The Darlington tube is also known as the composite tube. The Darlington tube is connected by two triodes, and the polarity only recognizes the front triode. The specific connection method is as follows. Take two triodes with the same polarity as an example. The front triode collector is connected with the back triode collector, and the front triode emitter is connected with the back triode base. The power of the front triode is generally smaller than that of the back triode. The front triode base is the Darlington tube base, and the back triode emitter is the Darlington tube emitter. The usage is the same as that of the triode The magnification is the product of the magnification of two triodes.