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The "Death Cap" Thread...

Discussion in 'Amp Central Station' started by cklingo, Apr 27, 2010.

  1. tap4154

    tap4154 Doctor of Teleocity Ad Free Member

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    I was installing a 220 V drop-in range years ago, and the customer flipped off the breaker and I yelled "that's it" then I proceeded to cut the wires at once with a small snipper. But she had flipped it back on. It's an odd feeling to be standing there with your hands clamped on cutters and conduit, entire body shaking with voltage and wondering if this is "it". I was finally able to toss the range across the kitchen, breaking the wires out of the wall, then sat down for about an hour.

    Needless to say, I always hit the breaker myself ever since, and see no reason to avoid properly grounding an old amp.
     
  2. Wally

    Wally Telefied Ad Free Member

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    Billm is meaning that there is a power transformer. This tranformer isolates the chassis from the wall voltage with the physical 'isolation' of the primary winding from the secondary winding. That doesn't mean that it is 'safe'. IT does mean that it is safer than an 'American 5' type of amp that has no power transformer or isolation tranformer.
    That Guild probably has a two-prong power cord and therefor is not grounded....thereby making it less safe than it could be. IT will also have a 'death cap', which makes it less safe than it could be. With a 3-way power cord and removal of the death cap, it will be as safe as any electonic amplifier can be.
    I agree with BillM that the polarity reversal switch is useful...but there is that death cap again, right? I like proper wiring in the amp and an outlet tester to tell me if the wall outlet is properly wired. Then, things are 'safe' as they can be.
    All of this said, I grew up with amps that had two-wire power cords. IF the amp hummed, you flipped the cord at the wall or flipped the polarity(ground) switch and the hum went away. Luckily, I lived through those dangerous times! LOL All of my shocks were light ones.
     
  3. Jaybird

    Jaybird Tele-Meister

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    Just wear your rubber suit when playing. lol.
     
  4. sean79

    sean79 Poster Extraordinaire

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    Probably a stupid question, but what is the death cap? What will it look like, and how would I go about removing it?

    I just looked at my two-prong cord. One side of the plastic plug end is fingernail polished red. Is that an old-school trick to keep track of the polarity?
     
  5. Billm

    Billm RIP

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    The death cap on the Thunderbird 1 is a .05uF 600V cap. It's attached to the center of the ground polarity switch and to ground.

    It should be removed when the line cord is replaced and the ground switch should be disconnected from both sides of the line.

    The Thunder 1 is a pretty cool amp. Interesting design, nice features.
     
  6. sean79

    sean79 Poster Extraordinaire

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    [​IMG]
    I'll have to do a little digging to figure out where that cap is. When you mention a ground polarity switch, are you talking about an actual switch (slide, toggle, rocker, etc.) that I would flip to reverse polarity? I don't see anything like that on the amp. Thanks, again, for your help.
     
  7. Billm

    Billm RIP

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    The schematic I found had a ground polarity switch. Yours may be a different model. There were several in the Thunder 1 line.

    If there is no ground switch, you would have (back in the day) unplugged, flipped it over, and replugged if you got hum.
     
  8. TNO

    TNO Friend of Leo's

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    I had a Supro Bantam for a very short while. Unsafe at any speed.
     
  9. tonydj

    tonydj Tele-Meister

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    If there is no polarity switch does that mean that there is no 'death cap'? I have an old Alamo Titan (5Y3, 2 X 6v6, and 2 X 12AX7) and I want to convert it to a 3 prong. It has 2 transformers but are a power transformer and an isolation transformer the same thing?
     
  10. Billm

    Billm RIP

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    Most old amps without a ground switch have a death cap. It reduces hum when the line cord is plugged in backwards or when the outlet is miswired. It conducts AC to the ungrounded chassis as it ages and becomes defective.

    Here's a snip of a schematic from a 5C2 Princeton. The .05uF cap is the death cap:

    [​IMG]

    The death cap can always be found somewhere between the line cord and the transformer primary wires.
     
  11. sean79

    sean79 Poster Extraordinaire

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    Those death caps can just be removed? Do you need to replace them with anything?
     
  12. cactusrob

    cactusrob Friend of Leo's

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    I had my Princeton worked on last year and my tech insisted that I replace the two-prong cord with a grounded three prong. He assured me, as some on here have said, that it won't affect the value "if you're gonna play it anyway". If you're never, ever, ever gonna play it, leave it stock,,,

    I simply kept the two prong cord, the original tubes (even though one was bad - they were the originals from the factory) and other parts he had to replace and IF I should ever need to sell it, I will just include that stuff in the deal...

    I'm no expert, but the risk of electrocution isn't worth having a stock amp that's a danger if I'm gonna play it...IMO, YMMV, etc, etc...

    Good luck.
     
  13. Billm

    Billm RIP

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    When you do a 3-wire conversion, you just throw away the death cap. But the wiring needs to be correct:

    Green wire to ground, of course. One of the transformer bolts is a typical, good location.

    White wire (neutral) direct to the transformer primary. Use a fully insulated crimp connector, crushed with a proper crimp tool. No wire nuts, no tape!! Optionally, twist and solder, cover with shrink tubing.

    Black wire (hot) to switch. Switch to fuse. Fuse to other transformer primary.

    That's all.
     
  14. stingray_65

    stingray_65 Tele-Meister

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    Every one who gigs should have one of these in their grip bag,

    This allows you to check the receptacle you are plugging into to see if it is wired correctly.

    there are so many bars that are wired by a patron.

    These are useful too when you use an old amp with a 2 prong cord.

    My son has 2 small amps that are still wired with a 2 prong plug and no power transformer (series heated tubes)

    we used a multimeter to trace which prong on the cord is neutral (wired to chassis) and colored it with a sharpie.

    the neutral is the big slot on a modern receptacle.

    with the above tester, you KNOW which lead is neutral and which one is hot.

    you then plug in with careful attention .

    while this is by no means the safest way and does not replace a properly installed 3 prong plug, but it does offer one more level of safety that otherwise isn't there.

    https://www.hardwareworld.com/Ground-Fault-Receptacle--Outlet-Tester-pKZR1O2.aspx
     

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  15. Jead

    Jead TDPRI Member

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    Right On Billm - It's not rocket science but it is al ittle confusing. What's your take oninline fuse?
     
  16. robt57

    robt57 Telefied Ad Free Member

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    Last edited: May 1, 2010
  17. Dan German

    Dan German Doctor of Teleocity

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    The Lighting instructor in my theatre program always includes this question on his tests: "How do you ensure that the circuit you are working on is safely off?" The only acceptable answer is: "You turn off the breaker, you check to make sure the correct breaker has been turned off, you place tape over the breaker saying 'only to be removed by [your name here]. Any other answer got a zero for that question. He hasn't lost a student yet

    Three prong cords and an outlet tester. Too cheap and easy to skip.
     
  18. robt57

    robt57 Telefied Ad Free Member

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    I use one of those sensor testers. If there is power any where near it it buzzes. Especially when doing 220 stuff, and in this house I got a lot of 220 stuff going on.

    I still check with it even when I think I tripped the right breaker and am alone in the house. ;) Last stop gap for my bod.
     
  19. Tele-Champ

    Tele-Champ Tele-Holic

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    Man, I wish the amp repair place here (pretty much the only game in town) only charged 25 bucks to put a 3-prong cord on my 1969 silverface Champ.. They quoted me $50 + tax when I called to inquire about this job..

    I guess of course it would be worth the fifty bucks not to get zapped, but they also told me if I just play it at home and not out in some bar, etc., there should be no problem...

    Who do I believe??....Do I really need to do the 3-prong conversion? Opinions seem to be about 50-50 on this...
     
  20. Dan German

    Dan German Doctor of Teleocity

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    Sounds about right. The 50% who put the plug in the "right" way say don't do it, the 50% who put it in the "wrong" way say do it.:lol:
     
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