Dummy Load

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Simple, but effective.

4 x 2R on each side.

It can run a couple of 100W for minutes - much longer with a big fan on it!
 

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Mine are different but that's the same basic resistor. If you're going to drive them over their rated power, I'd suggest making some simply wire (coat hanger or similar) clips to mount them. That way you can force air through their center hole to promote a bit more cooling.

If you're going to drive a sine wave into them for hours on end at anything near 1200 watts, you may need to use 12 of them. For testing where you use a full power sine wave for short periods or music up to clipping (repeatedly) for long periods of time (hours), you can use 400w worth of resistors for a 1200 watt amp (with plenty of air flow). The ones made my Ohmite are virtually indestructible.

I'd suggest using high temp wire (XLPE or similar) unless you can ensure that the insulation will never touch the resistor body.
 
If you can effectively get the heat out of them many lower rated parts will perform just fine. I'm reminded of 50KW water cooled RF dummy loads that used 200W ceramic resistor elements.... But I also recall making WHITE FIRE PLASMA out the side of one I pumped 12KW into without remembering to turn on the pumps.
Doc
 
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