NOS Tubes--Are they worth it? or accurate?

I've been playing around with tube amps since I was in high school 35 years ago. I've owned dozens and have designed and built around 8 or so (I have degress in electrical engineering and physics). Garfish's points are all accurate.

Speaking of accuracy, what makes you think that the original manufacturer had any special direct line to accuracy. Most high end equipment is "voiced" which means the engineering ends and the subjectivity takes over.

On asylum, this very topic came up, and someone posted that the old NOS tubes had somewhat different electrical characteristics than, say Sovtek 6922s. So, yes, you are distorting the original design parameters by putting NOS tubes in. Contrary to your claim, many manufacturers state that they do strive to design for accuracy as well as sonics.

To Saxo:
Individual tubes from the same manufacturer have slightly different electrical characteristics. Hence matching on various parameters. If "many" manufacturers strive for accuracy in their tube designs, which I doubr but I'll take your word for it, I would have to say that since every piece of tube equipment I have ever heard has a noticable sonic signature, that those manufacturers have not succeeded.

Pls 1, since you have engineeering background, do you believe that it is not possible to design an accurate tube amp or preamp? If, for example, you look at bench measurement frequency response on a Sonic Frontiers Power 2 or 3, you will find almost a dead flat response. You don't see that very often in tube amp reviews, I know. However, again, into an actual load, who knows? But doesn't that apply to transistor designs as well?

Regarding the SF amps, from my experience and everything I have read, listeners still find there are deviations from flat in these amps. Maybe I'm answering my own question here. That we don't know how to design a truly accurate piece of equipment.

Be that as it may, it still seems that pieces that show gross frequency response deviations show these dips and peaks in their sonics as well. So, what do measurements tell us? Something and nothing both.

You raise some good points. I've got a bunch of client stuff over the next few days so it will take me some time to get my thoughts together for a more complete answer.

In the mean time a quick response. I am fairly fanatical about flat frequency response and correct phase/impulse response. I own Dunlavy SC-V's and use wall treatment and a Sigtech Digital DSP to get very flat reponse.

The Speaker/room combo is usually never anywhere close to flat. Almost every amp is virtually ruler flat compared to that or to a cartridge. If you care about accurate frequency and phase reponse the speaker/room combo is where to start.

As far as measurements on electronics, it gets interesting when the steady state sine wave measurements are replaced with impulse measurements.

In theory a simple triode amp in a well designed circuit should be linear over its designed operating range. In practice it never is.

For example, the instantaneous whap of a bass drum may drop the voltage on the B+ rails that powers the tube so severely that for the instant the amp is operating nowhere near in spec. This can be detected with a 'scope and heard as a congested sound.

Some tubes are very microphonic, that is they vibrate when disturbed. In a guitar amp, this creates a desired sound that isn't "accurate". Loud music may cause vibrations in the audio amp coloring the sound.

These are just two of the dozens of these readily known departures from a completely "accurate" amp. All real world amps have these faults to some degree. This doesn't even count all of the depatures from linearity that happen through the electrical interaction of the speakers, crossovers and the amplifier playing real music.

Some faults, like even order harmonics in a SET, can be perceived as euphonic. There is no accurate mapping from the engineering circuitry to auditorily perceived accuracy. Our ears are non linear transducers. Evolution has tuned then to be amazingly sensitive to some signals and insensitive to others.

The reason "Reference" models cost so much is that every component and build decision is (should be) made around minimizing every possible fault with the hope that then the amp will be perceived as accurate. (Plus they are usually hand built in single digit qualtities).

At what point you find the sound acceptable becomes a matter of taste. Hence my comments on NOS. Your ears will detect sonic signatures from virually any piece of tube equipment. A designer who listens only to small jazz ensembles is of no use to be personally because I listen to large scale orchestral music.

More later