(Topic ID: 161392)

Why are these resistors wired in series with the lights?

By mg81

7 years ago



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  • 6 posts
  • 4 Pinsiders participating
  • Latest reply 7 years ago by mg81
  • Topic is favorited by 1 Pinsider

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    #1 7 years ago

    This is a photo of a 1938 Stoner "Chubbie" machine.

    The playfield lights that are controlled to go off when the playfield bumper is hit have these 50-60 Ohm resistors wired in series with the bulbs.

    What is the purpose of these resistors (I think they are old style resistors, they have a wafer of mica inside the wrap length of wire)?

    The playfield lights have ~15 volts of power going to them and they are an odd threaded base bulb, I think a #52.

    But the controlled backglass bulbs that show the score are #44/47, don't have any resistor and are powered by the usual ~6 volts that these bulbs would normally use.

    So why the two different types of bulbs? Why not just use #44/47 bulbs in the whole machine and why the resistors?

    Resistors wired in series would just make the bulb dimmer.

    Are they trying to give the light circuit more power draw so something else will work better?

    Thanks for the help and any other info someone might have about this old machine.

    chubbie_resistors_(resized).jpgchubbie_resistors_(resized).jpg

    #2 7 years ago

    Those are "wirewound" power resistors. Typically used to drop voltage or limit current draw.

    #3 7 years ago
    Quoted from mg81:

    The playfield lights that are controlled to go off when the playfield bumper is hit

    I'm gonna guess that they are powering the bulbs with coil voltage and used the resistors to drop the voltage to a safe level for the bulbs.

    #4 7 years ago

    Any idea why they would not just use the 6 volts to power the bulbs like in the backbox instead of a different, higher voltage and thus higher voltage bulb in the playfield?

    I guess I am just at a loss as to why use two bulb types, they already had the transformer present with the lower voltage tap.

    The only thing I can guess is you mentioning the "reducing current draw", perhaps they wanted the power available for the playfield switches which also use the same power supply and they did not want to run two separate power supplies on the playfield. (when I say playfield "switches", that is a stretch. They are rings of graphite with a metal rod down the middle. The rod gets pushed by the ball and hits the graphite ring to trigger the relay. Did I mention you get a nice bright arc with each switch "closing". The metal rods are quite eroded from all of the arcs.)

    #5 7 years ago

    Gottliebs did this on select lights in some of their 60's games that I have.

    My guess is it was cheaper/easier to add a switch to an existing coil voltage circuit as opposed to adding a whole additional lighting relay.

    #6 7 years ago

    The more I get this game working the more its design makes sense. The power gets turned off to a playfield switch once is has been hit once, so the lights also go out to indicate that bumper/switch has been hit. I now get why they are using that power supply for the lights, it saves on a lot of wiring.

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