This is the circuit diagram of 40W wideband RF power amplifier 88 - 108 MHz build based MOSFET MRF171A. The purpose of this circuit is to boost the output power of low power FM broadcast band exciters, a number of these are available commercially, both as kits and ready made.
This design is based on a new MOSFET device, with the attendant advantages of high gain, high efficiency and ease of tuning.
The amplifier was constructed in a small aluminium diecast box. RF input and output connections are made by coaxial sockets. The power supply is routed through a ceramic feedthrough capacitor bolted in the wall of the box. This constructional techniques results in excellent shielding, preventing RF radiation escaping from the amplifier. Without it, significant amounts of RF radiation could be radiated, interfering with other sensitive circuits such as VCOs and audio stages, also significant amounts of harmonic radiation could occur.
The base of the power device sits through a cut-out in the floor of the diecast box and is bolted directly onto a small extruded aluminium heatsink. An alternative would have the base of the power device sitting on the floor of the diecast box. This is not recommended for two reasons, both concerned with providing an effective path to conduct heat from the FET. Firstly the floor of the diecast box is not particularly smooth, which results in a poor thermal path. Secondly, having the floor of the diecast box in the thermal path introduces more mechanical interfaces and hence more thermal resistance. Another advantage of the chosen constructional technique is that it correctly aligns the device leads with the top face of the circuit board.
Using the specified heatsink will require the use of forced air cooling (a fan). If you plan not to use a fan, a much bigger heatsink will be required, and the amplifier should be mounted with the heatsink fins vertical to maximise cooling by natural convection.
The page source of 40W wideband RF power amplifier 88 - 108 MHz: irational.org. Go there for detailed explanation of this circuit. This is a demonstration about 01A RF Amplifier which is build used old tube component to amplify the signal.
Watch the video: