12AU7 Gain Question

The right tube tester will give you the gain for each triode, but I don’t think that a 12AU7 can have a gain of 2016, that number may just be to mark the box of the tube intended for your power amp. I think you have 3 tubes with a gain of 16 for each triode.

The seller may have selected one of the tubes for the amp for another reason, though. I don’t see any harm in swapping the tubes around to see if one combination sounds better than another. Call the tube seller and ask him how the tube for the power amp is supposed to be different. There may be no difference between the tubes.  If you need to get them tested for some reason, I can do that.

The 2016 is clearly an error or "misprint". That’s more like a transconductance reading than mu (not possible to have mu that high). I wonder if the doofus seller mixed those readings up (don't do drugs).

Don’t use a multimeter. I’d just use them as is. Whether that mu is actually 16 (good!) or 20 (ok) it’s probably fine. 20 to 16 is still within 20%, which is close enough for most applications.

12AU7 has a mu (usually indicated by the Greek letter for “m”) of 16. If your tubes are all 12AU7s, then mu = 16. Mu is linearly related to gain, usually indicated as “A”. But mu is a product of transconductance (Gm) multiplied by plate resistance (Rp). These parameters vary somewhat according to plate voltage, grid bias, and plate current. 12AU7 has a Gm of about 6700 micromhos, when new. But if you measure Gm of several, they’ll vary a fair amount around that value. So all these numbers are “soft”, just a rough estimate. Your vendor may have sorted those tubes based on noise, but you can use any of them in any socket fit for a 12AU7.

Thank you very much guys, that is all very good information.