cbrookhart.
After you start the engine,you have to reset the engine gen switch,for that engine,repeat for all four engines.
This is what i think you are failing to do.
The Gen switches look as if they are on,but without reseting them,they are off line,so you are trying to use the radios from batt,which on a real aircraft,the pilots radio should work,but in the FS9 c-130 they will not work.
Regards alan. 8-)