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Electrical Risk or Not?

Discussion in 'Amp Tech Center' started by Milspec, Jan 24, 2021.

  1. Milspec

    Milspec Poster Extraordinaire

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    I just aquired an early '50's Kalamazoo amplifier which was serviced by a very good tech, but the previous owner chose to retain the original reddish-brown AC cord with a 2 prong plug. Normally, I would just have it changed out, but must admit that the original cord is in excellent condition and has a ruddish brown tone which matches the chassis so I kind of what to keep it as well.

    Hence the safety question. Since the chassis is housed in a wood cabinet which would not conduct electricity, one would have to contact the metal chassis to complete a circuit if there was a short. The knob is bakelite so it shouldn't conduct electricity and one could use a piece of wood to flip the on/off switch as an added precaution. That would just leave the instrument cable plugs as the risk which could could easily be avoided until the amp is powered down.

    I guess what I am trying to do is decide how much of a risk is there really in using this serviced amp with only a 2 prong cord? It isn't an amp that will be played a lot, but I am trying to decide if it is dumb to keep the cord?

    Are there any options to provide safety without replacing this cord or is there a resource that could match the original cord in a 3-wire for replacement?
     
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  2. Boreas

    Boreas Friend of Leo's Silver Supporter

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    Death by amplifier was not a common problem since that is all there were before the changeover to grounded outlets. But people were also used to getting shocked on occasion. NOTHING was grounded before that - unless it had a separate ground wire that most people left dangling.

    Question is - do you feel lucky? Also, consider anyone else who may come in contact with the amp. I would recommend saving the original cord, but replace it. Not only is it ungrounded, it is OLD. That means potentially failing insulation internally. Try to source a power lead that is the same color.
     
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  3. Jon Snell

    Jon Snell Tele-Holic

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    If you remove the death cap C5, that will help to make it safer. Screenshot 2021-01-24 at 22.08.32.png
     
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  4. kbold

    kbold Friend of Leo's

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    My thought too. More like playing Russian roulette than roulette.
    Do you feel lucky ..... well, do ya?
     
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  5. dogmeat

    dogmeat Friend of Leo's

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    yep, dump the C5 cap for sure. maybe keep the cord, put on a modern cord cap. just make sure you get the small blade on the hot side.
     
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  6. BobbyZ

    BobbyZ Doctor of Teleocity

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    Try this experiment. Take a voltmeter set it to measure wall voltage, go from the chassis of your two prong amp to a ground. (chassis of a properly grounded amp works fine)
    Now see what you get for voltage, flip the plug and try again. Try it with the amp turned on and off. Remember that all the parts on the guitar that are hooked to the chassis via the cable's "grounded shield" will have whatever voltage potential you find on that chassis. Strings are often "grounded".
    Screwing around a few minutes like that, is probably going to make you want a grounded cord.
    Every time I've done that, on a two pronger, I've found wall voltage on the chassis, depending on the orientation of the plug and the ground switch.
    Current is another matter. If the amp has a power transformer and good "death cap" it's just whatever AC the cap can pass, it'll shock you pretty good when your lips hit the mic or you stand barefoot on concrete though!
    With a "widow maker" or shorted "death cap" it's like sticking you finger in a light socket.
    "Back in the day" players plugged in then touched the mic with the back of their hand, if they got shocked, they changed the ground switch or flipped the plug. That was fairly safe, but properly grounded cords are so much better.
    I'm actually surprised a tech would leave a two prong cord on anything. I wouldn't, someone wants to keep the cord they can have it back on a zip lock bag or go somewhere else.
     
    Last edited: Jan 24, 2021
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  7. Milspec

    Milspec Poster Extraordinaire

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    Thanks for the replies, I agree that it always makes more sense to upgrade the cord, but I just wasn't certain it was a likely risk. We all know that the moniker of "death cap" is based on potential risk rather than any real history of it causing death for example. I am old and grew up in the days before grounded outlets and can't remember ever being shocked by anything with the exception of a power drill that had a short in it....that one hurt a bit, but my hand was wrapped around the metal housing. For an amp that will receive limited use, I just didn't want to seem paranoid.

    My amp tech is a wizard with over 40 years with Fender and is a factory authorized tech for most of the big names out there, but at the end of the day he still follows directions of the customer. He pointed it out to me, but didn't lecture and admitted to playing a lot of 2 prong amps in the course of his business without being shocked.

    I think I will check the chassis with the multimeter out of curiosity now as well as start shopping for a vintage looking lamp cord or something to match.
     
  8. strat a various

    strat a various Friend of Leo's

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    Ha. So, in Vegas there was this really talented tech (great player, too). He was a Fender master, knew all the circuits, all the tricks. He absolutely did not want to alter the original circuit in any way. Amp came with a two prong plug? Amp is leaving here with a two prong plug. No mods, no added bias pots. Original everything. Didn't bother me. I know how to install a three prong grounded pigtail.
    What a character, though.
     
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  9. edvard

    edvard Tele-Afflicted

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    I just did a little search, and it looks like brown 3-conductor power cables are a bit hard to find. Closest I could find was cable with a brown braided cover, which might actually look nice.
     
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  10. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Yeah, if it was named after a real history of it causing death, it'd be called the "Relf cap." :(

    This sentence worries me or puzzles me. If you 'avoid' the instrument cable plugs, your amp won't make much music. If you plug into 'em to make music, you need to read what @BobbyZ said:

    and *then* read about Keith Relf...

    Oh, and the problem with replacing with a modern 'polarized' cord (or just plug) is that a scary proportion of homes, not to mention rehearsal spaces and clubs, have hot and neutral wired backwards at the socket.
     
    Last edited: Jan 24, 2021
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  11. OldPup

    OldPup Tele-Meister Ad Free Member

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    If it's good enough for an exemplary tech, then it's fine, leave it. Is the previous owner offloading it because he died by electrocution? Maybe don't play barefoot in a puddle while you kiss a mic and sing. You can't do that. But if you just want to play guitar, do that and leave the cord alone.
     
  12. dogmeat

    dogmeat Friend of Leo's

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    look at the diagram.... once C5 is gone, the wall power doesn't have ANY connection to the chassis. it only goes to the primary side of the transformer all that is isolated from everything else. the secondary side is using chassis for common ground.... that means the "danger", such as it is comes from the secondary (making the primary power polarity a moot point).

    this is what I had in mind.....
    [​IMG]


    [​IMG]

    put the power on the fused side. this was chosen at random off fleaby.... there are other choices. anyway, thats what I'd do.

    and yes, I still slap the mic with the back of my hand out of habit. can't remember the last time I got a zap but it's been decades
     
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  13. Paul G.

    Paul G. Friend of Leo's

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    1. You probably won't be killed by the amp.
    2. You may get shocked occasionally (your guitar is connected to the chassis, and you're touching the guitar).
    3. However -- if you do develop a short to the chassis (old amp), there is nothing to prevent any stray voltage from traveling through your body to ground. That's not good.

    Wire it up to modern standards, wrap up and keep the original cord with the amp for "originality". Absolutely remove the "death cap". It's a no-brainer.
     
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  14. Milspec

    Milspec Poster Extraordinaire

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    That is the problem (albeit just cosmetic), finding a brown wire. I found a supplier of braided lamp wire which looks intersting, but not sure if a cotton braiding is all that durable for a guitar amp. Still, it would actually look very vintage.
     
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  15. strat a various

    strat a various Friend of Leo's

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    There's a flexible paint designed for vinyls, plastics and leather that car restoration guys use on auto upholstery and dashboards, door liners, etc. Can't remember the name. It will stick to cable insulation that hasn't been treated with armor-all. One could paint a cable brown if the color is important.
     
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  16. edvard

    edvard Tele-Afflicted

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    If it's durable enough for a guitar cord (which would probably be moved around a LOT more than a power cord), then I think it would be fine.

    Good grief, now I have GAS for one to put on my '52 Deluxe when I get enough pennies saved up... :cool:
     
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  17. edvard

    edvard Tele-Afflicted

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    I thought of that too, but didn't know if there were a product for that. I think it might get to looking ratty after a while, but some people pay for things like that... :confused:
     
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  18. strat a various

    strat a various Friend of Leo's

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    I'll see if I can get the name from my hot rod buddies.
     
  19. Milspec

    Milspec Poster Extraordinaire

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  20. Peegoo

    Peegoo Poster Extraordinaire

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    If you're playing guitar with an amp that has a fault--a chassis live at mains voltage--it can travel through the guitar cable to your hands. If you're holding the guitar and you grab a mic or other item that is grounded, you can get a bad shock (or worse).

    Many modern appliances and power tools are safe to use with no ground wire in the mains cable because they're double insulated. Amps are not.
     
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