Vacuum Tube Break-in

Is there such a thing as tube break-in? I been laying with many tubes in about 20 tube amps for 40 years and never heard a difference in a new tube vs same tube with 50 hours use. I always bought and used NOS tubes, not used. I believe if a difference is heard with break-in, it is the placebo effect.


i believe there is some break in, depends on the tube, its age/history, whether it has been burned in... takes em a good couple hours, to overnight, to fully reach their peak performance, in my personal experience

i have alot of older tubes collected in the 80-90-00’s, when i tube roll, the first 30-60 minutes are certainly not indicative of how they will sound

You might not believe it, but some folks can't hear a difference between tubes of the same type either. Personally I never make decisions about tubes until they have run in for 24 hours. :-)

I will run things in with FM in the background.   I believe speakers have break in , but it's short.    Electronics,  I'm not so sure.   I think it's a mix of maybe a slight change and you as a listener acclimating to the new "sound" .

I know this about tubes, you can take a bunch of like ones and they all test different.    New, NOS , doesn't matter.  Some are simply better than others. 

I have some new tubes that sound fantastic and I found some to be weak or triodes don't match.    

I have some NOS that were from a large hoard. All from 1956.  Some are great , some are ok , and two had shorts.  Thankfully I rooted those out before damaging my amp

The problem with tubes is that the "tone" is so subjective.  I happen to like JJ 6l6gc,  they could sound horrible in your amp.

I paid a little extra the last time I bought 12ax7 and au7 to have them matched and to be screen for noise.   That's what I would recommend,  the remainder of the tubes that don't pass end up at Guitar Center and mom and pop music shops 

Trust me on that one.  I had purchased a few tubes in a pinch at a mom and pop , yes they worked but they were not strong, matched emmisions 

Buy from Brent Jessee or someone with real knowledge of tubes


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Yes, but how much sound difference there is varies with each brand and type, and is largely effected by the rest of the system, room, music source, and listening habits.

I think burn-in is greatly exaggerated, especially in passive, not electronic equipment.  But tubes get hot and metals change when they glow.  I do believe tube burnin is isn't always positive.  

I put in a set of Russian tubes last week and they sounded best 10 minutes after I installed them.  Still good but I liked them best then.


In my experience, it can vary greatly from a minimal discernible effect during the first 50 hours to multiple drastic qualitative changes over the course of the first hour or two of usage.

But tubes get hot and metals change when they glow.  I do believe tube burnin is isn't always positive.  

Agree with @carlsbad and I'll add that the circuit and the entire chain may determine if you hear these changes. I use all NOS or "tests as NOS" and do hear changes in tube sonics, I trust my ears. 

I did try new Linlai 6SN7's which have a 200 hr. burnin (according to manufacturer). I did hear many changes from bad to worse to better. After the 200 hr. mark, I didn't like their sonics even though they had improved. 



     This is a verbatim quote, from a letter Brent Jessee sends, whenever one buys valves from him:

     New tubes need a break-in period before they can fully exhibit their true sonic character when used in audio circuits.

     Preamp tubes especially benefit from a good break-in. This period may vary widely, but NOS vintage tubes usually need at least 48 hours of use, sometimes up to 100 hours.

     New current production tubes need 24-48 hours typically.

     Good break-in can be accomplished by either leaving your tube unit turned on in a no-signal condition for 2 days, or you can just enjoy the tubes for several hours each evening and they will be broken in after several weeks.

     New tubes, especially NOS vintage tubes, may sound a bit edgy at first, but after the break-in period will mellow out and sound wonderful."

IMO everything has a break-in period but results heard vary depending on your listening skills and the component.

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I acquired a quad of Genlex KT88s for my VAC amp at one time to replace the factory tubes.  When I initially started using them I disliked the sound immediately and for the next 20 hours compared to the factory quad.  I ultimately swapped them out and put them away for a few months.  When I tried them again they were still not what I hoped for but suddenly over the next 10 hours they opened up and smoothed out. I thought I had given them enough time the first trial, but I eventually grew to really enjoy them.  Break in?  I don’t know, but many times there seemed to be improvement to be had in the first 20-40 hours of both power tubes and small signal tubes in my systems

The break-in period for tubes is real. At least 20hrs. but for true sonic improvement even more like 50 hrs or so depending on brand and tube.

If the tubes are new and not burnt-in before testing/matching them they will lose their closely matched condition after 20 hrs. The operation point and the plate voltage of the amp in which the tubes are used is an even more important factor for matching and how they will finally sound. Tubes should be matched for the plate voltage and quiescent current of the actual amp.Some companies do that (upscale audio as far as I know). Adjusting the bias after a while (if possible) is important.


there is always the conundrum with break-in/burn-in

is the gear or item burning in, or are we as listeners getting more accustomed to the sound over time, being exposed to it repeatedly? - we all hear our systems sounding different day to day, each time we turn it on... what we sense can vary, conditions can also change

age old question this is...

my sense of this, regarding tubes, is that for most well functioning tubes, they do take some time (in my view an hour to a day, or overnight) for their sound to stabilize, after that, our ears are also getting acclimatized, sometimes in a good way, sometimes not

@jjss49 So true in regard to listener acclimation period with any new component/variable being inserted into system. This especially true when I'm already contented with system sound quality.  My comfort zone is upended when something new placed in system, I'm in analytical mode which detracts from that comfort. Over time I can settle back into comfort zone, especially if change is positive. If change is negative, I find it hard to get back to comfort zone, in which case  I come to understand that particular change not good.


As for tubes, I find power tubes most sensitive to burn in, found at least 85-100 hours is time of great change.  Rectifier tubes sensitive as well, signal tube somewhat less. The fewer the tubes, the more I hear changes. SET, DHT especially sensitive.



It it’s on youtube, it must be factual.  you have posted a few opinions.  Beware of opinions.  And especially be aware of opinions from people who have something to gain from them.

    My first post to this thread was a quote from Brent Jessee.

     I doubt many would dispute his knowledge/claims, as regards vacuum tubes.

     Anyone that was interested enough to have checked my previous post would notice: my first reference was to an individual that showed how burn-in affects tubes, on a tube tester (iow: MEASUREMENTS).

    The next three, "opinions" were from well recognized equipment manufacturers.   I'll simply state that their experience mirrors my own.

    Denyin'tologists will never exhaust their reasons to dispute why, whatever the topic might be, won't/can't/shouldn't exist in this universe.

     Of course: the vast number of variables extant, as regards systems, room acoustics, source materials, ones listening habits/goals and (PERISH THE THOUGHT) aural acuity, must remain a non-issue in their belief system/doctrine/preaching.



I’ve rolled a pair of NOS and I didnt noticed a break-in so far on either set. However on some new modern tubes I’ve definitely noticed a break-in. So I guess it’s not placebo for me or else all my tubes would have broke in. I think it’s important to not tell other what they hear or don’t hear as it only leads me to believe nah sayers are using a lesser system perhaps flawed with bad synergy. As I know mine has great synergy and is resolving and I hear every change from speaker positioning to interconnects to different styluses with the only exception being that of the NOS tubes as previously stated. And even then I wasn’t the original owner and have no proof they weren’t partially used since 1942 and have already been broken in so who really knows. What I do know is what I hear and I’m not interested in convincing myself something sounds good ad I have pulled the plug on many systems as good as they were bcs they just couldn’t climb that last 5%. For the changes I heard after break in it was not subtle, rather significant. So sorry if your not hearing your gear break in then i truly believe likely your rig is masking sound. Fix it or move on from it, you shouldn’t live with something that’s not reaching its full potential. Best of luck.