(continued)
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.
(see next post for the continuation)