Hybrid power supply noise canceling amplifier

For those for whom "hybrid" means nasty, a purer approach is to use only a capacitor to introduce the power supply noise to the 300B's cathode. The added capacitor at the grid circuit is there to bootstrap the noise to the grid. The resistor ratio should favor the top resistor so as not to tax the feedback mechanism. For example, if the original grid bias resistor was 300k, then the top resistor should be around 270k and the bottom resistor, 30k. A .5µF capacitor is sufficient to couple to the cathode at 120 Hz.

For those for whom "hybrid" means nasty, a purer approach is to use only a capacitor to introduce the power supply noise to the 300B's cathode. The added capacitor at the grid circuit is there to bootstrap the noise to the grid. The resistor ratio should favor the top resistor so as not to tax the feedback mechanism. For example, if the original grid bias resistor was 300k, then the top resistor should be around 270k and the bottom resistor, 30k. A 0.47µF capacitor is sufficient to couple to the cathode at 120 Hz.