WTF just happened?!?

[Maldeve]

If I had a cam id post the pictures but never have I had this happen with any amp I own.

Ok just got home from work went up stairs turned the amp on (Mark4 med. head) and went down to grab a beer and my smokes. The amp was in standby like always it was maybe warming up for about 2min tops.

I hit the standby switch off and grabbed my guitar by the neck with my fingers gripping the strings. It was instant fire, not a shock , intense heat so much that it burned 7 str imprints into my hand! I instantly dropped the guitar and was in shock, completely scared the **** out of me.

I grabbed the guitar by the base thinking i was going to catch the rug on fire but there was no sign of heat or anything? I lightly touched the strings and they were cold.

I though I was having a flashback but I looked back at my hand to still see the 7 strings burned across my fingers....

What the hell just happened? It has completely put me on edge now. I keep tapping my strings before i pick my guitar like it was a hot plate or something.

Has anyone ever had this happen? Should i have the amp looked at? Its been working flawless up to this point.

 

[ketiov]

Sounds like you got shocked, as in by electricity. Definitely not good.

 

[Monsta-Tone]

It definitely needs to go to the doctor.

It could be a bad filter cap, or if the amp is a version A, it might be a bad capacitor on the Ground Switch.

 

[stokes]

Sounds like you got some serious B+ on your ground.Have that amp checked before you get fried.DONT PLAY THAT AMP TILL YOU GET IT CHECKED!!!If you had been grounded ,say,by touching a mike,that was properly grounded,you probably wouldnt be reading this now.You are looking at 450+ volts.

 

[Anonymous]

Post removed.

 

[user 7737]

****... scary :shock:

 

[Herbie the Rad Dorklift]

I played through a gig all the while being shocked by the mic everytime my lips touched it....

Never even thought at the time how dangerous it was!

 

[Monsta-Tone]

I played through a gig all the while being shocked by the mic everytime my lips touched it....

I got so mad at a gig that I ripped the sleeves off of my shirt and put them over the mic with a hair tie. Freaking annoying and dangerous.



The Ground Switch does this, I may have the + & - backwards:

+ or "A" Provides a reference to ground for the Hot or 120 volt side of the power cord

"Off" Provides no reference to ground, other than the ground itself

- or "B" Provides a reference to ground for the Neutral or return path of the power cord

In Europe and most other countries with other than 120 volts, the "B" will provide a reference to ground for the other Hot wire, as there are 2.



This reference to ground is provided by a 450 or 600 volt capacitor. Usually the same make and model that you will find on the circuit board between gain stages and in the Tone Stack.

If this capacitor fails, it provides a path for the electricity to flow directly to the chassis of the amp.

Your guitar is plugged into the jack on the front, this jack is grounded to the chassis usually.


These have been illegal in most countries since the late 80's, or early 90's (I think that is the correct time) because of this fact.


It is usually customary to remove the capacitor on the ground switch when doing a cap job or changing from a 2 prong cord to a 3 prong cord. Most Fender and Marshall techs call it the "Death Cap."


:lol: On the other hand, I have almost enough Astron and Paktron capacitors to make a complete Twin Reverb now. :lol:

 

[Monsta-Tone]

I played through a gig all the while being shocked by the mic everytime my lips touched it....

I got so mad at a gig that I ripped the sleeves off of my shirt and put them over the mic with a hair tie. Freaking annoying and dangerous.



The Ground Switch does this, I may have the + & - backwards:

+ or "A" Provides a reference to ground for the Hot or 120 volt side of the power cord

"Off" Provides no reference to ground, other than the ground itself

- or "B" Provides a reference to ground for the Neutral or return path of the power cord

In Europe and most other countries with other than 120 volts, the "B" will provide a reference to ground for the other Hot wire, as there are 2.



This reference to ground is provided by a 450 or 600 volt capacitor. Usually the same make and model that you will find on the circuit board between gain stages and in the Tone Stack.

If this capacitor fails, it provides a path for the electricity to flow directly to the chassis of the amp. This is usually not a direct short, but a gradual one.

Your guitar is plugged into the jack on the front, this jack is grounded to the chassis usually.

It was used in late 50's, 60's and early 70's amps to reduce the hum that was sometimes associated with different wiring in different venues.

The ground switch was made obsolete when the advent of grounded power cords happened sometime in the early to mid 70's. I have no idea why manufacturers kept using them, other than the "Don't fix it if it's not broken" attitude.


These have been illegal in most countries since the late 80's, or early 90's (I think that is the correct time) because of this fact.


It is usually customary to remove the capacitor on the ground switch when doing a cap job or changing from a 2 prong cord to a 3 prong cord. Most Fender and Marshall techs call it the "Death Cap."


:lol: On the other hand, I have almost enough vintage Astron and Paktron capacitors (removed from ground switches) to make a complete Twin Reverb now. :lol:

 

[sbalderrama]

So what is the safest position to run a Mesa with the 3 position ground switch? What is the intent of the 3 positions anyway?

Ok, found the following on a FAQ. So if a Mesa switch is in the middle position and the amp has a 3 wire plug, then is any connection through a cap avoided?

----------------------
What is a "death cap"?
The cap is there to provide signal coupling between earth and chassis ground. You want the chassis to be referenced to earth ground and not to float in order to shield stray RF. This coupling is achieved not by hard wiring, but via a .02-.05uF/400-600V capacitor.

The neutral (white) 120VAC wire is grounded at the service panel (fuse box to old-timers). In the (bad) old days of nonpolarized 2 conductor plugs, you had a 50% chance that a particular AC leg would be the one which was grounded. That's not particularly good odds. Hence the selector switch which would connect one or the other leg to the chassis-coupling cap. If this cap becomes electrically leaky, you have a 50% chance that the chassis will be energized @ 120VAC. Thats why you get shocked when you touch chassis on some old equipment. If the cap is in good shape, then there would be no problem if the switch is in the wrong position, other than some additional hum. Old caps (especially the wax/paper ones) do become leaky in time and act more like low value resistors than caps. OUCH!

With a 3 wire plug, you now have a real connection from chassis to ground via the green wire. No way to mix it up, unless the venue's service is miswired. Thus, there's no reason to keep the old grounding cap.

-Mike Schway

 

[stokes]

I dont believe this is a "death cap" issue.That cap is dealing with 120vac,I dont think 120vac on the chassis then going to the strings via the guitar ground would cause the heat described.It sounds more like he has something in the B+ leaking to ground,it should blow the fuse,but who knows for sure what is going on there,sounds like it may have been an intermittent problem,and if the ground lug on the 3 prong are working properly it shouldnt be a problem,but with that kind of voltage,I wouldnt take a chance.I think if he touched something grounded at the right moment,the outcome would have been very different.Dont take any chances,Maldeve,get that amp checked out before turning it on again.

 

[stokes]

Certainly sounds like this amp is posessed by some kind of demon.In all the years I have been involved with amps,I have never heard of the strings getting hot like this.Obviously my warnings here are not based on having seen this before,but common sense dictates that lots of heat from something that has lots of volts,where it shouldnt even be getting warm is cause for serious concern.

 

[bryan_kilco]

this is by far the most satanic story I've ever heard on this forum. ****.

:!:

 

[Shep]

just sound to me that you were shreding SO hard when you last played it that the strings were Still hot??? well thats why JP has special string that can exceed the temperature of the sun???? :shock:

 

[stomper]

The high voltage in an amp is DC and travels in one direction. Usually towards ground or the output transformer. Sounds like you have AC leaking to the chassis somewhere. I bet it was making your strings work like the heating element in a toaster. AC travels in both directions, and can get you from the chassis. I've even heard of people being hit by lightning via their washing machine. Anyway, check this page for some insight.

http://geofex.com/ampdbug/shock.htm

 

[stokes]

The high voltage in an amp is DC and travels in one direction. Usually towards ground or the output transformer. Sounds like you have AC leaking to the chassis somewhere. I bet it was making your strings work like the heating element in a toaster. AC travels in both directions, and can get you from the chassis. I've even heard of people being hit by lightning via their washing machine. Anyway, check this page for some insight.

http://geofex.com/ampdbug/shock.htm

Dc current flows from ground to the positive end of different points of the circuit,such as the plates of tubes,not towards ground.If the amp is not properly grounded via the 3rd prong at the outlet,different scenarios can cause the chassis to become "hot" putting high voltage on your strings via the chassis.Of course it is possible that the ac is leaking to the chassis,but in order for the strings to act like a heating element you would need both ac lines connected to the string.If the cap on the ground switch shorted,you would only have one side of the ac line shorting to the chassis.