A High Sensitivity Power Pentode Using the 'Shadow Grid' Technique
Using an old idea, the Shadow Grid technique, and applying it to a new tube design, an audio power pentode, a tube with very desirable characteristics was obtained. Following the introduction of the 6FG5 Shadow Grid pentode, a logical extension of the low screen current advantages of this construction ws to incorporate it in a power pentode for audio applications. Because of the unique field configuration it is possible to obtain substantial plate current and power output with a high turns-per-inch control grid, leading to extremely high values of power sensitivity. With suitable shielding to reduce interelectrode capacitancees, this same design may also be adapted to perform vertical output and video amplifier functions in television applications. Characteristics and construction of an experimental pentode are given, with typical output and distortion figures. Featuring very low audio input drive voltages, this new design may in many cases permit a reduction in the number of amplification stages required.
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