OffsetGuitars.com

hi all -

I have posted this in the "members from eu - how much for a recpap" thread
but didnt want to hijack orangs thread - its a new topic really anyway.....

whats the diddley with discharging caps?

i have read that you can turn the amp on standby
and pull the power lead and it will drain the charges

I have also read that you can just pull the power lead
while the amp is on and when the sound fades away
the caps have been discharged

is there any meter or anything that can be used
to test it is safe and how would you approach this?

i have bought a 25yr old 60w all tube amp
and a couple of the knobs are getting dodgy,

i would have to take time off and lump this heavy thing
into the nearest (congested) city for any minor repairs,
that i'm sure will occur,

I want to put this fear behind me and get in there

rgds

4

Don't depend on any method like turning the amp on and unplugging it.
You can take a 10k ohm/2watt resistor bent into a u-shape and tape it to a Popsicle stick, or solder the resistor to the middle of an insulated wire with gator clips on each end. If you have two cables with gator clips on each end then you can just clip the 10k Ohm resistor in between them. Then with one hand behind your back, either touch the resistor across the top of each cap, or clip the gator clip across each cap. If there is any charge in the cap you should see a spark, but maybe not. ONE HAND BEHIND THE BACK is so, if you do get shocked, the current goes through your hand, not through your heart.




Just so you know, you don't need to have the resistor, you can just use a wire or a screwdriver, but the resistor slows down the discharge so you won't damage anything. If you just touch a screw driver across the cap, the quick discharge can damage the rectifier or the cap.
DISCLAIMER: I AM NOT RESPONSIBLE IF YOU HURT YOURSELF!  I recommend buying a Multimeter with at least a 500v rating and checking all the caps by clipping the neg side to ground and (with one hand again) checking each cap for voltage before noodling inside of the amp.

as you may have read in OrangGoreng's thread, look here (click) for all the desired Information.

Greetings - the Fenderizer

good advice about building the resistor on the popcicle stick, but i wouldn't advice snapping them with a screwdriver etc.  that will damage the caps.  whenever i'm working on things if i do that accidently or something i always replace those caps.  i'd recomend a 1MEG resistor, at least two watts.  ceramic or sandblock 5w power resistor work very well.  and any multimeter set to dc voltage will show you if there's anything left in the cap.  never rely on uplugging or whatever to drain them.  some amps will discharge but others won't.  especially older ones, like old ampegs etc.  it all depends on the design.  you don't need to be afraid of electricity, just be smart about it, be informed, and be careful.  one hand behind the back is always a good rule if you are nervous.  good luck!