Vintage Guitar - September 2018 - Open - 48

an EL84 but contains a triode usually applied
to preamp duties, along with a pentode for
output. The triode of one 6GW8 is used as
the driver stage, while that of the second
is used for a split-load phase inverter. The
two pentodes are for the fixed-bias, push/
pull output stage, running into an output
transformer that feeds a 12" CTS speaker.
From there
things continue in
a similarly oddball
- though effective
- manner via the
aforementioned
line-level (DI) tap
from the speaker
output into the reverb spring pan. Two stages
of 12AX7 pick up the reverb signal from the
output of the springs, then send it via the
Reverb level control and an on/off switch
to another unusual tube, a 6BM8 (a.k.a.
ECL82), which contains another preamp
triode and output pentode in the same
bottle. Using these as a driver stage and a
single-ended output tube, respectively, the
reverb signal is pumped into its own small
output transformer to be amplified through
an 8" CTS speaker. Rather than just dumping

to ground or lifting it from the signal path,
as most would do, the amp's reverb on/off
switch shunts a connection between either
the reverb preamp for a wet output at the 8"
speaker, or a tap of the dry signal coming
off the driver triode prior to the main amp's
phase inverter, so you get sound at the reverb
amp either way, dry or wet.

The tremolo is a simple circuit that uses the
spare half of a 12AX7 to modulate the bias
at the output tubes' grids. Like most basic
bias-modulated tremolo effects, it doesn't go
to extremes, but sounds warm, organic, and
appealing. The reverb itself has the potential
for anything from gently liquid room sound
to all-out splash and wash, and all with impressive depth and dimension. Add tremolo
and there are tasty atmospheric sounds to
be had from the Thunder 1 Reverb. The dry
amp isn't particularly girthsome or inspiring;

September 2018

48

VINTAGE GUITAR

it's predisposed to clean tones and wringing
what headroom can be had from its 12-watt
push/pull configuration, until you wind it
right up toward the top and a little crunch
and sizzle chimes in. But put it together with
the well-conceived effects and there's a lot of
tone to be had.
Rare early versions of the Thunder 1 Reverb
(like this one) were
built on a simple
L-shaped chassis
made from folded
steel and had a simpler outer livery
of black vinyl and
wheat-and-gold
grillecloth. More often seen is the look of a
year or two later, with fawn-colored vinyl
over the cab, a nifty two-tone grillecloth,
and a more-conventional four-sided chassis.
Peak into the back, though, and you discover
a point-to-point circuit with Philips/Mullard
"mustard cap" signal capacitors and other
lust-worthy components. In all, it's a clever
and conscientious design for an amp that never
quite captured the mainstream, yet pointed the
way to what was arguably the optimal means
of slathering reverb over robust guitar tone.


http://www.hammondmfg.com http://www.vintageguitar.com/

Table of Contents for the Digital Edition of Vintage Guitar - September 2018 - Open

Contents
Vintage Guitar - September 2018 - Open - Cover
Vintage Guitar - September 2018 - Open - IFC
Vintage Guitar - September 2018 - Open - 3
Vintage Guitar - September 2018 - Open - 4
Vintage Guitar - September 2018 - Open - 5
Vintage Guitar - September 2018 - Open - 6
Vintage Guitar - September 2018 - Open - 7
Vintage Guitar - September 2018 - Open - 8
Vintage Guitar - September 2018 - Open - 9
Vintage Guitar - September 2018 - Open - Contents
Vintage Guitar - September 2018 - Open - 11
Vintage Guitar - September 2018 - Open - 12
Vintage Guitar - September 2018 - Open - 13
Vintage Guitar - September 2018 - Open - 14
Vintage Guitar - September 2018 - Open - 15
Vintage Guitar - September 2018 - Open - 16
Vintage Guitar - September 2018 - Open - 17
Vintage Guitar - September 2018 - Open - 18
Vintage Guitar - September 2018 - Open - 19
Vintage Guitar - September 2018 - Open - 20
Vintage Guitar - September 2018 - Open - 21
Vintage Guitar - September 2018 - Open - 22
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Vintage Guitar - September 2018 - Open - 25
Vintage Guitar - September 2018 - Open - 26
Vintage Guitar - September 2018 - Open - 27
Vintage Guitar - September 2018 - Open - 28
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Vintage Guitar - September 2018 - Open - 30
Vintage Guitar - September 2018 - Open - 31
Vintage Guitar - September 2018 - Open - 32
Vintage Guitar - September 2018 - Open - 33
Vintage Guitar - September 2018 - Open - 34
Vintage Guitar - September 2018 - Open - 35
Vintage Guitar - September 2018 - Open - 36
Vintage Guitar - September 2018 - Open - 37
Vintage Guitar - September 2018 - Open - 38
Vintage Guitar - September 2018 - Open - 39
Vintage Guitar - September 2018 - Open - 40
Vintage Guitar - September 2018 - Open - 41
Vintage Guitar - September 2018 - Open - 42
Vintage Guitar - September 2018 - Open - 43
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Vintage Guitar - September 2018 - Open - 45
Vintage Guitar - September 2018 - Open - 46
Vintage Guitar - September 2018 - Open - 47
Vintage Guitar - September 2018 - Open - 48
Vintage Guitar - September 2018 - Open - 49
Vintage Guitar - September 2018 - Open - 50
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Vintage Guitar - September 2018 - Open - IBC
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