I mentioned in this post the concept of using surface mount resistors as thermal bridges. I've had a chance to explore this now and after various tests I'm completely satisfied this is a suitable way to heat-sink SOT-89 surface mount transistors in 1W HF amplifiers.
Balancing cost versus ease of installation I settled on 4 pieces of 1MΩ 1210 resistors for each transistor. A 1MΩ resistor needs no further modification to isolate the collector voltage from ground. On an extended test the two parallel transistors had a case temperature of around 130 degrees while dissipating a total of 3.4W and delivering 1W of RF to the dummy load.
I hope you find this tip useful.
73's
Richard
ps Please excuse the soldering. I'm using up some solder I would not recommend and and it's difficult to get a good joint without using too much. That's compounded by it being too thick.
My preferred solder is presently this one.
My preferred flux is presently this one which I apply with a nylon type small paintbrush trimmed short to make the bristles a bit stiffer.
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