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My resistive dummy load

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  • #16
    I use "braking resistors". Used in industrial machinery and EV's, and someone smart spotted a market and started making them in audio impedances, 4/8/16Ω. Available in high wattages and cheap. I've got several 4Ω 1000W. These also need a heatsink to handle their rated wattage, but even derated they're good to about 250W. I usually try to keep it under 100W per to avoid them getting too hot to handle. I regularly service high power multi-kW output PA amps, so need the high power ratings for soak testing.
    Available from ebay/aliexpress. Cheapest "off the shelf/ready to go" option I've found. Less fuss than heater elements and buckets of water or big heatsinks.


    • #17
      I have been using a pair of 10 Ohms 25W Wirewound Chassis Mount Resistors bolted to the case of a dead car inverter as my "close enough" dummy load for stereo equipment. I am inspired to make it better now and thought I would parallel a 40 ohm power resistor with it to bring it down to 8 ohms. I then realized I have three 750 ohm 65W adjustable ceramic resistors (Ward Leonard ST750WL) lying around that I picked up 20+ years ago at a ham swap meet.

      Is there a reason not to use the adjustable resistor? I kind of want to parallel it with the 10 ohm because I am a bit worried that the sliding tap might fail and leave me with no load. (I have a handful of the 10 ohm resistors lying around too...perhaps from the same ham swap.)


      • #18
        Here's my dummy, FYI. Four 4R/50W resistors mounted on 0.090" aluminum, BNC tap for scoping waveform, and line out tap.

        Click image for larger version

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        I build and repair guitar amps