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amp manufacturers, and just four of these
are seen in any great numbers. The four
most common output tube types are the
6L6GC, 6V6GT, EL34, and EL84. A handful
of contemporary makers still offer amps
with KT66 and 6550 tubes, and a few even
manufacture unusual designs using more
esoteric tube types, but you’ll see one of
those first four in a good ninety-nine percent of amps you encounter today.
Other than EL84s, which are the same diameter as preamp tubes (although taller) and
bilities of some of these more common
output tube types.
6L6GC. Think “big Fender amp tone”
and you’re thinking 6L6 (also sometimes
substituted for the interchangeable 5881,
essentially a ruggedized 6L6). This is the
big-amp output tube traditionally seen in
American-made amplifiers, and it has a
bold, solid voice with firm lows and prominent highs, which can be strident in loud,
clean amps, or more silky and rounded in
softer, “tweed” style amps. A pair of these
are known for their juicy, well-rounded tone
and smooth, rich distortion, which occasionally exhibits an element of grittiness
that is not necessarily unappealing. They
produce about half the output of their big
brother, the 6L6, and are therefore more
easily driven into distortion. The 6V6 was
used in many Fender designs—the Champ,
Princeton, and Deluxe lines among them—
some great vintage Gibson amps like the
GA- 40 Les Paul Amp of the nineteen-fifties
and early sixties, and countless others. From
the late eighties to late nineties no reli-
6L6GC 6V6GT
use the same 9-pin socket, all of the most
common output tube types use large 8-pin
(octal) sockets. While they might appear
interchangeable in terms of socket size,
however, most have different circuit, voltage, and bias requirements, so they cannot
simply be substituted one for the other
in most amps. There are a few makers
today producing amps that are specifically designed to let you swap between
output tube varieties for “tube tasting,”
and models such as THD’s UniValve and
BiValve, and Victoria’s Regal II and Two
Stroke can take any of the common 8-pin
types without needing rebiasing or other
adjustment. For the most part, though, a
maker will design an amp with a very specific tube type in mind, and will work very
specifically to the performance and sonic
characteristics of that tube. Let’s take a
little look at the signature tones and capa-
will generate around forty to fifty watts in
an efficient Class AB amp; a quartet (with
two pairs working in teams on each side of
the phase-inverted signal) can put out up
to one hundred watts. In less efficient, but
juicily toneful, cathode-biased designs (
so-called “Class A” amps) like TopHat’s Super
Deluxe or Carr’s Rambler, or a mid-fifties
tweed Fender 5E5 Pro, a pair of 6L6s will
put out around twenty-five to thirty watts.
This is the tube of anything from the Fender
tweed Bassman and blackface Twin and
Super Reverbs, to early Marshall JTM45
heads and “Bluesbreaker” combos, to the
Mesa/Boogie Mark Series and beyond.
EL34
able current-manufacture 6V6s were available, so few manufactures designed new
amps around this tube. This is the course
of events that led to the virtually unthinkable release of smaller Fender amps that
used EL84s, such as the Blues Junior (the
early-sixties Tremolux, which briefly carried
EL84s, being something of an anomaly).
The release of a rugged and reliable 6V6
first from Electro-Harmonix, then from other
contemporary makers, has led to a renewed
popularity for this tube, and it proliferates
again in the twenty-watt-and-under range.
6V6GT. Think small-tweed amp and you’re
hearing the 6V6GT. Smaller American-made
amps of the nineteen-fifties, sixties and seventies most often carried 6V6 tubes, which
EL34. Take your aural imagination across
the pond, conjure up that big, British crunch
tone, and your mind’s ear is hearing the
EL34. The classic Marshall tube, the EL34
was the big boy of British amplification from
the late nineteen-sixties onward. It can be
driven at higher voltages to produce a little
