What is a Single-ended amplifier?
Named for the configuration of the output stage. A single-ended output stage is so arranged that the output device amplifies the entire signal. There is no phase splitter and the output transformer primary is used as a straightforward anode load. SE output stages operate in Class A by definition. The circuitry of a single-ended amp tends to be simpler than a push-pull design and the electrical/magnetic design characteristics of the output transformer is also more straightforward. The downside is that it becomes more difficult to obtain higher levels of output power, as Class A is the least efficient operating mode. The output transformer primary also has to carry the quiescent direct current for the output valve and consequently needs to be both physically large and constructed with an air gap in the core to avoid saturation. These design compromises again limit the power achievable.
