I cannot locate replacement resistors.

Discussion in 'The Projects Forum' started by CJay, Apr 30, 2015.

  1. CJay

    Thread Starter New Member

    Apr 30, 2015
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    I am currently working on an old set of Gemini DJ speakers. There's a 15 watt 75 ohm resistor in the piezo curcuit on the crossover that is shot. It's an old ceramic/cement style. The only place I have found a direct replacement is in Russia, no joke. I'm not sure how to proceed. Are there any ideas on alternatives that will work effectively?
     
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Any 75 ohm 15 watt resistor will work. Or are you trying to keep the speakers "authentic"?
     
  3. CJay

    Thread Starter New Member

    Apr 30, 2015
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    Authenticity is not a concern. I was under the impression that I needed to keep with the same style of resistor ie. non-inductive ceramic etc. Is this not the case?
     
  4. #12

    Expert

    Nov 30, 2010
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    The ceramic part is only about heat. The non-inductive part matters.
     
  5. joeyd999

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    Jun 6, 2011
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    I'd be surprised if a standard wire wound had enough inductance to make a difference. But, non-inductive wire wounds are available at a premium.
     
  6. #12

    Expert

    Nov 30, 2010
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    Check again on that, "non-inductive" requirement. It does seem a bit odd.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @CJay You can also put a pair of 150 ohm resistors in parallel to get 75 ohms. 150 is way more common than 75.
     
  8. CJay

    Thread Starter New Member

    Apr 30, 2015
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    All good info to consider. Thanks a million. I'm still trying to wrap my head around the "need" for this resistor in the piezo circuit. I assume it's for protection only since by design piezo's do not need crossover considerations. This "crossover" is odd anyhow. The woofer wires straight thru from input, there's a 10 watt 19.5 ohm resistor and a 10 mFd 100v capacitor in the horn circuit. If it's only for protection could I not fuse the piezo circuit?
     
  9. CJay

    Thread Starter New Member

    Apr 30, 2015
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    Answered my own question on that one. I would need to add a pot for that circuit if I would eliminate the resistor and the pot would have to fall in the range of the resistor I'm dumping etc, etc. I'll get this figured out yet. Thanks again for all the suggestions so far.
     
  10. joeyd999

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    No pot....that'll likely become noisy at some point.
     
  11. CJay

    Thread Starter New Member

    Apr 30, 2015
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    Agreed. I'm trying to figure out if there is a formula for changing the values/ratios for this resistor to get the same limiting result ie. can I drop wattage rating and increase ohm rating or vice versa etc.
     
  12. MikeML

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    Oct 2, 2009
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    I also cant believe that a wire wound would have enough inductance to matter. However, Mouser has these that are "non-inductive"
     
  13. Alec_t

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    Sep 17, 2013
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    Wiring two (or more) resistors in parallel would have the advantage of spreading the heat load and lowering inductance (if that is important?).
     
  14. CJay

    Thread Starter New Member

    Apr 30, 2015
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    I think I've got the solution. I'm gonna go with Ohmite B12J75RE's. I'll replace them in both cabs. They're a 12 watt vs 15 but that should not be an issue. Axial, wirewound, vitreous enamel; much better platform than the old ceramic bathtubs. I also wanted to say "Thank You" to everybody that offered some advice on this. I look forward to asking more dumb questions in the future!
     
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