I think there are some people who enjoy listening to music and are fighting for tube amplifiers as a choice to enjoy higher quality music in the future, but what is a vacuum tube in reality? I think you have questions and concerns about what to do with after-sales maintenance during use. This time, I wrote about the after-sales maintenance of such vacuum tubes.
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Vacuum tubes are light bulb-like components that have been used for decades before the invention of transistors and semiconductors, and control audio signals and currents. In addition, vacuum tubes of the same standard and compatibility are manufactured by various manufacturers around the world, and you can replace them with tubes from different manufacturers than those that came with the amplifier. What materials, manufacturing processes, and environment are used in vacuum tubes of the same standard? Each manufacturer has its own characteristics of sound. Therefore, the fun of pursuing your favorite sound by replacing it with one from another manufacturer is also a major attraction of tube amplifiers.
As for replacement, the pre-tube, which has the role of adjusting the disturbed sound signal and delivering it to the power amplifier, can be easily replaced. However, the sound signal sent from the pre-tube is amplified and enlargedoutput tuberequires bias adjustment to match the amount of current to the vacuum tube to be used. Thankfully, many amplifiers now have self-bias adjustment, so there is no need for troublesome bias adjustments, and it is possible to easily replace tubes of the same type and compatibility.
Even if the vacuum tube has not been replaced, just as a light bulb is a consumable, the vacuum tube will lose its function and need to be replaced after long-term use.
So, what is the lifespan of a vacuum tube, when and when to replace it?
One of the timings is when the vacuum tube breaks for some reason. It is easy to understand because air enters the glass tube, which is in a vacuum state like an incandescent bulb, or the internal wires are broken, and the amplifier does not work properly and there is no sound. It's more of an accident than a lifespan.
And the other thing is lifespan. In general, vacuum tubes are quite long-lived, with a usage period said to be about 5,000 hours. With such a long life, there are almost no regulations regarding when to replace them. In fact, many vacuum tubes available on the market, including those from manufacturers hailed as famous brands, are unused stock produced decades ago or used second-hand items. In the case of use in audio equipment, some excellent tubes can still produce good sound even after several decades, depending on how they have been used. Even so, deterioration gradually progresses, so precisely because they are long-lived, it is not uncommon for people to continue using them without realizing their performance has already declined.
Unlike the obvious patterns of failure where no sound comes out at all, symptoms of lifespan issues are very ambiguous when listening, such as wondering if there’s some noise in the sound, is the sound slightly distorted? Is it maybe a little quiet... If the sound is different from what you remember, suspect the tube’s deterioration or aging. This may sound careless, but factors like getting used to the sound or changes in the system make it that hard to notice. That’s why some amplifiers are equipped with meters that allow you to check the vacuum tube condition at any time.
The product page for the amplifier in the photo is here.
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Generally, the lifespan and deterioration of a vacuum tube can be visually confirmed by changes in the mirrored part at the top of the tube. This is the getter, a substance inside the vacuum tube that absorbs impurities to prevent deterioration of the vacuum inside, and it is applied to a part on the backside of the glass tube. Over time or with continuous use, this silver, shiny part may peel off and become lighter in color, or the inside of the tube may darken. If these conditions are visually observable, they can serve as a criterion for determining the tube's lifespan. Therefore, as a rough guide for lifespan, periodically check the depletion of the getter.
The product page for the amplifier in the photo is here.
https://www.exclusive-audio.jp/shop/products/detail.php?product_id=511
However, there is no need to be overly concerned about lifespan. As mentioned above, simply occasionally replace the tubes with the same model or compatible types to enjoy the difference in sound quality, carefully wipe the glass tubes, and when replacing them, clean the pins thoroughly using something like anhydrous ethanol. Such simple maintenance is sufficient.
To put it simply, you can enjoy a vacuum tube amplifier with the casual feeling of thinking 'I should replace it' when the bulb you are using has recently been flickering, become dim, or is making a popping sound. I want even beginners to feel free to give it a try.
