Grounding question

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Elmo89m

Elmo89m

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My friend is thinking about buying a 1974 fender super Reverb for a reallly good price but he has a problem with the grounding. It is a two prong outlet on the amp and the amp has a grounding switch. THe man at the store said that basically to get the grounding right you keep changin the switch until you don't get shocked anymore. THis scares him and i was wondering if it would be possible to replace to two prong electric inlet with a three prong and the connect the grounding piece on the three prong to a grounding point on the amp.? thanks
 
Elmo89m said:
THe man at the store said that basically to get the grounding right you keep changin the switch until you don't get shocked anymore. THis scares him
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The guy at the store is an idiot, and your friend is right to be scared. Those ground switches are just a cap to ground which gets switched between the hot and neutral legs of the power.




They have a nickname too.









Death caps.



Caps have this nasty habit of occasionally shorting out, and when they do the chassis (and the strings) go live at 120V.



Shortly after that, you go completely NOT live.




As in, dead.



Which is not a good thing.




They best thing to do is have someone who knows what they are doing replace the two prong plug for a three prong cord, and get rid of the death cap. (Even when unpluged, tube amps carry voltages which can kill you. Don't do it if you are even a little uncertain about what you are doing.) It is a minor thing, and only the most hidiously anal vintage idiots care about it. Even the king of all "vintage" amp wierdos (Gerald Weber) suggests this mod. Without doing that mod, I wouldn't even think of playing one of those amps, personally.


Light

"Cowards can never be moral."
M.K. Gandhi
 
A good way to test that amp would be to play an outdoor gig in the rain and sing into a mic. If he lives, the switch was set right. :D If he dies it was wrong :eek: ...Light is right. Tell your friend to have the mod done. Staying alive is much more important than preserving the vintage death trap of an old amp.
 
Light said:
Death caps.

Caps have this nasty habit of occasionally shorting out, and when they do the chassis (and the strings) go live at 120V.
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Jesus H Christ on a Crutch..!!! Brutal...

Reminds me of a show we went to several years back at the TOMB of DOOM here in Memphis...

Dr Hook...

Ray cam out on stage and started the set.. Got about 3 words into the song and jumped back from the mic cussin' and spittin'.. A few minutes later it happens again.. This time he caught his beard on fire... You could see it smokin' from 20 rows back at least...

--
Rob
 
Crash © said:
Jesus H Christ on a Crutch..!!! Brutal...

Reminds me of a show we went to several years back at the TOMB of DOOM here in Memphis...

Dr Hook...

Ray cam out on stage and started the set.. Got about 3 words into the song and jumped back from the mic cussin' and spittin'.. A few minutes later it happens again.. This time he caught his beard on fire... You could see it smokin' from 20 rows back at least...

--
Rob
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Well, that's not quite the same thing. That is having the amp and the mic on seperate circuits, which ends up with the guitar player completing the circuit. That actually kills people all the time too, though.

I actually worked with a guy who WANTED a little voltage going through the mic. He always wanted to get 12V on his mic. Said it made him feel the more in the moment. He didn't get it very often, though, because there is no real way to create that deliberatly.


Light

"Cowards can never be moral."
M.K. Gandhi
 
I've completed the circuit between a guitar and a mic (and lived to tell about it) and any of you guys who have never had this experience can take my word for it...IT IS NO FUN AT ALL! Everything needs to be grounded properly or sooner or later you WILL become the ground connection. A good service person can quickly and easily make the modification to an ungrounded amp, this will be a few dollars well spent and might even (seriously) save a life. At the very least it will eliminate some hum problems and avoid a few shocking experiences.
 
I remember an amusing little story where I was at a band practice many, many years ago and I sat down on a drain pipe that came away from the wall on a 45 degree angle. I got 120 VAC directly up the ol poop shoot. Do the mod.
 
Elmo89m said:
My friend is thinking about buying a 1974 fender super Reverb for a reallly good price but he has a problem with the grounding. It is a two prong outlet on the amp and the amp has a grounding switch. THe man at the store said that basically to get the grounding right you keep changin the switch until you don't get shocked anymore. THis scares him and i was wondering if it would be possible to replace to two prong electric inlet with a three prong and the connect the grounding piece on the three prong to a grounding point on the amp.? thanks
Click to expand...

As others have said, don't muck about in a tube amp if you don't know how to drain the voltage off the filter caps. The mod is very easy, though. AFTER DISCHARGING THE FILTER CAPS, just remove the old power cord, and put the new one in, connecting the black and white wires the same way as the old cord. The extra wire (green) goes to the chassis. An easy way to make that connection is to put a crimp eye on the wire and find a conveniently located mounting screw in the chassis that you can take out temporarily and reset though the eye. Make sure that the conducting part of the eye is sufficiently far away from any other connections that even if things move around a bit, nothing will touch it.

Oh, and while you are at it, make the new power cable nice and long, a lot of the old two prong cables were pretty short.
 
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I gig very regularly and worry like hell about this stuff.

Is there a good FAQ about electrical safety for guitarists and singer/guitarists when playing live?
If not I wonder if we could put one together from all the assembled knowledge here and make it a 'sticky' thread?
 
okay nevermind, my buddy didn't know what he was talking about (and neither did the salesman) turns out it is a three prong and is fine. thanks for the entertaining replies though
 
Um...... technically, voltage can't kill you.

But the current it carries can!

As little as 18 MILLIamps in the right conditions.

.018 amp.
 
c7sus said:
Um...... technically, voltage can't kill you.
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That's correct. A taser pulses 50,000 volts of pure fun through your muscles but doesn't kill you. Ouch :eek:
 
Elmo89m said:
okay nevermind, my buddy didn't know what he was talking about (and neither did the salesman) turns out it is a three prong and is fine. thanks for the entertaining replies though
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Still, if it has a ground switch, it is probably a death cap, and should be removed.


Light

"Cowards can never be moral."
M.K. Gandhi
 
I used to carry a volt meter with me. Connect one side to the guitar and the other to the mic. Then you know for sure if you will fry. I have had that ecperience a few times. I agree change the cord and trust but verify of course.
I didn't trust the road crew to check this.
 
That third prong won't do you a bit of good if the outlet you plug it into isn't wired to code. A cheap but possibly lifesaving addition to every electrified musician's gig bag should be a circuit tester. Radio Shack sells a little yellow block with LED's on it that will alert you to open ground, hot-neutral reversed, etc. I highly recommend having one and checking an outlet before you plug your amp into it.
 
ggunn said:
That third prong won't do you a bit of good if the outlet you plug it into isn't wired to code. A cheap but possibly lifesaving addition to every electrified musician's gig bag should be a circuit tester. Radio Shack sells a little yellow block with LED's on it that will alert you to open ground, hot-neutral reversed, etc. I highly recommend having one and checking an outlet before you plug your amp into it.
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Amen brother!


Light

"Cowards can never be moral."
M.K. Gandhi
 
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