Homebrew_PCBs

The transistor is being used as a diode. I’ve seen this on amplifiers to monitor the power transistors and adjust the bias so it don’t go into thermal runaway.  In all heater circuits I have dealt with we always used a temperature control with a thermocouple. These withstood the higher temperatures . they also had some form of high limit protection in case of a shorted thermocouple or controller failure.if the thermocouple failed open the controller simply shut the heat off altogether.