Do power tubes need to be burned in?

[Mikelamury]

I know it's a good idea to get power tubes matched but I see some sets advertised as burned in and matched. Is this process necessary and is one able to do it themselves? What does being burned in mean? Thanks for the education.

[FuseG4]

Burned in means they run the tubes in some state of operation to try to weed out the bad ones that fail on startup and,
brand new fresh tubes from the factory may change their bias characteristics when first powered on and supposedly over the first several hours of use. Matching them after letting them "settle in" gives better likelihood that no tube will drift enough to become unmatched as soon as the customer has it installed a few hours.
Imo, worth it for pairs. For singles of you get a bad one just take advantage of defective product return policy at your store.

[El Dunco]

I don’t really think they do any more than a lightbulb does. Conveniental wisdom states it takes “10-14 days to hit the sweet spot” but practically speaking, most people notice a difference within a day, sometimes within an hour. I wouldn’t want tubes advertised as “broken in” to have been used any longer than a couple of weeks, otherwise you’re might be getting tricked into paying for tubes on their way out. I got an EL-34 set like that and one of them flickered and sounded like a lawnmower within days. Luckily they were cheap. You get what you pay for.

[ICTGoober]

Things used to be different when we had American made tubes like RCA and GE... Now? Russian and Chinese crap. Does Mullard make tubes in England anymore?

[eclecticsynergy]

Things used to be different when we had American made tubes like RCA and GE... Now? Russian and Chinese crap. Does Mullard make tubes in England anymore?

Nope. Same with other reused vintage brand names like Tung Sol and Tesla.
Modern ones are made in one of three factories and labeled for whoever bought the name.

[NegativeEase]

So a couple valuable points here.

The most likely place for infant failure in a tube is where the metal and glass seal to hold the vacuum. What a burn-in does is assure that in the early stages of heat cycling a tube, that that seal holds and of course conducting, plates and such remain working. Every factory does the basic QC test, but this only insures that they left the factory after 1 successful cycle. Every cycle effectively matures the metal (anneals the surface further) and the glass slightly.

It's just a way to know a tube can be predicted for an effective long life.

SO if you are buying a lot of tubes for a tour as backups, need high reliability, or have really expensive amps and don't want to risk damage from infant failure (it can happen) -it would seem like a good use or your money.

[Ewizard]

The idea of " burned in " tubes is sound as a marketing approach, but realistically it is of little importance. Tubes will wear out at different rates regardless of their initial level of matching. I do agree that you should buy matched tubes, but only because you want to have tubes that initially start their life at about the same performance level. If they were close at birth, they should be close enough at death. There is a pretty wide margin of difference that they can operate at and still be healthy, but there is a limit.

I would say that a difference of more than 2-3 watts of dissipation difference between any pair of tubes is getting close to the realm of no Bueno. The only reason is that one tube could be biased particularly hot, while the other is running fairly cold. In the case of a cathode-biased amp where you are shooting for roughly 90-95% of max dissipation, with a 2-3 watt difference in operating point, one tube could be biased to 95%, while the other is nearly red plating, or running closer to 70% of dissipation. It only takes a few milliamps to acquire that difference.

If a set of tubes is relatively close in operating point when the bias was set, they should all drift fairly relative to each other. The idea that bias is set and forget is a bad one! A competent tech will bias a set of tubes and let the amp run for several hours before checking again to see if any drastic changes have occurred. If the change is significant, they will re-adjust. The same goes for the home brewer; you set the bias and check on it again at some other point to ensure that it is still within margin.

[Demanic]

To me it's the same as buying jeans that already have holes in them. If you're getting them from Goodwill, fine. Pay extra for them...

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[JMP/HBE]

No not really any decent new vacuum tube should be ready to go out of the box.

[Demanic]

No not really any decent new vacuum tube should be ready to go out of the box.

Um, I think that that was my point.

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[formula73]

No