Dummy loads are very simple devices, they are a resistor, with 50ohm impedance, and a heatsink to dissipate heat.
I picked up a 50w heatsink from rs components, for $4.80 delivered overnight.
Arrived this morning, attach an SO239 and good to go.
For short bursts of power I’ll be using this for, <5-25w while tuning down commercial radios to legal limit it should do.
But I’ll need to add a heatsink for anything more or anything sustained.
Nice idea: For us vintage folks a similar device was buried in a 1 gallon can filled with oil. The connector on the outside lid of the can.
I’ve seen them! Was it to help with the heat?