I have been happy with a design by David, G0MRF, which is described at:
http://www.g0mrf.com/5W%20linear.htmThe PCB or kit is available if you want to save yourself some work.
Mine has a gain of more than 35 dB on 630 m, so 0 dBm input gives a few watts out. I'm using mine to bootstrap my way on to 630 m, with the ultimate intention of using it to drive a larger linear.
I've found this a better approach than using common audio power ICs, many of which have slew rate and stability issues in the driver application.
73, Peter.