I got tired of the 100W low duty cycle audio dummy loads at the shops I worked at, and my lack of decent dummy loads in my workshop.
I was lucky enough to find four 1kW 77V heating elements, with fins. I have no idea what they were for, being 77V, but they are air heaters and will happily dissipate 1kW with a modest amount of forced air. I was lucky enough to find a meter at the same time and place (the now closed Wacky Willie's in Portland, OR) that is 1mA and already labeled for 1kW full scale. A 75k resistor and it is accurate to a couple of percent.
At 5.9 ohms per element, they work just fine to stand in for an 8 ohm speaker (ever seen a speaker impedance chart?) The impedance shows so little drift with temperature that it is less than 0.1 ohm from room temperature to 1kW with forced air (not sure of the temperature at that point) and the impedance is resistive with no appreciable signs of inductive or capacitive reactance up to 2MHz.
So anyway... I was thinking about water heater elements. A 2000W 120V heating element works out to 7.2 ohms and is $10. I'd suspend it in a can of oil, I think. But I have no idea if they have a positive temperature coefficient or if there is enough inductive impedance to make a difference.
[u]Digi-Key[/u] has 50W 8-Ohm resistors for about $4 USD. Four of those in series/parallel would be good for 200W. (It's always a good idea to derate resistors, and for 100W continuous I'd want 200W resistors.).
So anyway... I was thinking about water heater elements. A 2000W 120V heating element works out to 7.2 ohms and is $10. I'd suspend it in a can of oil, I think. But I have no idea if they have a positive temperature coefficient or if there is enough inductive impedance to make a difference.
Since you'd be running it at less than 1/10th of it's nominal power, it shouldn't get hot enough to worry about the temperature coefficient and you shouldn't need an oil bath. However, it might have enough temperature coefficient to measure differently (maybe lower) when cold or with "only" 100W or heat.
I built a 200W 8-Ohm load resistor out of a handful of resistors once... Probably 20 8-Ohm 10W resistors if there's a way to wire 20 8-Ohm resistors in series/parallel and end-up with 8-Ohms... I don't remember the details... I remember the resistors were the white rectangular type... I put it in a nice box with 5-Way binding posts, and I think I still have it somewhere.
I've worked on 1kW per channel amplifiers. 200W of dummy load just won't do.
Sure, as long as the total is divisible by 4, you can combine them series-parallel to get 8 ohms.
I'd put the heating elements in oil because they are only rated for 2000W when under water. Oil rather than water because it won't corrode the metal. I think oil has a lower heat capacity than water, and that 2000W is rated to heat an entire water heater full of water and not be on all the time, so I'd seriously derate them. A big can full of oil would provide more surface area to dissipate the heat. Maybe even solder some fins on before filling it.
I am so happy I found those 1kW air heaters. They look a bit like that water heater, but a little thicker and wider spaced, with heat sink fins spirally wrapped around them. No derating necessary.
Most people can do just fine with 200W dummy loads.