hi i bulit 555 timer circuit running at 100khz square wave driving the gate through a 10 ohm resistor the with source connected to ground i want antenna connected at the drain and want apply 12 volts to the drain but i want to limit the through the drain to 6 amps or 72 watts how is this normally achived as a 10watt resistor would burn up

 

You don't us a resistor for an RF load. BTW such a signal would be illegal at those power levels. Expect large fines and or jail time if you get caught.

 

what do you use as a rf load on a mosfet rf amplifier

 

You use something that has the appropriate impedance at the frequency of operation.