Desperately seeking the elusive tube sound

Marakanetz, I just wated to clarify your statement. If your are talking about a TUBE POWER AMP, then the most critical (as well as affordable) sound comes from the low level driver/input tubes. A VAST sonic improvement can be gained by replacing the stock Soviet, Chinese, or Yugo tubes with GENUINE NOS tubes (Euro or American...'70's or earlier only!!) Sure, replacing the power output tubes would be nice, if you could find the quantity (4 and up to 16 or more that may mono-blocks require) and the price! Also, low level tubes will have a lifespan of 2 or 3 time greater than that of a power output tube.

Marakanetz, I agree...EI Yugo's are a good tube, especially since they are a great choice for power tubes (over Soviet and Chinese). And they're good to go, right out of the box. The trouble with NOS tubes (besides the scarcity and cost...and again, we're talking about the low power pre/driver tubes) is that they were not made specifically with high-end audio in mind! Some can be wickedly microphonic. And every simplton, huckster, and his brother is out there selling tubes. And people see a matched Quad of Telefunkens 12AU7's for $150-, and they bite! They get em delivered and WHOOPS, where's the diamond logo etched on the base? Congrats...they've just bought counterfeits, probably Chinese crap, worth maybe $20-...on a good day! Or the BIG NAME tube "guru" who's selling "Mullard" 12AU7's (CV4003) manufactured in 1985 that are total crap, and sound nothing like real Mullards from the '70's or earlier. The reason that many people don't believe in NOS, is due to the fact that they tried to save a few bucks and ended up with rebrands, fakes, or bad NOS tubes. Hey, the only place to get real NOS tubes that are suitable for your particular audio application is from Andy at Vintage Tube Services. He's the "pro-in-the-know".