Amplifiers contain voltages high enough to Kill you even after the amp has been powered Off !!! If you don't have enough electronic experience to identify and discharge the Filter Capacitors which contain these Deadly voltages, take your amp to a Qualified tech. If you don't know a qualified tech in your area, post a request in the alt.guitar.amps newsgroup, the folks there will be happy to help you.
This is for all those guitarist-amp-tech-wanna-be's that would like to learn how to service or modify their own amps. If you've done any research at all, you'll know that unless you discharge the caps inside your amp prior to poking around, you're asking to get killed or at the very least painfully zapped! The following steps detail a couple methods of removing those potentially dangerous voltages.
1. The items you'll need are:
- 2 foot of 18 gauge wire
- 1 150-Ohm 10 watt resistor (round not rectangular)
- 1 alligator clip
- 1 Multimeter type probe
- 1 foot of heat shrink
2. Strip the wire on one end and attach the alligator clip (solder it on if you can). Then cover that soldered connection with heat shrink.
3. At the middle of your length of wire, cut and strip each end. Solder in the 150-Ohm 10 watt resistor. Then cover the resistor and the solder connections with another piece of your shrink wrap.
4. On the remaining end, slip on a piece of heat shink. Attach your multimeter probe (solder it on if you can). Then shrink the heat shrink over the connection.
Now You're Ready To Discharge Those Nasty Caps...
5. Unplug your amp.
6. Pull the chassis out, being VERY Careful not to touch anything inside yet.
7. Clip the alligator clip end of your discharging probe to the metal of the chassis, making sure it's good and tight.
8. Now go through the chassis with the probe end and touch the + side of every cap you see.
9. That's it !!!
The only thing this leaves out is how to tell what is a capacitor. If you don't know this, you should really reconsider whether or not you should be screwing around with your amp. But if you insist... The caps look like little cans usually of a solid color. They can also take on the appearance of a flat circular disk. They also are usually marked with + and - markings. When in doubt, use your probe to touch both sides of the component to ensure that it has been discharged.
There "is" one other method I hesitate to mention, but here goes... You can also discharge caps with what is known as the "BFSD" (Big F***** Screw Driver) method. What you do is get a large screwdriver, and while keeping the shaft in contact with the chassis, touch the tip to the + sides of all the caps.
If you choose this method, Wear Goggles and keep your face away from the caps! It's not unusual for blue sparks to fly along with molten bits of the tip of the screw driver! It works in a pinch, but you're better off constructing a probe because those bits of screwdriver tip can also end up in your amp...