Introducing
the THD UniValve™
Amplifier!
The
new THD UniValve is a Single-Ended Class A amplifier head
with a single output tube that can be switched at will among
many octal-based power tubes, including 6L6, EL34, 6550, 7027,
KT90, KT88, KT77 and KT66, for different tones without re-biasing
the amp. Likewise, the two preamp tubes can be any combination
of 12AX7, 12AT7, 12AU7, 12AY7 or 12AZ7. The UniValve delivers
tones from smooth and clear to very aggressive overdrive.
It is easily capable of driving a 4 x 12" cabinet, yet
quite small and light. It has a built-in Hot Plate™ Power
Attenuator that allows for full output distortion at almost
any volume. And it doesn’t cost as
much as you might think.
Guitar
Player Magazine Bench Test of the Univalve (PDF)
Guitarist
Review (PDF)
Download
the Univalve Manual (PDF)
What
is a Class A?
Class
A is a term given to an amp that runs its tubes at full current
all the time, unlike most tube amps that alternate between
running one set of tubes and the other set, each for one half
of the wave. The set not in use is turned off by a positive
swing of the grid voltage. Single-ended out-put stages always
operate in Class A. Most push-pull amplifiers, including the
venerated Vox AC-30 operate in Class AB when overdriven, even
if they are in Class A while clean. The upshot is that Class
A operation has its own unique tone characteristics that set
it apart from other tube amp classes. Class A amps sound great
at low volumes, and even better as you turn them up. Thus,
with the relatively low wattage of the UniValve you can turn
up the amplifier to take full advantage of its stunning output
distortion tone without deafening anyone.
Why
the self-biasing feature?
The
UniValve’s circuitry senses the current needs of the
output tube and provides the correct bias volt-age to the
cathode of the output tube regardless of tube type or wear.
This means that, without any trip to an amp technician, you
can simply replace the output tube with one that has different
sound characteris-tics. (Of course, you can also change the
preamp tubes at will for even more tonal variations.) For
example, a 6550 will stay cleaner at higher volumes, but when
overdriven, has an astoundingly "woody" character
to the overdrive. On the other hand, an EL34 will break up
earlier than a 6550 and gives a more "British" sound.
The ever-popular 6L6 family of tubes gives a tight overdrive
with less power than a 6550 but more detail than an EL34.
Even within the same type of output tube there are "harder"
and "softer" tubes, so two guitarists playing with
the same guitar through the same UniValve, but simply switching
the tubes to their preference, can have noticeably different
tones.
Controls
and Features
The
UniValve has two inputs: one for high gain and one for low
gain ranges. The low gain input with 12AX7 preamp tubes in
the amp gives a wide range of clean sounds from "Country"
clean and crisp to Jazz-direction warmth. With the controls
pegged and a relatively high-output humbucker, the low-gain
input can deliver a very convincing "Texas Blues"
type of overdrive. Plug into the high-gain input and you are
in a whole different world from early "British Invasion"
tones to contemporary Heavy Metal sounds. The most surprising
aspect to the UniValve’s high-gain overdrive is that
even with stunning levels of grind, you can still play complex
chords and hear every note of the chord clearly. There is
none of the mush and confusion normally associated with high-gain
tones.
The
controls are the traditional Volume, Treble and Bass controls
along with what we call an "Attitude" control. The
Attitude control is not a Presence control, as the amplifier
has no negative feedback from the output transformer back
into the driver stage. The Attitude control determines how
the driver stage responds to signal and how it drives the
power tube. There is also a built-in THD Hot Plate power attenuator
that lets you have full output distortion at any volume level.
The Hot Plate has its own hard-bypass switch on the front
panel, which com-pletely removes it from the circuit for Full-Power
playing into a speaker.
The
UniValve features a light bulb on the front panel that not
only glows when the amplifier is played, but it also provides
very effective noise-reduction. For occasions when you do
not want this feature, there is an On-Off switch for the light
bulb circuit right on the front panel.
The
UniValve has a GREAT-sounding transformer-isolated line out
on the back panel complete with an adjustable level control
and a switch to choose Line-Level or Instrument-Level signal.
The transformer used in the line-out was chosen for its pickup-like
im-pedance and tonal characteristics. Most amplifiers’
line-outs only work well when used to drive other power amplifiers,
and sound harsh and thin when plugged into the guitar input
of an amplifier. Not so with the THD UniValve! Even into the
input of a Marshall 100-watt head, the UniValve provides a
warm, fat, tight and sweet sound that FEELS like an amplifier,
not like a preamp-amp rig. The UniValve can drive any speaker
load from 2 ohms all the way up to 16 ohms. When there is
no speaker plugged into the speaker jack, the amp uses its
own built-in dummy load so no damage will occur, and to allow
the silent use of the amp for direct recording purposes when
miking a cabinet is not practical.
Configuration
The
UniValve will initially be sold only as a head. It is a metal
chassis, powder coated and enclosed in a perforated steel
cage to protect the tubes. In the coming months, we will be
introducing a number of different combo cabinet and head box
configurations. The UniValve can be installed in any of them
simply by screwing it into the box. There will be a huge range
of choices and options in the cabinets including head boxes,
1-12" combos, 2-12" combos, 2-10" combos and
others. We will periodically produce "Limited Edition"
cabinets with special hardwoods or other unique features.
Anyone with a UniValve will be able to use these as swapping
cabinets only takes about five minutes!
So,
go to your nearest THD dealer and try the new THD UniValve™
amplifier. You will be glad you did.
