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EBS Fafner lamp mod.

Discussion in 'Amps and Cabs [BG]' started by Bloc Riff Nut, Dec 15, 2013.

  1. Bloc Riff Nut

    Bloc Riff Nut

    Nov 28, 2009
    Thinking about putting a LED in my Fafner because the light keeps failing.

    My lamp stopped working for the second time so I'm thinking of replacing it with an LED. So I sent an email to EBS asking what they thought of the idea and they replied with this;-

    Dear Philip,
    On the socket for the light bulb you have 42V AC.
    So, in order to use a LED lamp you need to put a series resistor and optionally diode.

    Best Regards

    Are there any tech heads that can elaborate on the values of the resistor and diode type?
    My solderring skills are much better than my theory


  2. 96tbird

    96tbird PLEASE STAND BY Supporting Member

    Better luck in the amps forum. This is hardware as in tuners and bridges.

    Click the "report post" button and ask a mod to move it to amps.
  3. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    42V AC doesn't make a whole lot of sense to me. For an incandescent lamp 6-12V makes more sense. Before you begin, I would actually measure the lamp voltage to ascertain the 42V is correct. What is the identification for the old lamp??

    A typical LED drops around 2V and can safely be run from AC. It will require a series resistor to limit the current passing. I usually run mine at between 10-15mA. More for brighter, less for dimmer.

    The value of the resistor can be calculated using Ohm's law. If the 42V turns out to be correct then a 2.7KΩ 2W resistor should be all you need. I would think about using an old lamp base to mount the parts. This would eliminate making changes to the amp itself.
  4. Bloc Riff Nut

    Bloc Riff Nut

    Nov 28, 2009
    Cheers Paul,
    The volts are correct, but the old lamp was 22V and 0.025A. This was not the original lamp.
    I think Ill use a blue LED. I recently changed the existing JJ ECC83S for a Mullard 12AX7 with balanced/matching triodes with a value of 1.0mA. The drive/character functions are much creamier and more to my liking. Im not sure if this is the difference between the two valves or if the JJ was damaged or used up in some way. It looks ok...
  5. vbchaos


    Sep 5, 2011
    Groningen, The Netherlands
    Uncompensated endorsing user: fEARful
    42 is always correct :bag:

    Isn't your resistor calculation only suitable for DC? I'd check for the breakdown voltage of the LED as well, you might need another diode in front to protect the LED
  6. Steve Dallman

    Steve Dallman Supporting Member

    As the safety director for a large manufacturing plant, I was in charge of making sure the exit lights were working. Before LED's, these used incandescent lights in them. They burned out in maybe 6 months, nearly insuring that at the time of any inspection, at least one would be burned out.

    I made a small, but simple modification to each light, adding a series diode (1N4001 or higher) to one wire feeding the AC bulb. This would change the AC to pulsating DC.

    The AC would minutely vibrate the bulb filament, which would hasten failure. Changing to DC lessened the vibration due to the polarity of the voltage changing 60 times a second.

    The result was that bulbs would last 2-3 years instead of 6 months.

    It might be a better solution for you...just one diode on the socket.

    With an LED you would need to change to DC also.
  7. jazzy grille

    jazzy grille - Arrogant Bastard

    Aug 15, 2006
    Palm Bay, Florida
  8. Bloc Riff Nut

    Bloc Riff Nut

    Nov 28, 2009
    That may be the simplest answer. Really shouldnt over think things.
    Cheers, Ill do a search.