Someone suggested I put this on my blog, so here goes with a brief introduction.
My favorite method is series modulation using a transistor as the "modulation" stage. The modulated RF stage is set so the stage voltage is close to half rail. With modulation the voltage swings to close to full rail (4 times the power). This stage is followed by a linear amplifier to bring the power up to that required. I used this in my Fredbox and Sixbox rigs without a linear. If I ever do a simple Tenbox AM rig I'd add a linear RF stage.
See Fredbox .
See Sixbox .
Don't forget that if you click on a picture or schematic on my website a larger version is usually available.
AM rigs are simple to build. I am truly surprised that these have gone out of favour in recent times. Surplus PMR AM rigs can often be found for almost nothing. Back in the 1950s and 1960s AM was the predominant mode on HF and VHF.
There is plenty of space for AM on 10m, 6m, 4m and 2m. A decent AM rig should only occupy 6kHz or less of bandwidth.