Introducing the THD BiValve™ Amplifier!
Bivalve
When you see two power tubes in this THD BiValve-30, don't be confused. This is not a push/pull, Class AB amp. It's two sparkling clear Class A circuits running in parallel. And just like the revolutionary UniValve introduced in 2001, each side allows power tube switching at will. Imagine the possibilities: What would a 6V6 and a 6550 sound like together with a 12AX7 and a 12AU7 in the preamp? How about an EL84 and an EL34 with two 5751s in the preamp? THD's BiValve-30 amplifier gives you the opportunity to mix and match preamp and power tubes in a single amplifier unlike any other amp in the world. With this feature, you can tailor the amplifier's sound to your personal taste and needs like never before.
With the BiValve's unique dual-primary output transformer design and dual self-bias circuits, the BiValve-30 can combine different power tube types without any rebiasing or adjustment. (Naturally, you can also put in two power tubes of the same type to reinforce the tube's characteristics.) Try a 6L6, EL34, 6550, KT90, KT88, KT77 or KT66. With the amp in 'LoV' setting you can also use 6V6, 6F6, and 6K6 power tubes for reduced output power and added richness.
Not every combination of tubes will yield a full 30 watts, but THD's proprietary custom-wound output and power transformers used in the BiValve-30 allow every possible watt of power to be heard, felt, and appreciated. Similarly, the two preamp tube positions (Input and Driver stages) can take any combination of 12AX7, 12AT7, 12AU7, 12AY7 or 12AZ7 tubes.
The BiValve-30 includes a THD HotPlate power attenuator built in to the output section of the amplifier that lets you have full output distortion at any volume level. The HiV/LoV switch also cuts the power to about half. There's also a great-sounding transformer-isolated line out as well as a switchable noise reduction circuit that minimizes hiss and hum, a 'Cut' switch that reduces the entire range of the Treble control for a mellower, less bright sound preferred by many jazz and fusion players, and an effects loop.
What is 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, which alternate tubes for one half of the wave. Single-ended output stages always operate in Class A. Single-ended 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.
Being single-ended, the BiValve-30 has a much fuller harmonic content to its overdrive and distortion because it is rich in both even and odd harmonics. The push-pull configuration found in most amplifiers cancels even harmonics, leaving only half of the sonic spectrum offered by the BiValve-30.
Why the self-biasing feature?
The BiValve 30's circuitry senses the current needs of each individual output tube and provides the correct bias voltage to the cathode of the output tubes regardless of tube type or how old they are. This means that, without making a trip to an amp technician, you can simply replace the output tube with one that has different sound characteristics. (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 than most other tube types, but when overdriven, it 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 BiValve-30 can have noticeably different tones, simply switching to the tubes they prefer.
Controls and Features
The BiValve 30 has two inputs: one for high gain (More) and one for low gain (Less) ranges. With 12AX7 preamp tubes in both positions, the low gain (Less) input gives a wide range of sounds from 'Country' clean and crisp to Jazz warmth. With the controls at full, the low-gain input can deliver a very convincing 'Texas Blues' type of overdrive, especially when using higher-output pickups.
In the high-gain (More) input, a different world opens up, from early 'British Invasion' through Fair Warning-era Van Halen lead tones, to contemporary aggressive hard rock sounds.
Playing the BiValve 30 for the first time, you will immediately notice its fast response, and the way it combines the harmonically-rich chime of an AC 30 with the attack and performance of a Hiwatt and the gain of a hot-rodded JCM 800. The most surprising aspect to the BiValve 30's high-gain overdrive is that even with stunning levels of grind, you can still play complex chords and hear every note clearly. There is none of the mush and confusion normally associated with high-gain amplifiers.
The controls are the traditional Volume, Treble and Bass controls along with what THD calls an 'Attitude' control. The Attitude control determines how the driver stage responds to signal and how it drives the power tube.
The Cut switch reduces the overall treble-response of the amplifier. In the up position, there is more than enough treble to 'cut' through a mix, while in the down position it 'cuts' the extreme high end, for reduced treble and a softer, rounder tone.
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 completely removes it from the circuit for full power.
The BiValve 30 features a light bulb on the front panel that not only glows when the amplifier is played, but also provides roughly 6dB of noise-reduction. For occasions when you do not want this feature, there is an On-Off switch for the light bulb circuit directly on the front panel.
The BiValve 30 has a great-sounding, transformer-isolated line-out on the back panel with an adjustable level control and a switch to choose Line-Level or Instrument-Level signal ranges. The transformer used in the line-out circuit was chosen because its impedance and tonal characteristics closely resemble those of a guitar pickup. Most amplifiers' line out circuits 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 BiValve-30. Even into the input of a Marshall 100-watt head, the BiValve-30 provides a warm, fat, tight and sweet sound that feels like an amplifier, not like a preamp-amp rig.
The BiValve-30 can drive any speaker load from 2 ohms 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 BiValve-30 has a metal chassis, powder coated and enclosed in a perforated steel cage to protect the tubes.
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