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backdrifter
01-31-2012, 01:31 PM
Hello guys and gals,

Electrical is my weak spot and I'm hoping for some help from the experts (or at least those better informed than myself :)). I've got a late 40's/early 50's Gibson amp that I acquired from my grandfather. It has the original two prong power cord. I've read that this can be dangerous and it is recommended that you swap them out for a modern grounded plug to avoid the risk of electrical shock.

I currently keep the amp in the basement and have never had any issues. I like the idea that the amp is 95%+ original, so I haven't been motivated to swap out the plug.

But now, I find myself playing it quite a bit more with a newer guitar and have decided I would like to bring it up into the living room. My biggest concern is that once in the living room, it will be in proximity of my 3 year old daughter. How dangerous is the two prong plug? If there is any risk at all to my daughter, it's a no-brainer and a done deal, I just wanted to get some input first.

Thanks in advance!

Jef Bardsley
01-31-2012, 02:46 PM
There's a simple explanation here:

http://electronics.howstuffworks.com/everyday-tech/question110.htm

So, IMHO, the danger to your daughter is minor. The thing you need to worry about is her getting in the back and touching hot tubes.

The danger to you is slightly greater, as, if the amp melts down and drops 120V on the chassis, that's connected to the ground in your cord, which is connected to your strings..... and the amp is unlikely to melt down unless you're playing it.

All of this assumes your living room carpet is flooded with water, or you have a death grip on a cold water pipe... or some stupid appliance that has a grounded case. If you're not grounded, you can touch hot wires all day and no current will flow. That is, in most cases (PTP!), 3-prong plugs increase the opportunity to get electrocuted by providing more available surfaces at ground potential.

To be really clear, it would be silly to add a grounded steel case to an amp in a wooden cab and you'd need to cover the front panel with, say, Plexiglass. Otherwise, a 3-prong plug would have no advantage. As the article states, in a three wire circuit, two of the wires are connected at the fuse box end. If they go to the same place at the other end, it's pointless.

Peteyvee
01-31-2012, 02:59 PM
I've been zapped by a two prong plug equipped Gibson amp from the 60s (in a wooden case) on a carpeted floor, while wearing shoes. Roll the dice if you want. I'd get in changed over if you're going to use it.

mbeards
01-31-2012, 03:58 PM
It is always a good practice to add a 3 plug cord to any and all vintage amps. If something goes wrong with the amp and high voltage gets sent to the metal chassis (and through the guitar cable to your strings), any dangerous voltage will go to ground directly because it has less resistance than your body, effectively a short in comparison. Then the fuse will pop and the amp will shut off.

I was once debugging some noise on a DIY tube stereo preamp for my ipod while it was on. I accidentally shorted out the wall voltage to the chassis with a screwdriver while holding the metal chassis. Lucky when I designed the thing, I put a fuse in the AC wall line and had a grounded plug. There was a huge spark but the voltage went through the chassis into the ground plug and blew the fuse inside of amp due to the increased current draw instead going through my hand and body to ground.

So yeah a 3 prong plug is always good practice.

charveldan
01-31-2012, 04:15 PM
Get a 3 prong for sure. :agree

'58Bassman
01-31-2012, 04:29 PM
If the chassis is hot and you're touching the strings or anything else that's connected to the guitar's ground, you'll be the load if you touch anything in the building that's grounded. This means, if you touch the strings with one hand and ground with the other, the current can pass through your heart and you'll be electrocuted.

A little tingle is one thing but dying can be avoided.

GrungeMan
01-31-2012, 05:27 PM
To be really clear, it would be silly to add a grounded steel case to an amp in a wooden cab and you'd need to cover the front panel with, say, Plexiglass. Otherwise, a 3-prong plug would have no advantage. As the article states, in a three wire circuit, two of the wires are connected at the fuse box end. If they go to the same place at the other end, it's pointless.

:huh

Not sure what you are talking about?
Did I read this guys post right???

Most amps have a metal chassis and the PT's ground lead is usually attached to a PT bolt(the bolt(s) is used to attach the PT to the chassis), the ground wire from the 3-prong cord is also attached to the chassis most likely at the same spot the PT bolt so there is no ground loop which could add hum to the circuit.

Live or Neutral(common) do not touch the amps metal chassis or metal receptacle/light switch box in your house wiring at all.

Hopefully ones home is wired with a proper ground therefore it's less likely to have any deaths from electrocution.

I touch the metal chassis's of my amps all the time and suffer no ill effects because my amp and home are properly grounded.

Be safe and install a 3-prong cord and make sure your house/home electrical circuitry is wired and grounded properly as well.

3-prong plug/receptacle
White wire-neutral/common-wide blade
Black wire-hot-narrow blade
Ground-bare wire/green-round blade

Grungy :D

charveldan
01-31-2012, 05:31 PM
Early 82' i was playing a gig in a lower level through a 50 watt Marshall with a 3 prong adapter that wasn't grounded, i was barefoot on concrete and stepped in water/liqiud......all i can say is i'm fortunate i wasn't killed. :omg:omg:omg:omg

modernp
01-31-2012, 05:38 PM
Why would you choose to make yourself the ground. Been bit bit hard in the old days by ungrounded amps. Especially when your lips touch a microphone.

Jef Bardsley
01-31-2012, 06:00 PM
So, would any of you like to explain just where to connect the extra ground wire to make the amp safer?

Backdrifter, I applaud your concern for your daughter's safety, I just don't want you lulled into a false sense of security.

ROKY
01-31-2012, 06:01 PM
Ask Keith Relf .

Ramblin Hymns
01-31-2012, 06:35 PM
The third prong will help to make sure the polarity is right if hooked up right. I could go into the whole explanation but try walking across a HVAC vent holding your guitar by the neck touching the strings. Make sure the polarity on the amp is wrong and you are barefooted. You will see very quickly why the third prong will help. I really don't advice this because I did it not thinking. You can connect the gnd to the chassis. If anything shorts to chassis it will go to gnd. The neutral and gnd are two different things. At the power companies xformer,if you don't tie the neutral to gnd the neutral will eat you up and it has voltage on it. If you get between the neutral and gnd at the xformer it can kill. That is where the neutral and gnd needs to be tied together. and so on

modernp
01-31-2012, 06:55 PM
http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/Mods/safe.html

kiki_90291
01-31-2012, 07:20 PM
If you're not grounded, you can touch hot wires all day and no current will flow.

Unless you can levitate, when you are standing on any surface, you're grounded.

'58Bassman
01-31-2012, 07:26 PM
The third prong will help to make sure the polarity is right if hooked up right. I could go into the whole explanation but try walking across a HVAC vent holding your guitar by the neck touching the strings. Make sure the polarity on the amp is wrong and you are barefooted. You will see very quickly why the third prong will help. I really don't advice this because I did it not thinking. You can connect the gnd to the chassis. If anything shorts to chassis it will go to gnd. The neutral and gnd are two different things. At the power companies xformer,if you don't tie the neutral to gnd the neutral will eat you up and it has voltage on it. If you get between the neutral and gnd at the xformer it can kill. That is where the neutral and gnd needs to be tied together. and so on

The neutral is tied to the ground at the electrical panel, not at the transformer. Service entrance is supposed to have appropriate ground stakes, as deep as required by local code or the NEC and the ground conductor is supposed to be unbroken from the panel to the far ground rod. A residential service feed has three conductors- two hot (these provide your 230VAC for electric stoves, furnaces & water heaters) and one that serves as the neutral/ground reference. The service is grounded from the panel.

gatordoc
01-31-2012, 07:28 PM
Put it this way, every time my heart rhythm feels a little abnormal I just plug a Strat into my trusty old 2-prong '66 Vibro Champ and hit the switch.........best little defibrillator around and it even has that retro 60's charm.

backdrifter
01-31-2012, 07:56 PM
Thanks for the responses, everyone. Sounds like a quick and easy fix, and one that's not worth putting off.

Sadly, I'm an engineer by education (chemical) and took a few electrical engineering classes, but electrical has always been a rough subject for me.

Three prong plug it ts!

Ramblin Hymns
01-31-2012, 09:16 PM
Hey 58 Bassman,Not to get really involved but the Xformer is grounded. I've been an electrician for over 40 years. I worked high voltage for last 15. 25000 volts. The xformer is grounded as is the panel. In the panel the grd is seperated from the neutral. You are tied at the xformer in the new systems. The grd bar at the panel goes to the grd field and usally the nearest structural ground.That separates the neutral and ground at the panel. NEC does not allow you to wire the neutral and ground together in the panel or the outside disconnect for said structure. I'm not saying it wasn't done in the past but not now. It has to do with computers and noise in the lines and safety.Now if you want to get into some weird problems,play with an open neutral on the power company side. It can fry the electronics in your house. By the way,at the university I worked at we used 7200 or 15000v for the primary. It doesn't jump like 25000 does and is safer. Oh yea NEC supercedes local and state codes. Also panels are four wire. That is the reason you see four wire stove hookups now. I do understand the way people get around the 3 and four wire hookups. I've done it myself.

GT100
01-31-2012, 09:26 PM
Unless you can levitate, when you are standing on any surface, you're grounded.

Yes, the only difference is that if you are simply standing on the floor v.s. say holding on to a pipe is that the electrical shock will be less.
But is it safe? Not likely and I wouldn't want to find out the hard way...

Lloyd

gatordoc
01-31-2012, 09:46 PM
I have never been shocked through the guitar itself but have taken a couple of good jolts directly from the amp over the years when I switched it on and just happened to touch the metal face plate at the same time - yes, it's a lot of amps, wearing sneakers did nothing, it does really hurt, and you won't want to do it again.

LSchefman
01-31-2012, 09:52 PM
Older gear can be a problem. I have a good friend who lost her sister a couple of years ago to accidental electrocution. She was at a club, stepped on a frayed ungrounded power cord powering an amp on the bandstand, the carpet at the club was wet from a spilled drink...

She was killed instantly.

She was a teacher with little kids. It was a very, very sad thing.

backdrifter
01-31-2012, 09:55 PM
Really, really sorry to hear that - such a pointless and avoidable loss.

GibsonSGgirl
01-31-2012, 10:04 PM
I have been thinking about this recently...if people played through these amps when they were new in the 60s, and no one seemed to get electrocuted (or at least no one famous), what is the difference today? Why do they need to be grounded, with a 3 prong cord?

Did they not have 3-prong cords in the 60s, or did no one care about that back then? Was safety not as big of a concern as it is today?

Sorry to sound ignorant, but I'm just curious...

Ramblin Hymns
01-31-2012, 10:16 PM
They didn't take a third ground wire to the receptacle back then. It worked but not the safest way to do things. The reason I would recommend a three wire is so you don't have to worry about your polarity being wrong and it helps you from being zapped. A safety mod that is not going to cost very much. I've been hit hard and I don't like it and I imagine no one else likes it.

modestcargo
01-31-2012, 10:27 PM
I have been thinking about this recently...if people played through these amps when they were new in the 60s, and no one seemed to get electrocuted (or at least no one famous), what is the difference today? Why do they need to be grounded, with a 3 prong cord?

Did they not have 3-prong cords in the 60s, or did no one care about that back then? Was safety not as big of a concern as it is today?

Sorry to sound ignorant, but I'm just curious...

Ask anyone that played gigs back then and they will tell you about having the amps polarity switch set wrong and getting their lips zapped on a mic. Or touching the other guitarists strings.

gatordoc
01-31-2012, 10:35 PM
Ask anyone that played gigs back then and they will tell you about having the amps polarity switch set wrong and getting their lips zapped on a mic. Or touching the other guitarists strings.

Yep, mics were very bad back then, especially if you were outside on a wet stage. Mick Jagger's lips didn't always look like that!

Also, if you were practicing in a tight space like a garage and backed up against a major electrical appliance like a metal freezer.

Seems like a lot of shocks back then were caused by several factors all lining up at the same time so not everyone was getting shocked all the time.

teleman55
02-01-2012, 01:05 AM
There's a reason that, to this day, that I always hold my guitar touching the strings and uber quickly and lightly touch the mic. Just give it a quick tap. It's an ingrained habit. And I came of age when the 3 prong was already coming into vogue. Be we still used a lot of older amps. And a lot of places still had crappy old wiring that had not been updated.

GrungeMan
02-01-2012, 03:38 AM
So, would any of you like to explain just where to connect the extra ground wire to make the amp safer?


Reread my post

GrungeMan
02-01-2012, 03:39 AM
Ask Keith Relf .

I agree!


Roky did you get my PM's?

sockeye
02-01-2012, 05:29 AM
Unless you can levitate, when you are standing on any surface, you're grounded.

And if you can levitate, then you're half of a capacitor.

gtrnstuff
02-01-2012, 06:29 AM
With 2 wire cords, we got a lot of small shocks. But sometimes a big one. I saw a guy's guitar strings get burned off in a flash of blue light when he touched the neck to a support pole in a basement.
Get everything up to today's code, please!

Jef Bardsley
02-01-2012, 06:49 AM
Reread my post
You mean the part where you admitted you don't understand these things? :rotflmao


Guys, adding a three-prong, three wire cord to an old tube circuit does not magically upgrade it to a modern three wire computer circuit. All you've done is add an extra ground wire between the chassis and the outlet, and while redundancy is good, the amp's chassis isn't any safer than it was before.

Ramblin' brought up a legitimate point about the polarity of the plug. However, before you count on that you should go to Lowe's and get an outlet tester. The very fact there's a market for those things says a lot. (If the polarity is wrong, then the amp's chassis will be 'hot' even when the amp is switched off.)


Backdrifter, my advice is get a circuit tester and check your outlets.

Inspect the amp's cord for cracks in the insulation, replace if necessary. If you keep the old cord, or buy a (vintage correct) duplicate, mark the plug so you know which way to insert it in the outlet.

Close off the back of the amp with screening or mesh to be sure your daughter can't touch the chassis, tubes or capacitors (or the speaker cone, which won't be a danger to her, but could give you a heart attack!). This is seriously more important than worrying about the cord.

Live with the fact that IF the amp is plugged in wrong and IF she touched the front panel, and IF she's touching ground with her other hand (actually rather unlikely unless you have steam heat) she might get a jolt, or come up with a way to cover the panel.

Obviously, just putting the amp up, out of reach, would solve these issues for a year or two. ;)

GreenKnight18
02-01-2012, 07:16 AM
You mean the part where you admitted you don't understand these things? :rotflmao


Guys, adding a three-prong, three wire cord to an old tube circuit does not magically upgrade it to a modern three wire computer circuit. All you've done is add an extra ground wire between the chassis and the outlet, and while redundancy is good, the amp's chassis isn't any safer than it was before.

Ramblin' brought up a legitimate point about the polarity of the plug. However, before you count on that you should go to Lowe's and get an outlet tester. The very fact there's a market for those things says a lot. (If the polarity is wrong, then the amp's chassis will be 'hot' even when the amp is switched off.)


Backdrifter, my advice is get a circuit tester and check your outlets.

Inspect the amp's cord for cracks in the insulation, replace if necessary. If you keep the old cord, or buy a (vintage correct) duplicate, mark the plug so you know which way to insert it in the outlet.

Close off the back of the amp with screening or mesh to be sure your daughter can't touch the chassis, tubes or capacitors (or the speaker cone, which won't be a danger to her, but could give you a heart attack!). This is seriously more important than worrying about the cord.

Live with the fact that IF the amp is plugged in wrong and IF she touched the front panel, and IF she's touching ground with her other hand (actually rather unlikely unless you have steam heat) she might get a jolt, or come up with a way to cover the panel.

Obviously, just putting the amp up, out of reach, would solve these issues for a year or two. ;)

With an old two-prong plug you can plug it in either way right? (the newer ones have a bigger and smaller prongs). At least with a three pronged plug you'd know the correct direction and not have to be concerned with the polarity [once you verify that your outlets are correct].

Ryan07
02-01-2012, 05:39 PM
So.. If you get shocked by a 2-prong amp, is it BECAUSE your house has reversed polarity?

I just got my first vintage fender :) A SF Vibro Champ. It tested fine in a guitar center (though noisy when guitar volume was not on 10. ?), but when I got home I plugged it into an already plugged in power strip it sparked instantly and I could smell smoke. One side of the plug was black! So I called 2 local amp tech's...both seemed surprised. Have you guys heard of this? Upon suggestion of the 2nd tech, I plugged it into a new power strip (The 1st one that shocked and smoked (lightly) still works, btw).

Voila! It works... The little champ sounds fantastic..and no hiss!

But: Day 2 comes around and I get shocked...twice! Is is because I potentially plugged the 2 prong the "wrong way" (as indicated by posts above)? Both prongs look to be of equal size though... how to tell?


And back to the OP: How Dangerous? Besides touching caps or some interior chassis piece.. How dangerous are these little "shocks"? Yea, nobody like to get shocked, and if a 3prong helps, im on it; But how dangerous is just playing these old guys? How often are you guys getting the little "shocks" on your 2-prongs?

Thanks!

ROKY
02-01-2012, 05:47 PM
I agree!


Roky did you get my PM's?

Indeed, I did my brother !

I meant to get back to you on that; very sorry ... :o

VintageKnob
02-01-2012, 06:53 PM
1972, left hand fully grasping neck and strings, with right hand I reach out and turn off a tiffany lamp with an inline switch, the kind that roll to turn on and off.

I think I flew pretty much all the way across the room screaming foul language.

One of many good zaps from the old days.

Get the 3 prong.

- D

Jef Bardsley
02-02-2012, 08:10 AM
So.. If you get shocked by a 2-prong amp, is it BECAUSE your house has reversed polarity?
My bad, perhaps, for assuming everyone knew the rule we followed in the bad old days. The chassis is grounded to reduce noise. So the rule is, plug the amp in, turn it on, and listen to it. Then turn it off, flip the plug around, turn it back on and listen again. The way the amp makes least noise is the right way for it to be plugged in. (some old amps had a 'polarity switch' to make this easier)

I just got my first vintage fender :) A SF Vibro Champ. It tested fine in a guitar center (though noisy when guitar volume was not on 10. ?), but when I got home I plugged it into an already plugged in power strip it sparked instantly and I could smell smoke. One side of the plug was black! So I called 2 local amp tech's...both seemed surprised. Have you guys heard of this?
This tends to happen when you plug in something that's already switched on. Dust in the outlet doesn't help either - power strips really shouldn't face upwards.

And back to the OP: How Dangerous? Besides touching caps or some interior chassis piece.. How dangerous are these little "shocks"? Yea, nobody like to get shocked, and if a 3prong helps, im on it; But how dangerous is just playing these old guys? How often are you guys getting the little "shocks" on your 2-prongs?
How bad the shock is depends on how well you're grounded. How dangerous it is depends on where the current travels through your body. That's why there's a "one hand" rule for people working with AC (if you're changing a fuse, for instance, put one hand in your pocket). Unfortunately, it's very common for a guitar player to hold his guitar with one hand while leaning over to adjust an amp with the other. When you get an AC shock from one hand to the other the current travels up your arms and across your chest, where your heart is. Shocking your heart muscles so they don't respond for a few minutes is obviously not a good thing.

Possibly the hardest thing I ever tried to teach my daughter was risk assessment. Before you consider the risk, you have to consider the loss. If no loss is acceptable, then no risk is acceptable.

I could point out that, despite the dangers, very few of us died using the old amps in their day. But the OP was asking about his daughter, so I tried to cover all the risks. I'm fairly certain that's a "no risk" situation. On the other hand, if you're a young rock and roller, living the life, then drugs, drinking, and driving put the risk of an old amp way down the list of dangerous things in your life.

Ryan07
02-02-2012, 12:52 PM
Thanks for the reply and the tips.

What exactly do you mean by this?
power strips really shouldn't face upwards.

Peteyvee
02-02-2012, 04:05 PM
Ask Keith Relf .Or Les Harvey, Alex Harvey's late brother. http://en.wikipedia.org/wiki/Leslie_Harvey

I have been thinking about this recently...if people played through these amps when they were new in the 60s, and no one seemed to get electrocuted (or at least no one famous), what is the difference today? Why do they need to be grounded, with a 3 prong cord?

Did they not have 3-prong cords in the 60s, or did no one care about that back then? Was safety not as big of a concern as it is today?

Sorry to sound ignorant, but I'm just curious...

You don't consider The Yardbirds famous? Keith Relf was their lead singer and harmonica player. There are a few guys that he played with in that group that you might recall: Jeff Beck, Jimmy Page and Eric Clapton...
http://en.wikipedia.org/wiki/Keith_Relf

And to answer your question, we used to get zapped all the time back then. One time in the early 80s we were playing at Magic Mountain and I reached for a microphone while holding my guitar (on a concrete stage) and I didn't know where I was for a minute or two. I am also very lucky that I'm here to tell the tale. My rig at the time was 2 JCM800 100 watt stacks and their house PA was massive.

Jef Bardsley
02-02-2012, 07:05 PM
power strips really shouldn't face upwards.
What exactly do you mean by this?
I mean when outlets are mounted in the wall vertically, dust and dirt aren't much of a problem. When they're facing upwards on the floor in a power strip, dust, dirt, hairballs, sawdust, etc, can get in them and cause a fire hazard if there's arcing as was described when plugging something in. Not a major concern, perhaps, but it did happen to me once. I no longer vacuum just the easy-to-get-to parts of the shop floor. :bonk

Greaser
02-02-2012, 08:53 PM
Hey guys, I have a question. I have a hand wired tweed bassman clone. It has a 3 prong cord, but also has the polarity switch. One day i was swapping some preamp tubes to see which I liked best. I had the back off while doing this, obviously. I was turning the amp on and off between switching tubes. The last time I reached to turn the power on (or off, don't really remember) I touched the power switch with my index finger and my middle finger touched the chassis right next to the switch. I got ZAPPED through my middle finger! That was the end of tube testing for the day...I can still feel the path the shock travelled up my arm when I'm thinking about it.

That hasn't happened before or since, what would cause that?

NashSG
02-02-2012, 09:05 PM
"I like the idea that the amp is 95%+ original, so I haven't been motivated to swap out the plug."

I wouldn't think this change would really alter the value of the amp. Keep the parts and I think all is good.

Jef Bardsley
02-03-2012, 05:28 AM
Hey guys, I have a question. I have a hand wired tweed bassman clone. It has a 3 prong cord, but also has the polarity switch. One day i was swapping some preamp tubes to see which I liked best. I had the back off while doing this, obviously. I was turning the amp on and off between switching tubes. The last time I reached to turn the power on (or off, don't really remember) I touched the power switch with my index finger and my middle finger touched the chassis right next to the switch. I got ZAPPED through my middle finger! That was the end of tube testing for the day...I can still feel the path the shock travelled up my arm when I'm thinking about it.

That hasn't happened before or since, what would cause that?
Sounds like the polarity switch was in the wrong position.

Having a polarity switch sort of defeats the 3-prong plug. Odd build. You definitely should have an outlet tester (or DMM/VOM), and you need to know which position of the polarity switch is "normal".

Kiwi
02-03-2012, 08:18 AM
"I like the idea that the amp is 95%+ original, so I haven't been motivated to swap out the plug."

I wouldn't think this change would really alter the value of the amp. Keep the parts and I think all is good.

I believe the vintage-gear guys agree that changing to a 3-prong plug won't hurt an old amp's value. It's such a sensible mod. Might even help with resale since the next owner won't have to do it, or worry about getting zapped.

I've never quite understood why collectors want you to keep the old cord (and replaced caps and other items that wear out) but that seems to be the common practice. Easy enough to toss them in a ziplock bag, though.

=K

Ryan07
02-08-2012, 08:26 AM
So does anyone know....

Why doesn't my 2-prong Dwarf amp from the 70's ever shock me? It doesn't have tubes, fwiw.

http://www.jedistar.com/images/amp2/Dwarf_amp.jpghttp://cdn2.sulitstatic.com/images/2011/0506/183320907_dwarf3.jpg

Blue Strat
02-08-2012, 08:33 AM
Simple answer: If there's one in a million chance of danger (actually, it's much higher) would you want your daughter subjected to it?

Really, this isn't difficult and doesn't require 4 pages of OPINIONS.

Ryan07
02-10-2012, 09:25 AM
So I just got my first blackface :). When I play the PR plugged in by itself (Or with freestanding fuzz pedals) all is fine..no shocks. But when I plugged in my DMM (3-prong grounded) I got a slight shock when I touched the DMM. Also, when playing my guitar (with dmm) I felt "electric". You know that feeling you can get in your nerves when playing an old amp (probably extra electric flowing through you!?).

Do you guys avoid pedals that need to be plugged in with 2-prong vintage amps?

Thanks

Jef Bardsley
02-11-2012, 06:35 AM
Again, two-pronged plugs on amps were not meant to be plugged in randomly. To be safe, you should test the outlet to determine the 'hot' side, and trace the cord to determine which of the prongs should go to the hot side.

Do not trust an "electrician" to wire the outlets properly. I've seen the white and black mixed up on adjacent outlets in a defense plant laboratory, and I've lived in a house where the entire second floor had 120V on the neutral and ground.

Do not believe the internet lore that adding a 3-prong plug will magically make your amp safe. It won't. Especially not in bars and churches where the wiring, at best, was done by the lowest bidder and at worst was done as a 'favor'. At least with a two-prong, non-polarised plug you can flip it over and make things right.

hunter
02-11-2012, 07:00 AM
While I support the three prong plug concept, don't ever let that lull you into a false sense of security. Many, yes many, clubs have wiring that is not correct. You can find instances where there is a three prong outlet on the wall with no wire to the ground, + and - reversed, and worse. I have gotten nasty shocks off of three prong outlets. Identical to the ones you get off of two prong outlets.

Best to always use precautions such as mentioned earlier, listen for excessive noise, static, hum, pops when you touch the strings, always touch your guitar string to the mic before touching it with your face. You can see the spark jump if your polaritys are wrong! Touch the chassis of your amp with your guitar, touch your buds amp, guitar, or the PA when you are not touching your plugged in guitar (until you have checked things out). Do the spark test on everything. If you really want to be thorough, get the outlet checker at Radio Shack and always test your outlets. Note that this may not be enough when you have house sound since the house probably won't take kindly to you unplugging the PA to check outlets.

I played amps for years with two prong plugs (still even have a couple although I typically swap em) and learned to listen and test. On the old school two prong amps, I even marked a small dot on the plug to indicate the right way to plug it in based on properly wired sockets, and still check when in a club or studio or in any setting I haven't tested.

Also, a three prong cord/outlet will not protect you from exposed hot leads on a frayed or poorly insulated cord. If you have cut extension cords, toss em.

Three prong is safer yes, but don't rely on it to save you.

hunter

guitarcapo
02-11-2012, 07:39 AM
Unless you can levitate, when you are standing on any surface, you're grounded.


Rubber shoes.

guitarchris
02-18-2012, 08:20 AM
In the panel the grd is seperated from the neutral. You are tied at the xformer in the new systems. The grd bar at the panel goes to the grd field and usally the nearest structural ground.That separates the neutral and ground at the panel. NEC does not allow you to wire the neutral and ground together in the panel or the outside disconnect for said structure.

Unless in GA you guys follow state codes that are different than the NEC I have to say you are wrong. I am an Electrical Contractor in NC. In a sub panel you are correct, it would be 4 wire (2 hots,neutral and ground), ground and neutral must be seperate. At the service/ main panel the neutral and equpment ground (which is the "3rd prong wire, tied to ground bar then to a ground rod in most residentail instances and bonded tobuilding steel and metal piping/waterline) are tied together hence the name the NEC gives to the "neutral"= Grounded conductor. Sounds like you are in Xformers and more industrial type situations....I I work on or install residential services on a daily basis. Just for for fun take a peek at your service at home, read back over your post, you'll see what I'm say'n.

To the OP, get it grounded (3 prong cord) by a tech ASAP. It's not worth the risk. Plus if there is a short to the chasis it will trip the breaker and possibly prevent damage to your amp!!!

GTMS
10-30-2013, 11:16 AM
I got an 1967 trully vintage tube amplifier with 2 prong wire plug. Which I am thinking to connect a cable with 3th prong grounded. However I read somewhere that some circuits sledom runs live on the chassis and if you ground you are exposing yourself even more. I am a bit in doubt as if I should ground or not my combo amplifier. I got the schematic diagram of the circuit from the web now any one any ideia if it is safe to connect the 3th prong on the chassis of this ampliflifier?
sorry dont know how to attached a photo here!

beerijuana
10-30-2013, 11:40 AM
I've been zapped by a two prong plug equipped Gibson amp from the 60s (in a wooden case) on a carpeted floor, while wearing shoes. Roll the dice if you want. I'd get in changed over if you're going to use it.

I had this happen while playing through a brown-face Bandmaster (two prong). Same as you, shoes and carpet. It sure tasted like 125 volts.

always touch your guitar string to the mic before touching it with your face. You can see the spark jump if your polaritys are wrong!

I used a multimeter to test for many years, after I got shocked. I still carry it around, as has been mentioned, bars, clubs and rehearsal spaces are not always as safe as some think; a lot of these places are wired by DIY guys to save money.

I also bought one of these (should be standard in everybody's gig bag):

http://d74bwl3dcueqd.cloudfront.net/images/guide/15edb54123564e6c803661f44ba068e8/315x500_ac.jpg

If you don't have a multimeter, those cheap two lead neon voltage testers can be great for preventing zaps.

http://image.made-in-china.com/2f0j00JMCtiehFyLcZ/VoltageTester-FHT-9805-2-.jpg

GTMS
10-30-2013, 01:50 PM
what I meant is. Can any vintage tube amplifier be grounded on the chassis? or somethimes does the chassis is by design conducting live current?

Kyle B
10-30-2013, 01:58 PM
what I meant is. Can any vintage tube amplifier be grounded on the chassis? or somethimes does the chassis is by design conducting live current?

Some older TV's conducted along the chassis. But they're wrapped in plastic.

It's pretty safe to assume if you can touch the chassis, it's not designed to conduct current.

GTMS
10-30-2013, 02:23 PM
thanks Kyle it makes sense. I am wondering if I should replace to a 3 pin. Based on Jef comments "Again, two-pronged plugs on amps were not meant to be plugged in randomly. To be safe, you should test the outlet to determine the 'hot' side, and trace the cord to determine which of the prongs should go to the hot side.

Do not trust an "electrician" to wire the outlets properly. I've seen the white and black mixed up on adjacent outlets in a defense plant laboratory, and I've lived in a house where the entire second floor had 120V on the neutral and ground.

Do not believe the internet lore that adding a 3-prong plug will magically make your amp safe. It won't. Especially not in bars and churches where the wiring, at best, was done by the lowest bidder and at worst was done as a 'favor'. At least with a two-prong, non-polarised plug you can flip it over and make things right."

Kyle B
10-30-2013, 03:04 PM
Personally I'd do it.

The overwhelming opinion of the Professional Amp Techs and Electrical Engineers on this forum is that a 2-prong plug should be changed to 3-prong. There are some who say "no", but they're in the minority. Those who say 'no' usually cite some noise, tone, or some other ethereal reason not to do it. The fact is, with the chassis grounded to earth, you have the safest possible situation. A f*d up vintage tube amplifier that's not grounded has the potential to kill you.

People speak of tone to die for, but that shouldn't be taken literally!

Blue Strat
10-30-2013, 03:20 PM
At least with a two-prong, non-polarised plug you can flip it over and make things right."


It doesn't make sense to "be safe" (which is debatable) for the least common cases, and unsafe for the most common cases.