V18-112/V18-212 Tube Guitar Amplifier with Reverb
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A Brief History Of The Tube:
In 1883, Edison discovered that electrons would flow from a suspended filament when
enclosed in an evacuated lamp. Years later, in 1905, Fleming expanded on Edison’s discovery
and created the “Fleming Valve.” Then, in 1907, Dr. Lee de Forest added a third component
– the grid – to the “Fleming Valve” and the vacuum tube was a fact of life. The door to elec-
tronic amplification was now open.
During World War II, data gleaned from their intensive research on the detectors used in radar
systems, led Bell Telephone Laboratories to the invention of the transistor. This reliable little
device gained quick support as the new component for amplification. The death of the vacuum
tube seemed imminent as designers, scientists, and engineers reveled in the idea of replacing
large, fragile glass tubes with these small, solid-state devices.
However, there were (and still are) many serious listeners who realized that the sound pro-
duced by a “transistor” amplifier is significantly different from that produced by a tube ampli-
fier with identical design specifications. They considered the sound produced by these new
solid-state devices to be hard, brittle, and lifeless. It was determined that solid-state devices
produced a less musical set of harmonics than tubes. When pushed past their limits, they tend
to mute the tone and emphasize the distortion.
Tubes, on the other hand, produce a more musical set of harmonics, the intensity of which
can be controlled by the player. This characteristic adds warmth and definition to the sound
which has become the hallmark of tube amplifiers. When tubes are driven into clipping, the
harmonic overtones can be both sweet and pleasing or intense and penetrating, depending on
the musician’s musical taste and playing technique.
Over the years, application engineers have designed a number of outstanding solid-state
amplifiers that sound very, very good. Some use special circuitry which enables them to simu-
late the distortion characteristics of a tube amplifier. However, the tube amplifier, still held in
the highest esteem by many musicians, offers a classic “vintage” sound in a contemporary
market.
Tube Types And Usage:
Tube amplifiers are based primarily on two types of tubes – preamplifier tubes and power
tubes. The tubes used in preamplifiers (12AX7, 12AU7, 12AT7, etc.) are smaller than the
power tubes. These tubes amplify the signal from your instrument and shape the sound. They
are inherently microphonic (they can mechanically pick up and transmit external noises). Since
these tubes are used in the critical first stages of a tube amplifier’s circuitry, it is very impor-
tant to use high-quality, low noise/low microphonic tubes for this application. Although tubes
of this quality may be difficult to find and typically cost more than “off-the-shelf” tubes, the
improvement in performance is worth the investment.
Preamplifier tubes are also used to drive the power tubes. When used in this application, a
12AX7 will produce a more distorted tone than a 12AT7, which produces a clearer, sweeter
sound. A 12AU7 is even cleaner and brighter than a 12AT7, giving more definition to the
sound. (In some cases it is possible to change the sound by changing the type of preamp
and/or driver tubes. When making any modification to your equipment, it is highly recommend-
ed that you consult with a qualified service center.)
Important Information about Tubes and Tube Products: