Simple HF Power Amplifier

Pradeep G.


Here is an inexpensive but powerful RF 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.

A9C_1The 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.


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