Dummy Load
A Project that Flopped

Things don't always work the way you expect and I've had my share of projects that flopped.  The most recent was a Heathkit Cantenna rebuilt.

We all know they are a bit light duty for use with today's 1500 watt amplifiers.  I had one around that wasn't very healthy after some extended amplifier testing and it bugged me.  The mental gears started turning and meshed on the idea that I should use the new thick film resistors.  After all, if that 3/4" x 4" carbon pole resistor (rated 50 watts?) could handle a Kw for a couple of minutes in oil then four 50 ohm 100 watt thick film resistors in series parallel on a 4 x 6" copper 1/4" slab in oil should be a lot better.  The numbers showed that the pole resistor had about 7 square inches of conducting surface to the oil and the copper plate had about 44 square inches in the oil (48 less 4  for the resistor housings).  To boot, I reasoned it was going to take some serious emery to even heat up that mass of copper.

WRONG!   Those thick film resistors are rated at exactly the maximum amount of heat is they can transfer out through a relatively small ceramic pad on the back.  Turns out, 100 watts means 100 watts with the best heat diffusion you can muster.

But, if you need a 100 or 250 watt dummy load that is very accurate, the thick film resistors are a nice way to go.