1 TUBES ARE WAY MORE THAN
JUST “AMPLIFIERS.” Sure, tubes
are the amplifiers within our amplifiers
because they make the signal
louder. But they do way more in the
process. Players rave incessantly about the
beauty of tube distortion (and we will do
some more of that here), but even when you
achieve what you perceive as a gorgeous
clean tone from a tube amp, an element of
tube distortion is still responsible for shaping
that tone. Even when present at lower
levels, distortion adds harmonics to the fundamental
note the guitar delivers, helping
your tone sound thick and lush and shimmery,
rather than something like the pure
note produced by a powerful audio amplifier
with very low THD (total harmonic
2 TUBE DISTORTION VS.
SOLID- STATE DISTORTION.
The beauty of the way tubes distort—
in a well-conceived circuit—
is that they ease gradually and
smoothly into breakup as a higher signal is
applied, evoking a lot of depth and dimension
and an ear-friendly quality as they do
so. Transistors, on the other hand, clip off
their output abruptly and harshly when
finally pushed too far. Explanations of this
phenomenon are usually accompanied by
two diagrams: the smoothly rounded if
slightly off-balance sine wave of a clipping
signal through tubes, and the angular square
wave of a signal clipping through transistors.
Doesn’t even look as pretty, does it?
Plenty of solid-state amps can sound great
too, but the require a lot of added circuitry
to help them sound “tube-like”.
3 THE “WARM” MYTH. One of
the main adjectives applied to
tubes, by marketing departments
at least, is that they sound
“warm”—but this can be misleading. The description is often used to
plug gear that might include a lone preamp
tube in an otherwise hybrid design
that also uses transistors for other preamp
and output functions, but the 12AX7 they
are usually boasting about has an inherently
crispy, bright tone when driven to
distortion. Play an all-tube late-’60s Fender
Deluxe Reverb alongside solid-state amps
made by Kustom or Polytone at around the
same time, turn each up to about half way,
and you can bet the Deluxe Reverb will
have more treble bite than the relatively
warm tranny amps alongside it. Tubes
sound great, but for several reasons other
than their “warmth”.
4 PREAMP TUBE DISTORTION.
Preamp tubes and output tubes
produce rather different tones
when distorting. Both can sound
great for particular applications,
but it’s worth knowing what you are after.
In a good high-gain circuit, preamp-tube distortion
can produce lots of juicy sizzle,
endless sustain, and shedloads of jagged harmonics.
Think lead channel on a Mesa/
Boogie Mark Series amps, Soldano SLO,
Bogner Shiva, and the like. In a poorly conceived
(or simply cheap-o) high-gain circuit,
preamp tubes can sound buzzy, fizzy, and
harsh, emitting that “can of wasps” tone that
has given poorer such efforts a bad name.
5 OUTPUT TUBE GRIND. Output-
tube distortion is produced
when an amp’s preamp isn’t distorting
significantly, but it is
passing a full and high-level signal
on to the output stage. This form of tube
distortion is usually heard as thick, creamy,
and dynamic, with perhaps a little more
openness and body than preamp-tube distortion.
Think cranked Marshall JTM45 or
Vox AC30. In truth, we very rarely hear pure
output-tube distortion because an amp’s preamp
and phase inverter tubes usually distort
at least a little by the time the output tubes
break up, but we call this brew “output-tube