I made two kids of linear amplifiers for SDR 1W transceiver( Peaberry SDR V2 and SoftRock RXTX Ensembl). One is based on B class push pull with two FETs, Toshiba TK10E60W and its output power is 50W. The other has four FETs Alpha & Omega AOT5N60 for 150W output. Thoes FET are usually used for switching regulator and are easy to get. The important parameter of TK10E60W FET are Pd=100W, Id=9.7A , Vd=600V, and Ciss=700p. Those for AOT5N60 are Pd=130W, Id=5A , Vd=600V, and Ciss=500p. The circuit diagram of 50W amplifier is shown below. The key part is the control of the bias voltage(gate voltage) compensating temperature of FET. Without temperature compensation, just 10W can damage FET in a short time. I use the thermistor mounted the fin of FET and two LEDs. When temperature goes up, the resistance of thermistor deceases and reduces Vg. The LED blocks over compensation in the case of very low temperature. The system of 150W amplifier is almost same.
