For this PA we need a good cooling. Heat producing parts are of course the two FETs, but also the 3 dB Attenuator (5W).

We have to get rid of all this heat. For this, I use a cooling block of 180mm x 100mm x 45mm.

On the cooling block I place a copper plate of 10mm thick. To screw nice holes in Copper is quite a challenge. Use specific drills for Copper, they look a bit like Copper, but are hardened. Use a drill device, don't drill by hand,....!! Start small and slowly, and use cooling oil to make sure the drill is not stuck in the Copper. The drills will brake immediately.

To fix the cooper block tightly on the Aluminum cooler, I drilled M4 holes in the cooper plate, exactly on the places marked on the Amplifier module PCB. At the ribs side of the cooling Alu, the screws are tightened with proper bolds. All the other holes are M3. At the down side of the copper plate I widened the M3 holes to M6 (about 4mm) and I put bolds in the room I created there. So at the bottom side of the copper block the bolds are tight in the copper. This makes it very easy to fix the FETs, the power IC at the left upper corner and the attenuator to the copper plate. It is also used to fix long M3 screws at the corners to fix the Filter Module to the Amplifier module.

After cleaning and flattening (polish for at least half an hour with polish power!) the Alu block and the Copper plate, they can be put together. I used heat conducting pasta, very thin, to make sure that the copper plate and the alu block are having very little heat resistance. After putting the cooling pasta on the alu and copper, polish it in the metal and flatten again, to make sure it is flat ! If it is flat you can put both parts together and can hardly move them over each other. The FETs, the Power IC and the Attenuator are directly screwed to the Copper plate. The PCB is screwed to the Copper block with the 4 M4 screws, and the 4 M3 long screws.