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  1. #1

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    I recently bought a vintage Gibson BR-6F amp (seems to be a 1954 model). I'm pretty new to buying any old gear at all. I'm still relatively new to tube amps in general, though I bought a Fender Deluxe Reverb Reissue a few years ago. My main reason for seeking out these amps is because I've seen Pasquale Grasso use a variety of vintage Gibson amps, whether it's the GA-50 or the Gibsonette, and I even believe he used a BR-6 before, in one of those streams with Rossano Sportiello.

    All of this is to say, I've read stuff online about people upgrading the 2-prong plugs that are on these amps to a 3-prong plug. My questions are:

    1. What is the use of this?
    2. Is it relatively simple for any electrician to do?



    It looks like the original plug is still there in the one I bought.

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  3. #2

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    You take it to an amp tech and they'll fix it for you. With a 2 prong plug there's a chance you will plug it into an incorrectly wired outlet and your strings will be live instead of neutral. A potentially deadly issue. Keith Relf, Yardbirds lead singer, died from this and there is a gnarly video of Keith Richards taking a shock on stage back in the 1970's.

  4. #3

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    Quote Originally Posted by AllanAllen
    You take it to an amp tech and they'll fix it for you. With a 2 prong plug there's a chance you will plug it into an incorrectly wired outlet and your strings will be live instead of neutral. A potentially deadly issue. Keith Relf, Yardbirds lead singer, died from this and there is a gnarly video of Keith Richards taking a shock on stage back in the 1970's.
    I'm from Belize. No such thing as an amp tech down here!

  5. #4

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    Quote Originally Posted by Loreto
    I recently bought a vintage Gibson BR-6F amp (seems to be a 1954 model). I'm pretty new to buying any old gear at all. I'm still relatively new to tube amps in general, though I bought a Fender Deluxe Reverb Reissue a few years ago. My main reason for seeking out these amps is because I've seen Pasquale Grasso use a variety of vintage Gibson amps, whether it's the GA-50 or the Gibsonette, and I even believe he used a BR-6 before, in one of those streams with Rossano Sportiello.

    All of this is to say, I've read stuff online about people upgrading the 2-prong plugs that are on these amps to a 3-prong plug. My questions are:

    1. What is the use of this?
    2. Is it relatively simple for any electrician to do?



    It looks like the original plug is still there in the one I bought.


    1. It's a safety issue, and is very important. It a) helps to greatly reduce the possibility of your amp catching fire and b) you getting the shock of your life. 2. Yeah, it should not cost you an arm and a leg, and may spare you from serious injury. Many guitarists have died of electrocution because of improper grounding. Safety first. Always.
    Last edited by citizenk74; 01-15-2022 at 02:06 PM.

  6. #5

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    Quote Originally Posted by Loreto
    I'm from Belize. No such thing as an amp tech down here!
    You can do it yourself, e.g. by following this instruction set. But amps that old often have patches of frayed, worn, or otherwise ineffective insulation on wires. Solder joints get cold, metal things corrode, non-metal parts crack, etc etc. And you don't know if you're looking at a previously modified or inexpertly repaired amp unless you have the knowledge, skill and experience to do so.

    You may be better off taking it to a local electronics shop, of which I see a few on a single Google search. Even if the shop is pure audio, a good tech should be a lot better at keeping you safe than you are unless you have experience. The schematic is easily found. Here's the one I have in my file:

    Gibson_BR-6F_schematic.pdf
    Attached Images Attached Images Upgrading 2-prong plug on vintage amp to 3-prong?-gibson_br6_schematic-jpg 

  7. #6

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    ^^ so much valuable advice.



    looks like a fine little amp, Field coil speaker, octal pre-amp ...

    ask around and find an amp technician, to have the amp gone through, that will make for a perfect home / studio amp.

    big vintage Gibson Amp fan here.


  8. #7

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    If you are going to gig with it, and by this I'm thinking about regularly going into unknown situations, changing to a 3 prong isn't a bad idea. If you're going to use it at home or in the studio and the original cord is in good shape, I might not mess with it. I suppose you have already pugged it in and played it, and you didn't die! In fact many many many two prong amps exist and guitar players aren't being electrocuted right and left. It can happen but it isn't as simple as plug it in one way and you're good and the other and you get a shock. A series of things have to line up and go wrong to get a shock.

    So back to gigging where you don't know the condition of the other equipment you may touch and the electrical systems, a 3 prong takes one variable out and decreases the chance of something going wrong. If you plug in at home and it's working fine and you never even move the amp. It will continue to be fine, even with out a 3 prong.

    If you're uncertain or uncomfortable making the change, any electronic repair shop should be able to help. For this, it doesn't have to be an amp repair shop.

  9. #8

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    Quote Originally Posted by Grez
    If you are going to gig with it, and by this I'm thinking about regularly going into unknown situations, changing to a 3 prong isn't a bad idea. If you're going to use it at home or in the studio and the original cord is in good shape, I might not mess with it. I suppose you have already pugged it in and played it, and you didn't die! In fact many many many two prong amps exist and guitar players aren't being electrocuted right and left. It can happen but it isn't as simple as plug it in one way and you're good and the other and you get a shock. A series of things have to line up and go wrong to get a shock.

    So back to gigging where you don't know the condition of the other equipment you may touch and the electrical systems, a 3 prong takes one variable out and decreases the chance of something going wrong. If you plug in at home and it's working fine and you never even move the amp. It will continue to be fine, even with out a 3 prong.

    If you're uncertain or uncomfortable making the change, any electronic repair shop should be able to help. For this, it doesn't have to be an amp repair shop.
    The amp hasn't actually been in my hands yet! It'll be one more week before it reaches down here. I'm really excited for it!

    I'd probably gig with it every other month or so, swapping between my current Deluxe Reverb and the BR-6F depending on the sound I'm going for, or laziness (weight haha, DRRI is 40lbs).

    From what I heard, the previous owner of the amp did audio and instrument repair, so I suppose the amp was well serviced.

    It's just that I saw other BR-6's online that were "upgraded to 3-prong", and the ones that Pasquale Grasso use appear to have gone through that as well - I guess it made me a bit uneasy and wondering if I should do some about that as well. I'm still on the fence about it, because on the one hand, I suppose "if it ain't broke don't fix it" - but I guess there is still that "potential risk" too...

  10. #9

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    Quote Originally Posted by Loreto
    The amp hasn't actually been in my hands yet! It'll be one more week before it reaches down here. I'm really excited for it!

    I'd probably gig with it every other month or so, swapping between my current Deluxe Reverb and the BR-6F depending on the sound I'm going for, or laziness (weight haha, DRRI is 40lbs).

    From what I heard, the previous owner of the amp did audio and instrument repair, so I suppose the amp was well serviced.

    It's just that I saw other BR-6's online that were "upgraded to 3-prong", and the ones that Pasquale Grasso use appear to have gone through that as well - I guess it made me a bit uneasy and wondering if I should do some about that as well. I'm still on the fence about it, because on the one hand, I suppose "if it ain't broke don't fix it" - but I guess there is still that "potential risk" too...

    You will definitely want to make sure your power supply and coupling capacitors have been changed (as well as the 3 prong cord). It is a cheap, absolutely necessary procedure that will make the amp reliable and save it from serious damage. This is the case for all vintage amps, so don't worry about it. Do it once and it will be good for another 30 years.

    Enjoy!!!

  11. #10

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    I have a 1964 Princeton that was all original when I got it. I used it on gigs and I got a painful shock on stage on one of those gigs. The next day, I took it to an amp tech and had a three prong conversion done. I kept the original 2 prong chord for the sake of "originality" and the value that comes with that, but my only regret is not doing the conversion before taking it out to gigs.

    Electricity is downright dangerous.

  12. #11

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    Quote Originally Posted by Stringswinger
    I have a 1964 Princeton that was all original when I got it. I used it on gigs and I got a painful shock on stage on one of those gigs. The next day, I took it to an amp tech and had a three prong conversion done. I kept the original 2 prong chord for the sake of "originality" and the value that comes with that, but my only regret is not doing the conversion before taking it out to gigs.

    Electricity is downright dangerous.
    What are the prerequisites for that to happen though? Is it avoidable with the proper precautions, or is it just out of my control? Any methods other than converting to three-prong that would save me from this?

    I'm somewhat resistant to it, because I honestly don't trust "technicians" here in Belize, especially to make modifications to an amp from 70 years ago. So while I'd love for it to be three-prong, I'm scared somehow they'd mess up the amp. Is this a rational fear?

  13. #12

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    It's a safety issue, as others have noted.

    An extreme case is that the chassis gets hot (meaning a power carrying part is making electrical contact with the metal frame of the amp). Something would have to break for that to happen, but it's a very old amp.

    In that case, the guitar strings could carry the same voltage as the socket in the wall. If you then touched a piece of equipment (or anything else) that was properly grounded, that could be deadly. If I'm wrong about that, hopefully someone will say so.

    Back in the day, when nothing had three prong power cables, getting mild shocks by, say, touching a mic, were commonplace occurrences. The 3 prong stops that too (polarized plugs too, I think).

    I have also heard, from one experienced tech, that the old Gibsons were not as well made as the old Fenders which contributes to my concern.

    Which leads me to wonder, did anyone ever bother to put a fuse in the string ground in a guitar?

    And, finally, based on reading ads over the years, I don't think that the 3 prong plug really lowers the value of the amp. I've never seen an ad touting "original 2 prong plug!"

  14. #13

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    Quick polarity test for a 2 prong is to plug a cord into the amp but not a guitar, give it a little volume and listen to the hum. Reverse the prong, listen to the hum. Orient the 2 prong the direction that produces less hum. Now you won't get a shock from 3 prong gear if you touch them both. If using 2 two prong amps do the hum test on both.
    Learned this back in the day from a old hand when I was pairing a 2 prong Ampeg V4 with a 3 prong Twin. The big thing is the power cord insulation , if it is cracking etc.... Replace immediately.

  15. #14

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    Quote Originally Posted by Loreto
    What are the prerequisites for that to happen though? Is it avoidable with the proper precautions, or is it just out of my control? Any methods other than converting to three-prong that would save me from this?

    I'm somewhat resistant to it, because I honestly don't trust "technicians" here in Belize, especially to make modifications to an amp from 70 years ago. So while I'd love for it to be three-prong, I'm scared somehow they'd mess up the amp. Is this a rational fear?
    This link gives an excellent explanation as to why old amps with 2-prong plugs can be dangerous.

    If all is working correctly in the amp, it's plugged in "backwards", and you touch another device that is at a different ground (such as a mic/pa plugged into a different outlet), you will get a nasty (but non-fatal) shock. If the amp is broken in such a way as to short circuit the wiring directly to the amp chassis (which can happen if the so-called "death cap" fails, or some other wire touches the chassis), the shock can be fatal because it results in delivering full wall current/voltage to you.

    The first scenario used to be pretty common in my neck of the woods, where the wiring in music venues was often full of grounding issues and amps were often 2-prong (or 3-prong plugged into a 3-2 adaptor without grounding the adaptor). I haven't gotten zapped in a long time because wiring has improved and amps are rarely 2 prong anymore. But I'm still careful not to touch a mic while also touching my guitar, just in case.

    The second scenario is pretty unlikely, since the amp has to be broken in a specific way for this to happen (I've had many shocks, but I'm still alive, (I think)). Despite all the talk of death caps, the truth is that guitar players back in the 70s and 80s were not constantly getting electrocuted. The real, common risk was an unpleasant zap.

    A properly installed 3-prong wire/plug eliminates the risk of either scenario (though I think that there can still be risk if the outlets involved are wired wrong). As a precaution, when you're holding a guitar that is plugged into your new amp, if you need to touch some other device (e.g., by putting your mouth against mic opening your fridge), brush it lightly and quickly with a finger while the other hand is touching the strings. If you get a shock, don't touch more firmly. Also, it's good practice to plug everything (guitar amp, effects, PA) into the same circuit, or even the same outlet.

    An electrician who really is an electrician and understands grounding and circuits and can read an amp schematic should be able to install the chord properly. A handyman who does a little wiring and fixes a toaster here and there, maybe not. I guess all you can do is talk to the person and try to get a sense of whether they understand the issue. Meanwhile take precautions when plugging stuff in and touching stuff.

  16. #15

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    Quote Originally Posted by John A.
    This link gives an excellent explanation as to why old amps with 2-prong plugs can be dangerous.

    If all is working correctly in the amp, it's plugged in "backwards", and you touch another device that is at a different ground (such as a mic/pa plugged into a different outlet), you will get a nasty (but non-fatal) shock. If the amp is broken in such a way as to short circuit the wiring directly to the amp chassis (which can happen if the so-called "death cap" fails, or some other wire touches the chassis), the shock can be fatal because it results in delivering full wall current/voltage to you.

    The first scenario used to be pretty common in my neck of the woods, where the wiring in music venues was often full of grounding issues and amps were often 2-prong (or 3-prong plugged into a 3-2 adaptor without grounding the adaptor). I haven't gotten zapped in a long time because wiring has improved and amps are rarely 2 prong anymore. But I'm still careful not to touch a mic while also touching my guitar, just in case.

    The second scenario is pretty unlikely, since the amp has to be broken in a specific way for this to happen (I've had many shocks, but I'm still alive, (I think)). Despite all the talk of death caps, the truth is that guitar players back in the 70s and 80s were not constantly getting electrocuted. The real, common risk was an unpleasant zap.

    A properly installed 3-prong wire/plug eliminates the risk of either scenario (though I think that there can still be risk if the outlets involved are wired wrong). As a precaution, when you're holding a guitar that is plugged into your new amp, if you need to touch some other device (e.g., by putting your mouth against mic opening your fridge), brush it lightly and quickly with a finger while the other hand is touching the strings. If you get a shock, don't touch more firmly. Also, it's good practice to plug everything (guitar amp, effects, PA) into the same circuit, or even the same outlet.

    An electrician who really is an electrician and understands grounding and circuits and can read an amp schematic should be able to install the chord properly. A handyman who does a little wiring and fixes a toaster here and there, maybe not. I guess all you can do is talk to the person and try to get a sense of whether they understand the issue. Meanwhile take precautions when plugging stuff in and touching stuff.
    Thanks. That's a great link. Explained the situation very well and I learned something about replacing the death cap properly. I had my old Ampeg converted to 3 prong, but I never realized there was another question to ask -- about the death cap.

  17. #16

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    Quote Originally Posted by Loreto
    I'm from Belize. No such thing as an amp tech down here!
    Unfortunately, that is a strong reason to not buy vintage amps. Basically anyone who can't do a fair amount of upkeep and repairs should avoid buying them. Bench charges for work can add up quickly. Another thing one might not think of is that some older can amps require tubes that are very difficult to come by and are priced accordingly. You might think you're getting a bargain until you learn that the tubes you need are $$$$.
    Last edited by whiskey02; 01-17-2022 at 09:22 PM. Reason: spelling

  18. #17

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    Quote Originally Posted by whiskey02
    Unfortunately, that is a strong reason to not buy vintage amps. Basically anyone who can't do a fair amount of upkeep and repairs should avoid buying them. Bench charges for work can add up quickly. Another thing one might not think of is that some older can amps require tubes that are very difficult to come by and are priced accordingly. You might think you're getting a bargain until you learn that the tubes you need are $$$$.
    That's what my family members told me who were trying to dissuade me from buying the amp, and I stubbornly ignored it for the novelty of owning a beautiful 1953 Gibson tube amp. Maybe I end up finding someone who know their stuff, but I suppose that's a big risk.

  19. #18

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    I'd look at it as a opportunity to learn more about hand wired tube amps. Properly sorted a good tube amp is very reliable. Tubes can be sourced and installed as needed but at jazz guitar gain levels last a.long time. The mechanics of component replacement are straight forward, the safety aspects of doing those jobs can't be ignored as capacitors can store enough juice to kill you. The information is readily available. Why not learn about something you appreciate. Worse case scenario, learn to pack really well for shipping to a boutique tech elsewhere.

  20. #19

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    It’s not difficult to convert a power cable to 3 prong, I did it in a couple if my vintage amps, I taught myself. Read about it and check some YouTube movies and do it yourself if you can’t find a tech. All there is to it, is that the chassis needs to be connected to the ground wire. The other wires stay in place.

    Safety over originality!

    BUT: are all outlets grounded in Belize? Presumed safety can be more dangerous than danger anticipated for….. I’ve played in places where the wall outlets were of the grounded type but the ground pin was not connected at all!



    Any does or dont's replacing 2 prong with 3 prong on old amps? | The Gear Page

  21. #20

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    Quote Originally Posted by Little Jay
    BUT: are all outlets grounded in Belize? Presumed safety can be more dangerous than danger anticipated for….. I’ve played in places where the wall outlets were of the grounded type but the ground pin was not connected at all!


    Any does or dont's replacing 2 prong with 3 prong on old amps? | The Gear Page
    From what I heard, there are some really old buildings that aren't grounded (or at least, buildings that are over 50 years old). In fact... I record sometimes in an old building that has the three prong outlets but is not grounded. I believe that it's mandatory for all buildings to be grounded - but if they've been around for a while, they slip through the cracks.

  22. #21

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    Quick question. When changing it to a 3-prong, is it necessary to rewire the grounding? Or simply replacing the cord as-is, and having the ground-prong be a "dummy" simply to get the direction right work out?

  23. #22

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    Quote Originally Posted by Loreto
    Quick question. When changing it to a 3-prong, is it necessary to rewire the grounding? Or simply replacing the cord as-is, and having the ground-prong be a "dummy" simply to get the direction right work out?
    That sounds like a very dangerous approach to me! Do it right or don't do it at all- the next owner might think it's correct and get zapped, even if you don't!

  24. #23

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    Quote Originally Posted by Loreto
    Quick question. When changing it to a 3-prong, is it necessary to rewire the grounding? Or simply replacing the cord as-is, and having the ground-prong be a "dummy" simply to get the direction right work out?
    I wouldn't just use an ungrounded 3 prong plug as a polarity control. You need to make sure that amp is safe to use.

    • I think the power transformer primary winding in your amp is connected to the chassis through a capacitor. This was a common practice to minimize hum - it's the reason for reversing the 2 prong plug in the outlet to find the position with lower hum. But that cap is known as the "death cap" because if it fails and shorts, it will connect your chassis directly to the mains power. Even if it's fine, it allows a tiny amount of AC current to flow to the chassis when the 2 prong plug is in the socket so that the wrong wire is hot. This will give you a tingle (or worse) if you touch the chassis or anything wired directly to it and you're grounded. Here's a link to a good discussion of this with some alternatives for dealing with it.
    • I've seen old amps converted to 3 prong plugs but wired with the neutral wire switched and the hot wire unswitched. This is another recipe for disaster and should be corrected.
    • You need to make sure you have a solid chassis grounding point, both physically and electrically.

    Be careful if you decide to try this yourself !! It's easy to do if everything is right, but you can get into serious trouble if you just connect the green wire to a chassis grounding point without checking and understanding the entire amp.

  25. #24

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    Quote Originally Posted by nevershouldhavesoldit
    I wouldn't just use an ungrounded 3 prong plug as a polarity control. You need to make sure that amp is safe to use.

    • I think the power transformer primary winding in your amp is connected to the chassis through a capacitor. This was a common practice to minimize hum - it's the reason for reversing the 2 prong plug in the outlet to find the position with lower hum. But that cap is known as the "death cap" because if it fails and shorts, it will connect your chassis directly to the mains power. Even if it's fine, it allows a tiny amount of AC current to flow to the chassis when the 2 prong plug is in the socket so that the wrong wire is hot. This will give you a tingle (or worse) if you touch the chassis or anything wired directly to it and you're grounded. Here's a link to a good discussion of this with some alternatives for dealing with it.
    • I've seen old amps converted to 3 prong plugs but wired with the neutral wire switched and the hot wire unswitched. This is another recipe for disaster and should be corrected.
    • You need to make sure you have a solid chassis grounding point, both physically and electrically.
    I went to an audio repair guy and he told me he used somewhere on the chassis as a grounding point. I'm guessing from what you're saying, this is an okay way to go? He seemed to know what he was doing, though I'm no expert at electrical stuff. He said it was safe, but it's Belize, so you never know.

  26. #25

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    As a budding EE and musician in 1957 I built myself an amp. When I started gigging and found myself onstage with several amps & a PA, I realized that death by electrocution would be an ironic exit for someone with my aspirations. In those days, long before grounded outlets were a thing, I decided on a defensive measure, building this:

    Upgrading 2-prong plug on vintage amp to 3-prong?-ground-saftey-tester-1-jpg

    It's just a neon pilot light with two 25' test leads. I had couple of slip-on alligator clips to hold things in place if necessary, and used it faithfully after setup to test for voltage between my stuff and everything else on stage. Found many dangerous situations over the years. Finally retired it after all equipment and venues were three wire, but I still carry an outlet tester and plug-in GFCI that I use for outdoor gigs or indoor gigs where I'm on the end of an extension cord of unknown origin, or where I'm picking up noise that suggests a missing ground. I'm long-retired from an engineering career, but still have no intention of death by electrocution.

    Danny W.











    Attached Images Attached Images Upgrading 2-prong plug on vintage amp to 3-prong?-ground-safety-tester-jpg