Is this what I think it is?

Discussion in 'General Electronics Chat' started by Man_in_UK, Oct 22, 2013.

  1. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
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  2. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    I think at this point it's probably not worth much in the sense of actual money, but it probably holds some sentimental value to some people. If you got it from your grandfather, you may want to hang on to it as a keepsake. It'd make a fantastic conversation piece.

    Matt
     
  3. #12

    Expert

    Nov 30, 2010
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    A museum might want it.
    It might be the last one in existence for all I know.
    50 years as an electronics nerd and I have never seen one of those.
    That means it's either rare or none of them escaped from the UK.
     
  4. Brownout

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    Jan 10, 2012
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    Whatever it is, it's cool.
     
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  5. WBahn

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    It might be worth something to someone, but it might be impossible to find out who might be willing to pay anothing for it. You could put it up on Ebay with a Reserve price high enough such that if the reserve is met you really would be willing to sell it. That might (might) give you some idea of what it is worth.

    If you have any kind of mantle or knick-knack shelf I would probably put it there. Perhaps make a little stand of some kind for it. Then you can occasionally recall some times with your granddad when you see it or use it as a conversation piece or a trivia puzzle when people are over.

    If it glows even when the switch is off, that concerns me. Where is the energy coming from? That probably means that you have a wiring problem and that your switch is switching the neutral and not the line. But I have no idea how it works unless the fixture that it is intended for makes a case ground available to it somehow.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The reason it glow with very minute current is it is neon.
    I was trained in the electrical industry in the UK but never saw that one.
    We did use neon screwdrivers that were used to test the live side of a socket, these used your body leakage to earth ground, you had to make sure you held the metal clip.
    I am not sure if they use these today?
    I would put it at around circa 1930-1940?
    Max.
     
  7. WBahn

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    Okay. That helps some.

    Don't neon bulbs require a fair amount of voltage to start conduction but then a much smaller voltage (but still well above 0V) to maintain it?

    If this bulb uses a similar strategy, then it would still need a path to ground. If it is for finding wiring faults, then I doubt they would want the user to be touching the base guard. I don't see that touching the bulb itself would do the trick.

    Still confused.
     
  8. Brownout

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    Ive used one of those. I do remember touching the metal clip and getting it to glow. Never knew why though.
     
  9. paulktreg

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    Jun 2, 2008
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    Found one here!
     
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  10. WBahn

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    Ah, and knowing that they are called beehive lamps, I was able to find some more information. Apparently they use an neon-argon mixture to get easy ignition at mains voltages.

    But that still leaves the question of why/how the OP's bulb glowed even when the lightswitch was off. These appear to be simple two-terminal devices, so even if the neutral was hot, what what the return path for the current?
     
  11. #12

    Expert

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    It only needs a few nano-farads to get the necessary current. Every half cycle ionizes the neon while the peak voltage is more than about 90V.

    Consider that an NE-2 is full on with a 120k in series with a 120 RMS line.
    That would resemble 50 Hz, 240 RMS = 13263 pf for full "on". Then consider that a lot more of a 240V signal is higher than 90V compared to a 120 RMS signal.

    170 Vp:340 Vp
    minus 90V
    80 Vp:250 Vp
    1:3.125

    Triple the dwell time allows 4244 pf
    Drop the current to 1/10th to get to "just barely visible" and the answer is 424pf

    Some old formula scratched in a notebook says, "Human model for static suppression = 100pf with 1.5k in series".
     
    Last edited: Oct 22, 2013
  12. Brownout

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    It's a neon bulb then. I'd love to have one. It's probably worth a few bucks.
     
  13. WBahn

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    But a few nanoFarads to what? Peak voltage relative to what? One terminal is connected to hot. The other terminal is connected to a wire that is not connected to anything. The person plugs in the bulb and steps back and watches it glow. The necessary capacitance for it to keep glowing is between the dangling wire and what?
     
  14. #12

    Expert

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    I just realized I was dead wrong about the human body being part of the circuit.

    The only route I can think of right now is the gap between the points in the wall switch and whatever distance the neutral wire is in proximity to a ground plane.
     
  15. Brownout

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    I think what gram-pa meant is he used it for testing neutral by connecting hot to one wire and touching the other wire to neutral. What the OP is seeing, I can't explain.
     
  16. #12

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    It's supposed to be a 5 watt light bulb. I love it! Great way to get a large area of ionized neon. Has a resistor in the base.
     
  17. BillB3857

    Senior Member

    Feb 28, 2009
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    If testing for a switched neutral rather than a switched hot lead at a lamp socket, body capacitance alone would allow the light to glow when being inserted into an improperly wired socket. If, on the other hand, the switch were properly installed in the hot lead, the lamp would have no energy source to cause it to glow. A NE-2, with both leads twisted together will glow when held in the hand and the leads touched to 120VAC.
     
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  18. Brownout

    Well-Known Member

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    I just like the one shown.
     
  19. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Photos please! We like glowey things. :)

    And "green" is not neon. Neon only glows orange, so green must be some other gas, and likely needs a fluoro phosphor to convert UV to green, unlike neon where the gas itself actually glows with a pure orange light.
     
  20. WBahn

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    Thinking back to my undergrad physics lab, I think neon produces a couple of green lines (and even perhaps blue?) that you can filter to just let the green pass. Also, isn't the spectrum of neon smeared pretty widely across the red-orange and even yellow part of the spectrum?
     
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