![]() ![]() On the anode side of the tube I found a rail voltage of about 388V DC-neither the highest nor the lowest one sees in contemporary 300B amps. Filament voltage for each directly heated 300B is rectified, and appears to be just a shade over 5V. (The Cayin's packing materials are good enough that the amp can be shipped with every tube in place.) There's also a heater-balance pot for each output tube, so the user can adjust the outputs for minimal hum as the tubes age. My review sample of the A-300B arrived perfectly well adjusted for the Chinese output tubes supplied, and has required little in the way of further attention. The output tubes are run in fixed-bias mode, and each channel has its own easily accessed bias trim pot (a decent-quality digital voltmeter is required). The full waveform then goes to the grid of a 300B output triode-biased, of course, for pure class-A operation. The final plate of that tube drives the grid of a 6SN7 dual triode, configured as a cathode follower for low impedance. The Cayin's amplification design is similarly straightforward: The high-level input signal is directed to a 100k ohm volume potentiometer, from whence it's capacitively coupled to the grid of a 6SL7 dual-triode cascade, for pure voltage gain. Each channel has its own 5AR4 tube for B+ rectification, while lower voltages (for tube filaments and logic circuits-a lovely if odd juxtaposition) are uncurled with solid-state rectifier blocks. I'm also struck by the size and quality of the electrolytic capacitors chosen to smooth the AC: They share a pi filter of the usual sort with a hefty, frame-style choke. The A-300B's power supply holds no surprises, although I am impressed that, forward of the AC transformer (a toroid), it's an entirely dual-mono design. Inside my review sample were no rough metal edges, no questionable solder joints, and not so much as a speck of dust. The wiring is neat, the soldering is saintly, and the parts are nice enough, with a sprinkling of such names as Multicap, Nichicon, and Alps. Remote-control circuitry, a phalanx of relays for input selection, and other bits and pieces account for the circuit board, while the wiring is well represented-and remarkably well executed-throughout most of the audio and power-supply circuitry. Inside the A-300B is a mix of circuit boards and point-to-point wiring, each doing the job it ought to be doing. An alloy remote control is also a part of the scenery. The package in question is a lushly chromed chassis with a terraced aluminum alloy faceplate, sculpted housings for the mains and output transformers, and a thickly enameled protective cage that fits so beautifully, you'd think someone actually cares whether or not you like it. ![]() ![]() Ten or more years ago, you might have been able to find a 300B integrated amp this well built, and you might have been able to find a 300B amp this affordable-but you certainly wouldn't have found both in the same package. That power, of course, is the People's Republic of China-from which I'm happy to see new single-ended products regularly emerge.Ĭonsider the Cayin A-300B integrated amp, made by Spark (aka Zhuhai Spark) of Guangdon Province. The genre has also had a lucky break: the SET revival was followed closely by the emergence of a new manufacturing power, one with both a flair for tube electronics and the geopolitical wherewithal to keep consumer prices low. There will always be manufacturers who want to build SETs, just as there will always be people who want to perform Shakespeare or distill absinthe. ![]() And while no amp of such questionable relevance to the average loudspeaker will ever be considered the norm, so is it true that the SET's charms have earned it a permanent seat at the table. Epstein."-Dick Rowe, Decca Records, 1962īy now, even the shortest-sighted cynic has to admit that the single-ended-triode (SET) amplifier, which reappeared on the domestic audio scene over a decade ago, represents more than just a passing fad. ![]()
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