Yamamoto Sound Craft A-03S KT88/6550 Directly connected single stereo power amplifier

The A-03S is a single stereo power amplifier that uses the KT88/6550, the most popular and easiest to obtain, as its output stage.
The KT-88 and 6550 are designed with the aim of achieving 100% performance and sound as a single, full-fledged amplifier with a large vacuum tube with almost the same rating.
Standard includedoutput tubeis Tungsol6550.

In A-03Soutput tubeBy separating the plate circuit and screen grid circuit, we obtain a high output of 12W/12W.
The circuit configuration uses a direct connection system, which is well-known for its good sound and circuit stability. A direct-heat type pentaode tube is used for the first stage,output tubeBy directly connecting with the sound, it produces a sound full of responsive and dynamic. The first stage 1D5G uses a constant current ignition system, and by converting the constant current, including the cathode bias resistance,output tubestabilizes the bias voltage of output tubeThe current stabilization has been greatly improved. This unit allows you to easily replace various KT-88s and 6550s from around the world, compare and listen to them, and enjoy.output tubeIt comes with an ammeter that allows you to check the current.
The A-03S power supply unit uses a power transformer, a cut core transformer that uses an orient core for the choke coil and output transformer, and the output transformer uses Teflon insulating paper with excellent electrical characteristics, achieving excellent high sound quality.
Furthermore, most parts of the power supply filter capacitors are polypropylene film capacitors with excellent transient characteristics and distortion rate, exploring sound with excellent transparency. The charge/discharge time is significantly better than that of a typical chemical capacitor, and the distortion rate of the capacitor itself is incomparable. Even if it is a capacitor in the power supply, the sound quality is reflected in the reproduction sound as it is. The use of this film capacitor is a major contributor to the fact that this machine is clear and has excellent characteristics.
The rectifier tube in the output stage is 5U4G, and in order to efficiently supply the large current of the KT-88/6550, the two are luxuriously connected in parallel.

The other parts also use many of the finest parts. It has no cornering designs, including Dale's non-induction winding resistance, a pure copper-made speaker terminal, a 3P power input terminal, a luxurious champagne gold chassis and transformer cover. The robust wooden frame made of cherry wood and the total non-magnetic structure made of aluminum expels magnetic distortion.
The high current and high-voltage parts are used to prevent current from flowing to the board as much as possible, and by using an extremely thick glass epoxy substrate of 2.0mm thick, the board has a satisfactory sound quality.