Using 115V neon lamp for power indicator

Discussion in 'Shock Brother's DIY Amps' started by milocj, Feb 8, 2009.

  1. milocj

    milocj Friend of Leo's Ad Free Member

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    I'm messing around with converting a Hammond reverb amp right now and I'm not sure where I'll eventually be placing all of the holes for the jacks, switches, and lamp. I also don't have a spare jewel lamp assembly handy where I can take a feed off of the heater wires.

    I did find a 115v neon lamp that will fit an existing hole in the chassis and was thinking about wiring that in for the time being. It says that it can handle 1.2mA maximum. Can I just run a set of wires in parallel off of the power cord/power transformer junctions to feed the lamp without worrying about blowing it?
     
  2. celeste

    celeste Friend of Leo's

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    if the tube does not have a ballast resistor in it already, you need to put one in circuit. Once the tube strikes off, it's internal resistance drops to almost 0, so you need series resistance to limit current flow to a safe level.
     
  3. milocj

    milocj Friend of Leo's Ad Free Member

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    The package doesn't say there is a resistor, so I'm guessing it doesn't have one.
    What value range should I use?
     
  4. mojo2001

    mojo2001 Tele-Holic

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    if it is an NE-51, use 220k.

    If an NE-2, use 100k.

    Make sure there is not resistor in there already....measure between ac terminals and bulb contacts.

    If in doubt, use 220k first.
     
  5. marshman

    marshman Friend of Leo's

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    Isn't putting a neon bulb IN an amplifier like asking for hum? Wouldn't the bulb drive the circuit crazy, like playing a tele under a beer sign would?
     
  6. milocj

    milocj Friend of Leo's Ad Free Member

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    I have no idea. I had seen a couple of schematics that showed one right across the main black and white power cord leads and figured it might be a cheap and easy way for a temporary indicator while I'm still messing around with the project. Maybe it's just better to use nothing until I need to order some more parts and can snag the bayonet assembly at the same time.
     
  7. mojo2001

    mojo2001 Tele-Holic

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    The noise from neon bar signs actually comes from the high voltage transformer (3000V) that those things use.

    I have seen neon indicators in sensitive test gear and so on...not a problem.

    Plus neon does look a bit cooler than the usual #47 bulb, if you ask me!
     
  8. GUITARmole

    GUITARmole Tele-Afflicted

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    I use them (as others do) as a permanent indicator for Marshall builds wired to the power switch (effectively across the power cord leads when turned 'on') and there are no hum problems whatsoever. The ones I use though are rat shack Marshall type and are 120V rated instead of 115V.
     
  9. Alnico Sunburst

    Alnico Sunburst Tele-Meister

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    I have an old Garnet amp that uses a neon bulb for a pilot light. It's nice knowing it will never burn out.
     
  10. shadowfan

    shadowfan Tele-Meister

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    Hi

    A neon indicator should not induce hum.
    If your neon pilot light is sold as an "assembly" it will have the resistor built-in. You can't measure resistance at the terminals as a neon bulb is an open circuit. Since the resistor is in one leg, in series with the bulb, it's still an open circuit.
     
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