What is single ended, parallel single ended and push-pull.

Single ended means the amplifier tubes are operated in a single ended mode, the audio signal goes in one end of the tube and re-appears at the other end, very simple but it has its drawbacks because of increased distortion and noise problems. Parallel single-ended is the same thing but instead of one tube, more a used together in a daisy chain fashion. Push-Pull is the preferred use of circuit topology for Tube Technology because the audio signal is spilt between positive phase and negative phase, increasing power output with decreased distortion and reduced noise. This mode of operation is more complicated and involves careful transformer design to achieve good results; hence most companies opt for single-ended designs because they are easier to design.