I know, another of my controversial statements. But, is your amp only as good as the tubes installed? I say for the most part yes if you have a higher end system. The only tube that performs with the clarity my Revel M22s speakers are capable of are Siemens 6BM8. These power tubes are as important at least in this incident as the preamp tube. Of course, the preamp plays a large role too. I tried every 6BM8 made and only the Siemens performs well. If the Siemens 6BM8 were not available, I would pursue another tube amplifier. It does not stop here. I rebuilt and upgraded a Scott 299A for a member here with I believe the most critical ears I ever encountered. And, I have had over 100 customers. The tubes that worked for the member here were RCA 12AX7 black plate in the phono and Mullard 12AX7 long plate in the preamp. The Sovtek premium EL84M were also required for my customer. These are the better EL84 vs the cheaper Sovtek EL84 tubes. Anyways, he was satisfied only after the best tubes were installed. Perhaps he will 'chime in' here. If you have just average speakers and a cheaper TT plus a lower end cartridge the tubes do not matter as much. But, higher-end equipment do need the best tubes to extract the best performance. I also assume the amp is high-end using good audio transformers and good audio coupling capacitors to extract the best out of the tubes. The better tubes can add greatly to the cost of your tube amplifier, but that is the game. No way around it. Your thoughts?