The Benefits of Burn In Power Tubes
New tubes have always sounded and performed better when burned in prior to final testing and installation. By running a tube at full operating voltages (and not just the 6.3 heater voltages) for 24 hours, the cathode is allowed to stabilize and any oxide contaminants on the metal surfaces evaporate and are collected by the getter. The burned in tube is "cleaner" inside and better able to reproduce sound.
For burned in power tubes, the initial matching is less likely to drift and rebiasing isn't needed. The stability is immediately apparent. And for preamp tubes, the improved tone is instantaneously accessible without having to wait for the tube to stabilize making "tube rolling" much easier. And the combined benefit, the burn-in process quickly weeds out weak and suspect tubes before they get into your equipment.
If you want the best for your equipment and your listening enjoyment, burned in tubes are the most effective methods to insure your satisfaction. You don't have to wait for the best.