Death Cap , fact or fiction

[gardo]

[video=youtube_share;MMTN3B-zClo]

he also did one on the shock hazzards of electric guitars I found them both entertaining

Edited May 26, 2015 by gardo

[knotty]

Why is he reversing the AC feed?

[gardo]

Why is he reversing the AC feed?

 

One thing I know is that if I put the old two prong plug in the wrong way I got zapped if I touched a ground while playing.Reversing the AC field can make a difference in hum for some reason

Edited May 27, 2015 by gardo

[1001gear]

He went over the schematic that shows the cap shunts some of one side to ground. He also said caps can't pass DC - something I could have inferred from guitar but was unaware of. So the cap comes right after the plug on one side. Flipping the plug grounds the other side. Apparently this has only trace effects on the hum. I kinda think the guy has clean AC to begin with and the caps were included to cover field use and possibly thin the herd.

[1001gear]

Oh and sorry I stole the bait.

[knotty]

A bit too obvious eh! .png' alt='16x16_smiley-happy.png.a1cb19ed0a13aa15d5339265141016d6.png' alt='smiley-happy'>.png'>

Edited May 27, 2015 by knotty

[WRGKMC]

Another idiot looking at it from the wrong perspective. Its not a death capacitor, its in fact it was put there for just the opposite reason. Its a ground capacitor which is where that video goes wrong from the start.

 

Its a safety feature added so you don't feel the whole force of the AC voltage yet it grounds hum in the process. A chassis has to be grounded to prevent audible hum. The cap provides a path for that hum to get to ground while providing safety to the musician.

 

There were many radio chassis back in the day that had the ground side of the AC lead connected directly to the chassis. When those were plugged in backwards the chassis was seeing 100% AC. The user was protected by not having access to the chassis. Knobs were plastic as was the front of the casing. They put lethal warnings on the back as well as a ground lug in many cases and people were supposed to ground them.

 

Engineers knew the problem and they didn't have many options because the wiring was all 2 way in buildings. Industry switched to 3 prong before homes and most of your industrial stuff was designed to protect workers with grounded chassis. Building code changes eventually outlawed 2 way wiring in home so everything today is pretty much 3 pronged in order to pass UL inspection.

 

The biggest issue with musical gear is, you may have several of these amps connected together. What if one chassis was hot wired without the cap to the ground side and plugged in backwards? You'd have the full 15 amps between to amp chassis or an amp and a PA instead of through the cap. Guitar in one hand, mic stand in the other is truly lethal.

 

 

The Caps were the best solution to adding safety while having proper operation at the time. Each piece of gear had a cap so touching two chassis with one reversed meant you were protected by two caps. One on each piece of gear. There weren't put there to kill people, it was the complete opposite. The cap value is the key. Its passes hum to ground while preventing the full 15 amps from the socket from charging the chassis. A shock is still possible if the cord is plugged in backwards but its much less likely to kill you.

 

 

The fix is simple. Remove the obsolete AC wiring and ground the chassis to the third prong on an AC cord.

Edited May 27, 2015 by WRGKMC

[badpenguin]

And add a ground phase switch.

[1001gear]

If I can spot it...

[1001gear]

This makes sense.

[gardo]

I completely agree that a 3 prong cord is the answer,but are you saying the "death cap " is actually a safety cap and should not be removed ? I'll admit this is somewhat over my head

[gardo]

It was actually guitarcapo's comment about getting rid of the death cap that got me wondering about the whole issue.I really don't know what the truth is about death caps

[soundcreation]

I had two death caps on my Gibson Falcon. Took them both out and grounded it myself. WRG can correct me if I'm wrong but I think he was saying, and what I understood when I did mine...is that basically "death caps" are simply not up to the standards of today. A more primitive form of "safety" if you will.

 

I wanted them out and a properly grounded three prong plug. So I did it. I'm not willing to take any chances on obsolete engineering. It's one "vintage correct" feature I don't really understand why anyone would want.

[Danhedonia]

The initial "this idiot ...." remark echoes recent posts where I am distracted from your posts by the tone. Is it possible that you might take a different tack in the interest of readability?

[WRGKMC]

I had two death caps on my Gibson Falcon. Took them both out and grounded it myself. WRG can correct me if I'm wrong but I think he was saying, and what I understood when I did mine...is that basically "death caps" are simply not up to the standards of today. A more primitive form of "safety" if you will.

 

I wanted them out and a properly grounded three prong plug. So I did it. I'm not willing to take any chances on obsolete engineering. It's one "vintage correct" feature I don't really understand why anyone would want.

 

Actually the reason for them is a historical event based on electrical wiring back in the day and yes it was there for safety and proper functionality. It was not put there to be something to hurt you, it was there to do the opposite and protect you from direct contact to live AC voltage carrying 15 amps.

 

Today that we have grounded outlets but allot of people didn't grow up in the 40's ~ 60's when most buildings still had 2 prong outlets so they don't understand why those amps had those caps. Before they had two prong they even had screw in outlets like light bulb sockets. Over time, laws changed for the better making things safer, but you want to understand the reason why older amps had these features you have to understand the only options for safety back then.

 

The manufacturers assumed people would run the amps back then safely too, make sure the polarity wasn't reversed, and make sure you didn't do something stupid like reverse the leads. That was taught to you as a kid growing up in a home. When I grew up then, my parents taught me the difference and I either did it the right way or I got kicked on my ass.

 

When those tube amps were built back in the 50's and 60's most homes had two prong outlets. This didn't mean they were ungrounded outlets, its just one of the AC wires acted as AC and DC ground to the chassis. As new gear came out and much of it higher ampage stuff it would be sold with a grounded plug.

 

The way you'd connect them to a 2 prong outlet was to use one of those ground adaptors and screw the third prong to the screw of the outlet box itself. The box of the outlet is hard wired to ground so you essentially had a 3 way ground available if you took the time to connect it right. This third prong on the plug is grounded the same as AC neutral is at the circuit breaker box.

 

Building codes changed and people were first made to install outlets to except one large and one small prong plug. Its changed again and the third backup ground was added. Any new construction had to have it and any home being sold had to have the upgraded wiring.

 

The home I grew up in was built in the 30's I think. My father eventually rewired the place during the 60's and 70's to meet building codes. (an important item if you have an electrical fire in a home and want to collect) This change over coincided with gear manufacturers selling gear with the proper wiring.

 

3 way plugs can only plug in one way with your neutral and hot always be on the right sides. This doesn't make it fail safe however. You can cheat a 3 way outlet in many different ways, its just less likely to happen if people do things right. Hopefully the electrician wired both the outlet and breaker box properly.

 

The thing is without the cap, the amp is actually many times more dangerous if you do connect it up with the ground lifted and the polarity reversed. Having those caps go away wasn't the best thing to happen when you look at it from that perspective.

 

During the change over from two prong to three prong you'd always find guys ripping the ground prong off of amp and extension cords or using ground lift adaptors. That's when things get dangerous because you now have an ungrounded chassis and if you get the polarity reversed, you don't have that ground cap in there to save you.

 

The ground caps were there for 2 reasons. To ground AC hum and to prevent a full AC on the chassis. In other words it prevented direct contact of AC to the chassis.

 

The hum is due to the circuit type. Most guitar amps are unbalanced high impedance circuit and you have to encapsulate all the amplifying components, beginning at the pickups, Guitar cord, and shielded chassis to act as a "Faraday cage" This cage is then grounded to prevent EMF from penetrating that barrier to get into the circuits and being amplified.

 

The cap connects the entire faraday cage from the pickups to the chassis to earth ground and prevents stray EMF from getting inside the shielded barrier and being amplified by the components and producing a loud AC hum. Again this works fine so long as the neutral side of the amp is plugged in properly.

 

The thing is what if you touch another amp, mic etc, that's reversed? If that cap isn't there you fry yourself with the full 15 amps right there between the two amplifiers. With the cap in place, the current that gets through the cap is fairly low. It will still bite you real good but unless you have a weak heart and a number of other factors are there you probably wont die.

 

I've been zapped by mics on the lips hundreds of times but I didn't die. The voltage is still 120 but the current is very low.

 

Of course a grounded plug is the best option, but, its still not going to protect you from other amps that have bad wiring. If your amp is dead ground and the other amp is seeking ground because its leads are reversed you can die. With the cap removed from the circuit, there is no safety device to separate you from the full amount of AC current and killing you.

 

This is why you should buy one of those three prong AC testers to tell you is the outlet juice is good. (a absolute necessity for a gigging musician whose always dealing with beat up stage outlets.) You can still have ground loops but its still less lethal.

 

Putting a ground cap in your guitar in series with the ground wire to the strings is essentially the best safety measure you can have fore preventing direct contact to AC. Its the exact same thing as having it mounted in the head except you put it in a different place.

 

Always remember, Its not necessarily "your" amp that might be the problem, its the "other guys" gear that you have to watch out for.

Edited May 27, 2015 by WRGKMC

[gardo]

So a 3 prong plug is the only way to go and removing the "death cap " without going to a 3 prong plug seems like a very bad idea

What about the idea of touching your guitar to the mic stand to make sure the polarity is the right?

Will this blow something out if it's reveresed?

[WRGKMC]

Definitely a stupid idea. Believe me I used to work on some old table top radios that didn't have that cap and they are as dangerous as can be. We used to put the caps into gear that didn't have them just for safety purposes.

 

Of course if the caps goes bad and shorts its no different then having it wired hot. If the cap gets weak then hum increases because the grounding it does provide isn't very good. Changing it out is the best way to go if you're keeping it vintage or replacing it with a grounded cord is very inexpensive.

 

The idea of touching a mic can be fixed in two ways. Add the cap in series with the ground wire in the amp or putting it in the guitar so its between you touching the strings and the ground wire. You may get a little zapping but much less then a dead ground. The only other option is to break out a meter and test things when setting up.

 

Since the voltage is between the AC leads its not going to be directed through the rest of the amp so its unlikely you'd damage the amp.

 

If things are reversed it will work but you are now the conductor between the hot chassis and anything you touch that's at ground potential. It can be the floor, the mic, and amp and the only things that's going to blow is you when your heart stops.

 

If you touch the guitar cable of a reversed polarity chassis to another amp that's grounded properly, you'll likely see big sparks and or or blow the circuit breaker. I've seen this too and my only advice is learn your basics and don't get into those situations.

 

I lit up my bedspread as a kid messing with those old amp cords once and nearly started a fire. Old beat up amp cords is a dangerous game. If an outlet looks bad replace it. If a cord is flakey, throw it away and buy another. Its not worth messing with just to keep something vintage. You can buy a 3 way cord that will handle an amps current in most dollar store for a buck. Any computer cord can have the one end removed and wired into an amp and make it safe.

Edited May 27, 2015 by WRGKMC

[WRGKMC]

The initial "this idiot ...." remark echoes recent posts where I am distracted from your posts by the tone. Is it possible that you might take a different tack in the interest of readability?

---

I'll stick by my statement because the guy begins his premise on a faulty assumption. If he had said, what's known as a death cap is actually a safety device, then I'd know he knew what he was talking about and approve of his premise.

 

Instead he goes along making you think the circuit design is faulty which is not the case. It was what they had to work with back then. The part is not there to cause death, its there to prevent it.

 

My concern is the video could be misinterpreted by some young amateur who may want to remove it thinking the amp would be safe without it. It should only be removed if you add the third prong plug which prevents polarity reversal. Without the third leg the amp would actually be a 50/50 death trap and it may not be you that gets killed it could be some other musician or family member.

 

I know how to wire my amps. I'm not worried about my gear hurting me, I'm worried about the other jackass whose using gear that isn't properly wired up because you get in a band situation and this guys got a floating ground cord because he's to cheap to buy a decent cord. Or he has a busted ground jack stuffed into a cheap 2 wire extension cord.

 

This is why I say its a bad presentation. Its like starting a presentation saying seat belts or air bags are there to kill you. Some kid may actually believe that, and some where in the back of his mind thinks its OK not wear his seat belts because they could kill you anyway. There are circumstances where those items can cause fatalities, but they actually save way more lives then they ever cause.

 

Therefore the premise of them being called death caps is stupid at best and only used that way by people who don't understand their function. They provide a soft ground less likely to kill.

 

Yes I think its important enough to speak in raw language when it comes to peoples safety. Its well worth the trade off being misunderstood by a few in order to stress its actual purpose and make a few understand that people who call them that don't know what they are talking about and should be avoided.

 

I can be soft on harmless things, but when there is "No" grey area involved between safety and great harm I'll side of safety and let the chips land where they are supposed to. If someone wants to be an stupid I cant stop them but if only one to listens its is better then none.

Edited May 27, 2015 by WRGKMC

[knotty]

I dont beleive ANYBODY else thought he meant the "death cap" was actually designed to kill you.

[Chordite]

Since these caps are on the mains supply lines presumably you are damping hum for the whole neighborhood right?

[Grant Harding]

Move to the future peeps. Those old things have no business in the modern world and should be upgraded. It should be illegal to sell an ungrounded mains voltage device full stop.

 

Yes, we know that it's a "Prevent Death Cap", but that doesn't have much panache.

 

Just like a burglar alarm doesn't mean you get burglers if you install one.

[WRGKMC]

Why stop with the neighborhood, why not the entire grid system. The resistance/conductivity of one body is a matter of scale like a single grain of sand compared to all the sands of earth. Yes a person can add to the load which is an important perspective when dealing with electronics. You deal with those opposites all the time in physics, its just we're used to seeing things from a "Me" perspective and looking at it from an equal and opposite perspective can seem a bit ridiculous at times but it is very good you can see things that way.

 

Another example in science is gravity. We've always been told gravity pulls us down to earth and weight is a matter of attraction. If you believe Einstein's theory we are actually pushed down to earth. I think its both myself but it does make for some interesting thought when you examine pre conceived ideas you're taught from birth and carry around with you for an entire lifetime.

 

Being able to examine fixed laws from an unbiased understanding is the doorway to higher knowledge which can lead to enlightenment. you just have to be sure you can handle giving both views equal weight while straddling that fence between the two. Its a balancing act that can easily land you on your backside.

[WRGKMC]

That's why the building code laws changed and why most gear manufacturers include grounded cords today.

[guitarcapo]

I usually remove them and install a basic 3 prong grounded cap. Whatever reduction in hum you are going to hear is eliminated that way anyway. They weren't installed to eliminate hum...they were installed for safety reasons. The reverse polarity switch was invented to reduce hum. The death cap was installed to provide safety for reversed polarity situations before grounded electrical huose wiring became common.

Edited June 15, 2015 by guitarcapo

[HamerMonaco]

From robrobinette.com

With a two prong power cord and no death cap the chassis voltage will float since the power transformer primary is not connected to the chassis. A normally functioning amp's floating chassis will not be electrified by 125v no matter the orientation of the power plug in the wall socket. Floating chassis are not used in tube amps for two main reasons: A floating chassis will provide no RFI noise protection and there is no protection from a hot AC power transformer primary wire coming loose and electrifying the chassis to create an extreme shock hazard. The now mandatory third power cord wire, the safety ground to chassis, mitigates this risk by shunting any stray voltage and current on the chassis straight to ground. The safety ground also provides RFI noise protection. 

The death cap serves no safety purpose. The death cap provides only AC RFI ground, not a safety ground. With the ground switch in its usual quietist position with the chassis and death cap connected to neutral (ground), if a loose wire electrifies the chassis the death cap will limit AC flowing through it to 2.4ma, the rest of the current will flow through anyone that touches the chassis. Of course no DC can flow through the death cap to ground so again, it will flow through anyone that touches the chassis.