Cary CAD-1610-SE monoblock power amplifier
The aluminum faceplate of the lower chassis features a raised "eyebrow" above the retro-green eye-tube that reminds me of the AT&T building—er, the Sony building. The CAD-1610-SE's upper chassis is supported by two wide flanges per side, sunk deep into the power-supply chassis below. Peering more closely, one can just make out the huge, heavily shrouded output tube socketed into the lower chassis. The KR Enterprise T-1610 triode tube is mostly hidden by huge lumps of transformers and black-clad capacitors, and its bulbous tip protrudes only slightly through the second stage of the Cape Canaveral–like gantry, but this fire bottle is the very device the phrase "drop trou" was invented to describe! Holy moley, it is one BIG tube.
Fact is, I tried to get a pair of these amps for review a long time ago, observing through a glass darkly the initial we-got-'em/we-don't-got-'em, cha-cha-cha over the Western Electric version of the original 308-type transmitting tube the amp was built for. The 308 was finally successfully (and beautifully) manufactured, in the old Tesla works, by KR Enterprise of Prague. Talk about pedigree. The T-1610 output triode is known as the "Kronzilla." That makes me smile, but there's no doubt that it looks and sounds every bit the single-ended cannon shell on steroids that it is.
As Cary's ebullient Dennis Had describes it, after many visits to the KR factory and lots of feedback about the tube's design, consistent production of the Kronzilla finally began. Had claims that his amps began flying out of dealer's showrooms shortly thereafter. So I hadda wait for 'em—like many worthwhile things in life, no? [sigh] They say you can't have everything, but I'll bet a lot of aging Boomers (like me) think you can. At least I felt that way late at night, sitting in the Ribbon Chair with my best recordings on the player, bathed in the sound and light of this Prague-born Supertube.
Setup involved first herniating myself while positioning these 130-lb monsters on appropriate stands. Once the bare chassis were positioned, I carefully installed the T-1610 Ballistic Audio Missiles, along with the rest of the support tubes on the top platform. Standing front-and-center before the upper story of the T-1610 sits an unusual-looking 300B tube, the KR300BXL. It's made with a 6550-like glass envelope that eschews the classic shouldered 'B shape, and appears quite solidly built. The KR300BXL drives the T-1610 directly, and is flanked by pairs of squat 6SN7s and 6BL7s fanned out over the top chassis. (Their exact jobs are described in "Circuits Matter," below.) Like proud grenadiers on either side and to the rear of the T-1610's protruding dome, two 5R4s stand at attention and provide the all-tube rectification. The 5R4 is, in my view, the ugly duckling of the tube world: a glass artichoke stuffed into a gray plastic cup. Cary should offer high-roller customers with swanky girlfriends a choice of color-coordinated 5R4 cup covers—snaz it up a bit! [slap!] Thanks. I needed that.
The two elegant brushed-aluminum front panels are dominated by three Flintstone-scale control knobs. Lower left is the T-1610 output tube's Off/Operate knob. The gaily green and retro "cat's eye" output power indicator—the centerpiece of the lower front panel—lights up when the T-1610 does. Seeing it jumping around sometimes gave me a quick jab of nostalgia—it reminded me of the Telefunken Multiwave in my folks' room. [slap!] Thanks. I needed that. Again.
Last (but actually the first that should be powered on and the last to be powered off; one reads the Cary's front panel from right to left) is the brontosaurus-sized 300B Off/Operate knob. Two blue LEDs on the upper front panel over this knob indicate Ready (the 6BL7 is supplying a bias voltage to the T-1610) and DC (the 300B has high voltage). Two more blue LEDs on the top left indicate that AC and filament voltage have appeared.
The robustly proportioned knob at the center of the upper chassis is actually an input level attenuator. Wanna bi-amp? No sweat, you can get four of these monsters. All you'll need then is an environmental control system to evacuate the heat before your roof floats away. The CAD-1610-SE runs hot—it's more a winter than a summer amp, I can tell you—but four of them would be an impressive sight. Yet, as I pen my purple prose in early October, I'm the first to admit that their dense and warm gestalt is just what the doctor ordered. The CAD-1610-SE ain't exactly for roastin' marshmallows over, like the VTL Wotans with 48 cookin' 6550s, but between the glowing T-1610, its support tubes, and those Yuletide-toasty transformers, K-10 and I are cozy warm now, thanks!
Around back, the bias current to the T-1610 is indicated in milliamps on an old-fashioned ballistic meter centered on the back of the lower chassis. The output tubes were very stable; one channel required only a small tweak after about three months of hard use. (The manual recommends having a look every six months.) Clustered to the left of the bias meter are three fuses, for the line and the amp's upper and lower chassis. An IEC mains-in is placed below an AC Out, with a Neutrik Powercon Powerkord umbilical supplying the AC for the top floor. To the upper right of the meter is a screw for adjusting the eye-tube's intensity. Turn it up for parties, turn it down to prolong life—the tube's, that is. A single pair of heavy-duty WBT binding posts sits under a 4 ohm/8 ohm output tap switch, which I always left at 4 ohms (recommended for the JMlab Utopias). There's also a High Voltage Signal BNC connector for a wire to take the signal from the upper to the lower stage.
The upper-floor rear houses the Powercon AC In connector, a locking bias-control adjuster, a single-ended and balanced input connector with a selector switch, and another High Voltage Signal BNC connector.
The basic circuit design of the CAD-1610-SE is used in many of Cary Audio's pure class-A single-ended triode designs. And the new KR T-1610 low-mu audio power triode allows, it is said, for a very-low-distortion implementation of this basic topology. Output power is rated at more than 100W "peak envelope power," the steady-state continuous sinewave power at 55W RMS into loads of 8 or 4 ohms.
Each CAD-1610-SE amplifier has two separate high- and low-impedance bias supplies, so there's no need to worry if the lower amplifier section, carrying the T-1610, is mistakenly powered up without the bias voltage being supplied by the 300B. Dennis the Tube Menace: "The high-impedance bias supply automatically controls the T-1610's plate current. The actual operating bias is supplied from the driver section on the top chassis to the T-1610 output tube."
The "specially designed" output transformer is an air-gap design with full continual bias. Had considers the output transformer an amp's most important component. This one's wound with oxygen-free copper wire, with "portions" of the primary and secondary windings done in what's called a bi-filar process: two inductors interleaved; in this case, 26 times.
"The bi-filar wind," clarifies Had, "yields the closest balance and coupling of any design currently used in vacuum-tube output transformers. The EI Laminates are silicone-impregnated hypersil steel, which contributes to extremely low loss and a seductive midrange!" Man, he knows how to go around a curve! The design is similar, he proudly claims, to the single-ended air-gap transformers in all Cary single-ended output transformers.
Here's the audio circuit, for all you kitchen-table designers: The audio drive signal is applied to the control grid of an input 6SN7 dual-triode tube. The second 6SN7 operates in the first tube's anode circuit, supplying operating voltage and current. After the signal is amplified by the 6SN7, the output anode section is directly coupled to the grid of the 300B triode gain stage. According to Had, this type of direct coupling eliminates the need for a coupling capacitor and a bias supply on the 300B. Rather, the 300B's gain stage is supplied voltage on the anode by a high-inductance voltage choke.