Here is an inexpensive but powerful high frequency power amplifier for the 40m (7MHz) band. The circuit accepts only 20-30mW RF power and amplifies it to the wattage level. So its input can be directly connected to a VFO and the output can be fed to an antenna.
High frequency power amplifier circuit
The amplifier works off 24V DC. Adjust potmeter VR1 for maximum power output. The RFC coil comprises 15 turns of 36SWG wire wound over a TV ferrite balun core. Coil L1 has 30 turns (15T+15T) of 24SWG copper-enameled wire wound over a 1.5cm dia. plastic tube. It is centre-tapped, with air core connected to the collector of transistor T1. Coil L2 has five turns of 24SWG wire wound over L1 centre. Transistor T2 should be mounted on a 3mm thick aluminium heat-sink.
The article was published in February 2007 and has recently been updated.