Break in period for tube amp. How long?

Can you please share your experience on break in time and initial sound of new tube amps. Mine are sounding awful out of the box (NAGRA VPA).
power tubes should be allowed about 100 hours - but "awful"? it shouldn't be THAT bad.
I would recommend letting then run at least 100 hours before doing any series listening..They will probably even improve a little more after about 150 to 200 hours or more.. I would run CD player ect. on repeat at low volume levels and let run a few days straight to break in a little quicker..
Good luck,
Musicslug is correct, they should not sound aweful though, i would check other possiblities out that can cause this possibly..
Please define "awful". And what was your previous amp? Are you still using the same speakers...what are they?
Breaking in the capacitors, especially if is a common capacitor coupled design (rather than interstage tranny), is very critical. Takes hundreds of hours for the caps to be broken in fully.
Thank you everyone for your kind input.
I went from ARC VT100 MKIII to a used pair of NAGRA VPA's.
Well, I was so impressed with the improvement (dynamics,air, soundstage, placement ambience etc.) that I upgrade to the current new VPA model. With the new unbroken in model, however, the sound seems congested and harsh........i.e.awful. I'll try to break them in to 100 hrs as suggested. So far I have about 10 hrs break in time.
Fatparrot. I am using the same speakers B&W CM4 as I await my ordered PARSIFAL OVATION's. Thanks for your input.

C123666 how would unbroken in capacitors affect the sound?Thank you
Something about the capacitors "not reforming" is what several techs advised me of
C123666, yup, "congested and harsh" seems to indicate an entire amp [not just tubes, alone] that has not yet broken in. By 24 hours, you should notice an improvement...72 hours should get you 90% there, for the tubes! Some equipment, especially speakers, takes quite a while to fully break-in.

Use only one CD for break-in, preferably one that you know, and is of audiophile quality. That way, you can monitor fidelity changes, without confusing your ears. DO NOT USE A CRAPPY CD...THE SOUND MIGHT APPEAR TO GET WORSE!
Capacitors should not be an issue with a "new" tube preamp; guess I was daydreaming and thinking of tubed preamps that have been unused for a long time....those should be checked out a by a tech before putting into service.

A friend and I fired up an Audio Research PH3 tubed phono stage that had been unused for round 8 years. It came up OK and sounded pretty good. Problem is there is an audible buzzing noise coming out of both speakers; we shut it down immediately after listening for ten minutes. It goes to the shop next for a complete inspection with cap and tube upgrade.
if it sounds awful, it isn't a break-in situation.
Hello. Probably one week, most likely two or three...I had the same experience on purchasing a new ARC SP9MkIII pre-amp some years ago - having heard a used MkII with great results, I could not believe how 'awful' the new MkIII sounded straight out of the box - after a week it was a good, and after a month it was perfect. I've been recently auditioning tube power amps as potential replacements for an ARC D125. The shop, Audio Connection in Sydney, Australia, has a great choice, so much so that their demos are virtually unused - this meant a Jadis Defy 7 and an ARC VS110 both sounded 'awful' in exactly the way you've described. Congested and harsh. The store suggested a few weeks before they would at their best - in the meantime I'm meant to 'use my imagination' during auditions! Hooking up used amps to the same system saw much smoother results. Good luck. Rob.
It's funny, but when I bought my first Jadis, I experienced EXACTLY the same thing you are going through. Awful, and I do mean awful. Congested, constricted, constipated, absolutely no extension in the bass or treble, and a harsh, irritable midrange. You want to talk about buyer's regret?!? I had it like never before or since. It's one thing to insert a component and hear little or no improvement. It's quite another to buy something you auditioned carefully, spent more than you ever have for, and come home and have it be day and night inferior to the mid fi components I had in the house.

Despite the absolute heartache that only someone who has experienced can empathize with, I soldiered on, and let it run in. The fact is, it wasn't anything noble I did, I had little recourse in getting a return from a dealer I kind of sold my soul to the Devil for to buy in the first place (breaking one of my life mantras - You lay down with dogs, you get up with fleas). And, a truly ugly duckling to beautiful swan story it turned out to be. Was it the tubes? Maybe. But, how much the capacitors, resitors, wire, etc. also had to run in I cannot say.

I do know that after about 50 hours, I was beginning to calm down. And, things just kept getting better and better and better. I looked up one night, three months after my purchase, and was getting the absolute best sound I have ever gotten. I was in a near nirvana state. Happy in having persevered the initial out of the box performance, that again, was truly awful.

Not that this is the case always, as a bad speaker - amplifier, or preamplifier - amplifier interface, or broken component could be the issue. But, in your case, as your Nagras are replacing another pair, I would tell you to just hold on and try to be patient enough to give the new babies a full chance to run in before you make a final judgement. Unless something in those amplifiers is broken, and the odds that the same thing in a pair of mono amps would be broken in both is kind of small.

After my experience, anyone who tries to tell me that "the component doesn't break - in, you become 'used to it'" has an impossible task in trying to get me to buy that.
Trelja, thank you for sharing your experience. You described exactly how I felt. Well now, after about 25 hrs the VPA's are opening up......the best yet to come I'm sure, as you suggest.
Thank you for your kind words, Jjwa. I just needed to share my experience with you, as it truly is a feeling of absolute desparation.

As you already had a pair of these, you should have a ballpark idea on how they will sound. Whether or not the final result will be more to your liking than your last pair has yet to be determined. But, to experience truly bad sound is more than probably a result of things needing to break in. The fact that you are already beginning to hear the positive improvement shows that this phenomena is more than just the audiophile, not the component, breaking in.

Please let us know when the amps get a hundred hours, then a few hundred hours, on them, and tell us what your reactions are. We all become richer when you do this.
Will do. Are your Jadis's still improving or have they peaked?
Well, the Jadis was actually bought in 1999. But, I would say the sound peaked in the 3 - 4 month area. After that, I didn't perceive things improving.

Interestingly enough, I retubed the amplifier early this year, when I sold it, and it leapt forward tremendously. To the point, where I went from one end of the spectrum to the other - from buyer's regret to seller's regret. But, since then, I have picked up another Jadis, one step higher. Though, in many ways, it has yet to equal the former amp.