Since the tubes in a preamp can last a very long time, how will you know when it’s time to replace your tubes?
As we explain [here], the tubes that we provide in Backert Labs preamps may never need to be replaced, because our circuit design runs them very gently.
However, you might decide to try a pair of older, used tubes that are somewhere near the end of their lives… how will you know when they are truly in need of replacement?
The signs that the tube going to one of your speakers needs replacing are usually quite obvious:
- you begin hearing noise in one speaker, which might sound like:
- hissing
- erratic bursts of static
- short “pops”
- or hum
- one speaker begins playing at a much lower volume than the other, or produces no sound at all
- one speaker sounds distorted
- one speaker is much more bass-shy or much more muffled-sounding than the other
We say “one speaker” because it’s unlikely that the tubes for BOTH channels of your preamp will go bad at the same time.
If one speaker shows these signs, do you need to replace both tubes? No. Different tubes can have very different life spans, even if they are the same brand and were made at the same time. Simply replacing the tube that leads to the bad-sounding speaker with the same kind of tube is perfectly fine. However, if you cannot find another tube of the same kind, you may wish to install a different matching set.
“What about tubes that glow brightly — are they near the end of their lives?” Perfectly healthy tubes can glow brightly. This does not mean that a tube needs to be replaced.
“What about tubes that flash brightly when turned on?” Again, perfectly healthy tubes can do this. Do not worry.
“What if one tube glows or flashes, but the other one doesn’t? Is this pair of tubes getting old?” Nope. Flashing or glowing can happen with just one tube in a perfectly healthy pair.
“Will a bad tube look charred, or burned, like a blown fuse?” No. The appearance of preamp tubes almost never changes like this. It’s usually not possible to tell if a preamp tube is bad simply by looking at it.
“What if I turn out the lights, and in the pitch dark I cannot see any glow at all in the filaments of a tube?” That tube has probably died. But in that case you would already know it is bad, because the speaker associated with that tube will not be playing music.
If you have a Backert Labs preamp and you’re using the stock tubes, you’ll probably never need to worry about this subject because our preamps make tubes last so long, they might just outlast all of us. But you might decide to experiment with some older used tubes, or you might own a preamp from a different manufacturer, so in those cases, these points are good to keep in mind.
