I've seen PCB amps where the ground of all filter caps, bias supply and relays supply was in fact one big common square PCB track on the PSU board from which cables are running to the preamp and power tubes section. It was grounded to the chassis at that side of the circuit and the input jack had only a 100n cap from preamp ground to chassis. Although a high gain it was dead quiet. It looks like this arrangement works as well. I guess that big piece of PCB copper can be considered a star ground
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