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"HANGOVER" EFFECT: "Hangover effects", or transients caused by the loud speaker cone vibrating at its natural period when shock excited, are greatly reduced by the use of inverse feedback. Hie lower plate resistance provides a considerable amount of damping so that the oscillations or transients are reduced. With regular beam power tubes the shunting effect of the tube is exceedingly small with the result that the damping is negligible. As a result, unnatural "boominess" may result when the speaker is shock excited and the cone vibrates at its own natural period. The natural period depends upon .the physical construction of the speaker and is usually in the neighborhood of 50 to 150 cycles.

REDUCTION OF HUM: Hum originating within the feedback loop is cancelled out in much the same way as distortion since the hum developed in the stage or stages included within the loop and the voltage feed into the grid circuit are out of phase and tend to cancel. It must be remembered however, that distortion or hum originating in a stage outside the feedback loop will not be reduced by inverse feedback. Great reductions in plate circuit distortion and plate resistance may be obtained by the use of large amounts of inverse feedback. However, the limiting factor in inverse feedback, assuming there is negligible phase shift occurring in the stages over which feedback is applied, is the amount of desired gain from the stage in question. In actual design, the amount of inverse feedback is a compromise between the gain and the desired reduction in distortion. If there is enough gain in the previous stages and if the driver tube can supply the necessary peak voltage, it will be advisable to increase the amount of inverse feedback in order to reduce the plate resistance and the plate circuit distortion. However, if the plate resistance is fairly low and if the plate circuit distortion is a reasonable value, there is not much advantage gained in further reducing the gain by the addition of more inverse feedback.

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