hi, i have this linear amplifier project https://tzitzikas.webs.com/irf640-1.JPG with 2 irf640 mosfets.
My problem is, when i adjust the both mosfets drain's current at 400mA (current without input signal), after some minutes
when the heatshink is warm (with input signal), the current becomes very high and one of the 2 fet goes off, and i must
replace it. Do you have any idea-schematic (with thermistor or diode) to control this current and to keep it stable at 400mA?