W Power Amplifier
My 100 W is based on the design by
David Bowman G0MRF  and I can recommend the approach used by
David. A copy of the circuit diagram can be found at
The power amplifier (PA) has been fitted with a low pass filter to
prevent the radiation of harmonics.
I had trouble finding the 2SK413 MOSFETs as originally specified by
David, so I ended up using low voltage 2SK400 devices. I also had trouble finding a
suitable transformer for the 30 volt power supply. During testing, I inadvertently
destroyed two of the 2SK400s and David suggested using high voltage IRFP450 devices.
These more rugged devices have performed very well and appear to be indestructable.
The limiting factor continued to be my power supply which restricted power output
to 100 W.
Nevertheless the G0MRF PA provided good, reliable service and enabled me
to make the first Wales-Scotland QSO to Dave GM3YXM/P (395 km). For many months,
this contact remained my best DX on 136 kHz. It also enabled me to provide the first
GW contact with over 20 stations.