Making a Dummy load with a salvaged computer heatsink

Contributed by G0VFS

27 Apr 18

This dummy load was constructed using an Aluminium processor heatsink and a 32-1007 thick film 50-ohm resistors from the internet (eBay). They are rated at 40 watts CW and much more for short durations(Peak Power: 400 Watts (based on 10us pulse width and 1% duty cycle). On a large heat sink, they are supposedly able to handle 100 watts SSB for a few minutes.

First a hole was drilled right through the heatsink to take the inner coax conductor and PTFE insulator. Then using a taper drill, clearance for the UHF socket pin and insulation was made.

This allowed the socket to fit nice and flat on the heatsink ready for the fixing holes to be marked and drilled.

Fixing holes drilled out and then tapped

The heat sink ready to take the socket and coax feeder

The thick film resistor in position ready for marking out and drilling

Resistor fixed in position with good quality thermal paste and feeder soldered to the flange. This connection is very delicate so great care when soldering should be taken.

Some copper sheet has been shaped to protect the resistor and also help to transfer heat away from it. After checking that this is the case visualy, the ends are covere with more copper sheet and soldered in place, as can be seen in the picture far right.

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