FM Power Amplifier BLY87A, BLY89A, KT920A, KT925B


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A very simple fm power amplifier which can deliver 4W rf power with 12V power supply and BLY87A or KT920A and 20W with BLY89A or KT925B.
If you use BLY87A or KT920A the input power must be 0.5W and 4W if you use BLY89A or KT925B. This fm power amplifier is designed to work on 50 Ω antennas and a maximum power supply of 14V and in 88 108 MHz band.

Use only metallic trimmers, a good heatsink for the transistor and ceramic capacitors and keep the pins very short.
FM power amplifier circuit components:
C1 = C8 = 10-40pF + 22pF in parallel ||
C2 = 10-70pF + 120pF ||
C3 = 2.2nF
C4 = 33nF
C5 = 4 x 180pF
C6 = 1nF
C7 = 2.2nF
C9 = 10-70pF + 47pF ||
R1 = 380Ω
R2 = 47Ω
R3 = 5.6 Ω
L1 = 3 turns / 0.8mm / 6mm / legth = 8mm
L2 = 6turns / 0.5mm /over R2
L3 = 5 t / 0.6mm / 6mm
L4 = 4 t / 1.2mm / 8mm
T = 4W with BLY87A, KT920A
T = 20W with BLY89A, KT925B

FM amplifier circuit schematic