Paul,
I'm getting around to my 2 meter kilowatt SSPA. My question is which of
the multitude of heatsink compounds do you recommend? I have read some of
the comparisons mostly dealing with CPU cooling. But, would like some
input from piratical experience. The silver formulations seem to do a bit
better.
When I looked for data on these compounds, the best rated one I could
find was Arctic Silver 5. It's about twice as heat conductive as the
best ceramic-based compounds, according to its data sheet. But I haven't
yet measured whether those claims are true.
Between the different ceramic based compounds, there are some large
differences too. They are not all equal! I found differences up to a
ratio of ten between them! Check the specs and compare before you buy.
In addition, I am assuming that I want a layer of the stuff between the
copper heat spreader and the heatsink?
Yes. Assuming the spreader is large, and lies very flat against the
heatsink, a decent grade ceramic compound is good enough there - but a
better compound is always better! Between the transistors and the
spreader instead, really the best is soldering! Solder is about 8 times
better than the best silver particle compound. If it's not practical to
solder the transistors to the spreader (as is often the case), use the
best compound you can find. You need only a tiny quantity there.
And if your transistors are expensive, do the math about their cooling
BEFORE you build that amplifier! If they are cheap, or if you have a
free supply of them, you can use the empiric method and just see if they
survive... ;-)
Manfred
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