Draining filter caps question.

[zackd]

I have a marshall super 100jh and in process of finishing putting mustard caps in it. The guy i bought it from put in the first 3 .1u. I have put 1 .o22 in. I know you can get juiced by the filter caps. Should i drain them before finishing the cap job? What tools are needed and how do you do it? I did'nt get zapped by changing the one resister in the tone stack either. will i get zapped if change the other .022's with out draining the filter caps? Thanks

[Big Mike]

I'd drain the caps. Just takes a few min. and it's much safer.

[mwm523]

ALWAYS drain the filter caps before poking around in there. You never know when you might slip and touch something that will kill you.

Here's what you need:
http://metroamp.com/wiki/index.php/Draining_filter_caps" onclick="window.open(this.href);return false;

[Spodeeodee]

I have a marshall super 100jh and in process of finishing putting mustard caps in it. The guy i bought it from put in the first 3 .1u. I have put 1 .o22 in. I know you can get juiced by the filter caps. Should i drain them before finishing the cap job? What tools are needed and how do you do it? I did'nt get zapped by changing the one resister in the tone stack either. will i get zapped if change the other .022's with out draining the filter caps? Thanks

To any new guys reading this thread, DO NOT ATTEMPT WHAT IS WRITTEN ABOVE, it is HIGHLY DANGEROUS and could KILL YOU.

Let me say that again, IT CAN KILL YOU

Always drain the caps. It only takes two minutes of your time.

[zackd]

I forgot to mention I used the a screw driver method before i poked around. I remember cesar diaz doing it that way. I know u can die if you dont discharge the filter caps somehow. I am happy I know another way to Drain the caps.

[saxophonist56]

where are you measuring to check if the cap's are drained? on the caps?

[neikeel]

where are you measuring to check if the cap's are drained? on the caps?

Yes on the mains caps usually to earth. Some early amps will not drain via the V1 crocodile clip if you do not switch standby (obviously with power off) on as the HT will not be in continuity.

First thing you must make before you build the amp is a double ended insulated crocodile clip (colloquially known as a 'frig' lead in the UK - guess why )

[Structo]

I forgot to mention I used the a screw driver method before i poked around. I remember cesar diaz doing it that way. I know u can die if you dont discharge the filter caps somehow. I am happy I know another way to Drain the caps.

Not only is that a dangerous method to discharge caps it can also damage things.

It can arc and throw slag into your eye(s).

It can destroy a component lead.

It can also damage the insides of the cap.

BAD IDEA AND BAD TECHNIQUE.

Sometimes these things get perpetuated through the internet and pretty soon it becomes gospel.

FIRST, MAKE SURE THE POWER CORD IS UNPLUGGED BEFORE SERVICING THE AMP!

Yes, use the test lead on the V1 plate resistor or make a test lead with a 1 watt 100K resistor in line with the wire, with clips at each end.

If you are not familiar with the amp you are working on and don't have a lot of experience, sometimes the resistor test lead is the best way to go.
Clip one end to the + end of a big cap and the other to a bare place on the chassis.

As mentioned, some amps have a cap or two before the standby switch so the switch should be switched to the play position so all the filter caps are connected in the power supply.
Wait a few minutes, then measure the DC voltage on the cap. Measure from the + end and have the black probe clipped to chassis ground.

ALWAYS check the voltage on the filter caps before sticking your hands inside an amp.

REMEMBER to pull the discharge lead off of the amp before powering up.

I like to leave my discharge lead attached while working on the amp as sometimes residual voltage can build back up in the caps. Not sure if it is enough to be harmful but better to be safe than sorry.

[demonufo]

I forgot to mention I used the a screw driver method before i poked around. I remember cesar diaz doing it that way. I know u can die if you dont discharge the filter caps somehow. I am happy I know another way to Drain the caps.

Not only is that a dangerous method to discharge caps it can also damage things.

It can arc and throw slag into your eye(s).

It can destroy a component lead.

It can also damage the insides of the cap.

BAD IDEA AND BAD TECHNIQUE.

Not only that, but probably not best performed with one of your favourite Snap-On's. I know from experience that the Snap-On guys tend to get a little pissy when you try and get warranty on a broken flat-blader after they spot arc-ing spots on it!

FWIW, some amps make great welders too. I had an Exposure IV hi-fi power amp that died in a big way, and I used to get some great arcs from the huge cans in that sonofabitch. These things are often useful to scare the crap out of apprentices!

[redlir]

Just so I'm understanding this correctly.

When we do this, we need to have the power cord still plugged in so the chassis is actually 'earthed'? Once drained, unplug the AC cord, and turn standby off? Does the standby need to be on, on the 50 watt plexi?

Cheers

[neikeel]

Just so I'm understanding this correctly.

When we do this, we need to have the power cord still plugged in so the chassis is actually 'earthed'? Once drained, unplug the AC cord, and turn standby off? Does the standby need to be on, on the 50 watt plexi?

Cheers

Depends if your stand by is after the diodes and the caps