You should learn how to replace and bias the tubes. This information is in the service manual!
Output Tube Bias Adjustment As shipped from the factory, the output “bias” adjustments are set for a nominal 65mA per 6550 tube. Under these idle conditions the tubes are each dissipating approximately 27 watts of their 48 watt rating (42 watt plate, 6 watt screen). This point of operation provides “enriched” Class AB1, and will satisfy the most critical listener. For best results, operate and adjust the Reference110 at 120VAC. Adjustment must be made under zero-signal conditions after at least 15-20 minutes of uninterrupted stabilization time. A digital voltmeter capable of accurate measurements with 0.lmVDC resolution is preferred for accurate adjustment (must have 31/2 digit display). Use the plastic alignment tool provided to make the adjustment. The measurement points are yellow and black banana test jacks next to each output tube. Adjust the “bias” for a voltage reading of 65mVDC (.065 Volt DC) at the blue bias pot for one of each output tube pair as follows, noting the voltage setting of the larger V number tube in each pair is slaved to the adjustment setting of its lower V number companion tube: Adjust V5 for 65mVDC and measure its companion tube V7 to verify a reading of 57 to 73mVDC. Repeat procedure by adjusting and measuring V9 to read 65mVDC and verify V11 reads 57-73mVDC; adjust and measure V6 to read 65mVDC and verify V8 reads 57-73mVDC, and finally adjust and measure V10 to read 65mVDC and verify that V12 reads 57-73 mVDC