Tube amplifier assembly including a power tube that is configured to be coupled to a grounding deck and positioned within an opening of the grounding deck. The tube amplifier assembly also includes a tube adapter that is configured to be coupled to the grounding deck. The tube adapter has a capacitive plate that extends parallel to the grounding deck and an adapter wall that is coupled to the capacitive plate. The tube adapter has an adapter opening that is aligned with the deck opening to form a tube passage. The tube adapter includes flexible conductive elements that are electrically coupled to the capacitive plate and surround the tube passage. The flexible conductive elements engage the power tube in the tube passage and electrically couple the power tube to the capacitive plate. The grounding deck and the capacitive plate form a capacitor assembly.