The 60 Watt linear amplifier is simple all solid state circuit
using power mosfet IRF840. The IRF series of power transistors
are available in various voltage and power ratings. A single
IRF840 can handle maximum power output of 125 watts. Since these
transistors are used in inverters and smps they are easily
available for around Rs: 20/-.
The IRF linear amplifier can be connected to the out put of
popular VWN-QRP to get an output of 60 Watts. The circuit draws
700 ma at 60 Volt Vcc. Good heat sink is a must for the power
Alignment of the circuit is very easy. Connect a dummy load to
the out put of the circuit. You can use some small bulb like 24V
6Watts as the dummy load. I have even used 230V 60Watts bulb as
dummy load with my IRF840 power amplifier working at 120Volts.
Adjust the 10K preset to get around 100 ma Drain current. I used
gate voltage of 0.8V with my linear amplifier. A heigh gate
voltage can make the power transistor get distroyed by self
oscillation. So gate voltage must be below 2V and fixing at 1V
will be safe.
Bifalar transformaer T1 is wound with 8 turns 26SWG on 1.4 x 1
The coil on the drain of IRF is 3 turns 20 SWG wound on 4 number
of T13.9 torroids (two torroids are stacked to form a balun
core). The RFC at the Vcc line is 20 Turns 20 SWG wound on T20