[stevehertz]

I restore a lot of vintage hi-fi receivers and it goes without saying they all have power transistors mounted on heatsinks and the use of heatsink compound to provide a good thermal connection between the two. I have never refreshed or replaced the compound unless I have replaced a transistor.

On a true knowledge basis, not the mere notion that it may be good practice, should heatsink compound be changed at some point in order to maintain its efficiency ? I'm not talking about changing it when, for whatever reason, an associated power transistor is removed and it's easy to do so. That quite possibly makes good sense if only for the reason that fresh compound will compress and mould easier to the transistor and heatsink, making a more intimate joint.

I ask for fact based responses because in vintage hi-fi circles a lot of people habitually 'write off' heatsink compound that has happily been in place for decades. Does heatsink compound lose its efficiency as it ages in an installation? On an undisturbed joint, is so called 'hard', aged heatsink compound poorer than when it's fresh?

As an aside, on package types that allow it, I whizz the flat side of new power transistors over fine abrasive paper on a flat surface to remove any potential hot spots and provide for better thermal conduction via the compound and heatsink.