From THD – “The THD Bi-Valve 30 is a Single-Ended Class A amplifier head with dual output tubes that can be switched at will among many octal-based power tubes, including 6L6, EL-34, 6550, 6CA7. 6V6, 6K6, KT-90, KT-88, KT-77 and KT-66, for different tones without re-biasing the amp. The two output tubes do not need to be matched in any way—you are free to experiment with any combination you want!
Likewise, the two preamp tubes can be any combination of 12AX7, 12AT7, 12AU7, 12AY7 or 12AZ7. The BiValve-30 delivers tones from smooth and clear to very aggressive overdrive, but with more power and a much more compliant output transformer for thicker lows. It is easily capable of driving a 4×12″ cabinet, yet quite small and relatively light.
Finally, it has a built-in Hot Plate® Power Attenuator that allows for full output distortion at almost any volume. The unique combination of our touch-sensitive input circuit and the wonderfully active and reactive tone control section (that we slaved for a year to perfect) make for a front-end that really responds to subtle and not-so-subtle changes in the signal being fed into the amplifier either by the guitar or any effect that may be between the guitar and the amplifier.”
The standard of construction is absolutely top class, as you would expect for a handmade amplifier of this nature. Underneath its large, perforated steel lid you’ll find large transformers and hi-fi style internal baffle plates to cut down on hum. On the front panel is a pair of input jacks labeled More and Less, followed by a Cut switch (high-cut filter), Volume, Treble, Bass, and Attitude (driver tube response control).
In the centre is a light bulb that glows as the amp distorts with a small switch to turn it off, a control for the built-in Hot Plate (output attenuator), and a defeat switch for the Hot Plate. The amp sports an acid-etched control plate with a delicate marine theme inspired by Glasgow artist Charles Rennie Mackintosh.
“The BiValve-30, running a 6550 and an EL34, produced a level of tonal complexity and sonic dimension that was simply off the scale. The BiValve-30 could easily be the richest, most detailed amp in its class” – Guitar Player Magazine May 2002.
This amplifier is in very good condition. It has only been lightly used and has been well taken care of. At the moment it is set up with 2 x 12AX7 pre-amp tubes and 2 x EL34s. But it accepts almost any type of output or preamp tube without bias adjustment, even in combination, for an astonishingly wide range of tones available for nearly any style of guitar playing.
Don’t let the 30-watt rating deter you. 30-Watts Class A is more than most people will ever need. It is loud.
Original retail price for the THD Bi-Valve was over A$3000.
This is a wonderfully versatile amp for many varied applications. Super strong and sturdy, it is a pro level piece of equipment used on stages and in studios worldwide.