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Yamaha B-5

Yamaha B-5

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The B-5 was released in 1979 as a successor to the B-3, the last of Yamaha’s SIT amplifiers, and it was developed with the goal of surpassing the charming sound quality of the SIT without using SITs. In order to accomplish this, it was necessary to use the advanced circuit design of the Linear Transfer Circuit to cover the conventional bipolar transistors’ weakness with respect to crossover distortion compared to the SIT. The principle of the Linear Transfer Circuit was that three groups of power transistors in a triple push-pull had staggered operating points with different bias current settings, and their combination was nearly a second-power characteristic, so that the linearity and distortion specifications at low signal levels, which tended to be poor with high-power amplifiers, were improved. The output devices were Yamaha-developed original 2SC2707/2SA1147 high-transition-frequency (broadband, high-speed) transistors with copper cases and copper screws to reduce current distortion, which achieved 240W + 240W (8 ohms, 20Hz — 20kHz, 0.005% THD) high power and low distortion, at levels that had not been attained with the SIT. Of course, the B-3 BTL (bridge-tied load) switch was eliminated. The huge power supply section used a giant toroidal transformer filling a full one-fourth of the volume of the chassis, professional-audio low-multiplier block aluminum electrolytic capacitors with the world’s first non-magnetic polypropylene case, and the heat sinks on both sides were an integral part of the structure enabling a streamlined chassis-less design, keeping the size down to 435×361.5×182.7mm, which was that of a typical economy-priced A/V amplifier, and the weight down to 20.9kg. The upper half of the front panel and the top panel were formed from a single sheet of perforated metal, allowing the interior to be seen, and although the technology was that of the most modern high-power amplifier, the appearance was that of a vacuum-tube amplifier.

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