When in an inactive state, Class B amplifiers have many advantages over the Class A amps. The reason is no current flows through the transistors. On the one hand, neither the output transistors nor the transformers dissipate any power when the signal is off. On the other, Class A amplifiers require a substantial amount of base bias, so they disperse a great amount of heat. And they do so even when there is no input signal present.
Class B Amplifiers: How They Work
Generally, to avoid extreme distortion at audio frequencies, there are two devices operating at the same time. In a Class B amplifier, the active unit conducts for 180º of the cycle. Each of the units directs for half of the cycle in a continuous way. Class B amps tend to be more efficient than Class A ones, for they are capable of amplifying signals with two active devices. Moreover, each of them is working over one half of the cycle. In addition, musicians generally chose Class B amplifiers over battery-operated devices such as transistor radios.
On Radio Frequencies
In radio frequencies, if you make the connection to the load made with a tuned circuit, you will only be able to use one unit working in a Class B amp. There is an explanation: the saved energy in the tuned circuit feeds the missing half of the waveform. In order to prevent distortion of the frequency-modulated signals that pass through the amplifier, the radio frequency output power has to be proportional to the square of the input excitation voltage.
The Push-Pull Stage
The push-pull stage is usually a practical circuit for Class B amps. Furthermore, other devices help to amplify the opposite halves of the input signals. And they are rearranged at the output. This combination provides high efficiency. However, it might also face a latent conflict regarding a tiny mismatch in the crossover zone, aka crossover distortion. In order to solve this problem, the user should bias the devices so that they are never completely off. The name of this process is Class AB operation.
