OUCH! Run-in with the famous "Death Cap"

[Twangbanger]

I made a trade for a SF early 70's Vibrochamp from a reputable dealer who does a thourough check of all his tube amps.

Well, Friday night was my first gig with this little tone rascal. I always check to see if there's a problem between my setup and the PA. Saw Redd do the guitar to mic test, by just holding the guitar by the body and touching the strings to the mic. We'll this one time I didn't do it that way, plus it was my first night with this amp. I got the fire shocked out of me and felt the effects through my upper arms for about 20 minutes. I plugged my amp into the Rackmount power conditioner and that lifted my ground.

As soon as I began to think about what the problem was. I thought about the posts where I heard of the Death Cap and that it goes from the AC hot lead to the chassis ground. That had to be it, since I lifted the ground with the rackmount power.

Got home the next day and snip'd that little dude out of there. And now no more shocks!!!!!

I kick my self in the arse for not checking my guitar to mic the right way, but also that fact that 2 days earlier I was in the amp making sure everthing was good and doing some mods to the amp. Then I got on the phone with a bud that I had worked on his SF champ and let him know that he needs to check for that cap and get rid of it.

It was a great idea before the invention of the grounded outlet.

OOOOOOOUUUUUCH!

[teledude66]

is this something only pertaining to certain amps? also can you explain the mic to guitar test and what to look for...thanks

[fullerplast]

The "death cap" is only a death cap if it shorts out. They actually don't short out very often at all. You almost definately got your shock because you lifted the ground....a very bad practice. The cap has no effect on shocking if it is not faulty. It's fine to clip out if you've added a grounded cord to your amp but keep the grounds on all your equipment. There are other ways to eliminate ground loops. Lifting a ground is the wrong way....

[CancerLeoCam]

...to fullerplast!

[charlie chitlin]

The 'mic-to-guitar' test is a good one.
Just touch your guitar strings to the mike and look/listen for a spark/pop.
Just flipping your ground switch might cure it.
It's a much less painful test than the "hands-on-guitar, lips-on-mic" test.

[FrankFoxBand]

test by touching the strings with one hand and the mike with the other. This will complete the circuit straight across your heart and could KILL you!
When in doubt, get your multimeter out.

Jimbo

[teledude66]

to clarify...this is on amps without ground plugs???

[fullerplast]

Originally Posted by teledude66

to clarify...this is on amps without ground plugs???

Yes, these caps were generally on amps without grounded plugs. If it has a ground switch on the back it will likely have this cap. They are very rarely used today, but they are still on *some* amps with grounded plugs.

[jhundt]

I never tried that Redd version with the guitar strings, but I guess it will work if it works for him. When I worked as a roadie in the 70's (before everything was perfectly wired and cordless and grounded like it is today....) we tested every guitar player's ground by holding the guitar-end plug between the index finger and thumb of one hand, then gently touching the tip of that index finger against the mic - in several places. You'll feel it if the ground is wrong, but the current won't run through your whole body and kill you; it'll just jump through your finger-tip to the plug that you're holding. A little jolt but hey, that keeps the roadies awake!

[jjh37854]

so if you have a wireless setup does that eliminate the possibility of getting zapped by the mic?

[tweedtone]

Yeow!

I always insist on a Shure SM-57 as my vocal mic because the metal part that might touch your lips is not physically connected to the rest of the mic.

Plus a good whack with a 58 or similar mic will definitely take out some tooth enamel ...

[Poppatwang]

for that very reason.

[Twangbanger]

To clarify things. My amp was properly grounded, with the exception of the shorted cap to ground. The PA has always been conneted to the line voltage ground, so I just tried the ground lift on the power condtioner. This was a temp fix, not a permant one. I almost opened up the amp at the club and took the cap out on the spot.

Some times it takes a wake up jolt to get people thinking on their toes again.

I count my blessings that the jolt didn't kill or do any major harm to me.

[David Barnett]

Originally Posted by tweedtone

Yeow!

I always insist on a Shure SM-57 as my vocal mic because the metal part that might touch your lips is not physically connected to the rest of the mic.

Plus a good whack with a 58 or similar mic will definitely take out some tooth enamel ...

You can still get zapped with a 57 if you happen to reach up and touch the barrell of the XLR connector on the mic cable.

[halouis]

Originally Posted by David Barnett

You can still get zapped with a 57 if you happen to reach up and touch the barrell of the XLR connector on the mic cable.

Thats why when I am playing and singing. I where thick rubber gloves throught the gig. and a foam mic cover. That way I'm safe.... My playing suffers just a little bit.... ;)

[fullerplast]

Originally Posted by Twangbanger

To clarify things. My amp was properly grounded, with the exception of the shorted cap to ground. The PA has always been conneted to the line voltage ground, so I just tried the ground lift on the power condtioner. This was a temp fix, not a permant one. I almost opened up the amp at the club and took the cap out on the spot.

If the cap was indeed shorted, you would have either blown a fuse on the amp or a breaker for the AC source, had the amp been grounded. I'm still not sure why your power conditioner was ungrounded, or why you would have lifted the ground. That's a very dangerous practice, as you discovered the hard way!

[clearfish]

This thread is an excellent argument in favor of active pickups such as EMGs--they do not have or need a ground wire to eliminate hum. The player is "isolated" from the amp.

Back in the day (in my case, the 70's) power supply typically involved some element of chance. I remember tripping the main circuit breakers in a club when we turned on all our stage lights and went into a crescendo song ending. Much safer these day, with things like GFCI outlets and breakers.

[fullerplast]

Originally Posted by clearfish

This thread is an excellent argument in favor of active pickups such as EMGs--they do not have or need a ground wire to eliminate hum. The player is "isolated" from the amp..

No, the guitar is still grounded via the shielded guitar cord going to the amp. That ground is normally connected to the pots and the bridge of the guitar, regardless of pickups. This thread is an excellent argument in favor of grounding your equipment properly! Solve the problem at the source.

[clearfish]

You are wrong--I will be glad to show you the inside of my EMG equipped Tele. I had a specific discussion with the luthier that installed them during a refret/refin. There is no ground path from the strings, or the bridge. I do not consider the cord to be part of the guitar.

I don't know how you concluded I was advocating improper equipment use. My gig bag has circuit tester in it. Active pickups simply give you another layer of protection from the kind of shocks the thread writer was referring to.

[fullerplast]

Originally Posted by clearfish

You are wrong--I will be glad to show you the inside of my EMG equipped Tele. I had a specific discussion with the luthier that installed them during a refret/refin. There is no ground path from the strings, or the bridge. I do not consider the cord to be part of the guitar.

I stand by my original post. Guitars are *normally* connected to ground via the bridge. All stock teles have the bridge grounded. You *can* open that connection, but that is not the normal configuration...you don't need to have EMG pickups to do it either.

The cord is what connects you to the amp and establishes the potential for shock. It most certainly is part of the path and is important in the context of a discussion on shocks.

You want to eliminate the potential for shock at the source by proper grounding. Anything else is a band aid. Suggesting that you should avoid shocks by using certain pickups or mics is attacking the problem at the wrong end.

Solve it properly and you can choose the equipment that actually sounds best for you rather than using it for shock defense.

[tiktok]

What bugs me is how it seems that I've never played in a club where all the stage outlets were properly grounded. I keep all my gear grounded and plugged into my grounded powerstring which I use at every gig, and I get to the club and theres a horrible ground hum half the time and the sound guy says "Must be something with your gear..."

[Rick S]

Fullerplast's info is spot on here guys. There is no way around chassis ground safety issues. Different mics, pickups, wireless, whatever, the answer is always no. No proper chassis ground and there is a potential hazard, period.

In this case, if the mic screen and amp chassis had both been at ground potential, this accident would not have happened, good cap, bad cap, whatever.

Twangbanger, your description is a little sketchy, but I think I have a pretty good idea of what happened from your quote below.

Originally Posted by Twangbanger

I got the fire shocked out of me and felt the effects through my upper arms for about 20 minutes. I plugged my amp into the Rackmount power conditioner and that lifted my ground.

As soon as I began to think about what the problem was. I thought about the posts where I heard of the Death Cap and that it goes from the AC hot lead to the chassis ground. That had to be it, since I lifted the ground with the rackmount power.

Here you stated that "goes from the AC hot lead to the chassis." This is incorrect. The cap should be on the neutral leg. What I'm thinking is, when the new "3 prong" was installed, the hot was installed on the fuse, where the cap is, so indeed it was on the hot leg. If you want to check this out for yourself, simply confirm which prong on the plug is connected to the fuse/cap leg. If this is the way it was, with the chassis ground lifted, you had a certain hazard.

On the cap thing guys, whether you have a ground switch on your amp or not, always remove the cap. With a proper chassis ground, it serves no purpose and removing it will not effect performance. It can only cause hum if not removed, and as you can see here, it can cause confusion that can lead to an accident.

Glad you're OK Twangbanger.

[Twangbanger]

That was it. The hot leads going to the fuse. I put a new 3-prong on the amp and checked for continuity on the old one. It was fine. I'm lucky though!

[Rizo]

Wait, I'm confused....

So if I go to play this weekend, when I lean to over share the vocalist's mic and do some backup I may get zapped in the mouth because I'm playing my guitar?

Or is this only if I don't have a 3-prong cord on my amp?