Yes, H.H - I did search...

Take just about any standard flatback heatsink. Now imagine taking 3 of them and laying them next to each other like this:

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If I take a piece of 1/4" aluminum flat plate and cut it to the correct dimension and then bolt the heatsinks to it (using grease), does this raise or lower the thermal efficiency? I'm wondering if I can buy smaller extrusion and ultimately achieve the same thermal efficiency as using a larger one...

This is what I'm envisioning (the vertical lines would actually be one continuous piece of metal):

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I ask this question because I've seen many TO3 style amps that have been designed using a "carrier" to mount the TO3's which is then bolted to the heatsinks... It seems to me that this would significantly raise the junction temps but it doesn't seem to be a problem... The carriers often look like this (only the heatsink is actually one large extrusion):

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How would one go about calculating the thermal sinking of the combination of the two pieces of metal? Just add their dissipations together and subtract the joint loss? Or, is it not so simple?

Any help would be appreciated!

Thanks,