There is a pervasive mystique about the sound of amplifiers and other electronics employing vacuum tubes instead of solid state devices. And while some might say, reflexively, that tube amplifiers sound more "organic" or "natural" or "musical" - as if the tube itself is a magic ingredient that could make fois gras out of chicken livers - this isn't so. In fact, there are plenty of tube amplifiers in the world that don't earn the mystique at all.
So what makes a great tube amplifier?
First, of course, is the circuit design. There are two schools, roughly speaking, and subsets within each. I won't sharpen this pencil too finely, but - as an overview - let's discuss the modern versus the traditional.
Modern tube amplifiers, based upon recent innovations, will often use a tube differently than intended by the designer such that it might lend a combination of attributes. In our stable of brands, E.A.R. is considered innovative in this regard as Tim de Paravicini (designer of E.A.R. gear) was very much a creative innovator. Among his innovations is "Enhanced Triode Mode" which uses a "Triode-connected" pentode to achieve a unique result.
This gets into some deeper technical issues, but suffice to say that "Triode" and "Pentode" simply refer to the number of elements within the vacuum tube: 3 elements in a Triode, 5 elements in a Pentode.
Tim's innovation was to force the Pentode to behave as a true Triode, all the while exhibiting greater linearity than most Directly Heated Triode amplifiers. The E.A.R. 869 integrated amplifier (pictured above) is an example of Tim's innovation, producing 15 watts per channel and able to drive moderately sensitive loudspeakers. This is a lovely way to have one's cake and eat it, too, in a way. Triode operation, with greater linearity and control than classical Triode designs.
In his V12 integrated amplifier, he uses a large bank of small EL84 tubes in a circuit unique to Tim: balanced bridge mode, which makes use of a unique way of connecting each end of the tubes (the anode and the cathode) to the primary winding of the transformer. The amplifier operates in push-pull Class-A, and this combination of attributes lends the power plant 50 watts (into 4 and 8 Ohms) of smooth, linear performance with very low distortion. It can drive just about any loudspeaker, and it delivers outstanding performance.
Traditional tube amplifiers, especially of the SET (Single-Ended Triode) variety, but also including variations of "Push-Pull" topology (a method of increasing the power and the linearity of a traditional Triode amplifier), are the objects of most of the mystique that surrounds tube amplification. Because these amplifiers tend to be low-powered, they usually need careful matching with loudspeakers that are sensitive enough to make the most of these designs,
These are quite simple amplifiers, but their simplicity is a double-edged sword: while the circuit may be simple and as old as the hills, they are so much more sensitive to implementation and parts quality! Differences in perceived (and measured) performance between two similar SET amplifiers will often boil down to basic choices made by the designer in terms of quality of parts, their method of implementing those parts, and may even be affected by the quality of connections between these components.
(more than meets the eye)
In all tube amplifiers except the OTL types, there is a saying: the sound of the amplifier comes from the output transformer more than it comes from the tubes. (OTL amplifier have no output transformers).Therefore it may be said that the quality of the transformer is paramount, and this seems especially true with SET and push-pull triode designs. In this way, the art of tube-amplifier design is inextricably interwoven with the art of transformer design ... and, to those who know, it is truly an Art.
An excellent output transformer is a costly thing to make, owing first to the fact that it requires a special skill-set in design, and can oftentimes be hand-wound (sometimes by the same person who designed it) This is some rare expertise. Add to that the expense of the core materials (and some of the core materials can be extremely expensive and rare), and a truly great output transformer can cost the manufacturer of a specialized Triode amplifier many hundreds or even several thousands of dollars (which is one of the reasons why truly great triode amplifiers are also quite expensive).
Concert Fidelity amplifiers, built by Masataka Tsuda at his small workshop in Japan, employ very special output transformers that are hand-wound by a specialist who has reserved some rare core materials just for Tsuda-san's use. Combined with Tsuda's elegantly simple topology, expert skills, and elevated parts qualities throughout the amplifier, we reach "otherworldly" performance that I sometimes refer to as almost psycheldelic with some music.
E.A.R. also employs some very high-end transformers that are bespoke designs, hand-wound in Cambridgshire, England. These output transformers are designed and built for ultra-wide bandwidth, providing extended frequency response at both ends of the spectrum.
This is one big reason to be skeptical of cheap tube amplifiers ... they just won't have the quality of output transformer and other parts required for authentic high performance.
Of course, as refinements in design and parts-quality are implemented, the quality of the output tubes becomes increasingly important to getting the best performance from the amplifier. No two power-triodes are alike, even if they have the same specification! This is a mixed-blessing, of sorts, because one can fine-tune the amplifier by swapping various tubes (known as "tube rolling"), but this can also become an expensive habit; some 300B Triodes can cost thousands of dollars per pair!
I have been using KR Audio power-triode tubes from the Czech Republic for some years now because they are built to an exceedingly high standard, and their performance stands at the top with the very few greats that are in production today. I personally like their performance for their ability to split the difference between the very seductive sound of vintage tubes with a modern sound that delivers more impact and excellent delivery at the frequency extremes - important for music recorded on very wide-band formats.
I hope that I've helped to illuminate the subject a little bit. Just because an amplifier employs vacuum tubes doesn't mean that the tubes themselves have conferred any magical power to turn lead into gold. Many important factors are at play, and as each factor increases in quality each successive factor becomes more important to the overall performance. Tube Magic is possible when all of these elements are optimized.
In my experience, and reflecting my proclivities (of course), excellent tube amplifiers mated judiciously with appropriately-sensitive loudspeakers offer a level of performance that can deliver the prized mystical experience of music, thereby earning the moniker. The immersive sound field coupled with gorgeous midrange, sparkling highs, and impactful bass makes for a combination of attributes that can be very addictive.
Coolness-factor and bragging-rights aside, a high performance tube-based system becomes the proverbial Time Machine.
This is an immeasurable thing, but as real as can be: to hear it is to know it, and then one cannot un-hear it. To quote Aquinas: "No explanation is necessary ..."
Nevertheless, I have tried to explain :-)
Get in touch with me and I'll help to connect YOU with the right tube amplifier for your system, and help you to build your personal Time Machine!
~ Chris Sommovigo