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Dummy load for amplifier

Discussion in 'General Electronics Discussion' started by mrmodify, Jan 7, 2012.

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  1. mrmodify

    mrmodify

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    Feb 13, 2010
    I have some Dale NH-50 2.5 ohm wire wound non inductive resistors laying around. Is there any reason why I can't wire them in series for a total of 7.5 ohms to be use as a load for a receiver while I am trouble shooting?
     

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  2. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    No reason at all, they're just perfect for the job.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
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    Jan 21, 2010
    None at all :)
     
  4. computerlen

    computerlen

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    Jan 22, 2012
    If your receiver is solid state,you don't need a load.
     
  5. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    While it may remain stable without a load - you won't be able to properly see all aspects of its performance, for example if the output transistors are open circuit.
     
  6. computerlen

    computerlen

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    Jan 22, 2012
    I agree with you but now people new to electronics know about solid state amplifiers not requiring a load when trouble shooting.One 'tool' I use when trouble-shooting an amplifier with an intermittent short, for example, is a series light. The defective amplifer is not connected directly to the 110 volts ac supply. I have made up a special socket connected to a two-position toggle switch which is fused of course. In one position the 110 volts ac is normal but in the other switch position the 110 volts ac is wired in series with a 100 watt light bulb which limits the current to the unit under test. While performing tests on the amplifier if the short shows up, there is usually no harm done because the light bulb limits the current to about 1 amp. This is also handy after replacing new parts in an amplifier. If I have made a wiring mistake or some other mistake when working on a repair-I always fire up the unit first through the series light just in case. This has saved me not blowing any newly-installed components.
     
    Last edited: Jan 22, 2012
  7. mrmodify

    mrmodify

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    Feb 13, 2010
    Hello computerlen, I am mediocre at electronics. I cant argue either way on a dummy load. But I can tell you the amp I am currently working on using a dim bulb with out a load will not light the dim bulb and will fry parts if you connect it to the 120 VAC. It will give a indication of a short with a 8ohm dummy load with a dim bulb and not fry parts.
     
  8. Rleo6965

    Rleo6965

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    Jan 22, 2012
    It's a good practice to have a dummy load resistor for temporary load than an expensive speaker. Resistor was cheaper than the speaker and won't disturb your neighbor if your testing the amplifier for higher volume.

    Still computerlen have a good practice to place lamp in series with amplifier unknown status for safety purpose. But you need to removed the test lamp. The lamp will cause voltage drop in the amplifier supply voltage and therefore cause inaccurate results in your test or repair..
     
    Last edited: Jan 23, 2012
  9. computerlen

    computerlen

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    Jan 22, 2012
    You're right about not bothering your neighbours. About 100% of the defective amplifiers that I work on will run on the series light as well as about 100% of working amplifiers will work fine at low volumes in series with the series light. Have you tested for shorted or partially shorted components with the power disconnected? What make is the defective amplifier?
     
  10. alfa88

    alfa88

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    Dec 1, 2010
    It's very bad practice to run an amp without a load. There are some solid state designs out there that won't tolerate it at all. I should know I have one of them and the output transistors can get pretty pricey.:eek:
     
  11. computerlen

    computerlen

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    Jan 22, 2012
    I'm confused.Are we trying to repair an amplifier? Why is it necessary to power it up at all? Checking for defective components is what I normally do first. If an amplifier comes in with an intermittent short, I usually run it via the series light with the speaker connected. By pressing 'here' and tapping 'there' while the amp is on usually locates the general area of where the intermittent short is and the series light simply lights up a little when the short appears.
     
  12. computerlen

    computerlen

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    Jan 22, 2012
    Hi again. Were you able to repair your amplifier? If not, is there any way I can help?
     
  13. dizignit.jason

    dizignit.jason

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    Jan 30, 2012
    Very helpful post. I just joined this forum. I am starting to realize how little I know about electronics. I may not even be at a level to join this forum. At one time I use to be very much into audio amplifier design and troubleshooting. I thought about this resistor theory for troubleshooting an amp but had a hard time finding one at a high enough wattage. Where can we get such a resistor?
     
  14. mrmodify

    mrmodify

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    Feb 13, 2010
    Not yet computerlen, Thanks for asking. This old girl was in very bad shape. Ben on this project for 2 years on and off. mainly during winter I work on it. I work on it when I can. I have the current issue of frying parts but I am checking the bridging circuits. It will run on 4 channel mode. 2 channel is the where the problem begins. After I get that straight I have a distorted channel and a issue with the panel lights. Both of these are minor.
     
  15. mrmodify

    mrmodify

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    Feb 13, 2010
    Its an old marantz 4300 quad. I have gone through the amp, and power supply boards with only a transistor, capacitor & ohm meter before unit was ever powered up. I repaired all the shorted and burnt parts that I had found. .
     
  16. mrmodify

    mrmodify

    157
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    Feb 13, 2010
    dizignit.jason
    I don't know if this helps or if you have not already seen this photo but these are what I used. If you want I can look and see if I have some extras laying around, Let me know how many you might need. They are 2.5 ohms 50 watt each.
     

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  17. dizignit.jason

    dizignit.jason

    9
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    Jan 30, 2012
    Mrmodify
    Thank you for your reply. I did see that image and did a google search and found exactly what I needed. I am thinking I am going to use them for a larger project. Thanks again.
     
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