To be safe I would reduce the power of your Ft-1802 to maximum 15 watts even on the medium and high settings.
You can do this in the service menu and then even if the rig is accidentally set to 50 watts it won't blow the input to the amp.
http://www.gi4sjq.com/sjq/index.php?option=com_content&task=view&id=13&Itemid=15Remember to note down the factory setting so you can restore it in future..
73 Rex - G8UBJ