Tube Power Amp Reviews

Most reviewers look for a "hook" or angle of some kind when it comes time to write a review. After all, how many ways are there to get excited about audio equipment? Kathleen and I like to focus on the human side of the High End. So it was with some amusement that I watched the obstacles swirl around what I thought would be a fairly straightforward review of the Vacuum Tube Logic MB-1250 Wotan monoblock power amplifier. My thought was to return from single-ended to push-pull with a bang! I'll say...

It all began at the January 1996 WCES, where I found my shorts positively welded to the listening chair during a memorable musical blast at VTL. Luke Manley and his extreme audiophile wife Bea had a good thing going and they knew it. People were talking. "Did you hear those monster two-storey VTLs on the Alón Vs?"

As I recall from my Vegas show report, "Wow!" was the operative word. I was sure the giant Wotans would sound superb on the Avalon Ascents. In due course, Luke showed up at our loft and talked the delivery truck down to a safe landing. (He used an age-old technique: pepper the shipping company with so many phone calls they couldn't wait to deliver and be rid of him! He could almost be a New Yorker.)

Svelte is in the eye of the beholder
Each monoblock mounts 24 power tubes on the top chassis, and a power supply with three massive transformers and four industrial-grade capacitors on a separate "ground-level" chassis. Imposing in their all-black livery, they make a 19" by 19" footprint and stand almost 2' high. And at 240 lbs each, they are a huge physical presence to deal with, despite VTL's new peekaboo cosmetics. (While heavy, and despite liberal use of damping material, the two-storey chassis' torsional stiffness and resonant signature left something to be desired. When I pointed this out to Luke, he told me he'd already specified future construction techniques to remedy this.)

Power tubes are latest-spec Russian 6550Cs, purported to be the best of the Svetlana litter. Inputs and drivers per side consist of a pair of 6350s flanking a single 12AT7. I'd never run across the 6350 before. "Think of it as a double-power 12AT7," Luke told me.

The lower chassis has a standard IEC power connector and a slew of fuses sharing the rear apron. A thick umbilical ties it to the upper deck. The top chassis is a wonder to behold, especially at night when lit up like a Christmas tree. The tightly packed power tubes surround the output transformer, located dead center on top. A pair of caps stand sentinel before it, the input and driver tubes set up before them. There are 24 separate bias pots countersunk into the top chassis, their separate reading points just behind the faceplate.

And yes, you must be something of a fanatic to run amplifiers that require 48 separate biasing operations. But Statement Products are what the Wotans are, and indeed, the fanatics who buy them are out there. In fact, you'll read about one of them shortly.

Exploring the rear of the upper chassis, one finds a single pair of Manley/VTL binding posts (fairly easy to work with), and an RCA single-ended input (balanced inputs are available). There's also a switch for tipping the amps back and forth between triode and tetrode modes. Just think of it...600W in triode, 1250Wpc in tetrode!

Up front, lower right is a large rotary switch, marked 0, 1, and 2, with which to trigger the electrics. You grasp the switch, cover your eyes (just kidding), and briskly snap it one stop to the right. The half-voltage startup instantly charges the caps. After a moment or two, snap the switch once more for full power.

The cacophony of clinking glass was notable during warmup, and positively hilarious when shutting down. So Luke—why 1250W? "The reason power is important is to provide as much TMC—Total Mass Control—as possible. Imagine you're swinging a massive weight back and forth. The more powerful you are, the more you can control that weight to move at any speed and frequency you want without distorting your intended movements. Similarly, the more power an amp has, the better it can control the speaker and air mass to move with the audio signal at any frequency and amplitude without distortion. This is an essential ingredient in what provides a clean and realistic sound."

Seeing he had my ear, he continued. "I feel you get substantially the same sound from our other amps that run 750, 450, 250, 175, and 125Wpc, and even from our two stereo designs with 150W and 85W each. I can tell you that each of them offers more TMC than any other tube amp in their class." Okay, Luke, sales promo over.

The best-laid plans of mice and men oft go awry
Content the amps were working properly, Luke and Bea took their leave. Kathleen and I burned-in the Wotans at low to moderate volume without paying much attention to their sound. Finally, one cool evening a week or so after setup (they run hot), I sat in the Ribbon Chair and cranked up the volume.

Uh-oh...something wasn't right. At lower volume levels, all was sweetness and light. But when I blipped the throttle—Kathleen's favorite thing—I noted gross distortion in both the bass and the highs. I thought it was surely the Grasshopper IV—it sounded so much like cartridge mistracking. I swapped in the Symphonic Line RG-8, and presto-chango...no improvement. Digital was also a wash. Could it be the preamp? Doubtful, I thought, as I swapped out the dual-mono Jadis JP-200 and found the fuzz still much in evidence.