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Preamp
Tubes |
These
are the tubes that shape the overall tone of the amplifier. They are associated
with Gain (or Pre-), Bass, Mid, Treble, and other preamp functions of the
amplifier. Almost always, 12AX7 tubes are used for preamps. Some manufacturers
sell preamp tubes which have been tested and graded to give some indication
to how they will sound in your amp. |
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Power
Tubes |
These
are the tubes that actually deliver the power to drive the speakers. The
power tubes (along with how they are designed to operate) determine the
overall tone qualities and the "feel" of an amp. The most commonly
used output tubes are 6L6GC, EL34 and EL84. Each of these tubes is associated
with certain tone characteristics... |
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6L6GC |
These
are probably the most popular output tubes in use today. They deliver
a powerful sound which can be fairly bright with strong attack. 6L6GC's
are often identified with the "American" amplifier smerican" amplifier sound
but, this is really an obsolete description because modern day manufacturers
are designing whatever characteristics into thier amp they wish regardless
of which tubes are used. 6L6's are used in pairs. 2 tubes = (approx.)
50 watts of output. A typical 100 watt head uses four 6L6 output tubes. |
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EL34 |
Another
very popular tube, EL34's are associated with the classic British
amplifiers of the 60's. In many amp designs, they are interchangeable
with 6L6's simply by flicking a switch and deliver the same amount
of output. EL34's are typically associated with high gain amplifiers
gain amplifiers
but deliver a good clean sound too. While each type of tube has it's
devotees, there are likely to be amplifiers which use either tube
that can put a smile on the face of most players. |
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EL84 |
These
tubes are typically associated with early "class-A" amplifiers.
They look like 12AX7's on steroids. Two EL84's deliver around 18 watts
of power. They deliver a very warm midrange but not a very punchy
bass response. The top end (treble) is smooth. They are ideal for
blues players and sound great for most other styles but don't deliver
the high-gain "stack" sound high energy, rock or metal guys
demand. This is often the tube of choice for the "tone-junkie"
croud. |
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Rectifier
Tubes |
Rectifier
tubes convert AC (alternating current) out of the wall socket into DC (direct
current) to drive the amplifier. It is less important which rectifier tubes
are used than whether the amp uses tubes for this function at all. There
are two common ways to convert AC to DC in amplifiers; silicone diodes and
tubes. Silicone diodes deliver more power, faster than tubes and, as a result,
deliver punchier bass, more gain and more headroom than tubes. Tube rectifiers
react more slowly and give the amp a "spongy" feel accociated
with many vintage amps. Most amps today use silicone diode rectifiers. One
line of amps (there may be more) allows the user to select either. These
are the Mesa/Boogie Dual Rectifier series of amps provided to us by the
genius of Randall Smith (please excuse the shameless plug). |
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