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why did i get shcoked?

post #1 of 7
Thread Starter 


I unplugged my tube amp today, took it apart, and touched one of the sockets by mistake. I was 'mildly' shocked. It was kind of a scary event. Anyway, how can this happen if the amp is unplugged? Do the components store electricity some how? How do i drain a circuit? Thanks
post #2 of 7
Yes, caps hold a charge for quite some time after power has been killed. You need to discharge the caps before messing with the circuit. Some of the larger caps can carry lethal voltages for a week or more!!

Never take electricity lightly and, when in doubt, drain and check with a meter. ALWAYS keep one hand behind your back so the charge doesn't go from hand to hand passing through the heart which can stop it!
post #3 of 7
The capacitors in the amp store charge and can give a good shock, especially in a tube amp. If you just leave it for a long time, the charge will eventually leak out, but depending on the quality of the caps and the way they are used, this could take awhile. The easiest way to drain them is to just hook up a resistor to the cap leads. What value resistor to use depends on the voltage stored in the caps and the amount of charge it can store. If you use too large a resistor, it'll take too long. If you use too small a resistor, it could discharge too quickly and burn up the resistor (if the caps are huge and the voltage is high, as it often is in a tube amp)
post #4 of 7
Just a note -- if you're going to discharge the non-DIY way (I.E., just leaving it off, no resistors or anything), you should leave it plugged in, yet off. In some circuits, disconnecting the power leaves the cap's no place into which to discharge.

This usually applies to CRT's, don't know if it's also true with tube amps.
post #5 of 7
Only if there's a drain to earth ground.
post #6 of 7
I read somewhere (on bottlehead's site I think?) that you can attach a 250kOhm resistor accross a capacitor permantely so you can have fast drainage all the time... not sure how it will affect everything else though.
post #7 of 7
Yeah, or LED (+resistor of course) would also do the trick...

For high voltage/high capacitance caps, i think there should always be a resistor there for safety....
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