The challenge of building a HF linear has the best chance if you look at the results and failure of other amateurs. So that's what I did. The best sites I found until now are:

• www.pa0fri.com  There are several subjects, so look for the one telling a lot about HF amps !  Thanks Frits !
• RF amplifier building
• How to design an amplifier; the basics
• Designing and HF amplifier class A, B, or AB
• Example of 50W with irf510
• Example of building it
• 5W QRP transmitter in QRC kit
• Lot of DIY Linear amplifier info
•  

I used a lot of info from these sites to build my own linear.