100W dummy load

FINISHING OFF The wiring was all point to point using tinned copper wire, insulated with heatshrink sleeving.
I used heatshrink sleeving on the twisted leads from the two resistors, too, ensuring they don't short onto the case. The resistors were mounted with the conductive metal pad upwards. A small amount of heat sink compound was put onto each of the resistors before the heat sink was positioned and screwed down.
Watch out for oozing heat sink compound as you tighten the heat sink fixings screws! Note: There is a threaded M3 fixing hole in the middle section of the heat sink that I used, intended as a fixing for the TO-247 (or similar) package. I sawed off a domed M3 screw to about 4mm long and tightened it into this hole to prevent the compound leaking out. Plus - I guess - it improves the heat dissipation by about another hundredth of a percent! Continuity between the metal enclosure and the earthy side of each connector was checked as was the electrical connection of the centre poles of each connector. The resistance was also checked and, using the components available to me, it was 49.9R. I then checked the load on a HF transmitter, starting at about 10W and then ramping the power up to 25W, 50W and 100W. Later the same day I tested the load at Pontefract Radio Club at 150W and, after about thirty seconds of continuous RF the heat sink had become noticeably warm (Just about comfortable to hold tightly - but only just!)
	How much does it cost to make?

		Buying everything new:
		Enclosure	1	73
		SO-239	1	22
		BNC	1	89
		Phono	1	47
		Resistors	11	44
		Heat sink	2	91
		Total	£20	66
		UK prices, inc VAT June 2007