65 Amps – Ventura Head

65 Amps – Ventura Head


Price: $1,495.00
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THD Bi-Valve

THD Bi-Valve


THD Bi-Valve

The THD BiValve Guitar Amp Head is a single-ended pure Class A design. However, it has two output valves that are wired in parallel and combined through a special output transformer to deliver up to around 30 watts. You can use almost any output valve you like without touching any kind of bias adjustment, and get this: in the BiValve you can use them in any combination as well. Combined with the capability to take almost any preamp valve, this makes the BiValve even more of an amp tweaker’s dream than its predecessor. Because there’s such a wide range of tone available, you create your own style.

The BiValve amplifier head sits in a compact well constructed pressed steel chassis. The control markings are screen printed, which makes them easier to see. Underneath the perforated steel lid there’s a larger pair of transformers to handle the increased output, and inside there are two ultra-thick PCBs: one for the power supply and one for the audio. The four valve bases are bolted to the chassis and secured by locking nuts, with hi-fi style internal baffle plates to cut down on radiated hum. The standard of construction is absolutely top class. THD are based in Seattle, which is also hometown to Boeing, and most of the BiValve’s heavy fabrication work is contracted out to local specialist companies who service the aircraft industry.

The front panel looks deceptively simple. Working from the left, there’s a pair of input jacks labeled “more” and “less”, followed by a treble cut switch then rotary controls for volume, treble, bass and what THD call “Attitude”. It’s not a fancy name for a presence control – there’s no negative feedback loop – instead Attitude works on the driver valve to change its response, and does more or less what the name suggests: either smoothing things out or making them more aggressive.

In the center, part of a clever noise reduction circuit, is a light bulb that glows as the amp distorts. Depending on your point of view it either looks very hip or very distracting, hence a small switch underneath to turn it off. Next to this is the level control for the Hot Plate – a built-in output attenuator that lets you run the THD BiValve into total meltdown without annoying the neighbors; there’s also a defeat switch for this function, which adds a little extra volume for live work.

The last three rocker switches are for mains, standby and power selection. The hi/lo power switch is like having a built-in Variac; switching to low voltage adds a squashy dynamic feel and reduces clean headroom, and it’s essential for valves like the 6V6, which can’t handle high plate voltages.

The BiValve’s back panel has a pair of speaker outlets with an impedance changer, and the excellent transformer-isolated line out – using a 6mm stereo jack socket – is balanced. Fuse protection is more comprehensive, and the BiValve also benefits from a pair of warning LEDs to let you know if a power valve is faulty.

When it comes to describing the BiValve amp’s sounds, it’s difficult to know where to start, or when to stop, for that matter. You can use almost any power and preamp valve combination under the sun, and as a result the tonal range is virtually unlimited.


• 2 output valves of nearly any type in any combination allows incredibly diverse tone possibilities
• No bias adjustment necessary
• Rackmountable
• Top class construction
• 2 input jacks
• Controls: volume, treble, bass, attitude
• Switchable noise reduction light bulb

Price: $1,200.00
Price: $749.00
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