It blew up in my face
I went through a very nerdy phase as a teenager, and instead of chasing women I spent a couple of summer holidays building pirate radio transmitters. (It was about 1990 and I wanted to be Christian Slater in Pump Up The Volume.) Anyway I was testing a new contraption, hunched over the circuit board while the thing was on air at full power, fine tuning it. In electronics there are these components called electrolytic capacitors, which you have to have the correct way round in a circuit (a bit like the way a battery is polarised, with positive and negative terminals) - and I must have put one in the wrong way round. This is a Very Bad Thing. Without warning, one of these things violently exploded right in my face. Luckily I was wearing stylish NHS glasses so my eyeballs remained intact. The room was full of noxious fumes and glittering dust particles though. (And god knows what nasty chemicals are inside those things - my lifespan's probably been shortened by a few years.) But the transmitter even stayed on air. I have a healthy respect for those little evil things now. Good job I'm short sighted too, otherwise my eyeballs would have little bits of molten metal and plastic embedded in them.
(Euan_Kerr, Mon 12 Nov 2012, 12:10, 1 reply)

check, same here
Used to salvage anything electronic i saw in a skip for components. Had loads of big, blued-copper-cased electrolytics out of old valve radios. Never noticed that the larger the capacity the lower the voltage tolerance printed on the cans. Then built a voltage doubler to take 12vAC from a transformer up to 24v DC, with a pair of 6v rated caps. Bang. Permanent damage to lounge carpet. I was also lucky not to be in the debris cone...
(Carpe Cyprinidae, Mon 12 Nov 2012, 23:25, closed)