Amplifier experiment

This RF amplifier experiment hit a bunch of firsts for me. It puts out about 4W at 7-14MHz, which is a new record for my attempts at amplifiers. But it's also my first using a milled PCB, and a few other things. It has some flaws (not as linear as I'd want), but it's a good milestone for my continued learning!

I didn't take this schematic from anywhere, per se (of course, I've read a lot in studying!). I'm happy that I know why I put every component in, why it's there, what it does, and can explain the whole thing. It's a three-stage amplifier, with a class-A voltage gain stage, a push-pull current gain stage, and the final in class A with the IRF510.

I did schematic capture and PCB layout in Kicad, and used FlatCAM for tool paths to cut the board on my OpenBuilds Mini Mill. It came out really well -- narrower traces than I've tried on a few test boards.

There were some burrs as a result of the milling, so I inspected it closely and did some cleanup.

Assembly was pretty straightforward. Some people say the milled PCBs are harder to solder, but I haven't had any issues. I set the bias to about 90mA of quiescent current. This heatsink on the IRF510 is too small -- I will need to find some better ones for the future; I wouldn't want to run this one full blast for very long!

This is the output, through a low pass filter. There are some signal quality issues that I will have to investigate. It's not as linear as I'd hoped, but would work fine for a non-linear mode as it is. I'll continue playing with it and see if I can figure out what's up -- this is my first three-stage design, so I'm sure there are plenty of gotchas I have yet to learn about!