For many years the debate among Audiophiles has raged concerning the differences between tubes and solid state electronics. There are sonic differences to be sure, and almost everyone is firmly entrenched on one side of the fence or the other. Frankly, my emotions are mixed. I have had the pleasure of auditioning wonderful sounding systems using both technologies. So my charge is not to declare a winner, but simply to explore the practical, objective differences so that you can make a more informed decision on which is right for you. I hope this treatise will help you to understand some differences between tubes and solid state, from the standpoint of day to day ownership. All you "seasoned" Audiophiles bear with me, if you have owned both types you are already well aware of the differences.
Most people agree that tube electronics excel in the area of dimensionality and lack of grain through the critical midrange and high-frequencies. Further, tube gear often possesses a richness or warmth that many find appealing. Solid state designs on the other hand offer a sense of power and control rarely, if ever, found in their tubed counterparts. Additionally, well-designed solid state amplifiers have little trouble coping with the demands of today’s difficult, low impedance loudspeakers. In fact, regardless of your preferences, you may be forced to chose based upon the electrical requirements of your loudspeakers. However, in many cases it is personal preference that dictates the preferred method of amplification. Beyond those subjective evaluations exist several important considerations facing the Audiophile trying to make that choice. Let's take a moment to investigate some of those concerns.
Tubes have a shorter life-span than transistors. Consequently, an owner of valve gear can expect to change the tubes one or more times during the span of ownership. The frequency with which tubes must be replaced depends upon the specific piece of equipment, the type of tubes used and to a great degree, upon the tubes themselves.
The cost of long-term ownership varies widely. Therefore, one should consider the cost of re-tubing before making a purchase decision. One brand may be considerably more expensive to own over a given period than another. Simply add the original purchase price to the cost of tubes needed over the expected period of possession to determine the long term cost of ownership. This figure will be a more meaningful comparison than just the sales price alone. As an example, if you plan on keeping an amplifier for five years, and you figure on listening about a thousand hours per year (or roughly three hours per day), and the amplifier requires re-tubing every thousand hours, you'll need five sets of tubes. Multiply the cost of tubes by the number of replacement sets needed to give you the total cost of ownership. Compare this figure with a similarly obtained number from another choice to make a valid comparison.
Please note however, that there is great latitude in anticipated tube life among competing brands. Topology and tube operation parameters dramatically affect tube life. More, the choice of tube itself has a direct bearing on the expected life-span. Some manufacturers quote as little as one thousand hours of expected life, while others may be five to ten thousand hours, or more.
System parameters greatly affect the life-span of tubes as well, especially the output tubes. Factors including the load presented by your speakers and how loud you like to listen determine the stress placed upon the amplifier and ultimately the output tubes. The amount of life in a set of output tubes may vary by fifty percent in two different systems. In other words, a guy with very efficient speakers, in a small room, who listens at moderate levels will get more life from the tubes than someone with speakers that require more power, has a larger room and likes to listen at a higher volume.
Another factor we need to ponder when considering the purchase of tubed electronics are the type of tubes used. This is important from two standpoints -- the cost of the tubes and their long-term availability. "Garden variety" tubes such as KT-88s, EL-34s and 6550s are likely to be around for a long time to come. However other less well known tubes may have a more questionable future. Additionally, the cost of these tubes differs widely among types. From most suppliers, KT-88s are about twenty-five percent higher than 6550s, and about fifty percent more than EL-34s. I certainly don't mean to suggest by this that amplifiers with EL34s are either better or less costly to own than those designs that employ KT-88s or 6550s, but tube cost does indeed play an important role. One must always consider the life-span of the specific tube beyond the cost of the tubes when finding long-term cost of ownership. Indeed, in some cases the more expensive KT-88 may conceivably outlast the EL-34, making the initial price differential trivial.
Solid state electronics are generally regarded as the reliable breed. Indeed, transistors are longer lived than vacuum tubes. However there are two sides to every coin, and that analogy applies here. While solid state is indeed less likely to fail, if it does go down, a return trip to the manufacturer is virtually inevitable. Conversely, if a tube dies, usually nothing more than replacing the tube will bring the music back. So while tubes are more likely to fail, it might be argued that they are more easily fixed.
Nothing is forever, and this statement is true for all electronic equipment - even solid state. Yes friends, transistors do age. Over time, transistors (as well as capacitors and likely other components) loose a measure of their performance. An amplifier that was made fifteen years ago, will not sound "like-new." Indeed, the degree of lost performance may be underrated by today’s Audiophiles.
Some listeners, however, are loath to fiddling with their systems. Understandably, these Audiophiles regard any failure as inexcusable, no matter how trivial. For this group, solid state seems the direction of choice. While no one can absolutely guarantee that a piece of equipment will never experience a problem, the likelihood of a good solid state amp or preamp failing is quite low. Of course reliability varies among brands, and one would do well to research the repair record of any manufacturers products before a purchase decision is made.
A careful look at the associated components is always a prerequisite for any equipment purchase. This is especially true when considering an amplifier or preamplifier, and even more important when considering tubes versus solid state. The electrical demands placed upon the amplifier by the loudspeaker and listening habits of the owner should be considered when choosing an appropriate match. Solid state offers much more power for the Dollar than to tubed units. Consequently, a system requiring a good deal of power will be less costly with solid state electronics.
In general, we can think of tubes as voltage devices, and transistors as current devices. Consequently, it is difficult for the tube amplifier to generate high current and solid state designs are less able to supply high voltage. Thus, a low impedance speaker prefers (electrically speaking) a high current (solid state) amplifier. A speaker with a rising impedance curve (some electrostatics) may be a better match (on paper) for tubed amplifiers. Of course these are not inflexible rules, merely suggestions based upon theoretical ideals.
The amount of heat generated by an amplifier or preamplifier may have a strong bearing upon your choice. Tubed electronics generally produce more heat than solid state components, especially when speaking of amplifiers. And while some pure Class A solid state amplifiers can run hot enough to actually constitute a burn hazard, most all tube amplifiers are hot enough to fry a finger. Consequently, extra ventilation must be afforded most tubed electronics when compared with the majority of transistorized offerings. Thus, location of the component becomes of prime concern, and one may be forced to revise their choice based on logistics, safety or cosmetics.
All components are sensitive to vibration. The sonically destructive effects of structure-borne and air-borne vibrations are just now becoming apparent. However, tubes in particular are prone to sonic degradation from these unwanted influences, and special care should be taken in their location/placement to avoid or reduce negative effects.
While more of a concern in years past than in modem times, widely varying electrical characteristics limit the ability of some equipment to function together. Tube preamps, in particular, were a real concern. Older designs often exhibited high output impedances, which could present a problem when matched with solid state amplifiers of low input impedance, or long runs of particularly high capacitance interconnects. Most modem designs exhibit far lower output impedances, reducing the concern. But caution is still suggested when considering a tube preamp to be used with long cables and/or a solid state amplifier.
If LP is to be a source, one must consider the ability of the preamplifier to provide adequate gain for the cartridge(s) chosen. This is especially true if you plan on using a low output moving coil phono cartridge. Tubed preamplifiers generally have less gain than solid state units, and are often noisier to boot. Few full-tube preamplifiers offer enough gain to noiselessly amplify a low (.2mV) cartridge. In those that can achieve this feat, the quality of the tubes become of utmost concern, with even small amounts of noise or microphonics unacceptable. The premium, low-noise tubes required for these circuits are quite costly and should be considered as part of the long-term cost of ownership described above.
Today, tubes and solid state designs seem to be seeking a middle ground. Solid state is taking on a more tube-like character, while modem tube designs offer greater extension at the frequency extremes, coming closer to solid state in that regard. However, even with a greater similarity between the two topologies, differences do exist. Chose the direction that best suit not only your audio palette, but one that fits your lifestyle as well.