ignites is a resistance of negative 30K or so. The point is a lot of EE work goes into the magnetic design of the transformer such that it current limits to some specified value. If you use a core material and shape that'll saturate at 10 mA but a ratio of number of turns such that it'll output 25 KV as long as the current is roughly zero, that would make a good neon sign transformer. Much like alcohol there is no minimum safe harmless amount of current thru the heart, but if you have what by neon transformer standards is a very low current transformer, like limited to 5 mA or so, that might be a low enough current to only kill like 0.0001% of the population or whatever. A kid will probably be fine. An old person with heart problems, maybe not so much.