Tube Power Amp Reviews

Big tube amplifiers were once scary monsters reserved for those who didn't mind heavy maintenance, careful tweaking, and the occasional explosion. Blown tubes required replacing, preferably with pricey matched pairs, then biasing with a voltmeter. Optimal sonic performance required regular bias monitoring and adjusting, and because of current surges on startup, you had to choose between leaving the heat-producing monoliths on, or turning them on and off for each listening session, thus shortening the life of the tubes.

The road to hell is paved with good inventions: clever ideas that appear, in hindsight, motivated more by a desire to sell clever ideas than to make musically superior products.

The DiaLogue tube amplifiers from PrimaLuna have, at their heart, a clever idea of their own: an output circuit that is user-switchable between triode operation, in which the screen grid of a tetrode or pentode power tube is defeated by means of connection to the tube's anode; and Ultralinear operation, in which the screen grid of a tetrode or pentode carries a portion of the AC music signal, supplied by a tap on the output-transformer primary, in a feedback-like effort to reduce distortion and increase power. Fans of the former often report a sweeter, more tubey sound, while fans of the latter report a tighter, more detailed, more timbrally neutral sound. Audio enthusiasts are given to reporting any number of things.

"We put music in the souls of our amplifiers. Every amplifier, every tube, every transformer has music in its soul."

Not to be cynical, but I've heard, over the years, countless variations on that sentiment. Not to be naïve, but it rang with somewhat-greater-than-usual sincerity when given voice by 45-year-old Richard Wugang—founder, with his late father, of Virginia-based Sophia Electric, Inc.

After I read Brian Damkroger's rave review of the Audio Research Corporation's Reference 5 SE line stage in the November 2012 Stereophile, I was excited about getting the review sample into my system so that I could do a Follow-Up (February 2013). However, the sample had already been returned to the factory, so I called ARC to see if it could be rerouted eastward to me. Chief Listener Warren Gehl answered the phone.

"Sure, you can listen to the Ref 5 SE, but I'd assumed you were calling about the Reference 75 amplifier."

"Reference 75? What's that?"

"It's our newest amplifier—a half-power version of the Reference 150."

The challenge is biblical in character, if not in scope: A half year after railing, in these pages, against our industry's overabundance of products that cost more than $20,000, fate has given me such a thing to review.

Do you believe in beginner's luck? If so, some of your personality traits should be quite predictable. Let's see. You're very likely an optimist with a "bull-market" mentality, play the lottery, and, most important, bought a CD player within a year of its introduction, or a solid-state amp in the '60s. You're apt to mail in a profusion of bingo cards (you know, the kind Stereo Review is full of) and spend hours perusing specifications in the hope of finding a kernel of truth in all of that chaff. You'd particularly be appalled at that fellow I ran into the other day, who had bought an AR-1 in 1956 and waited another decade before buying another speaker—just to make sure stereo wasn't a fad. Hey, relax, I won't turn you in; the mere fact that you're reading Stereophile is sufficient reason for redemption.

Ever since I became a Stereophile contributing editor, people have asked me, "How do you determine what equipment you're going to review? Do you get to pick your own, or does John Atkinson tell you what to do?"

I've chosen roughly 85% of the components I've reviewed for Stereophile, those choices made on the bases of what I find interesting, and what I think readers would like to know about. It's as simple as that.