Credit for the 1904 invention of the vacuum tube belongs to John Ambrose Fleming, but the device we associate with amplifiers came three years later when Lee De Forest gave us the three-terminal “Audion” tube, a crude form of what was to become the triode.
There was a time, certainly in my lifetime, when all there was were vacuum tubes. Television, hi-fi, car radios, even early computers had vacuum tubes. In fact, from the early 1900s all the way to the tumultuous 1960s, vacuum tubes ruled. Over time, transistors eventually displaced vacuum tubes in all areas with the exception of one: high-end audio. High-end audio has steadfastly clung to our tubes—a love affair that is still romanticized even today—as exemplified in modern amplification products like our own BHK series.
Tubes have advantages, especially as voltage amplifiers in input circuits. They have no physical connection between their controlling grid and amplifying elements. The same cannot be said for solid state devices. (They are, after all, solid.) Different tube styles and manufacturing methods can be used in the same circuit, netting very different sonic attributes.
But tubes have limited lifespans. Depending on how they’re used, how well they are manufactured, tubes eventually need to be replaced. In some circuits that’s a year—in others, far longer.
Tubes rarely die quickly. Instead, they just slowly get duller and duller. How does one know when to change tubes and what happens when you do?
I recently retubed the BHK system in Music Room One after a year of good service. The improvement in life and musicality was immediately obvious.
If you want to learn more about the life of tubes, I’ve put together a five-minute video on the subject How long do tubes last?
Here’s the thing about tubes. If you’re unsure about their life it’s probably best to keep a spare set around and try them from time to time.
You might be surprised.