How Long to Burn-In Western Electric 300Bs?

I have a new pair of reissue Western Electric 300Bs that I am running in my Morrow Audio SET amps. I read some comments in a Stereophile column published a number of years ago in which the reviewer discussed a very protracted burn-in time for the tubes. The reviewer had experienced a dramatic change in the sound of his WE 300Bs after a burn-in period of several hundred hours. He later ran into the principal at Western Electric (Charles Whitener) at a trade show and inquired about the manufacturer's recommendations with respect to burn-in of the tubes. In a follow-up column, the reviewer relayed Western Electric's suggestion that the tubes require a minimum of 500 hours of burn-in.

The Stereophile follow-up column goes on to say that the Western Electric 300Bs require a much longer burn-in period than most tubes because WE chooses not to use calcium oxide in their filament coating. WE apparently believes that calcium oxide shortens the filament life. The downside of this approach is that it apparently takes a LONG time for the filament to burn in without the calcium oxide acting to accelerate the activation of the barium in the filament coating.

For those of you running Western Electric 300Bs in single-ended amps, I would be interested in your experience with respect to burn-in. Were there truly significant changes in the sound of the WE tubes hundreds of hours into the burn-in process?

Frankly, I felt that the WE tubes sounded excellent right out of the box, and I can't imagine there will be significant improvements. Nonetheless, I'm curious about others' experience.
Baloney. Let 'em warm up for a few minutes and let 'em rip.
So on the one hand we have a reasonable explanation of why these tubes benefit from a burn in, a confirmation of this from someone involved in manufacturing them, and a first hand report from someone who experienced this phenomenon.

On the other hand we have someone who says it is baloney with nothing to back up their claim.

I can't say one way or another but I tend to believe they do benefit based on the information presented.
In some ways I agree with both answers.

My experience is that tubes do burn in, initially sounding slightly bright. Much of this dissapears in the first few hours, but I'm sure those of you with better ears or gear may notice it longer. Brand new tubes also test slightly higher.

On the other hand, I don't feel that the tubes need to be broken in for a number of hours before thet can be properly used. So, yeah, let em rip, just be aware that it will get better after many hours.

John C.
I have a pair of WE 300Bs with ~ 400 hours. For the first hour or so the sound was compressed and congested. After the first hour, the sound opened up. Beyond that, I haven't noticed much change in sound quality. The strange blue glow at the top of the tube becomes far less pronounced after a couple of hundred hours. Other than that, no changes to my ears.
To be clear, I'm not asking whether the tubes need to be burned in before they can be properly used. While the tubes are burning in, they will be in my SET amps making music. I'm simply wondering whether others' experience confirms the Stereophile reviewer's findings that the tubes require hundreds of hours before they "come on song," so to speak.

If you're interested, here is a link to the Stereophile column:

In Search of the Perfect 300B Tube

Pay particular attention to the last two pages of the column, titled "A Tale of Burn-In" and "Followup."

John, it's interesting you mention that bright character. I have noticed that, and I would certainly welcome that brightness settling down as it currently makes the WE tubes unsuited for the satisfactory reproduction of certain styles of music (massed strings, for example).

Incidentally, my tubes have 40 hours on them at this point, so I am a LONG way from the 500 hours discussed in the Stereophile column.
IMHO, about 250 hrs is what you can hear. 500 hrs may be the true time for 100% break-in but, as far as what you can detect,the first 30 hrs will be the most noticable from then on it gets less noticable as the time rolls on. Enjoy your WEs. They are the best 300B tube still by a long shot.
Herman; I'm no chemist so, the how's and why's regarding "calcium oxide shortening filament life" and "...activation of...barium...filament coating." Mean nothing to me. Heck he could be making those words up and I wouldn't know it.

My point is, through two new pairs, I've never heard a noticeable difference after this so-called burn in. Let your ears tell the truth.

While I'm willing to give the benefit of the doubt to the scientists that in theory, these things are true. I don't think it has a practical impact and can be heard through all the real-world daily fluctuations in sound quality happening on a daily basis (electricity quality, quality of the recording, tube quality in other components, needle wear, etc.)

As an analog, that's like saying Google's stock will go up if everyone in the company wrote smaller. In theory, they would use less ink, buy less pens, save on office supplies, expenses would go down, income would go up, market would recognize this increase in productivity and want to own the stock, increasing demand and increasing stock price.

In reality though there's too many other things going on overshadowing the small immaterial impact or, in other words - baloney.
Thanks for your input, guys.

Joe, in the end, what I think you are saying is that you have not experienced noticeable changes in the sound of the WE tubes in your system. Fair enough. There could be many reasons for that, including the nature of the specific components comprising your system and the type of music you enjoy.

Personally, I am hoping that there is some evolution in the sound of the tubes in my system, as the treble brightness I am currently experiencing at roughly the 40-hour mark is not pleasant when listening to classical music where strings predominate. On the other hand, the sound of the new tubes is already heavenly with vocals and with most jazz.

Time will tell, I suppose...
Hi Bob; don't underestimate the impact of rectifier, input and driver tubes. Honestly, those tubes can affect final sound just as much if not MORE than power tubes.
Joe, you raise a good point about the importance of the other tubes. I have been under the assumption that the other tubes in my amps (RCA 6SN7GTB driver tube and Chatham 5R4WGA recifier tube) are fully burned in as they now have several hundred hours on them. Another consideration is that the bright sound I am experiencing was not present with the TJ Mesh Plate output tubes in the system. The TJ Mesh Plate tubes are known to have refined air and treble, so I don't think those tubes were somehow counterbalancing an inherent brightness stemming from the rectifier and driver tubes. This is the background that has led me to look to the WE 300Bs as the likely culprit.
My guess is that WeCo's explanations as to break-in for the tube are true. The break-in process is not exactly a crowd pleaser, and perhaps for this reason, my experience is that manufacturers tend to understate break-in time if anything.
Well, at this point, I have about 120 hours on the new pair of Western Electric 300Bs. The sound of the tubes is definitely changing with burn-in. Fortunately, the bright characteristic I mentioned above began to noticeably dissipate at around the 80 to 100 hour mark. In listening to a string quartet this morning, I found that the peakiness in the middle to upper register of the violin is much more tolerable but not altogether gone at this stage of the game.

It will be interesting to see whether the tubes continue to change with additional burn-in. More news to come...
I'm checking back into this thread now with about 340 hours on my pair of Western Electric 300Bs. Regarding the brightness or resonant glare that I heard at certain frequencies in the middle to upper register of a violin, that problem has now completely resolved itself with burn-in. String quartets now make for pleasant listening. (No more fingernails on a chalkboard during peak passages featuring the violins.) My pair of 300Bs seemed to hit a plateau at around the 250 to 300-hour mark.

So, based on my experience in running the Western Electric 300Bs as output tubes in the Morrow SET amps, it appears the tubes really do require an extended burn-in time on the order of 250 to 300 hours to sound their best.

I will check back in here if I notice any further evolution in the sound of the tubes.