Draining Filter Caps

HEAVENandHELL

Member
Messages
471
When intending to work on guitar amplifiers, we get all manner of warnings about draining filter caps. Problem is that no one spells out how to properly, and safely, accomplish draining the filter caps. So I'm asking if anyone here would like to share their method.

I would think draining filter caps would be as easy as connecting a resistor between the two leads of the cap and waiting, but there are specifics that a person would need before attempting such an act. What size resistor is necessary? What safety precautions or equipment should be used? Others?

Are there any other areas for concern in a guitar amp?

Thanks for any advice.
Gregg
 

zep41

Member
Messages
3,054
i'd like to hear people's responses too. All the methods I've heard and read are so unclear its silly.

I best one (but I'm afraid to try it cause it sounds too easy) is just to play your guitar thru the amp and then turn off the power (not standby) switch only and play the guitar for another couple minutes or so. They say that drains out any voltage that can hurt you. But it just sounds too simple that it cant be effective.
 

Ray Gianelli

Member
Messages
1,344
I have a 1 watt 51 ohm resistor with insulated alligator clips soldered to each lead. Works fine, no arcing, and I used bright red insulated clips so I don't space out and leave it in.
 

KeithC

Silver Supporting Member
Messages
5,340
The easiest I found was to get two insulated alligator clips and solder a piece of wire between them. I just used cloth covered wire like you see on pickups.
Clip one end to pin 1 on the first preamp tube and then clipped the other end on to the closest edge of the chassis and waited.
Since there is already resistance on the preamp tube there is no arc or sudden rush of current.

Of course the amp is unplugged but switched in the on position with the standby in the Play mode.
Then I leave it clipped on while working in the amp to make sure no current builds up.
 

blackba

Silver Supporting Member
Messages
12,282
The easiest I found was to get two insulated alligator clips and solder a piece of wire between them. I just used cloth covered wire like you see on pickups.
Clip one end to pin 1 on the first preamp tube and then clipped the other end on to the closest edge of the chassis and waited.
Since there is already resistance on the preamp tube there is no arc or sudden rush of current.

Of course the amp is unplugged but switched in the on position with the standby in the Play mode.
Then I leave it clipped on while working in the amp to make sure no current builds up.

+1 this is what I do, its shown in the Kendrick amp repair DVD FWIW
 
Messages
1,395
I made a simple jumper with a couple of alligator clips with the rubber covers. In between them, I run some 20 gauge wire. In the middle of the jumper is a 1meg resistor. Clip one of the clips to the edge of the chassis and proceed to drain the caps with the other end.

It should look like this from end to end: rubber covered alligator clip>20 gauge wire>1meg resistor>20gauge wire>rubber covered alligator clip.
 

rockon1

Platinum Supporting Member
Messages
13,703
Simply powered down most(not all) amps without using the standby drains the caps. This is the method I use on my amps. I check the caps ith a meter to make sure. Bob
 

MarkL8

Member
Messages
1,466
If you leave the amp ON not in STANDBY with guitar plugged in, then UNPLUG the power cord to the amp and continue playing till the sound fades out. This will in fact drain the caps to a point. I then ground them with my resistored jumper stick. I also double check with my VOM to be sure. Nothing worse than to awaken on your shop floor in a puddle of your own Pee!:eek:
 




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