5 Watt FM Amplifier Board
This design is a 2 stage
amplifier that has about 17db of gain, suitable for an input of 50 to 100 MW. Its basically a Veronica 5 watt vco transmitter, without the vco.
The
transistors are a 2N4427 and a MRF237. Output power is 2.5 to 5 watts, depending on input drive and dc voltage. At 13.7 vdc with 50 MW of drive, the output was 2.5 watts. The maximum dc voltage recommended is about 15-16 volts.
The unit is constructed with copper clad board, a large piece is used as the construction surface and is mounted into a case. Other board material is cut into small pads, then glued to the construction surface for part connections. A heatsink is needed for the both transistors, a small "top hat" style will work for TR1 but TR2 requires a larger heatsink thats attached to the case. This is made from aluminum L stock, a 3/8" hole and a slot is made for TR2 to fit snuggly in. Up to 7-8 watts output is possible with this amp, but for continious duty only 5 watts maximum output is recommended.
5 Watt FM Amplifier Circuit
A fan is required and it is mouted on the case lid, with holes drilled for ventilation. The chokes H1, H2 and H3 are 5 turns of 30 awg wire on a ferite bead and choke H4 is a 330 ohm 1/2 watt resistor with 14 turns of 30 awg with a ferite bead on each end. Ferite beads need to be of type 43 material. The coils L1, L2 and L3 are made of 18 awg tinned wire. A 1.5 amp 3ag fuse is part of the dc
power cord assembly. I used BNC coax connectors for input and output, however SO-239 or F type connectors would be fine too.