Beverage preamp

Steve Bunting M0BPQ

Hi all

I have a CCW beverage preamp and I suspect I have accidentally put too many volts up the coax from a variable power supply. I was trying to see how much voltage drop there is in my 400m+ long coax run. Looking at the circuit, the only thing that can be broken is the active device. What type is this? I can happily replace it myself. 

I am now using 75R coax. Is it worth rewinding the transformer to match ?