Finally I found some time to build the amplifier.
The goal was to get at least 1 Watt output without too much distortion.
I made a push pull amplifier using two 2n3866 transistors. The result was not good.
The maximum output power was 0.5 Watt with 30% efficiency. I blew a few transistors.
The 2n3866 was not a good choice as it is intended for 28 volts. So I got some 2n4427 transistors. Those worked better. I can get >1 watt output. harmonics are -20 dbc down. Efficiency is better than 40%.
At the moment I am building a lowpass fiter to suppress harmonics. Using a 3 element lowpass filter I was able to get 1,5 watt output. This filter also improves the matching. Harmonics are -35 dbc . I am replacing this filter with a 5 element filter to get the required suppression of the harmonics.
So far it seems that the 3th harmonic is still too strong at -40dbc. I may have to use better capacitors. The coils are aircoils so those should be OK.
