A '''modulation transformer''' is an [[Transformer|audio-frequency transformer]] that forms a major part of most [[Amplitude modulation|AM]] transmitters. The primary winding of a modulation transformer is fed by an audio amplifier that has about 1/2 of the rated outputinput power of the transmitter's final amplifier stage. The secondary winding is in series with the power supply of thethat final radio-frequency amplifier stage, thereforethereby loweringallowing the audio signal to lower and risingraise the operatinginstantaneous DC supply voltage of the power amplifier (PA) tube or transistor. Considering that the PA tubedevice is operated inas a [[Electronic_amplifier#Class_C|class-C]] modeamplifier, i.e. likeas a switch, the modulation transformer is responsible for the AMamplitude modulation (AM) of the transmitter. There Is only one system of modulation that can be used without the modulation transformer with high power. "This is loop modulation"
