Of course, the same questions always comes up when any audio transformer is considered: where to find a good sample and how much will it cost? Several companies have come out with high quality interstage transformers that could be pressed into use. And the telecommunication industry might provide a ready source as well. Still this transformer is bound to be expensive. An alternative plan is to retain the coupling capacitor, but alter the bottom triode's cathode resistor bypassing scheme.
    The circuit below retains the coupling capacitor, but uses a different bypassing arrangement for the cathode resistor. The bypass capacitor's polarity has been reversed and it is now terminated into ground, rather than the negative power supply rail.

    Once again, getting rid of this noise can be handled rather nicely by using a coupling transformer instead of the coupling capacitor.  Now, the bottom triode's grid and cathode both see the same power supply noise, which prevents the noise's amplification. The triode will experience a varying current flow in response to that noise, but then so to will the top triode and in equal degree. The result is a cancellation of positive and negative power supply noise into a blissful null at the center point where the MOSFETs meet and the speaker attaches.

      This change will force the cathode to mimic the ground's lack of signal rather than the power supply rail's noise. Thus the bottom triode's grid and cathode will track each other much better. The top triode's topology has become a bit more complex, but with the reward of a higher impedance for the bottom triode to work into (more gain, less distortion  and noise) and a ready means of compensating for the DC offset, which otherwise could as high as 5 volts! While the noise is lowered substantially, it is not altogether nulled. Adding a small capacitor across the bottom triode's cathode resistor will purposely inject a small amount of noise to offset the small amount from the top power supply rail.

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