You've seen Jacob's Ladders in Frankenstein movies: you know, the gizmo with the two antenna things sticking up, and a bright arc of electricity rising between them, and making that wicked crackly sound. Nothing says "Mad Scientist" like this thing... and although it can be dangerous if you're not careful, it's actually not that hard to build. At its heart, it's really just a big ol' neon sign transformer (about the size and weight of a car battery), and a couple of thick wires... the rest is just safety stuff; housing, a switch, and insulators to make sure the spark only happens between the wires, and never travels through someone's body.
Yes, safety is incredibly important
with one of these things... it's a lot of voltage, and could actually be fatal if you let it pass through you. So DON'T let it pass through you! I'll be mentioning safety precautions as we go, but the biggest one is this: BE CAREFUL. Never touch any part of the device while it's running, and double-check, triple-check, quadruple-check that it's unplugged before you approach it. Just because it's not sparking doesn't mean it's safe!
Other than the basic transformer, wires, and some safety stuff, it's all just window dressing... You can put a lot of knobs, dials, pipes and such all over it -- I also added a little plasma lightbulb
which radiates pink lightning from its filament to its glass bulb (I saw a cool prop where someone had done that, and decided to borrow the idea).
Much of what I did on this prop was unique to my particular set of parts; as you look around for your own pieces, you'll probably need to adjust a lot of things, and improvise. But that's a good thing; in fact, it accounts for about 90% of the fun!