Marko Pavlin has been working on a HF amplifier project:
I followed the ARRL Homberw challenge 50 watt aplifier entry. It is low cost, simple HF linear amplifier designed and built by the author as an entry in the ARRL’s 2009 Homebrew Challenge contest. The requirements of the amplifier were: 40 meter band 50 watt output amplifier intended for use with a QRP transmitter as driver (less than 5W), constructed at a total material cost of not over $125.00.Project info at Mare & Gal Electronics homepage.
I redesigned author original design an put it on the double sided PCB with additional output banpass filters. I started with first prototype. It worked quite well for short periods. Main disadvantage was lack of heat sink. Then I soldered second prototype with proper transistor cooling. I also wound correct transformer using binocular ferrite cores
Next step was designing PCB. I started with the schematic diagram based on original project
