Break in period for tube amp. How long?

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.