I want to start with a cooling unit, that is big enough to cool the proto3 800W amplifier. Reason is that I want to do a lot of measurements, how the temperature behaves if a lot of power is dissipated. I am still thinking of how I put 1500 watt to this cooling unit, but I could do it with a iron which can be controlled, and a 230V power measuring device, which you can buy in hardware stores.

But let's first build it.

I looked at many examples of amplifiers and I decided to build a cooling unit according to the way PA0FRI did it. It looks solid and you can use a fan which also should be controllable.

So first try to get a piece of copper, real red copper. That was not easy at all. I searched on the internet and found several suppliers for a piece of 10mmx100mmx200mm. But the first offer was Euro 150,= for two pieces including transportation to my home. One piece weighs 1.8 kg, but the price was ridicules.

A second offer was expensive but much less, Euro75,= for two pieces (Allgau  Metal Germany). Than I got the golden idea from a fellow amateur and went to a company called Kelders in Boxmeer, Netherlands. I was a metal junkyard and sold copper for Euro 7,50 per kilo.

He had a bar of 10mmx100mm and at least 3m long. I had to saw two pieces from the big bar, which took me half an hour. But I got these two pieces for Euro 33,=

I think this is a quite good deal. I got some aluminum plate of 3mm too for 3 Euro per kilo ! Also I found there a piece of construction alu profile which was exactly 200mm long and 80mmx80mm. That was my cooling block ! If it doesn't cool enough, I can add plates in the middle of the block to increase cooling capacity.

 

I sawed the aluminum in 4 pieces to cover the copper plate which I screwed on the cooling profile. Before doing this I sanded both parts pretty long to make it FLAT. This is very, VERY important to conduct the heat coming from the copper plate, on which we are going to screw the FETs, the 5V power regulator, and the attenuator at the begin stage, to control the input power.

I also used conductive pasta to even improve the conductivity between the copper plate and the cooling profile. One of the things I need to measure is that the touching surface between the copper and the profile is big enough to get all the heat to the cooling profile.

On the aluminum side plates I made two holes for the connectors. One small BNC connector for the input, and one PL plug for the output. Make sure you have the best quality PL plug you can get. The Voltages and Currents will be pretty high. We will discuss this later.

Make some nice holes at both sides in the plates to give cooling air enough space. Use your creativity,...Finally pick a cooling fan out of your junk box (one with speed control and 80mmx80mm). Put everything nicely together. At the bottom side I also used some two component metal glue.

I screwed the 4 plates to the copper plate, and that was not as simple as I thought. Copper is terrible to make nice holes in. I went to the home store and got myself some copper drills (2.8mm, 3mm). The 3mm drills I used to start making a 1mm deep hole, the 2.8mm I used to drill the hole to about 10mm deep. Then use a 3mm screw to fix the aluminum plate to the thick copper plate. Very good fit.

So, we end up with quit a heavy firm box, on which we can work further with the electronics.

It looks OK, isn't it ??

 

We can not solder on the copper plate. The heat is flowing away very fast, which is just what is should do!

So, text step is to saw a piece of high quality PCB 100mmx200mm, and sand it to fit on the copper plate. I had to sand a bit at the ends to fit also perfectly to the connectors.

Time and date: December 15th 2019