Contrary to popular belief, vacuum tube technology is still in demand and currently many of the most popular audio tubes are still in production. Vacuum tube sales are actually increasing at the present time; many tubes which were out of production (7868 and 7591 for example) have recently been re - introduced due to high demand from audiophiles and collectors. Many high end producers of audio equipment still produce amplifiers and pre - amplifiers using tubes in ranges from the moderately expensive to the ultra - expensive. Cary Audio ™ produces a massive $30,000 dollar amplifier using enormous triodes two feet in height. Even moderately priced new tube equipment generally runs into 4 figures for a complete system - which has enormously increased the demand for vintage high - fidelity gear. Prices for good quality equipment from the 1950's and 1960's are soaring - especially since much of this equipment was shipped at dirt cheap prices to collectors in Asia during the 90's.
The question remains: why the continued interest in a supposedly obsolete technology ?
The most hotly debated issue is sound quality. My
perception along with many audiophiles is that good quality vacuum tube
equipment simply sounds better. Tubes are inherently lower distortion devices
that solid state devices - particularly triodes and pentodes/beam power tubes
operated in ultra linear mode. They are fast in operation and the
circuits using them are normally much simpler that circuits using solid
state devices. There are some technical reasons
here for those who are
interested. Certainly, any good tube amplifier will sound better than typical
mass market gear; the debatable area is in comparing high end solid state
devices to their high end tube type counterparts. Note that the most
universally quoted measurements of audio quality are not the entire story -
particularly distortion measurements. Modern components are designed to meet
specifications which may not entirely reflect their actual audio quality. The
most valuable and conclusive test of audio quality is actual auditioning by
musically trained listeners.
Vacuum tube equipment is much more accessible
than comparable solid state devices. The technically minded audiophile can
tinker with the operating values, change components, and most particularly,
experiment with different tube types to obtain the best sound quality.
Tinkering with solid state amplifiers is only the realm of professional
engineers - the slightest error will instantly reduce expensive hardware into
smoldering junk. This boils down to the simple statement that vacuum tube
equipment is just plain more fun.
Tube equipment is repairable. Parts for tube equipment
dating back to the 1930's are currently easily available. Parts from solid
state equipment produced as little as ten years ago may be impossible to
locate and repairs may mean substituting with generic components. Printed
circuit boards are very difficult to repair, and in the case of multilayered boards,
repair may
be impossible. These issues may make your expensive solid
state audio equipment obsolete in a few years - but the same investment in
vacuum tubes will result in an indefinitely maintainable system. Vacuum tubes
(contrary to popular belief) are extremely rugged electrically and even have
the courtesy to glow red to inform one when they are being mistreated.
They also are long lived if operated within their design limits and not
physically broken. This also means a higher resale value if you decide to
upgrade.
To get good performance from tube equipment requires a
little more finesse; solid state devices generally (again, except in the very
expensive units) get their performance from brute force engineering and
massive doses of negative feedback (technical discussion
here). Quality
construction and materials feature largely in any successful tube design -
particularly in the design of the output transformer. Since fewer
components are needed, they can be of higher quality - particularly the
capacitors and resistors in the circuits. Finally, the tubes themselves are
manufactured to close tolerances ( normally 10 %) whereas solid state devices
may vary by more than 100 % from spec - and circuits must be designed with
this variation in mind. Thus, a good piece of tube equipment is made with
quality and is a minor work of art. Mass market solid state equipment is an
industrial commodity with little lasting value: compare prices for
vintage equipment on EBAY (tm) to see what I mean.