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Message started by Donnie on 11/02/26 at 01:18:55

Title: Production variations
Post by Donnie on 11/02/26 at 01:18:55

So this time change stuff has me sitting in the dark starting at 5:00 PM and my mind is shifting into overdrive way too early for my own good.

As I read reviews of how different tubes of the same type sound profoundly different than other brands or even production runs, my quizzical mind kicks in.

While I believe that there are sonic differences between different tubes, I wonder if there are differences between the same exact tubes just because of production tolerances?

Has anyone changed in the same tube as an old one and things sounded completely different? If so do you think that it just needed to break in?

Then I've started wondering about what the tolerances of tube manufacturing is, less than 1%? 10%? 20%?

Close tolerances cost a lot more than sloppy ones.
Remember that at one time tubes were a commodity, like light bulbs or tooth paste. They were made as cheap as possible and as quickly as possible. Not exactly the formula for consistent quality.

Are my thoughts way out of what everyone's experiences are?

Title: Re: Production variations
Post by CAJames on 11/02/26 at 03:45:28

Quote:

Posted by: Donnie Posted on: Today at 17:18:55

...Then I've started wondering about what the tolerances of tube manufacturing is, less than 1%? 10%? 20%?

Like there is just one tolerance

. Look at a tube data sheet and there are many specs: capacitances, currents, voltages and transconductance. Transconductance (g_m) is what tube testers test, but it is not correlated to "sound." In other words tubes with very different g_ms can sound the same, and tubes with very similar g_ms can sound very different. In this context very different means greater than 20%.

This circles back to the fundamental magic of tubes, and you can generalize it to amps if you want. What do you measure to tell what it sounds like? You figure that out, and you've really accomplished something. And then we can start measuring tolerances.

My experience with tubes is "it depends." For a lot of tubes from the golden age of tube tech, the "same" tubes, i.e. tubes that were made the same, and look the same in detail, usually sound pretty much the same. Usually but not always. Russian tubes that I've bought in quantity, from the same factory and the same date code, can be all over the map. I think a big factor is that Western tube factories did real QC, and so the factory brand tubes generally performed pretty consistently. Yes, tubes were a commodity, but they were a highly competitive commodity and quality mattered. You could say it was a simpler time.