If you think he should put a four watt dead key into it go ahead and smoke that amp. As for 18 to 20 watts, thats the max amount of swing I would put into it. I know all about the 1:4 swng rule, but trust me if you put a 4 watt dead key into that amp it will not last long. For example a 1 watt dead key would only be 4 watts modulated power out of the radio if you followed the 1:4 rule, that would not drive that amp at all. Around 15 watts swing would be about right, and a 1-2 watt dead key is all I would put into that little amp. You should adjust your dead key on the radio to allow a 1:4 dead key and swing ratio out of the amp not the radio its self, as again that would only create 4 watts of swing out of the radio. Someone else could probably explian it better, but I hope this helped.