This is the homebrew six meter amplifier I use for HSMS. It uses one 4-400A and puts out about 600 watts. The design is pretty straight forward. The RF choke to the right of the tube is homemade. The rig uses a pi-network output circuit. The tank coil is five turns of 1/4" copper tubing about 2 inches in diameter with the turns spaced about 1/2". This is the grid tuning circuit.