B&K ST-140 power amplifier Sam Tellig 1987
You can build a decent tube preamplifier for under a grand, and quite a few manufacturers have done so: the MFA Magus), the Conrad-Johnson PV7, the Lazarus Cascade Basic, the Audible Illusions Modulus. But a tube power amplifier for much under a kilobuck? That's just not possible, although the Quicksilver monoblocks retailed for just under $1000 when they first came out. It's the transformers in particular that make tube amps so costly to build.
So if you're on a budget, you might combine one of the above-mentioned tube preamps (my current favorite is the Magus, by a slight margin) with such solid-state power amps as the B&K ST-140, the British Fidelity P170, or the Sumo Polaris.
I've discussed the B&K before, but I just recently received a sample of current production; a sweeter-sounding $440 amp I've never heard. The ST-140 strikes me as more tubelike than the typical modern-day tube amplifier, reminding me of an unmodified Marantz 8 or 8B. (I keep an 8 in my closet for nostalgia's sake.)
The ST-140's problem is that it sounds slightly rolled off in the high end—music isn't as crisp and lively as with the Jadis JA-30s. An outrageously unfair comparison, since the JA-30s retail for ten times the price; but the ST-140 doesn't sound any more rolled off than, say, the Conrad-Johnson MV50. The MV50 scores over the ST-140 in conveying more of that "palpable presence," but the ST-140 does surprisingly well.
As with most MOSFET amps I've met, though, the B&K ST-140 draws a certain veil over the music—I call it the MOSFET mist. The best way to characterize it, subjectively, is an overall softening, sort of a soft-focus effect, as if someone had smeared Vaseline or a fingerprint over a lens. The sound is not unpleasant, but very sweet (euphonically colored perhaps, but who cares?) and forgiving. Pair a B&K ST-140 with a tube preamp like the Magus or the Lazarus, and you can almost believe you're listening to tubes all the way through.
I suppose John Beyer might be able to get this amp to sound a little more detailed, but I wouldn't want him to lose the sweetness as he strives for transparency; the ST-140 is quite nice as it is, thank you. And it seems to work best with speakers that sound their worst when driven by many of today's solid-state designs. (I'm thinking of speakers like the Quad ESL-63s and the Spendor SP-1s.)
Where the Sumo Polaris loses out to the B&K is in that elusive area of sweetness of particular interest to classical music lovers, especially chamber-music aficionados. Violins, in particular, are just wonderful with the B&K. With piano music, on the other hand, I think I might prefer the extra crispness and cleanness of the Polaris. Both amps have an almost tubelike way of dealing with harmonics. With both, a tenor sax sounds almost like a tenor sax.
Soundstaging? I'd rank the amps about equally good. Bass response? Ditto—a draw. (The B&K ST-140 is improved in this respect, compared with earlier versions.)
Which amplifier would I prefer? That's a little like asking whether I prefer the old Carnegie Hall (the B&K, sort of soft and sweet) to the new, renovated version (crisper, brighter). I haven't quite made up my mind. But when I add price into the balance—the B&K costs 25% less than the Sumo—my first recommendation has to be the B&K.—Sam Tellig