Power Output Characteristics of the Pentode

The type of pentode considered in this paper comprises a cathode, a control grid, a screen grid, a grid connected to the cathode to prevent the flow of secondary-electron current from the plate, and a plate. A quantity called the "power sensitivity" is defined as the square root of the power output divided by the effective value of the applied sinusoidal grid voltage. This quantity permits a direct comparison to be made between two output tubes in terms of an equivalent amplification, or "gain." The mathematical theory of the Carson firstand second-order effects is developed. The production of harmonics by the second-order effect is calculated and is found to depend upon three non-related parameters representing curvature and fanning of the characteristics. The possibility of mutual cancellation of the terms involving these parameters when the grid bias is more negative than the point of inflection on the ip-egcharacteristic is noted. In these circumstances the remaining harmonic distortion is due to higher order terms and is small so that a maximum of undistorted power is obtained. An expression is obtained for the undistorted power as a function of the load resistance. Three types of power limitation are classified and discussed; (1) distortion due to curvature of the characteristic; (2) distortion due to plate current cut-off; (3) distortion due to the grid potential becoming positive. The circumstances of their occurrence and their effects are examined qualitatively.