The DC power to the final stage of your transmitter is 200 watts and the RF output is 125 watts. What has happened to the rest of the power?

In any electronic circuit, especially RF amplifiers, no device is 100% efficient. The efficiency of an amplifier is the ratio of its useful RF output power to its DC input power. In this scenario, the amplifier consumes 200 watts of DC power but only produces 125 watts of RF output. The difference between the input and output is 75 watts. Due to the laws of physics, this missing electrical energy does not vanish; it is converted directly into thermal energy (heat) by the components. This is why transmitter final stages require cooling mechanisms like heat sinks or fans. The 'lost' power is not recycled as feedback or used to magically increase efficiency; it is simply wasted as heat.