Calling all old fogies: Is a two prong cord that dangerous?

[RadioComm]

I'm currently changing a two prong to a grounded one on a vintage amp. Easy enough, but... Just curious:

I'm older. I remember no seat belts in the back seat, no shoulder belts in front, no bicycle helmets when riding bicycles, and no long disclaimers on repairing high voltage devices. I get it, we not as safety conscious as we are now a-days. Which is a good thing, I am doing what I believe is right for safety. I'm going with a three prong.

But truly, for those who remember using regularly a two prong cord, has anyone known anyone getting electrocuted using a two pronger? I haven't. Maybe I'm the lucky one. But I played a truck load back then. (still do!)

Take care all.

[tubeswell]

I'm currently changing a two prong to a grounded one on a vintage amp. Easy enough, but... Just curious:

I'm older. I remember no seat belts in the back seat, no shoulder belts in front, no bicycle helmets when riding bicycles, and no long disclaimers on repairing high voltage devices. I get it, we not as safety conscious as we are now a-days. Which is a good thing, I am doing what I believe is right for safety. I'm going with a three prong.

But truly, for those who remember using regularly a two prong cord, has anyone known anyone getting electrocuted using a two pronger? I haven't. Maybe I'm the lucky one. But I played a truck load back then. (still do!)

Take care all.

Depends how your wall outlets are wired, and whether they're wired differently to other wall outlets that you might have other stuff plugged into which your body comes into contact with at the same time, like a mic plugged into a separate PA. Where I am, the 'neutral' wire is supposed to be ground referenced, and the 'phase' wire is the 'moving voltage'. But how much do you trust 'supposed to be'? Who knows who wired up the mains plugs in your place? or in another place that you might go gig at? And what if its someone else using or touching your gear?

[jim]

Yeah..like the man said....if you play out a lot you could get into trouble sooner or later...  and of course pool parties are out.   Jim

[RadioComm]

Yeah..like the man said....if you play out a lot you could get into trouble sooner or later...  and of course pool parties are out.   Jim

I'm currently changing a two prong to a grounded one on a vintage amp. Easy enough, but... Just curious:

I'm older. I remember no seat belts in the back seat, no shoulder belts in front, no bicycle helmets when riding bicycles, and no long disclaimers on repairing high voltage devices. I get it, we not as safety conscious as we are now a-days. Which is a good thing, I am doing what I believe is right for safety. I'm going with a three prong.

But truly, for those who remember using regularly a two prong cord, has anyone known anyone getting electrocuted using a two pronger? I haven't. Maybe I'm the lucky one. But I played a truck load back then. (still do!)

Take care all.

Depends how your wall outlets are wired, and whether they're wired differently to other wall outlets that you might have other stuff plugged into which your body comes into contact with at the same time, like a mic plugged into a separate PA. Where I am, the 'neutral' wire is supposed to be ground referenced, and the 'phase' wire is the 'moving voltage'. But how much do you trust 'supposed to be'? Who knows who wired up the mains plugs in your place? or in another place that you might go gig at? And what if its someone else using or touching your gear?

Yeah I get it. I'm going for safety. No reason to gamble with the odds. But this is a call for us old fogies. Has anyone back in the 60's or 70's remember anyone getting electrocuted? My only memory was down in a friend's basement,  and whenever passing the cigarette around and the fingers grazed, there was a slight zing with no consequences. Anyone remember worse?

[British1011]

I have been shocked 2 times by 2 different amps.  Once at a house party we were playing.  I just had an old silverstone all original.  One of the caps blew mid show as I was singing on the mic. I actually watched the electricity come off the mic and hit my lips.  Damn near blew my lips off and im not joking.   The other a 65 bandmaster and during a bar show..  the bar must have had some bad grounding which back in the day was more common than now but still happens.  Same deal touched the mic with my lips and bam...knocked me off my feet. Needless to say I won't play a 2 prong anymore.

[thetragichero]

https://www.tdpri.com/threads/guitarists-who-were-electrocuted-while-playing.162036/

[PRR]

> getting electrocuted using a two pronger?

I learned to NOT touch metal on a record player and a off-board UHF converter.

[RadioComm]

I have been shocked 2 times by 2 different amps.  Once at a house party we were playing.  I just had an old silverstone all original.  One of the caps blew mid show as I was singing on the mic. I actually watched the electricity come off the mic and hit my lips.  Damn near blew my lips off and im not joking.   The other a 65 bandmaster and during a bar show..  the bar must have had some bad grounding which back in the day was more common than now but still happens.  Same deal touched the mic with my lips and bam...knocked me off my feet. Needless to say I won't play a 2 prong anymore.

omg! Hearing this, I'm glad went with three prongs a long time ago. Never been a gambler, so no reason to play the odds. Especially since installing a three prong plug is so easy.

Thanks for responses. Take care all.

[acheld]

Yup, my buddy was buzzed by a mike due to faulty wiring at the bar.  No major harm done.  As it happened, the owner was a fan of This Old Farce, and did the wiring hisself.   

I've moved quite a bit in my lifetime, and developed a habit of always checking the outlets whenever we moved in with a simple outlet tester.   Every house I've been in has had at least one outlet wired incorrectly.  Most often in the basement, where it was clear that a prior owner had done some wiring.  But I've also seen a couple where I would bet that hired help (not necessarily an electrician) wired it wrong. Some swapping of the neutral and hot wires, and some where the ground was not connected.

You really can't trust the wiring unless you check it out.  Especially in bars where code may not have been adhered to.

[thetragichero]

You really can't trust the wiring unless you check it out.  Especially in bars where it was likely done for free beer.

fixed it for ya 

[acheld]

LOL. 

East Lansing and Ann Arbor MI back in the 70's.   

[MWaldorf]

I got sucker punched by a mic that didn't agree with my two prong amp in the early 80s.  First gig, it was a real shocker.  Also played bar gigs where the bass player was plugged into a different outlet and any time he bumped me with the headstock of his bass - POW!!!  Small stages and bad electrical work are a great combo.

[MORE_Guitar_Solos]

Still two prong here in Japan. When I toured here it was 50/50 getting shocked my the mic every night at sound check. Learned to use my multimeter to check polarity and stopped getting zapped.

[Williamblake]

Please help me get this clarified: Having neutral and phase reversed is only bad when using neutral or phase as ground reference. Or with a shorted death cap.

[tubeswell]

Please help me get this clarified: Having neutral and phase reversed is only bad when using neutral or phase as ground reference. Or with a shorted death cap.

Neutral wiring in the house or building is supposed to be connected to ground (usually at the mains panel), so that the voltage reference for the appliance is not floating. In a 3-wire mains, the earth wire provides a separate 'fool-proof' earth connection to the house's dedicated earth contact, for safety, because with two wire mains, there can be mistakes.

[Williamblake]

Please help me get this clarified: Having neutral and phase reversed is only bad when using neutral or phase as ground reference. Or with a shorted death cap.

Neutral wiring in the house or building is supposed to be connected to ground (usually at the mains panel), so that the voltage reference for the appliance is not floating. In a 3-wire mains, the earth wire provides a separate 'fool-proof' earth connection to the house's dedicated earth contact, for safety, because with two wire mains, there can be mistakes.

Well this is a regional problem then. In Germany you do not connect anything to neutral and although you keep neutral and hot(s) seperate (neutral is always blue) you would never have consequences from reversing the polarity (if you only use one phase what all guitar amps do). The safety/earth only acts as a safety short in case of a failstate and is good for shielding, too. This seems to be handled differently elsewhere.

Anyway, if you are sure your guitar and your amp are grounded properly using your guitarstrings to touch anything you might get zapped from first should flip the fuse and prevent you from geting zapped.

[thetragichero]

fuse might flip but you might already be writhing on the floor before your slow blow fuse pops. proper safety isn't something to avoid in an effort to be lazy or keep a vintage vibe. i won't let an amp leave my shop without a disconnected death cap and properly-wired 3 prong power cable. i'd rather turn away money than risk someone's safety

[tubeswell]

Well this is a regional problem then. In Germany you do not connect anything to neutral and although you keep neutral and hot(s) seperate

If you're talking about appliances, that's the same here. I wasn't talking about appliances, I was talking about at the mains panel in the building.

[Williamblake]

I was once in the situation of redoing the electricity in a house according to standing safety orders and was wondering where to connect safety/earth to. Answer being not to any wire from the power company, sink those iron rods yourself. I had it all checked and the breaker box connected by an electrician (with a proper bill).

What gets this subject confused in my opininion is that the linked thread about electrocuted musicians is not about faulty grounding in guitar amps, they probably had good grounding but maybe they would still be alive if they plugged in the PA (Mic-Amp) the other way around. Thats why there is so many comments about not playing barefeat...

[Adrien]

I have a related question..

I recently moved into an older house (in Canada, built in the 50's) that has had most of the outlets replaced with 3-prong ones.  I tested some of the outlets and found that whoever replaced them didn't bother wiring the earth grounds to anything, since I'm guessing you'd have to run a separate ground wire through the wall to all the junction boxes.  I know this is definitely NOT up to code and will bring it up with the landlord.

My question is: is it unsafe to use my amps with these ungrounded outlets?  Obviously it's really not ideal.  The amps are all wired to modern standards with 3-prong cords and the chassis connected to earth ground.  I'm thinking the chassis (and by extension the guitar strings) would now be "floating" and this wouldn't necessarily be an issue unless something were to go wrong inside the amp...?

Or is there another way to reference the chassis to ground?   

[shooter]

I tested some of the outlets and found

did you open them up to see if there's 3 wires?

[Adrien]

did you open them up to see if there's 3 wires?

Yes I did, there are only two.

[ALBATROS1234]

I think as others have said the problem is not so much getting shocked by your amp unless it's a series filament and either the across the line"death" cap shorts or if the non polar plug puts the hot on the chassis. But if there is potential on the chassis and you say sing into a modern well grounded pa the path for that potential to ground has now become your lips through the mic. I got the shit shocked out of my lips many times in the 80s and 90s

[2deaf]

I recently moved into an older house (in Canada, built in the 50's) that has had most of the outlets replaced with 3-prong ones.  I tested some of the outlets and found that whoever replaced them didn't bother wiring the earth grounds to anything, since I'm guessing you'd have to run a separate ground wire through the wall to all the junction boxes.  I know this is definitely NOT up to code and will bring it up with the landlord.

Houses in the States built in the 50's typically used metal conduit with two conductors.  The metal conduit acted as ground in this scheme.  The screw hole for the outlet cover was continuous with the ears that were screwed to the metal outlet box.  If you wanted a three-prong that was grounded, you used one of those two-prong to three-prong adapters with the ground flange secured by the cover plate screw.

The modern three-prong outlets still have the cover screw hole continuous with the mounting ears as well as with the ground hole.  Screwing a modern outlet to the metal outlet box in a conduit system with metal screws connects house ground to the ground hole on that outlet.  I was never comfortable with this connection, so I would always drill a hole in the metal box and connect a wire with a sheet metal screw and then connect the other end to the screw on the modern outlet.   

[thetragichero]

if you feel comfortable trying this:

shut the power off to one of outlets. make sure it's off!
take out the outlet, take a driver (i prefer impact but a drill/driver will work) and a self tapping screw (i prefer hex head because Phillips heads like to strip) along with a little "pigtail" of 14 or 16 gauge solid core electrical wire from the hardware store (you should be able to buy it by the foot at the hardware store). strip one end (maybe an inch or so) and using needle nose pliers make a little loop slightly bigger than the screw shaft. put screw through loop, drive it into the back of the junction box away from the wires already in there (i find the corners make it easier to get it to bite). make sure it's reasonable secure. measure off some slack (4-6" is probably sufficient) and strip the other end, wire to the ground lug of your outlet. carefully reinstall the outlet. flip the breaker and test. if your tester says that it's grounded, you can go ahead and do this wherever you'll be hooking up your amps
no clue how landlords are in the great white north; many in the us would tell you to go kick rocks if you brought up something like ungrounded outlets that would cost them money (now, you could frame ungrounded outlets as a fire hazard which might perk up their ears)

PLEASE NOTE: i am not a licensed electrician; just a guy living in an old house that's falling apart and the ungrounded outlets have caused damage to some electronics with lightning storms in the area) so when the subfloor was torn up in my studio i sunk a ground rod into the dirt and wired all of those outlets with a proper ground, tied to the cold water pipe for other rooms (romex used in my house did not have a conductive outer layer so pigtail trick didn't work for me). any advice you follow is at your own risk

[PRR]

Much US 1950s residential wiring was plastic cable, no conduit.

This can be legal and safe IF a GFI is first in the run; then 3-hole outlets may be installed.

This does little or nothing for guitar buzz, of course.

> where to connect safety/earth to. Answer being not to any wire from the power company

AFAIK, you *always*, all places, connect Safety Earth to a power company wire. The connection may be indirect in some systems. But if truly not connected then "minor" company faults can blow out your walls.

[HotBluePlates]

... Has anyone back in the 60's or 70's remember anyone getting electrocuted? ...

I have been shocked 2 times by 2 different amps.  ... an old silverstone all original.  ... I actually watched the electricity come off the mic and hit my lips.  Damn near blew my lips off and im not joking. ... Needless to say I won't play a 2 prong anymore.

... my buddy was buzzed by a mike due to faulty wiring at the bar.  ...

I got sucker punched by a mic that didn't agree with my two prong amp in the early 80s. ...

... i won't let an amp leave my shop without a ... properly-wired 3 prong power cable. ...

Mid-90s, playing a 1967 Princeton Reverb with a properly-wired 3-prong cord.  Got shocked from Mic ---> Lip ---> through left arm ---> grounded strings on the guitar.  Either the mic/PA was wired differently than the stage outlet, or was a different-phase; felt like a good ~120vac buzz (I've accidentally touched 120v a few times).

So a proper 3-prong cord won't necessarily save you.

... i won't let an amp leave my shop without a disconnected death cap ...

Replace the "death cap" with a Class Y cap.  Now it becomes a "noise reduction cap" that is designed for use from Line-to-Ground, and is purpose-made to Fail Open.

[2deaf]

Much US 1950s residential wiring was plastic cable, no conduit.

 

My personal experience has been that houses built in the 50's had flexible metal conduit with individual wires inside.  That system continued well into the 60's for residential applications.  Of course my sample size is rather small and only in a few states.  I still have some pieces of flexible metal conduit and "Romex connectors" stashed in my garage.

Commercial and industrial applications used to require conduits, but I found out it wasn't required anymore when I remodeled one of my industrial condo's.  I put conduit in, anyways.

I remember along about 1964 when I first saw green Romex wire with two insulated wires and a bare ground wire incased in some sort of rubberized snake-skin like jacket.  I was eleven years old wiring that stuff up to outlets.

AFAIK, you *always*, all places, connect Safety Earth to a power company wire. The connection may be indirect in some systems. But if truly not connected then "minor" company faults can blow out your walls.

I took out the power company's overhead ground with a piece of oversized equipment on a trailer along about 1980.  It took out the TV and a blender at a beauty parlor.       



 

[Adrien]

Thanks for the replies guys.

Houses in the States built in the 50's typically used metal conduit with two conductors.     

There's no conduit as far as I can tell, just the romex with two conductors.

if you feel comfortable trying this:
...

Thanks for the advice!  Like I said above, last time I had an outlet apart I had a look and there doesn't seem to be any conduit so I'm not sure if this trick will work.  But I'll shut the power off and investigate further when I get a chance.  It may be the case that the sheathing is conductive like 2deaf says.  I remember it had an odd snakeskin kinda look to it.

Replace the "death cap" with a Class Y cap.  Now it becomes a "noise reduction cap" that is designed for use from Line-to-Ground, and is purpose-made to Fail Open.

Would a Class X or Y cap be of any use in my case?  I've wondered about these for a while.

[2deaf]

It may be the case that the sheathing is conductive like 2deaf says.  I remember it had an odd snakeskin kinda look to it.

The sheathing wasn't conductive on that Romex wire.

That was some pretty good sheathing.  I saw that stuff in a guy's garage just a couple of years ago and the snake-skin jacket was perfect.  I guess the electrician was baffled by the stuff because he had taken the bare ground wire and wrapped it around one of the nails that holds the box to the stud.  Then he ran the other two wires to two prong outlets.

[thetragichero]

Would a Class X or Y cap be of any use in my case?  I've wondered about these for a while.

class X is designed to fail short, so not what you would want here. class Y, as stated, is designed to fail open

[HotBluePlates]

Replace the "death cap" with a Class Y cap.  Now it becomes a "noise reduction cap" that is designed for use from Line-to-Ground, and is purpose-made to Fail Open.

Would a Class X or Y cap be of any use in my case?  I've wondered about these for a while.

It's worthwhile to Click The Links.   

You want a Class Y cap, which is why it was the only one I mentioned.  But the links also explain "Y" = Line-to-Ground.  "X" is "a cross" and due to that represents "Across The Line" (from Hot to Neutral).

[Mike_J]

Please help me get this clarified: Having neutral and phase reversed is only bad when using neutral or phase as ground reference. Or with a shorted death cap.

Neutral wiring in the house or building is supposed to be connected to ground (usually at the mains panel), so that the voltage reference for the appliance is not floating. In a 3-wire mains, the earth wire provides a separate 'fool-proof' earth connection to the house's dedicated earth contact, for safety, because with two wire mains, there can be mistakes.

As I recall looking in the box at my house when an electrician was doing some work the earth ground and neutral wires were both connected at the box so they all went to earth ground. Problem as I see it is a lot of the old cords had prongs that were the same size so there is nothing to ensure the cord is plugged in correctly thus the need for the ground switch in the old days. Nothing to ensure todays plugs are properly wired either for that matter.


There is a part you can purchase that costs less than $10 that you can plug into the outlet to tell you if it is properly wired. Modern plugs are designed to be foolproof with a three prong plug presuming the outlet has been wired correctly. May still be foolproof if the ground wire is sufficiently grounded to earth.

[Adrien]

It's worthwhile to Click The Links.   

You want a Class Y cap, which is why it was the only one I mentioned.  But the links also explain "Y" = Line-to-Ground.  "X" is "a cross" and due to that represents "Across The Line" (from Hot to Neutral).

Haha yes indeed, I should read more carefully.  Thanks for the info!  It's all making sense now.  I've been noticing some noise issues, so I'll give the Class Y capacitors a try.

[sluckey]

Haha yes indeed, I should read more carefully.  Thanks for the info!  It's all making sense now.  I've been noticing some noise issues, so I'll give the Class Y capacitors a try.

You can temporarily use a .047µF/500V regular coupling cap to see if it helps your noise issues. If you think it helps, then replace with a class Y .047µF. Better yet, get two class Y caps, one for line and one for neutral.

[Adrien]

You can temporarily use a .047µF/500V regular coupling cap to see if it helps your noise issues. If you think it helps, then replace with a class Y .047µF. Better yet, get two class Y caps, one for line and one for neutral.

Good idea!  I'll try that first.

To be specific on the noise, I've noticed that since I moved houses the string ground doesn't work as well on my single coil guitars.  Previously there was a bit of hum when I wasn't touching the guitar, and then if I touched the strings (ie grounded myself) the noise mostly went away.  Now there's more hum when not touching the guitar and touching it doesn't change the noise much, so I'm thinking this is another symptom of the chassis not being grounded.

I guess this is exactly the problem the ground switch on all those old Fenders was meant to solve. 

The proper solution would be to fix the house wiring, but this might be a good interim solution.  Thanks guys!

[shooter]

snake-skin jacket was perfect.

had the same thing in my barn, til you flexed it, then it cracked, crumbed, n died 
the tube n knob stuff in the attic was cool, great rodent trap, lots of skeletons.  I kept one run live, History is worth saving     

[Williamblake]

If there is a change in hum or background noise whether  you touch the strings or not than your guitar does not have a proper connection to ground.

[bmccowan]

I'm a fogie and have had the experience. My opposite arm was touching another amp when I got the shock. Went through my chest and blew out my arm. Knocked me out for a minute and left a golf ball size lump with an open sore. It did cure me of some annoying habits though. So electrocuted? Close call I'd say, and extremely painful.
Couple of comments - before we had a uniform national electric code, practices varied by region. So the conduit/romex can both be right. The flexible metal conduit is often called MC cable when the wires are integral to the cable. Its a good, but expensive way to wire up outlets in a basement.

[shooter]

So electrocuted?

yup, that's it, been there, done that, learn't the hard way!


worked repairing CB's in the way back days, when the owner was showing me around, I asked where's the AC on the bench, he laughed, told me the 2 wires running along the back, just gator-clip, way easier 
he went further, grabbed both wires, hummmm, breaker must be off.  I checked...with meter, nope live.  turns out his body R was some crazy high value

[RadioComm]

Still two prong here in Japan. When I toured here it was 50/50 getting shocked my the mic every night at sound check. Learned to use my multimeter to check polarity and stopped getting zapped.

Really! Is it just a lack of regulation? Or just... I don't know... Are other safety standards just as relaxed?

[pdf64]

If there is a change in hum or background noise whether  you touch the strings or not than your guitar does not have a proper connection to ground.

Dunno about that - it’s not my experience.

[bmccowan]

Dunno about that - it’s not my experience.

I'm glad you wrote that, I was just starting to take apart all of my guitars to check the ground
I think that if you touch the strings a get a significantly loud hum/buzz through the amp, there is likely a grounding problem.
But touching the strings, especially with single coil pickups typically does change the noise level in the amp to a noticeable degree. Touching the strings reduces the background noise a bit. Other factors come into play too, but I suspect we all experience this.

[HotBluePlates]

Dunno about that - it’s not my experience.

... But touching the strings, especially with single coil pickups typically does change the noise level in the amp to a noticeable degree. Touching the strings reduces the background noise a bit. ...

My (perhaps flawed) understanding is your body winds up being a little extra capacitance-to-ground when you touch a "grounded" point & lower noise.

[pdf64]

My understanding is that touching the strings etc (or otherwise grounding yourself) turns the fairly dense conductive object that is the guitarist’s body effectively into a large screening plate that acts to block out a fair chunk of the EMI that happens to be in the environment.
When ungrounded, the body acts as a passive radiator, eg it radiates all the EMI fields that interact with it. Hence when in close contact with an ungrounded guitarist, the guitar is likely to be noisier than otherwise.
What I’m unclear on is whether the ‘grounding’ needs to be an electrical connection to planet earth, or just the arbitrary 0V common of an ungrounded system (eg a battery amp).

[d95err]

Anyway, if you are sure your guitar and your amp are grounded properly using your guitarstrings to touch anything you might get zapped from first should flip the fuse and prevent you from geting zapped.

Fuses are there to protect electrical equipment from damage, not people. By the time the fuse flips, potentially lethal current will already have passed through your body.

[pdf64]

It only takes a few 10s of mA (which only requires maybe 60V to break across the skin barrier) for a fraction of a second to flip the heart into a fatal arrhythmia.
The purpose of the mains fuse is to prevent faulty equipment causing a fire / damaging the building’s electrical installation.
The risk of electric shock is mitigated by equipment safety regulations (ie which includes grounding as appropriate) and by RCD type circuit breakers, either as a wall wart or incorporated into the building’s electrical distribution box.
In the case of vintage electrical equipment, it’s the responsibility of the owner/user and their service tech to bring it up to current standard (as far as is feasible) and maintain it there.
In the UK it’s the responsibility of the building’s owner to maintain its electrical installation. Landlords must have the property’s electrical system inspected and certified by a registered electrician with each new tenancy and, for long term tenants, every 5 years. Electrical installations and equipment has been grounded since the early 50s.

[Williamblake]

If there is a change in hum or background noise whether  you touch the strings or not than your guitar does not have a proper connection to ground.

Dunno about that - it’s not my experience.

This takes me by surprise and i really wonder how according to the laws of physics this would be possible. Assuming you are not constantly generating a charge. I guess you wired significantly more guitars than i did, begging to be corrected.
// y u so fast? Thanks all for getting into this. Live and learn.

[Williamblake]

Anyway, if you are sure your guitar and your amp are grounded properly using your guitarstrings to touch anything you might get zapped from first should flip the fuse and prevent you from geting zapped.

Fuses are there to protect electrical equipment from damage, not people. By the time the fuse flips, potentially lethal current will already have passed through your body.

except for it would flow through the guitar strings and ground. Ok this only works if the fuse blows before the guitar grounding desintegrates.

[acheld]

I have some experience with this topic in my prior professional life, and scrounged an article to read -- bear in mind this was written by a young cardiologist, and NOT by an electrical engineer, thus you will find some niggling electrical errors which don't detract from the overall information presented.

https://academic.oup.com/eurheartj/article/39/16/1459/3746021

It does not take much AC current traveling through the heart to cause fibrillation, through the heart being the key issue. (Hence the idea of keeping one hand in the pocket when probing live equipment.)    DC current is less dangerous vis a vis cardiac arrhythmia, emphasis on less.   

You probably all know that defibrillators (the portable AED devices and others) are DC devices -- designed to deliver about 360 Joules, at 600-900 V, ie, less than an amp of current.   Those numbers should ring a bell with anyone on this forum. Although you would think that a defibrillator is bringing the heart back, and it does most of the time, it works by causing the heart to contract all at once, and if this happens at the wrong time in the cardiac cycle, it will cause arrhythmia.

My advice is to take risk of shock seriously, and, if you repair amps for other than family, pay attention to your liability.