Recent Developments of the Class B Audio- and Radio-Frequency Amplifiers

Class B audio-frequency and radio-frequency amplifiers have many applications and the distortion can be kept to a very low value if the necessary precautions are taken to prevent nonlinearity of such amplifiers. Undoubtedly, the most important factor in the design of a class B amplifier for low distortion is the characteristic of the driver system. Tube characteristics and the use of a proper load are also important but are more definite and more generally understood. The purpose of this paper is to present the results of recent developments of the class B audio and radio amplifiers to reduce distortion. The results of the investigations indicate that a heavily loaded driver system in general is undesirable because of the power consumed and because such loading results in greater distortion than obtainable by other means. The general procedure adopted to reduce distortion was to prevent distortion in each unit of the amplifier system. Distortion balancing schemes are not only critical to adjust but are likely to introduce higher order harmonics and sum and difference tones which may be more objectionable than a higher measured value of lower order harmonics. Actual performance data are presented for medium and relatively high powered audio and radio systems. The necessary input requirements to permit the performance obtained are discussed. Sufficient theory is given to make the paper complete and to show that the actual performance of such amplifiers can be quite accurately predicted if the necessary tube characteristics are known.