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ktone wrote: Use a light bulb. Put a 40-60 watt lamp in a pigtail socket.

That is my preferred way. I was going to add that to my post before having to run. I have a ceramic household light socket with alligator clips coming off it. You still get a little spark which is a good indicator something is discharging. Just make sure the light bulb isn't burnt out!
I don't recommend the screwdriver thing. Also, if you are using a high wattage resistor, be careful, they can get hot.

greg wrote:As far as discharging caps in general-
Turn off amp and let it sit for about 20 seconds or so. If there are bleeder resistors they will be draining the voltage away pretty quickly. If you measure a cap after a minute or so, and there is still voltage (more than 5% of charged), then there are may ways to go about it. A safe and slow way is clamping a suitable resistor across the terminals. You can use ohms law to find out the size of the resistor with a mind on the wattage it can take. Example: If you want to discharge a cap that has 200VDC on it and you only have 1/2 Watt resistors, the lowest value your resistor should be is 80kohm (really use higher than 100k). W=V*I and I=W/V so I=.5/200= .0025, then V=I*R, 200=.0025*R, R=200/.0025=80000

this is the wording that confuses me: "resistor across the terminals." i'm guessing that this means i should take one clip connected to the resistor and clip it to the negative terminal (or is it better to clip to the chassis??) and the other clip from the resistor and connect it to the positive terminal, but when you say "across the terminals"... i'm just not 100% sure i follow... and i want to make sure i do as the consequences seem pretty serious (to say the least... hehe).

also:

#1 - i know i can measure the stored charge of a capacitor with a multimeter. i'd like to open up an amplifier and first off check to see if the caps are holding a potentially lethal charge. i have a multimeter than can read up to 1000 volts DC and 600 volts AC. can i use it to measure a potentially lethal cap? if so, do i clip the negative probe of my multimeter to the chassis and then put the positive probe to the positive terminal of the cap (and of course, keep one hand in my pocket at all times)? or do i need to put the negative probe to the negative terminal and positive to positive (which makes more sense to me, but i don't want to accidentally kill myself)?

can anyone help me here? i think this would be useful as i'm not sure which amps have bleeder resistors and which amps don't. eventually i can probably figure it out, but i'll want to check the caps with my multimeter first before i start poking around trying to find them. oh... and maybe i should clarify: when i say potentially lethal cap, what i mean is a fully charged cap that would be found in an unplugged amplifier.

ptay wrote:This is a like a 10W-1k resistor, totally insulated with some alligator clips on the ends. Don't try to clip it to the capacitors, you'll slip and shock the shit out of yourself or die. Clip it to tool #2 always from the ground.

where do i put the other alligator clip? on the chassis?

sorry for being a little slow here guys. i just want to make sure i don't die

yes, the aligator clip goes to the positive of the first filter cap of the power supply to the chassis. but you should ALSO be aware that (depending on the amp) there can be another cap with potential charge left in it... any idea ???
THE NEGATIVE BIAS CAP !
make sure to discharge this one aswell !
goog luck

phildotidiot wrote:

greg wrote:As far as discharging caps in general-
Turn off amp and let it sit for about 20 seconds or so. If there are bleeder resistors they will be draining the voltage away pretty quickly. If you measure a cap after a minute or so, and there is still voltage (more than 5% of charged), then there are may ways to go about it. A safe and slow way is clamping a suitable resistor across the terminals. You can use ohms law to find out the size of the resistor with a mind on the wattage it can take. Example: If you want to discharge a cap that has 200VDC on it and you only have 1/2 Watt resistors, the lowest value your resistor should be is 80kohm (really use higher than 100k). W=V*I and I=W/V so I=.5/200= .0025, then V=I*R, 200=.0025*R, R=200/.0025=80000

this is the wording that confuses me: "resistor across the terminals." i'm guessing that this means i should take one clip connected to the resistor and clip it to the negative terminal

Yes. That is the only way to know for sure that a given cap will discharge. Sometimes the negative terminal/pole/leg is floating (not grounded).

(or is it better to clip to the chassis??) ...hehe).

If the chassis is a solid ground, which it should be, you can clamp to it and tag everything with the other end of your shorting device (resistor with alligator leads, lamp, etc.). If you are new at this, go slow and confirm with a DC volt meter that there is no voltage around before touching or soldering. Eventually you will learn how fast things discharge.

So, you connect both leads to the chassis? The positive and Negative?

just positive to the chassis, negative is already connected to ground (like greg says it should be ).
make sure you use well isolated aligator clips !

Don't get fooled by equipment with a negative supply. assume there may be floating voltages in anything you open ... meaning connecting stuff to ground may not close a circuit and therefore may not actually discharge anything.

while reading this thread I got confused, because or the #2 tool suggestion.. anyhow, Ok, one alligator with 10k 1w resistor.

I can try and connect it to the negative terminal and let it discharge, not to take any risks. no?

#2 is a big ugly Grand+Western after dark sized flathead screwdriver.

ptay wrote:#2 is a big ugly Grand+Western after dark sized flathead screwdriver.

yep.
So I connect the alligator to the screwdriver, then I shove the screwdriver under the cap, so it touches the terminal. the other end of the alligator is connected to the chassis. right?