Do 12AX7's change tone as they age?

[suncrush]

I now am the proud owner of two Micro Terror amps, one of which is 2 years old, and probably has about 1000 hours on the tube.

The other is brand new.

I did a tube burn-in on the new amp, but I noticed that it is much more nasal than the old one. You have to turn the tone knob about 2 notches to the left to even out the sound.

Do 12AX7 tubes get darker as they age, or is this likely to be due to minor variations in the electronic components?

[whoisalhedges]

As limited-life components age, their values change; which means yes, their sound can change. That said, I doubt it's that. Frequency-based sounds are usually all about filters; and most of the capacitors in commercial amps are +/- 10% tolerance - which means that a ".1u" cap can actually be anywhere from 90 to 100 nanofarads in value - so it absolutely makes sense that your likely culprit is there.

[rutabaga bob]

Quickest way to find out is to put the old ax7 in place of the new one, and try it out.

[whoisalhedges]

Quickest way to find out is to put the old ax7 in place of the new one, and try it out.

+1

[suncrush]

Quickest way to find out is to put the old ax7 in place of the new one, and try it out.

This is true.  And when the warranty ends, I'll pop the seal. 

MT's have a bit of a tendency to blow up in the first 90 days.

[whoisalhedges]

Quickest way to find out is to put the old ax7 in place of the new one, and try it out.

This is true.  And when the warranty ends, I'll pop the seal. 

MT's have a bit of a tendency to blow up in the first 90 days.

Wait - merely opening it to change the tube will void the warranty?

That's a deal-breaker for me; I will never purchase anything that performing routine, necessary maintenance voids the warranty... not cool, Orange.

[mth5044]

Who's to say they haven't change values in the circuit, or even the circuit itself? 2 years has 730 days to make bad decisions 

[suncrush]

Quickest way to find out is to put the old ax7 in place of the new one, and try it out.

This is true.  And when the warranty ends, I'll pop the seal. 

MT's have a bit of a tendency to blow up in the first 90 days.

Wait - merely opening it to change the tube will void the warranty?

That's a deal-breaker for me; I will never purchase anything that performing routine, necessary maintenance voids the warranty... not cool, Orange.

I actually looked at mine, and the seal is under the plate, not under the cage.  You can get to the tube without breaking it.  It pops when you get down to the circuit board.

[amptramp]

As triodes age, they tend to lose transconductance but gain Rp so the µ tends to remain the same.  I have seen huge variations in trnasconductance between sections of a dual triode so different tubes may give different results depending on the amount of feedback in the circuit.  I have an EMC model 215 tube and transistor tester and have seen this on various tubes I have tested.

[PRR]

Tube parameters can go worse OR better over many hundred hours.

But if you are talking two different tubes in two different boxes, I say they were just born different. Tubes are much fine hand-work, no two are alike. And as said, the box may have revised values as production goes along (the famous Tuesday-change in Mustang engines).

[LiLFX]

Yes. Tubes sound different as they age. Bob Katz made a statement about how tube amps are problematic for repeated critical listening sessions since they never seem to sound exactly like the last time you listened.