They were supposed to be far superior to the vacuum-tube amps they replaced. Deemed too hot and expensive due to their shorter life span, not a few vacuum-tube amps were hastily dumped for "more reliable" solid-state amplifiers.
The switch, however, created a cult of audio purists who remained underground loyalists. Some 40 years later, the much-ballyhooed solid-state amplifiers are still fighting for sonic legitimacy among audiophiles worldwide. The cult has grown to fuel the analog renaissance, and the seemingly outdated technology is still claiming younger fans year after year. There is only one reason tube-amps have succeeded in reclaiming their place in audiophiles’ audio racks: the sound.
I got hooked on tubes some two years ago and have remained dedicated without regret. Through the years, audiophiles have been at a loss on how to best describe the sound that tube amps recreate. Some describe it as either sweet or syrupy, while others say it gives out a warmer or full-bodied sound. Whatever it may be, many music lovers who grew up with solid-state are now surrendering their gear for the sweet sounds of yesteryear.
Solid-state amps do provide cleaner sound, but they seem to be wanting in depth, which is essential in creating a tri-dimensional sound perception. This is where our brains are tricked so that we actually hear and feel live music being played inside our music rooms.
There’s really not much difference between the two when they play normally or when both don’t overload. But a marked disparity occurs when the two systems overload. Russel Hamm in the 1973 Journal of Audio Engineering’s "Tubes Versus Transistors" says that "when distorted, both tubes and transistors sounded distorted and when in their normal, non-overload range, they both sounded very clean. The differences are a matter of when the overload ranges would occur."
Similar experiments were conducted which corroborated Hamm’s journal. Put simply, tubes overload beautifully as against transistors. Since overloading in tubes happens at the range of 20 decibels (dB) or more, what we thus hear are harmonics pleasant to our ears. Transistors would normally have an overload range of 10dB. "The overload margin varies widely between different types of amplifiers… It may be concluded that these inaudible harmonics in the early overload condition might very well be causing the difference in the sound coloration between tubes and transistors."
We all know that when music is distorted we shouldn’t expect it to sound good. This is not so with tube amps. When a tube amplifier distorts within its overload region, it produces a whole spectrum of harmonics, adding edge to the sound, which our ears interpret as loudness information. In contrast, a solid-state amp shows signs of a strong element of third harmonic distortion when driven into overload. This produces a covered or muffled sound, restricting sound quality.
Of course, solid-state amps lovers will always have something to say against tube amps. The debate still rages, especially in audiophile Internet forums. I do not wish to add to the already intense and passionate debate, but if you’re happy with what you have, then so be it. Either you like the added harmonics that tubes offer or you go for "clinically clean" solid-state sound. Nevertheless, tubes remain as fascinating as they were before and still hold a solid place in audiophiles’ music rooms, despite contrary claims when solid-state amps were introduced four decades ago.