Tube Power Amp Reviews

Closing his review of the AirTight ATM-1S amplifier in the November 2014 Stereophile, Art Dudley wrote, "The AirTight ATM-1S is right up there with the best I've heard: the artisanal, the small, the artistically sensitive, the colorful and characterful, the smart. The AirTight is as serious an EL34 amplifier as I've heard, offering texture, color, poise, musical drive, and rightness, all in good proportion to one another. It also looks nice and represents at least decent if not outrageously good value for the money."

Art's ATM-1S was a step in a long succession of tube amplifiers produced by AirTight since its 1986 founding. First came the original ATM-1; AirTight has also produced the ATM-2 (which used KT88 tubes), the ATM-4 (6L6GCs), the 1S that Art reviewed (EL34s; the S stood for "special"), the ATM-2 Plus, and now the ATM-1 2024 Edition ($14,975).

It's no secret, especially to those who've been following Stereophile for more than a short time: In the first half of 2007, I took the plunge and bought a Shindo preamplifier and monoblock amplifiers—handmade products characterized by low output power, generous numbers of vintage parts, steel casework finished in a signature shade of green, and richly textured, impactful sound with lots of sheer musical drive. And while we tend not to alert the major newspapers whenever someone on staff buys new electronics, the change was notable for two reasons: The compatibility of Shindo's amplifiers is limited to loudspeakers of higher-than-average sensitivity and impedance; and, throughout the seven years that followed my switch to Shindo (footnote 1) both my system and my point of view regarding domestic audio in general have evolved in the direction of the artisanal and the vintage.

Single-ended triode amplifiers (SETs) have a considerable following, but even their most devoted fans admit that its maximum power output is not among an SET's strengths. You'd be lucky to get an SET that puts out 7Wpc, and some (like those using the 45 tube) are closer to 2Wpc. Highly sensitive speakers (eg, horns) will tend to offset the power limitation, and SETs usually sound more powerful than their measurements indicate, but the laws of physics still apply: 2W is 2W, regardless of the kind of amplifier that produces it, and an amplifier's manner of clipping and recovery from overload take us only part of the way toward achieving greater volume.

Even at its humblest, a 300B is a fine thing. And at its best, this classic triode output tube can deliver some of the most intoxicating music playback imaginable. If tubes are liquor, the 300B is clearly absinthe. (The 2A3 is Cognac, the 45 is Armagnac, the F2a is Tequila, and the EL34 is vodka—which is to say, you can make almost anything out of an EL34, from the repulsive to the sublime.)

Anyone over 40 who's worked in a hi-fi or record store will remember the Pfanstiehl catalog, a pulpy thing that most shopkeepers chained to their counters, like a phone book. Pfanstiehl made replacement styli for virtually every record-playing device of the day, and their catalog contained page after page of tiny line drawings of nothing but phonograph needles, all lovingly rendered in three-quarter view. You couldn't browse it without being brought up short: My God, how many different needles are there? And how is it possible that a single company could tool up for so many products and still make a profit?

The Audio Research D-160B has been heavily modified since the D-160A, and uses the same technology as the D-70, D-115, and D-250. It embodies William Z. Johnson's latest transformer and power supply designs, his latest choice of capacitors and resistors, and the same independent regulation of screens, drivers, and front end. D-160s and D-160As can be converted to D-160Bs for $1500.

The D-250 is the flagship of Audio Research's power amplifier range and, at 250 watts per channel, is the most powerful all-tube stereo amplifier currently available in the US. Under the circumstances, then, it is not surprising that it should also be one of the heaviest and largest.