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RE: 6SN7 tube

Posted by cpotl (A) on January 7, 2015 at 08:01:06

In Reply to: RE: 6SN7 tube posted by connieflyer on January 7, 2015 at 07:17:57:

I am curious sometimes about tube rolling, and the extent to which one could ever really say that "brand X" has an intrinsically different tonal quality from "brand Y."

Any tube two tubes of the same type will inevitably have different values for the mutual conductance, the plate resistance, and so on. If one pulls out one tube and pops in another and it sounds "better," could it simply be that by chance the biasing set up in the amplifier happens to be more appropriate for hitting the ideal operating point of the second tube than it was for the first tube?

In other words, might one simply be roaming around in the parameter space of possible values for the characteristic properties of the tubes until one happens to hit one that is ideally suited to the way the biasing, etc., is set up in one's amplifier? If one, for example, changed the value of the cathode resistor in the amplifier somewhat, and then repeated the exercise, maybe now it would be a different tube amongst the set of candidate tubes that happened to be the one that hit the sweet spot for the newly-configured amplifier?

Even statements such as that "brand X systematically sounds better than brand Y" might be subject to the same kind of influences. For example, it might be that brand X systematically happens to have a lower mutual conductance than brand Y, and that given the choice of cathode resistor value in one's amplifier, this meant that brand X tubes ended up closer to the ideal operating point than brand Y tubes. But this would not mean there was a general statement that "brand X is better than brand Y," but merely that the person making the report happened to have selected a value for the cathode resistor that was better suited to brand X than brand Y.

I'm not saying there couldn't be any more to it than this, but I am just curious how one could make statistically significant general assertions about the superiority of one brand over another when there must be so many confounding factors involved.

Chris

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