1, as large as possible, the power amplifier will provide enough power to the load because of the power amplifier. The operation voltage and the working current of the power amplifier tube are close to the limit value under the condition of safe work, that is, the pipe works in the limit state.

2. The output power of the power amplifier which is as high as possible is to convert the DC power of the DC power through the transistor. The power pipe and the energy dissipation element in the circuit will consume the power when the power conversion is converted. The power of the load is expressed by P0. The total power provided by the DC power supply is expressed by PE. The ETA represents the conversion efficiency, then the ETA is ETA. = (Po/PE) *100%, the size of the ETA reflects the utilization rate of the power. For example, the efficiency of an amplifier = 50% indicates that only half of the DC power provided by the power supply is converted to the output power to the load, and the other half is consumed in the circuit, which can increase the temperature of the tubes and components, and will burn the transistors seriously. Attention should be paid to the heat dissipation of the power amplifier tube. In order to ensure the safety of the power tube, heat sink is usually added to the high-power tube. How to improve efficiency and reduce power consumption is an important issue in power amplifiers.

3, allowing the nonlinear distortion power amplifier to work in large signal state inevitably produces nonlinear distortion. The larger the output power of the same power amplifier, the more serious the nonlinear distortion. The requirements for nonlinear distortion of power amplifiers in different situations are different. The nonlinear distortion must be limited to the allowable range in the measurement system and the electroacoustic equipment. The nonlinear distortion in the driving motor or control relay is a secondary contradiction.  Besides, the power amplifier can only be analyzed by graphic method, and the micro variable equivalent circuit method is no longer applicable. In order to obtain large mountain power and efficiency, the power amplifier is matched with the load, the traditional power amplifier and the load are coupled with the transformer. The advantages of this kind of power amplifier are that the impedance matching and the output power are easy to be realized, but the transformer is large, heavy, and the frequency characteristic is poor, and it is not good for the power amplifier. Integrate。 It is seldom used in the power amplifier now produced, and is gradually replaced by complementary symmetrical power amplifier. The complementary symmetrical circuit eliminates the cumbersome transformer, and has the advantages of simple circuit structure, high efficiency, good frequency response and easy integration. There are two forms of complementary symmetric power amplifiers: a single power supply and a large capacity capacitor coupled to the load, called OTL circuits; a direct coupled complementary symmetric power amplifier using a dual power supply and a capacitor, called a 0CL circuit.