Complex sentence: The incoming audio signal to be amplified was applied to an electromagnet that vibrated a steel diaphragm attached to the carbon microphone, and a battery passed enough current through the microphone that the output audio signal was larger than the input.
Split into simpler sentences: The incoming audio signal to be amplified was applied to an electromagnet that vibrated a steel diaphragm attached to the carbon microphone. A battery passed a large enough current through the microphone that the audio output signal was larger than the input.