Why are older tubes so much sought after

Sirspeedy wrote: "Very tight tolerences!"

Just a comment on a minor point. Tight tolerances has nothing to directly do with sound qualities. It only means whatever the attributes of the design, the finished product consistently meets specifications.

That could just as easily mean that the tube is consistently not suitable for audio.

I've noted there is a tendency by some to almost automatically ascribe good qualities to the old stuff. However, having lived in the 50s and 60s, I know that period of time had its share of poor and mediocre products. There is little doubt in my mind some tubes from that era are less than they could have been.

Underlying the discussion of whether this or that tube is better than another is the notion that there is an objective standard and that each tube fits into a specific spot along a worst-to-best continuum. That is hardly the case. It is a matter of the designer or the user finding a personal fit. There are so many more choices in older tubes, it is not surprising that one can, if one searches diligently, find older tubes that better fit the bill.

Manufacturers have to use readily available tubes, meaning, in most cases, currently manufactured tubes. Why go through the considerable expense of selecting NOS tubes when there is a good chance those tubes will not be the customer's preference anyway? Also, for those not inclined to try different tubes, the manufacturer has to be reasonably assured that the same tube is available many years from now to service that equipment. Just by pure odds, it is unlikely that the particular tubes chosen by the manufacturer will fit any particular customers idea of an optimal choice.

I am sure that, wholly apart from sonic considerations, certain older tubes have because of their "exotic" and rare status (people actually collect tubes, such as 300As). But, i can assure you that I would be glad to use current 6sn7, 12ax7s, etc., if they happen to work well for me. I pay a lot for the EML meshplate 2a3s I run because, they outperform anything else I have heard. In other words, I am not paying for their rarity (they are currently being manufactured), but I am paying a premium for performance.

NOS tubes are compared with new production by listening to them. It seems to me that comparitive measurements of what the tubes do to the signal waveform could lead to an understanding of what needs to be changed in new production tubes to make them sound like the old ones which people prefer. The laws of physics haven't changed, so there is no reason that tubes made today can't be superior.

Eldartford- The reasons are, I "suppose" economic. Not enough demand to support the cost of higher quality materials, tooling, and labor.

I am not sure that you can get good engineers to work on tubes these days. People are what make products good or bad. If you are an EE, will you choose tube design as your career?

They did not even teach tubes when I was in the EE program, and that was a long time ago....