A FET switch to work together with the Arduino PWR / SWR meter and controllable by the PTT is published here.
The FET is a IRF4905 and it works well up to 48V. For higher voltages you might want to use a different FET.
It is very simple controlled by 2 cables connected to HEADER_2
Pin 2 of the header will switch the 48V on the PA, just by simply grounding this pin.
If pin 1 will go high, say +5V (in case of an alarm) the PA will switch off. This +5V comes from the Arduino PWR / SWR meter found on this website in case of a temperature alarm or a SWR alarm.
The FET requires some cooling but not much. The unit above is made for 48V.
Below is a picture of a double unit build in my 700W 1296MHz PA. Slightly different resistor values are used. The 2 PTT’s are grounded via diodes.