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There really isn't much in the way of settling in.
The exception might be new power tubes, which will benefit from having their filaments lit but no B+ on the tube otherwise. If left in this state for 3-4 days, this can double the life of the tube and reduce premature failure due to arcing.
Smaller tubes are good to go out of the box.
That can be a bit of a trick. If the amp has a B+ fuse that is independent of the filament circuit, you could remove that, but that might be tricky in some amps that don't have the fuse accessible. Another way would be to pull the rectifier tube if there is one, like in a Dynaco ST-70, but that's about it.
Your question can open a can of worms lol. Power tubes from what I have heard can take 100 hrs up to a few hundred from what some people swear by. I have always been skeptical of long break in times as others above mention. However, who am I to say when some audiophiles have experienced changes and I am sure their ears are decent.
I tend to always think 25-50 hrs and something else I haven't heard people discuss much. Heat cycles. I would think turning them on and off and getting a few heat cycles like breaking in an engine would help the burn in process. Just my 2 cents :)
The exception might be new power tubes, which will benefit from having their filaments lit but no B+ on the tube otherwise. If left in this state for 3-4 days, this can double the life of the tube and reduce premature failure due to arcing.Ralph might see it differently but I believe that if you buy the power tubes from Upscale Audio they are matched, cryogenically treated, and burned in for 72 hours. Jim McShane likely does something similar.
Or, you can take the path of just listening to music and not worrying about burn-in…leaving a tube amp on when you’re not around seems wasteful and kinda dangerous, and for me it seems that all the other factors like when you do your active listening relative to your local power grid seem to have more of an impact on the sound, although not a big deal. Trying different tubes also obviously has a real effect, and after a short while (hour or so maybe?) they seem to get where they’re going allowing you to hear the differences between tube types or brands. I do think that a well designed amp should sound great all of the time, and only display sonic variations that are so small to be simply musically irrelevant. Power tubes have lasted a long time for me in amps I’ve owned without any cryo treatment or anything other than simply listing to things…and I roll tubes around often enough that many last a really long time until I deem them unlistenable and replace ’em.
For me, the biggest difference in "burn in for sound quality" comes in brand new, new production power tubes. Some seem to benefit more than others. The biggest change from burn in came from Psvane 845 tii.
I just listen and definitely don't leave them running when I leave the house. After maybe 40-80 hours (usually less), any changes, to me, have pretty much been too subtle or too gradual to really notice or definitively attribute to further burn-in.
Ralph recommends running tubes without firing them up with B+ for a while (I don't recall the exact number of hours), and that doing so significantly extends their useful lifespanbdp24- IIRC, I believe that recommendation has to do specifically with the 6AS7s that are used in the Atma amps. Also, I believe he recommends 72 hours.
Yup swampwater, the power amp output tubes in his OTL’s. But further, Ralph says ALL power tubes will benefit (in terms of their useful lifetime) by pre-conditioning them before fully powering them up with B+. Very few amps allow one to do that.
His recommendation has nothing to do with a tube’s sound quality, only it’s useful lifetime. I believe it has to do with breaking in the tubes gently, rather than hitting them with high voltage out of the box. Sort of like breaking in a car’s new engine, not going over a given RPM until a certain number of miles have been reached.
Think about it: you have a thin piece of wire that is being heated up - why not be gentle with it?
metal expands when heated...
I WILL ADMIT that sometimes I just turn the power off on my ARC pre-amp without going thru the volume down, mute on, and only then power off sequence they say to use. But that may well be to reduce transients going to the amp & speakers, not saving the tube filaments.