In a
technical sense, one vacuum power tube works the same
as another, plate dissipation and current handling
abilities differ among a selection of power tubes,
but on paper current is current.
Yet
there exist enormous differences in the musical
styles created by different tube types, and these
styles are immediately detectable to most advanced
guitarists. These differences in both the dynamic
feel and the sonic character impart a unique
signature that is often recognizable as the
foundation of an entire musical style.
A good
example of this is exemplified by the very different
signatures of the 6V6 and EL84 power tubes. Both
tubes have modest power handling capabilities of
around 15 watts per pair. Both were widely used in
the 1950s and '60s, which were the formative years of
the electric guitar. And both types have nearly
identical plate characteristics. Yet their individual
musical signatures are vastly different.
The
6V6 was widely used by Fender during the '50s and
'60s for their low power models. These amplifiers
were popular with "electric blues"
guitarists who often found their amps underpowered,
and simply turned them up! Of course the amp ran out
of power and distorted heavily. But the distortion
quickly became used as a further tool of musical
expression when in the right hands.
Operating
below the distortion threshold, the 6V6 sound is
"skinny", not objectionably thin, but
bright nevertheless with bouncy, resilient dynamics.
When overdriven, the low order second and third
harmonics rise to predominance, obscuring the bright
high frequencies and "fattening" the sound
in a way which is a trademark of American blues. When
severely overdriven, the distortion characteristic
goes beyond what is desirable, producing an
inarticulate low end which is bloated and tubby,
obliterating most other frequencies with its
woofiness.
Meanwhile
in Europe, particularly in England during the same
period, the EL84 was the power tube of choice in
small amplifiers. The sound of this tube is very
different from that of the 6V6. The EL84 possesses a
glassy brightness whose emphasis is in frequencies
higher than the bright zone of the 6V6. The EL84's
dynamic character seems less resilient and when
driven into distortion, higher order harmonics
prevail, and an aggressive, snarling bite ensues.
Overdriven to extremes, it doesn't suffer from low
end bloatiness but retains a more balanced spectrum
with it's aggressive midrange character dominating.
It's
no wonder that when British guitarists began turning
up their amps and "playing the blues," it
sounded quite different from the Americans they were
imitating. It's fair to say that the difference may
have been less cultural and more technical, and
largely owing to the differing tube types: American
amplifiers used 6V6 or 6L6 types and the European
units (which were sometimes identical to American
circuits except for the power tubes) used EL84 and
EL34 types. The best example of this is the fact that
the "plexi" Marshall circuit is
identical to a 4x10 Fender Bassman. Since both of
these European tube types possess a more snarling,
aggressive midrange distortion than 6V6 or 6L6 tubes,
it's easy to see how "bad attitude" rock
and roll styles such as heavy metal developed from
blues-based music being played on amps fitted with
European tubes and cranked up into heavy distortion.
With
Progressive Linkage, the power amplifier is provided
with a plurality of tube types and includes a switch
to select different pairs of output tubes, either
alternately or combined for simultaneous performance.
The most useful, as well as logical, choice is an
amplifier which combines 6V6s with EL84s for low to
moderate power (as utilized in the Blue Angel) or one
which uses 6L6s with EL34s for moderate to high
power.
The
single amplifier can produce the actual signature
sounds of either of the two types of tubes making
genuine British or American musical styles obtainable
with true authenticity.
Another
feature is the selectability of output power. For
those who insist that only power amplifier distortion
is acceptable (and preamp saturation is not) the
problem of correct wattage is a major concern.
Differing room size, acoustics, and the number and
type of other instruments in the band dictate a
certain power level which is appropriate. Dedicated
players are often known to bring a small fleet of
different powered amplifiers so that they have one
that's right for the job.
Progressive
Linkage largely solves this problem by offering three
different and selectable levels of output power. The
lowest is the single pair of 6V6s at around 15 watts.
The next is the two pairs of EL84s operating alone to
produce approximately 33 watts. And the last is the
combined output oftwo 6V6s, plus four EL84s for a
total capability of around 38 watts.
Another
advantage of Progressive Linkage is the option of a
third sonic characteristic achieved by using all
tubes simultaneously. The tone produced is refined
and highly desirable, as the likable tonal elements
of each tube type seem to improve the weaknesses of
the other. The 6V6s soften the brashness of the EL84s
and add body to the lower regions. Simultaneously,
the EL84s cause the combined sound to retain
tightness and articulation while preventing
objectionable low end woofiness from taking over.
