deHavilland Electric Amplifier Company
Mercury 2 Line Preamplifier
A Winning Formula Based On Simplicity.
Review By Dick Olsher
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  I do not know if deHavilland's latest line preamplifier is in fact named for the wing-footed messenger of the Roman gods. Astrologically speaking, Mercury (the fastest planet) is said to inspire creative genius. How else might one explain deHavilland's designer, Kara Chaffee, choice of the type 85 tube? Similar in circuit topology to the UltraVerve preamplifier I reported on previously, the Mercury sports a different tube complement. A pair of 85 triodes replaces the 6SN7 gain stage and the cathode follower output stage now uses a pair of 6BL7 dual triodes connected in a cascode configuration. The common denominators are the 5AW4 tube rectifier, Goldpoint stepped attenuator, and similar point-to-point construction quality as seen below.

The Technology
Travel back in time with me, if you will, to the golden age of the radio. Predating 9-pin miniatures and the Octal 6SN7GA/VT-231, the 85 tube has never received any recognition in high-end circles. Its humble origins as a 1930s-era radio tube did not solidify its image as an exotic tube. Ditto for its internal complexity; being composed of dual-diode and single-triode sections housed in a single envelope. Such compaction certainly facilitated AM radio designs by combining a front-end detector, amplifier and automatic volume control into one stage.  But this is not the sort of tube likely to engender a cult following. It should be noted that the triode section is almost completely independent of the diodes, the only shared element being a cathode sleeve.

The top metal cap is electrically connected to the grid and therefore does not represent a high-voltage hazard. Leave it to Kara Chaffee to approach this tube with an open mind and thus discover its hidden sonic potential. What about the diodes, you ask? They are simply not used. Shopping for replacement 85s should present no problem: there is plenty of stock around and the pricing is dirt cheap. An interesting parallel to the choice of the 85 is my favorite 9-pin miniature - the 5687, which also did not start life as an audio tube, but rather as a ruggedized industrial type with applications in early computers.

Over the years I've developed a definite dislike for the ubiquitous trio of small signal or preamp tubes: the 12AU7, 12AT7, and 12AX7. I am told that the 12AX7 is the most popular tube on the face of the planet. In its many variations, it has been in continuous production since its introduction by RCA in 1947. Annual demand is estimated at two million, with most of it being taken up by musical instruments. In contrast, I doubt that annual demand for the 85 exceeds several hundred. Yet, for reasons having to do with harmonic textures and dynamics, I have never fallen in love with these tubes. In particular, the sound of the 12AX7 is to my ears the fast-food equivalent of the triode world: not particularly appetizing, but easy on the pocketbook. Many designers have come to regard it as a tube Pollyanna. If you want to fatten up the sound a bit, just throw in a 12AX7 into the signal path.

My basic point is that the sound any tube device is strongly influenced by the choice of tubes. This is especially true for simple two-stage designs such as the Mercury. The distinctive harmonic distortion spectrum of a particular tube, as well as its overload characteristics and linearity, produce a unique sound which imprints itself, much like "fingerprint" onto the overall sound of the device.

The Sound
You should know that my favorite preamp tube has been the 6SN7, and specifically, its military specification RCA VT-231 due its big tone sound. Since deHavilland was and still is a supporter of the 6SN7, you might get the impression that the 85's sonics are pretty much cast of the same mold. That is definitely not the case. The 85 insists on greater tonal neutrality, lacking the 6SN7's robust upper bass and lower midrange. To my ears the VT-231 generates a vintage romantic balance that complements the power range of an orchestra and does wonders for the foundation of a jazz combo. The 85, on the other hand, excels in the areas of harmonic textural delicacy and clarity. As a result, the Mercury offers an exceptionally clean window on the soundstage. It gives the soundstage the "Windex" treatment. The chronic veiling that afflicts lesser line stages vanishes like smoke with the Mercury in the chain. There's a purity of expression that makes it possible to resolve low-level detail even at low-volume levels.

We've all, I'm sure, experienced the urge at some time or another to crank up the volume so as to make the music more intelligible. Whether the Mercury spoke softly or loudly, its pristine virginal quality shone through. In addition, the music ebbed and flowed naturally and seamlessly - without the bright harmonic patina that afflicts so many tube preamplifiers. As a result, the Mercury was more tolerant of digital program material than most of the competition. Highly processed multi-channel recordings, i.e., most popular music, sounded more natural through the Mercury. A case in point is Light from a Distant Shore (Etherean Music), featuring the vocals of New Zealand's Hollie Smith and songs of Scotland's Steve McDonald, who also recorded, engineered, and produced the album. This, one of my favorite Celtic albums, was recorded on solid-state gear with loads of artificial reverb and EQ. The sound, on many front ends, comes through with a off-putting roughness and edginess. The Mercury was certainly the exception, as it allowed me to connect with the strong lyrics and the music's emotional fabric without emphasizing the recording chain's failings.

In concert with other tube preamplifiers, the Mercury's sound was slightly on the soft side of reality, as if some of the music's jagged edges were polished off; not necessarily a problem with digital sources, but most noticeable during vinyl playback. This is usually a consequence of frequency bandwidth limitation. Severe bandwidth restriction is known to result in an overly liquid and dark presentation. Here the slight blunting of transients was just noticeable, and frankly, rather welcome in a world run amuck with digital sound. The emotional content of the music was given full scope of expression with exceptional linearity. Tension and drama are coded into the subtle inflections of volume, pitch, and rhythm. The Mercury's reading of the core of the midrange was both dramatic and most affecting with a flair for the poetic — a major vindication of the 85 tube.

Bass definition, however, was a bit of a disappointment. Bass lines lacked the degree of tightness of expression I have come to expect even from deHavilland's own UltraVerve preamplifier. And this is my point again about choice of tubes. The Mercury and UltraVerve feature essentially the same circuit, implemented with differing signal tubes. The specs are hardly different. Yet, the sound of these two units is drastically different. The UltraVerve, even when outfitted with RCA VT-231s, lacked the midrange finesse and poetic expression of the Mercury. The latter was consistently judged to be the more refined and civilized of the two. There was a lovely harmonic bloom and crystalline purity about the mids of the Mercury that catapulted it well beyond the reach of even exceptional tube preamplifiers. Its reproduction of  the core of the music was breathtaking - nothing short of magical. But the lower octaves lacked that big tone authenticity of the UltraVerve. Now, if there was a way to splice the bass of the UltraVerve with the mids of the Mercury, that would positively define tube heaven on earth.

Soundstage development was definitely a strong suit, with excellent depth layering and convincing spatial extension to the side and front. Image outlines were recreated with convincing 3-D palpability. Space is the final frontier. Home theater is being promoted with multiple audio channels that can supposedly recreate the illusion of being there. What's typically missing in multi-channel systems is convincing soundstage extension into the room and depth layering. There is no need for more than two good front channels with the Mercury. It weaved a strong organic wholeness about the soundstage, as though all of the image outlines were inter-connected via bungee cords. The sensation of space was given free reign to expand much like an inflated balloon to fill the front quadrant of the listening room.

Conclusion
The type 85 tube harnesses tube magic never before experienced by audiophiles raised and fed on the sound of 9-pin miniatures: bold, linear and passionately expressive. It never struggles to find the musical groove. Kudos to Kara Chaffee for having the conviction and inspiration to embrace the 85 tube; surely a forgotten treasure dating back to radio's golden age. deHavilland Electric Company's winning formula is also based on design simplicity and tube rectification and I think now offers the best sound in tube line preamplification on this planet.

Specifications
Type: vacuum tube stereo preamplifier

Frequency Response: 20Hz to 80 kHz

Feedback:  Zero negative feedback

Maximum Output: 30 volts p-p, gain approximately 12dB

Signal Triodes: two Type 85

Cathode Follower: two 6BL7 cascode circuit

Rectifier Tube: 5AW4

Singlan to Noise Ratio: 85dB

Polarity: Inverting

Inputs: four stereo pair

Outputs: two stereo pair

Input Impedance: 50 kOhm

Output Circuit:  Cathode follower, minimum 10k Ohm load

Dimensions: 18 x 11 x 6 (WxDxH in inches)

Weight: 26 lbs. including shipping carton

Price $3,995

Company Information
deHavilland Electric Amplifier Co.
2401 NE 148th Court 
Vancouver WA 98684

Voice: (360) 891-6570
E-Mail 6sn7@abac.com
Website: www.dehavillandhifi.com