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judicata
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Tube break-in?

I have a little Bellari tube phono pre (the VP-530 - which is pretty much the WP-129 with an added usb out), and I decided to give a different tube a shot. I wanted to start cheap, so I went with the Sovtek 12AX7LPS, becuase some people had reported improvements over the OEM tube, and other sources suggested this one should be pretty quiet and is good for use in phono preamps.

Question: Do tubes need to be broken in before a judgment is made and, if so, how long? Also, when "breaking in" is mentioned in some components, some people say it is a myth. Is this the case with tubes? Also, is there a known science behind whether they need broken in, or is the notion based primarily on anecdotal experience? It's okay if it is, I'd just like to know. I don't want to start a debate on whether it is "real" or not; rather, I'd just like to know whether there is a consensus and, if so, what that is.

Thanks

Jan Vigne
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Re: Tube break-in?

I would tell you tubes require no "break in" time. They need to come up to a constant operating temperature and any existing gasses need to burn off. That should take less than an hour in most cases. After that, what you hear is what you get. If the tube is used in a power amplifier, the transformers also need to reach thermal stability, which could take quite a bit longer than the tubes themself.

Monty
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Re: Tube break-in?

I'm in the opposite camp. Tubes seem to improve after about 15 hours which, by
break-in time standards is the shortest of any component I've ever used.

Without completely getting into the woods with the why, I do believe it's somewhat measurable. At least
with output tubes. New output tubes usually require having to re-bias an amplifier. I've
had new output tubes that required 20 hours before the bias would remain constant.

Jan Vigne
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Re: Tube break-in?

Bias is a somewhat different item than the tubes themself. In the op's case we're talking about a 12AX7 as a pre amp tube.

judicata
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Re: Tube break-in?

Thanks, that was my intuition, but wanted to make sure before I start swapping the tubes back and forth to hear what difference (if any) I can hear.

On that note, is it pretty widely accepted that different tubes in a preamp such as mine can alter the sound, other than how noisy they are? I ask because google didn't help me much in this regard, since all my hits are from tube junkie sites (so, if there is an opposing view, I wouldn't have seen it).

JIMV
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Re: Tube break-in?

Agreed...my KT88's took 20 hours to get rid of the grain in the upper register.

Jan Vigne
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Re: Tube break-in?

I guess that's like anything else in audio where you have a subjective judgement being made. I would say, yes, tubes from the same manufacturer with the same tube designation (12AX7, KT66, 6DJ8, etc.) will sound different from one another. There are plenty of reasons why this might be. The same tube type from another manufacturer is likely to sound different also.

There are plenty of tube substitutions you can make which will affect the tone of your component, a 12AX7 has several variants that serve as drop in replacements. The idea of tube rolling is to find the specific tube(s) you prefer in your system. Sometimes I've found one tube to not be the best choice for one location, say a phase splitter or a line tube, in my system but to work well in another location, say, as a driver tube or in the phono stage. One reason here is each tube has its own level of gain, if you change the gain in the circuit by changing tubes, you'll possibly change how everything downstream from that change is affected.

On the other hand, I've worked with repair techs who felt all tubes were the same if they were the same tube type and measured well. Other repair techs were reasonably picky about the tubes they suggested but not nuerotic about it.

judicata
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Re: Tube break-in?

All very interesting. Thanks for the info all.

Monty
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Re: Tube break-in?

The LPS is a really decent tube, regardless of the price. The German Valvo tubes
are my favorite, but they've become almost as expensive as the Telefunkens. You
can still get the Amperex tubes for a bit less and they seem to provide the best
texture next to the Valvos. Mullards are too warm for my tastes and grossly
expensive for their limited virtues.

judicata
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Re: Tube break-in?

Thanks, that's helpful. A quick google search about a week ago showed the LPS to be highly recommended, so I decided it was worth the $10-15 to try a different tube. I like it so far, but I"m going to listen to it for a number of hours, and then switch back to see exactly what differences I hear. I suspect that it is quiet and warmer than the stock tube I had in there, but the last tube may have sounded better in the mids, but I don't completely trust my ears yet - more listening needed.

cyclebrain
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Re: Tube break-in?

Well to me, a non-tube user but a person with a technical understanding in electronic circuits, I can believe that tubes could have a breakin period. Since tubes obviously do deteriate over time and eventially fail then they must have a non-linear performance curve. Therefor they must have a period of peak performance. Impurities in their vacuum. Contaminations in their atmosphere caused by the outgassing from the deteriation of their filament.

JSBach
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Re: Tube break-in?


Quote:
Well to me, a non-tube user but a person with a technical understanding in electronic circuits, I can believe that tubes could have a breakin period. Since tubes obviously do deteriate over time and eventially fail then they must have a non-linear performance curve. Therefor they must have a period of peak performance. Impurities in their vacuum. Contaminations in their atmosphere caused by the outgassing from the deteriation of their filament.


From what you say Cyclebrian ( Cyclebrain? --conjures visions of delicious calf muscles ) it appears you're talking about a gradual break down, not break in. I've never heard mention of tubes breaking in and never experienced it but I'm willing to believe it's possible if someone can explain how it might happen.

SAS Audio
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Re: Tube break-in?

Hi Gents,

Years ago I use to use some special oxide coated power tubes and it took some hours before the cathodes "broke in".

By that I mean the characteristics, cathode current actually changed and reached a peak after some few hours. I haven't really scientifically tested audio power tubes, but I think I hear differences over some time just like some others have already mentioned.

Take care and hope this helps.

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