Is upgrading stock tubes standard proceedure?

Generally speaking, it does not make sense for manufacturers to use anything but readily available current production tubes. First, they must be assured of adequate supplies for continued production as well as supplying customers with replacement tubes. Also, because each customer's system is different, and each customer has a different particular taste, a change in tube may not necessarily be better; so, why put a LOT of money into NOS tubes that may not be appreciated by the customer?

I know a lot of manufacturers don't encourage experimentation with different tubes. That is understandable given the sort of trouble inexperienced (or not-so-bright) customers can get into. Some supposedly "drop-in" alternatives for some types of tubes may really not be compatible in the particular circuit design even though the customer had no problem with making a similar switch in another component.

If the choice of tubes made by the manufacturer turns out to match YOUR own "ideal," that would be pure luck. Besides, you could not possibly know this without doing some experimentation. I own a pair of amplifiers that actually comes from the manufacturer with NOS tubes that are not cheap: RCA 5692 red base small signal tube, RCA double-plate 2a3s. I've talked to the manufacturer and he agrees that, even by his own personal taste, these are not the "ideal" tubes. He thought that NOS single-plate 2a3s sound better. But, they are very hard to obtain in near-new condition and are crazy expensive (about $2,000 a pair in decent condition, and I would need two pairs). It's not hard to see why the manufacturer would not consider supplying this amplifier with the "best" tube.

Are there current production tubes that sound as good or better than the best NOS? I don't know. I currently run EML meshplate 2a3s in my amp and like them MUCH more than the stock RCA double-plates. But, I have not had the chance to hear NOS single-plates in my amp. As for some other tube types, in my system, I have not found any current production tubes that I really like: for 6sn7s I like old Tungsol round-plates or the French Neotrons (copies of Tungsol round-plates); for 12AX7s I like Telefunken ECC83 or ECC803S.

Mr L- I've got a pair of the TungSol round plates, and a pair of Sylvania 6SN7W(tall bottle) in my Carys. Rest assured: You won't find anything current that can come close(or anything better, NOS). From that and the choice of Teles- You must appreciate an un-colored presentation of your music. I can understand the manufacturers having to use current production. Especially with the cost/lack of consistant supply of NOS tubes. Have you seen these?: (http://www.kraudioproducts.com/tubes/2A3blue/)

How long does it take NOS tubes to break in?

A few hours, perhaps 10, at the most.

Dave Mitchell posted the following and he is spot on. It is quite excellent in its explanation:

07-26-07: Davemitchell
The answer depends upon whether you are referring to the tubes themselves or an entire tube-based circuit.

First, lets clarify that the popular term burn-in really refers to forming dielectrics. This is where electrons find and groove a path of least resistance through the insulation materials surrounding the conductors. Dielectrics (teflon, polyethylene, glass epoxy boards, etc...) act as an impediments or road blocks to the free flow of a signal.

The actual vacuum tubes themselves require little or no burn-in because they have so little dielectric material to form in the first place. The conducting elements are surrounded primarily by a nearly perfect vacuum, which is a superior dielectric to all others including air.

Tube circuits like all circuits which contain capacitors, resistors, wire and circuit traces, require significant burn-in because all of those passive parts contain all kinds of plastic dielectrics which need to form to sound best.

Thanks a lot this is very good info.