Yamamoto Sound Craft A-03S KT88/6550 Direct Connected Single Stereo Power Amplifier

The A-03S is a single-stereo power amplifier that uses the KT88/6550, the most popular and easily available 5-pole vacuum tube, as the output stage.
The KT-88 and 6550 are large vacuum tubes with almost the same rating, and the A-03S is designed with the goal of delivering 100% performance and sound as a full-fledged amplifier in a single amplifier.
The standard output tube is Tungsol 6550.

In the A-03S, a high output of 12W/12W is obtained by separating the plate circuit and the screen grid circuit of the output tube.
The circuit configuration uses a direct connection method that has a reputation for good sound and circuit stability. A direct-heat type pentuode tube is used for the first stage, and by directly connecting to the output tube, a responsive and dynamic sound is obtained. The first stage, 1D5G, uses a constant current ignition system, and the bias voltage of the output tube is stabilized by a constant current including the cathode bias resistor, which greatly improves the stabilization of the output tube. This unit comes with an ammeter that allows you to check the current of the output tube so that you can easily replace various KT-88 and 6550 around the world and enjoy comparison auditions.
The A-03S uses a power transformer for the power supply, a cut-core transformer with an orient core for the choke coil and output transformer, and a Teflon insulating paper with excellent electrical characteristics for the output transformer, which has succeeded in achieving excellent sound quality.
In addition, most of the filter capacitors in the power supply are polypropylene film capacitors with excellent transient characteristics and distortion rates in pursuit of sound with excellent transparency. The charge/discharge time is significantly superior to that of general chemical capacitors, and the distortion rate of the capacitor itself is incomparably superior. Even if it is a capacitor in the power supply part, the sound quality will appear as a reproduced sound as it is. The use of this film capacitor contributes greatly to the clear and excellent characteristics of this machine.
The rectifier tube of the output stage uses 5U4G, and two pipes are luxuriously connected in parallel to efficiently supply the large current of the KT-88/6550.

The rest of the body is also made of many of the finest components. Dale's non-inductive winding resistors, machined speaker terminals, 3P power input terminals, and a luxurious champagne gold chassis and transformer cover are all designed to keep you clean. Magnetic distortion is expelled by a strong wooden frame made of cherry wood and a total non-magnetic material structure made of aluminum.
In the parts with high current and high voltage, current is not passed through the substrate as much as possible, and an extra-thick glass epoxy substrate of 2.0 mm thick is used for the substrate to achieve a satisfactory configuration in terms of sound quality.