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Author Topic: Grounding info that could save your life.  (Read 3532 times)

Jeff Bankston

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Grounding info that could save your life.
« on: June 22, 2014, 05:34:43 pm »

http://www.youtube.com/watch?v=qNZC782SzAQ

i recomend watching the entire video. pay close attention starting at time mark 22:00. i have read comments on the forum about guys having a 2 prong power cord changed to a 3 prong grounded power cord on old guitar amps. i would never do such a thing. in fact if you thought it necessary to do it to an old guitar amp then you would need to do it to all stereo , tv , dvd players , tape decks , and other equipment that came with a 2 prong cord. i have ben trying to find other Mike Holt videos that would address this.
« Last Edit: June 22, 2014, 06:07:37 pm by Jeff Harrell »
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TJ (Tom) Cornish

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Re: Grounding info that could save your life.
« Reply #1 on: June 22, 2014, 06:32:54 pm »

http://www.youtube.com/watch?v=qNZC782SzAQ

i recomend watching the entire video. pay close attention starting at time mark 22:00. i have read comments on the forum about guys having a 2 prong power cord changed to a 3 prong grounded power cord on old guitar amps. i would never do such a thing. in fact if you thought it necessary to do it to an old guitar amp then you would need to do it to all stereo , tv , dvd players , tape decks , and other equipment that came with a 2 prong cord. i have ben trying to find other Mike Holt videos that would address this.
Old amplifiers commonly used "death caps" between hot, neutral and the chassis as a noise filtering component.  These fail, and are a frequent hazard, as they can fail to be a short circuit.  Updating the device absolutely needs to include changing from a 2-wire cord to a 3-wire cord, and is a very routine and well-understood operation. 

DVD players and other modern 2-wire devices do not have the same hazards for various reasons - being double-insulated, and/or of a modern design where energizing the chassis with line voltage is much less likely. 
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Jeff Bankston

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Re: Grounding info that could save your life.
« Reply #2 on: June 22, 2014, 06:43:07 pm »

Old amplifiers commonly used "death caps" between hot, neutral and the chassis as a noise filtering component.  These fail, and are a frequent hazard, as they can fail to be a short circuit.  Updating the device absolutely needs to include changing from a 2-wire cord to a 3-wire cord, and is a very routine and well-understood operation. 

DVD players and other modern 2-wire devices do not have the same hazards for various reasons - being double-insulated, and/or of a modern design where energizing the chassis with line voltage is much less likely.
i would not do it unless i absolutley knew it would make it safer. if your a manufacturer or have ben trained in this area to do the modification then thats different. i got in my first band around mid 1970. all the guys i was in bands with have fender amps and other brands from the 60's and i never knew of anyone to be electricuted then or now with 2 prong amps. i have never heard of or never know of anyone including me to be electrical shocked by old 1960's Dynaco amps or any other old amps with 2 prong cords. i'm not saying it cant happen. and if your are just connecting the ground to the metal chassis how do you know the neutral isnt also connected to the chassis and could possible cause a reverse flow of electricity through the ground and cause an electrical shock. an just because the cap fails how do you know it will cause an electrical shock ? have you done testing or have reports of this actually happening ?
« Last Edit: June 22, 2014, 06:46:53 pm by Jeff Harrell »
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Mike Sokol

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Re: Grounding info that could save your life.
« Reply #3 on: June 22, 2014, 07:15:50 pm »

Old amplifiers commonly used "death caps" between hot, neutral and the chassis as a noise filtering component.  These fail, and are a frequent hazard, as they can fail to be a short circuit.  Updating the device absolutely needs to include changing from a 2-wire cord to a 3-wire cord, and is a very routine and well-understood operation.

I agree with that statement, and have been "grounding" old tube guitar amps since the 80s. As far as modern "ungrounded" gear goes, it needs to pass UL inspection with double-insulated power supplies and have less than 0.75 mA leakage to ground. But even then I don't trust them completely since I've seen a few "2-prong" modern guitar amps fail with a lot of hot-to-ground leakage resulting a really big shock for the player.

Jeff Bankston

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Re: Grounding info that could save your life.
« Reply #4 on: June 22, 2014, 08:00:02 pm »

I agree with that statement, and have been "grounding" old tube guitar amps since the 80s. As far as modern "ungrounded" gear goes, it needs to pass UL inspection with double-insulated power supplies and have less than 0.75 mA leakage to ground. But even then I don't trust them completely since I've seen a few "2-prong" modern guitar amps fail with a lot of hot-to-ground leakage resulting a really big shock for the player.
i would want to see thest results from a testing lab that proves adding the ground actually makes it safer. i could add grounds to my stereo components but unless i have a lab with the proper equipment test it there is no way to know if its safer of more dngerous. there is a safty lab here in los angeles that we have used when equipment is modified. i would think it "might" be safer but unless there are facts from a test we really dont know.
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Mike Sokol

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Re: Grounding info that could save your life.
« Reply #5 on: June 22, 2014, 08:30:36 pm »

i would want to see thest results from a testing lab that proves adding the ground actually makes it safer. i could add grounds to my stereo components but unless i have a lab with the proper equipment test it there is no way to know if its safer of more dngerous. there is a safty lab here in los angeles that we have used when equipment is modified. i would think it "might" be safer but unless there are facts from a test we really dont know.

Jeff, I actually have a test bench with a calibrated/certified ground leakage tester and have done numerous leakage tests on stage amps over the years. I've also worked in a test lab that did leakage testing of equipment used to build and measure nuclear missile guidance systems in the 80's (really), so please believe that I know what I'm doing. 

And I've found bunches of guitar/stage amps that would easily leak enough current to the chassis to give you a serious shock. I can remember getting pretty good shocks from old Fender amps in the 60's if you had the stinger cap switched to the wrong side of the line, and I have a really early guitar amp in my junk closet with no power transformer and a non-polarized plug. Appliances with "grounded plugs" are limited by UL standards to 3.5 mA max leakage, which is a pretty good shock if you ground lift the power cord. 

So I'm convinced that any old/tube guitar amp with a 2-prong plug will be lots safer with a upgrade to a grounded power cord. Modern stereo gear should be perfectly safe without grounds if it was designed that way by the manufacturer.

Jeff Bankston

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Re: Grounding info that could save your life.
« Reply #6 on: June 22, 2014, 08:35:51 pm »

Jeff, I actually have a test bench with a calibrated/certified ground leakage tester and have done numerous leakage tests on stage amps over the years. I've also worked in a test lab that did leakage testing of equipment used to build and measure nuclear missile guidance systems in the 80's (really), so please believe that I know what I'm doing. 

And I've found bunches of guitar/stage amps that would easily leak enough current to the chassis to give you a serious shock. I can remember getting pretty good shocks from old Fender amps in the 60's if you had the stinger cap switched to the wrong side of the line, and I have a really early guitar amp in my junk closet with no power transformer and a non-polarized plug. Appliances with "grounded plugs" are limited by UL standards to 3.5 mA max leakage, which is a pretty good shock if you ground lift the power cord. 

So I'm convinced that any old/tube guitar amp with a 2-prong plug will be lots safer with a upgrade to a grounded power cord. Modern stereo gear should be perfectly safe without grounds if it was designed that way by the manufacturer.
this is what i wanted hear , someone that has done testing
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Tim Padrick

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Re: Grounding info that could save your life.
« Reply #7 on: July 02, 2014, 12:10:14 am »

When playing guitar, you have the amplifier chassis in your hands (by way of the cable connecting the strings/bridge/whammy bar/tuners to the amp).  In front of your mouth is a microphone that is grounded.  If something happens withing the amp and the chassis is not grounded, your guitar and you could well be live.  Touch that grounded mic, and it's funeral time.
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Steve M Smith

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Re: Grounding info that could save your life.
« Reply #8 on: July 02, 2014, 02:47:41 am »

I agree with that statement, and have been "grounding" old tube guitar amps since the 80s.

I started messing about with electronics at an early age and as far as I was concerned, things like guitar amplifiers were always grounded.  My earliest reference was a 1960s WEM amplifier (it had fuses on both live and neutral - but that's another story!).

I was very surprised when I first saw a Fender schematic with a two wire supply connection and a ground switch.  I had seen the ground switch before on amplifiers and wondered what it was, realising it was something different to what we do in the UK but it took viewing the schematic to realise what this madness was!


Steve.
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Mike Sokol

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Re: Grounding info that could save your life.
« Reply #9 on: July 02, 2014, 06:34:10 am »

I had seen the ground switch before on amplifiers and wondered what it was, realizing it was something different to what we do in the UK but it took viewing the schematic to realize what this madness was!

I had several Fender amps like this back in the 60's and 70's when I was a long-haired hippie child playing in a band. You would flip the switch back and forth and feel for the position of least shock (no kidding). IIRC my Kustom 100 also had this same sort of switch on the back. NOTHING was grounded in our backline or PA back then and we were always getting some kind of shock. But that was accepted as normal and part of playing "electric" instruments.

OT but really cool were the Red & Blue jeweled power lights on the front of old Kustom amps. They were visually hard to focus on which made them very easy to recognize from the back of the club.
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