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's Valve" and the vacuum tube was a fact of life. The door to electronic 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 amplifica-
tion. 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 produced by a "transistor" amplifier is sig-
nificantly different from that produced by a tube amplifier 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 musi-
cal 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 simulate 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.
T
ube Types And Usage:
Tube amplifiers are based primarily on two types of tubes – preamplifier tubes and power tubes. The tubes used in preampli-
fiers (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 (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 important 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 recommended that you consult with a qualified service center.)
The power tubes are the largest tubes used in an amplifier. These tubes convert the low-level, conditioned signal from the pre-
amplifier into a level that is sufficient to drive the speakers. There are several types of power tubes available, each of which
offers a different performance/sound characteristic. For example, the EL34 power tube produces a great Classic rock sound.
When an EL34 is driven into distortion it produces a unique sound ("crunch"). When compared to the 6L6, the EL34 distorts
more quickly, exhibits a "looser" low-end response and produces more harmonics at mid and high frequencies ("creamier"
sound). These differences become more noticeable at higher volumes.
The 6L6 tubes produce a big low-end thump and have a very good dynamic range. They offer a more traditional "American
Rock" sound. The 6V6 tubes produce a creamy sound with nice distortion. On the other hand, the KT88 produces a big low-end
but sounds more like an EL34 in the mid and high frequencies.
The 6550 power tubes are more rugged and stay cleaner sounding even at full power. When they do distort, the sound pro-
duced is more solid and has a tighter low end; more of a "heavy metal" type distortion with lots of power.
Some tubes are available in matched sets. These tubes have been extensively tested for optimum performance and longevity.
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Important Information About Tubes and Tube Products
SVT-VR Bass Amplifier
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