Grid Losses in Power Amplifiers

In spite of the widespread use of radio-frequency power amplifiers, apparently no measurements of the power required to drive such amplifiers have ever been made. In this paper, a study of driving power is made at 60 cycles. It is found that the power input to the grid is proportional to the d-c grid current raised to the 1.34 power. The proportionality factor depends on the type of tube and the plate circuit conditions. With constant grid current the grid power input is found to be practically independent of grid bias voltage. A simple theory, based on an assumed relation between grid current and voltage, agrees quite well with the experimental results. Data are then given on six types of commercial air cooled transmitting tubes showing driving power, a-c driving voltage, gross power output and efficiency as functions of the d-c grid current. Finally, the effects of primary and secondary electron emission by the grid on the driving power are considered.