Manley Labs 440 monoblock power amplifier Page 2

Output tubes are 10 "Russian uprated 6550s" per side, with no further details of their origin to be found in the manual. "We strongly emphasize that only the Russian 6550s should be used in this amplifier...they have been thoroughly optimized around this tube. Use of unapproved tube types can and will void your warranty." You've been warmed...(tube joke). I reviewed with the tubes supplied, with nary a thought of replacing them. Really.

The input of each 440 consists of a single 12AT7 dual-triode, with the driver stage made up of a pair of 6414s (an American military version of the 12BH7A—more current drive). "Replacement tubes of premium quality are always available from Manley Labs." I could almost hear David Manley clear his throat as he added that little tidbit in the manual. Ten-four, Dave.

"We run high voltages on the plates of the output tubes and are thus able to run them at lower current, which will result in longer life for the output tubes." In Tetrode mode, the amps "produce well over 440 watts," per the simply turned-out manual. (I confess, I was curious to know how that kind of tube power would sound on the Avalon Ascents.) In Triode mode the 440s "will produce half the power of Tetrode operation, but as fans of triodes know, nothing can match that sweet, seductive sound of triodes!" Well, it's his manual...

Now, David...correct me if I'm wrong, but half of 440 is 220, right? Are my sums wrong, or is this simply poetic license? Actual figures expressed in the specs call for 540W (at 1.5% THD, 5 ohm load) in Tetrode, and 168W (at 1.5% THD, 5 ohms) in Triode. Power consumption is quoted at 1329W, full power (at an atypical 1.5% again), while pulling only 30W in quiescent mode. My electric bill thanks you, Mr. Manley. While I'm spewing the numbers, let me mention that the input impedance is 100k ohms, and the load impedance is factory-set for 5 ohms.

The manual suggests Tetrode mode for demanding, energetic music; large rooms; or power-hungry, inefficient speakers. It goes on to say that most listeners should be satisfied with Triode mode. The only caveat: get those amps in Standby or turn them off before you snap that toggle!

Given their enormous differences, choosing between Triode and Tetrode not only proved a device for matching speakers and rooms, but was effective in matching the sonic characteristics of the front-end or the recording itself.

David Manley: "I don't compare these amps to pure triode; that's not the intention. Pure triode amplifiers just don't have the power we're seeking in this model. But pure triode should only be used when there's plenty of speaker sensitivity available. And you know, contrary to popular belief, triodes have inherently higher distortion—it's right there in the tube manuals. Triode only sounds better when it has the headroom comparable to what you have using pentodes (or tetrodes, as it's correct to say with these amps). I can't understand why people demand 10–20dB headroom in a preamp, yet are totally content to run an amplifier right up to its nostrils in the water, so to speak, functioning at 99% all the time, with no headroom at all." But how do you really feel, David? (I should talk...) Of course, EveAnna Manley says the 440s sound best...in Triode.

Manual: "We emphasize big, beefy reservoir capacitors in the high-voltage supplies, giving plenty of instant energy for dynamic performance of transient peaks and bass performance which often exceeds that of rival solid-state amplifiers." I see...

Surprisingly, no specs are given in the manual for total capacitance. Peering at two large blue caps inside the amps, I spied the following legend: "Kenetech/Windpower, 3300µF 450VDC, made in the USA." David's obviously never peered into a Symphonic Line Kraft 400.

I'm Elsa Klench, and today on CNN's style we'll be looking at the new bias cut from Chino, California that's taking the fashion world by storm!

There's an (old-fashioned, what else?) rotary switch near the top of the front panel for selecting each of the 10 output tubes for re-biasing—recommended every two to three months. Just slide a pair of probes from your digital Voltmeter into the color-coded sockets above the switch, choose the tube, and fiddle with the appropriate screw behind the bias-adjust cover plate. The amps must be warmed up, with no input for about half an hour before you start, but leave the speakers connected! Each bias trim pot should be adjusted to measure 275mV to 300mV. As you're measuring across a 10 ohm cathode resistor, by Ohm's Law that'll correspond to 27–30mA current draw for each tube. If you're unable to bring the bias voltage down to at least 300mV, you're advised to keep an eye on the offending tube, or replace it.

I'm fine with this scheme; I think "hands-on" promotes involvement and appreciation of the equipment. Mains fuses are a 10A Slo-Blo for 100–120V, with a 11/2A (250V) Slo-Blo for the B+ voltage rail. Mains-in is standard IEC. I powered the amps, and indeed the entire system, with Michael Griffin's superb The Essence power cords (Essential Sound Products, (810) 375-5093).

Discovery
After swapping cables and interconnects, we settled on the bright red, also–made-in-the-US Discovery Signature—Tel: (908) 359-0950, fax (908) 359-2170—sporting those terrific German Clearaudio connectors. Their RCAs are milled from a solid chunk of beryllium copper, then directly gold-plated. Upon soldering to the cable, they're filled with a potting material. The male pin is a spring affair that resolves the problem of differing-diameter female receptacles, and even the ground crown is made with three springs for superior contact. This very special connector has a specified capacitance of just one picofarad.

The cables themselves are uncoated, oxygen-free, multi-strand copper (all of the same gauge) in a reverse lay that cancels out EMI and RFI. The cables are twisted together under both a foil shield (Mylar with a metallic coating) and a braided shield with PVC jacketing, and tied to ground at the source end. Joe DePhillips told me they've used this dual-shielding technique since the beginning; a braided shield would permit EMI and RFI to enter when the cable is bent, as it almost always is.

Specified capacitance is a mere 15pF/foot, so long runs are easily managed. The cost is $450/meter terminated, and $140 each additional meter; and you can have the cables with either the Clearaudio RCAs—did I say how superb these are—or Neutrik gold-pin XLRs at the same price. It's a balanced design to begin with, so there's no additional cost to having them either way. Discovery will reterminate your cables for just the cost of the connectors—now that's what I call reasonable!

Company Info
Manley Labs
13880 Magnolia Ave.
Chino, CA 91710
(909) 627-4256
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