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?

[Les Paul Lover]

Yes, valves do wear away.

It takes a while, but they lose some brightness along the way.

It doesn't mean your MT valve needs replacing right away, but it sure wouldn't hurt to have a spare, or replace it and keep that one as a spare.

[Gladmarr]

Tubes are also not built to very tight manufacturing specifications now. That makes for variation between tubes of the same brand, model, and even build date. In theory, your 12AX7 will perform as a 12AX7 suitable for a guitar amp, but it's not like the old days when mil-spec companies were making tubes that had to go in fighter jets or military radar. Those tubes probably sounded the same tube-to-tube, day-to-day, month-to-month. This makes things harder nowadays, because finding the "perfect" sounding tube means digging through lots and lots of tubes to find what sounds just right to your ears.

[a.hun]

Every single valve out there will sound slightly different. More variation between modern ones (even of exactly the same make and type) than with old production ones because the old ones were both more tightly spec'd and MUCH better quality than anything made now. Simple as that.

At 1,000 hours old production preamp valves would just be getting into their stride, with many more years of good life in then. Any modern ones may well be fading.
(And preamp valves last several times longer than power amp valves!!!)

Generally as they age any valves (pre or power) will lose highs and lows and also dynamics. Even if they don't get noisy or microphonic the sound just gets flatter with more hours of use.


Andy.

[Ronnie Robinson]

Maybe the new one has cheap Chinese tubes or poor quality tubes while the old one has better quality tubes.

[Jondog]

Running through the same speaker? Or a new speaker with the new amp too? I've never noticed big differences in tone with a single preamp tube unless I was going from a 12AX7 to a 12AT7 or something. More just different gain structure, harmonics and clarity.

[a.hun]

I've never noticed big differences in tone with a single preamp tube unless I was going from a 12AX7 to a 12AT7 or something. More just different gain structure, harmonics and clarity.

Really???

Well, does depend on the particular amp(s) themselves to a fair degree, some are definitely much more 'valve sensitive' than others. But I've noticed surprisingly large differences to the overall tone of an amp / channel by swapping out just a single preamp valve of the same type. And when you start swapping in really special characterful ones like old RFTs, Brimars, Mullards to replace others, well it can almost seem like a different amp to me. Quite serious on that.


Andy.

[Jondog]

To elaborate, Preamp Tubes of different characteristics, yes I notice a tone difference. I notice more tone difference with power tubes. But assuming his two micro terrors have the same stock tube in and one is not near the end of its life, in my experience I've never really noticed big differences, such as nasally and dark . However, in the OP's case, with a 1000hrs, I'd probably replace the tube and on the new amp (don't like the Chinese tubes Orange uses), and I suppose with only one tube in that amp a difference would be more apparent. Also his question on the electronic components, if that amp is brand new never played, in my experience they do need to break in and can be harsh, bright. I swapped many new capacitors in amps, there's always a period of break in before it starts sounding smooth.

[fiveightandten]

The sweep of the tone control pot may just vary between the 2 amps. The Micro Terror has a 15V power supply. It can't possibly be running that tube at a voltage anywhere near what a normal amp is running at. As such, it will last MUCH longer than most amps. 2000 hours isn't much in that environment, IMO.

If you think it's worn, replace it. You may or may not hear a difference.

-Nick