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Drive a 12AX7 hard, however, and it will
induce quite a bit of sizzling, slightly fizzy-voiced distortion of its own. This can be a
great thing if you’re looking for a super-fried overdrive tone that’s cooking at all
stages, but not at all desired if you want
more headroom and clarity, or the fatter distortion that’s generated in the output stage
of the amp when a cleaner preamp signal
is driven into clipping at the output tubes
(more of which in the next installment).
often at the speaker too.
Some modern high-gain amps are
designed specifically to create extreme
yet controllable preamp tube distortion by
cascading multiple gain stages, one into
the other, with gain and master volume
controls between them to control the
drive levels at each stage. Used in this
way, preamp tubes can produce a scorching, harmonically saturated lead tone that
sustains all day—what we usually hear
as a classic shred or contemporary rock
tone—in an amp that really relies on its
output tubes just to amplify this sound,
rather than to add further distortion to it.
When driven into distortion in a simpler,
more basic amp with fewer gain stages (a
category that might nevertheless include
some very high-end, “boutique” tube
amps), preamp tube distortion becomes
just a part of the amp’s overall distortion
character, blended with clipping at the
phase inverter and output stages, and
C
Note: the term NOS, which
stands for “new old stock”,
is applied to tubes manufac-
tured many years ago but
never put into use.
Counter-intuitive though it might sound,
armed with the above knowledge regarding preamp tube distortion, many players
have learned to create a bigger tone by
using lower gain preamp tubes. To lower
the gain of a preamp stage a little, you
can swap a 5751 into any socket that
carries a 12AX7. To lower it even more
but retain the same performance characteristics (other than gain) you can use a
12AY7. Many players think the last thing
they want to do is lower the gain of a
preamp stage, but in doing so you can
often prevent your signal from dirtying up
in the preamp, and thereby pass a beefy,
full-frequencied signal along to the output
stage when the amp is cranked. This generates more output tube distortion, which
results in a fatter, fuller tone in many simpler tube amps. This tip doesn’t usually
apply to high-gain type tube amps, whose
whole raison d’etre is to generate preamp
distortion. This 5751 swap is a trick that
was used by Stevie Ray Vaughan, for one,
to help generate his signature tone, and
it has also been employed by plenty of
other great blues players. If you’re trying
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