Hello Markus, Stefan, Paul,
I'm back at 8170kHz and using now a class D Amplifier. You can see me at Markus Grabber.
Amplifier :
max. power on 2 Ohm: 500W
mac. power on 4 Ohm: 250W
Power supply range. 20..48V
Switching frequency: 400kHz
IC: Texas DTA8950
IC is fan cooled
Price,  mono mode: Ebay, 50 €

My actual values:
Power supply: 30V, 3A = 90W
PA output about 80W
Antenna current: 250mA
Temperature of cooler: 37°C
Fan mostly switched off

For more power I have to increase the voltage of power supply or to lower the primary turns of the transformer.
300Ws should be not a problem.

For receiving I wont to use a min whip. I hope that the noise is not to high.

73
Roland DL3NDR