Built a 2W linear amplifier today

The build came out pretty well -- played with a couple new things. This is an HF amplifier, intended for the 80m-10m bands, with priority for 40m, 20m, and 15m. It's based on the 2SCR573 transistor, which is a beautiful mid-power, in-production BJT for $0.73 (or so). Output power hits 2W as it goes into compression.

I'm trying to learn about controlling gain flatness with negative feedback and other tricks, as well as proper input impedance matching. I've also learned a lot about transformers recently, which shows up in a couple places here too.

After getting everything in place, I tweaked the ratio on the input matching transformer to 4T:3T, and ended up with a 10R || 1nF stage after that. Negative feedback seems to be working, keeping it at about 16-18dB of gain.

Tests show IP3 at 37dBm (5W), so it's quite linear. A decent 16-18dB of gain, though still tailing off a bit on the higher HF bands. I probably still have to tweak some things. I'm hoping to build this into a homebrew SDR transceiver in the near future, so this is one of many things that need to be prototyped and tweaked on the way!