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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.
cincy_bob
herman
2,259 posts
 
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.
hotsauce
108 posts
 
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.
cincy_bob OP
270 posts
 
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.
jeffreyds
115 posts
 
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.
philefreak
423 posts
 
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.
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