Highly efficient amplifier realized in the form which had wonderful sound quality and big output power!

KT88/6550 Direct coupled single stereo power amplifier



A-03S is the most popular and acquisition is also the power amplifier of the single stereo system which uses KT88/6550 which is an easy pentode vacuum tube for the output stage.
Although KT-88 and 6550 were large-sized vacuum tubes with the almost same rating, there were many examples of use in a push pull, and the full-scale amplifier in single amplifier was a small number.
At our company, this A-03S was planned for the purpose of demonstrating this KT88, the performance which 6550 has, and sound 100%. Generally it is popular to a sound delicate [ the single amplifier of a triode tube ], and clear. However, it is difficult to obtain a big output. The vacuum tube of big power is expensive.
Both KT-88 and 6550 are very popular, it is manufactured in every country in the world even now, and the frame in which conservativeness and a maintenance cost were also considerably restricted very much with budget prices is of use also for the cost.
It has succeeded in holding down the cost of a vacuum tube and holding down a maintenance cost low by constituting the vacuum tube adopted as this amplifier from a comparatively low-cost ball.
As an output tube, product made from Tungsol 6550 vacuum tubes currently reproduced are adopted by audition. Moreover, common triode tube amplifier needs the high voltage, in order to obtain big power. therefore, a part high the resisting pressure thing needed to be selected and the cost rise, the defective fraction by the resisting pressure of parts, etc. had a problem. In A-03S, the high output of 12W/12W has been obtained by separating the plate circuit and screen grid circuit of an output tube. As circuit composition of A-03S, the direct connection system which has established reputation in the merit of the sound and the stability of a circuit is adopted. Generally it is a side heat type output tube. Although the sweetness of sound is pointed out, in this amplifier, the direct heating type pentode pipe was used for the first rank, and it has succeeded in obtaining the sound filled with a good feeling of a lively motion of the reaction by linking directly with an output tube.
Moreover, 1D5G adopted as the first rank adopts a constant current ignition system, and stabilizes the bias voltage of an output tube by constant-current-izing also including cathode bias resistance, Stabilization of the current of an output tube is raised sharply.
In addition, the moderate braking effort has been acquired, having applied PG return to the output tube. In this amplifier, since the ammeter which can check the current of an output tube is attached so that 6550 may be simply replaced with various KT-88 in the world, a comparison audition may be carried out and he can enjoy himself, you can use for convenience.
The power supply part of amplifier is a source of energy, and if this portion is neglected, a good sound will not come out. The cut core transformer of Orient core adoption was adopted as both the power transformer large-sized in the power supply part of A-03S, and a choke coil and an output transformer, and also it has succeeded in high-quality sound-ization which was excellent by winding around an output transformer using the insulating paper made from Teflon which was excellent in the electrical property. Furthermore, it is searching for the sound which adopted the polypropylene film capacitor which was distorted with the characteristic to the filter capacitor of the power supply at almost all portions, and was excellent in the rate, and was excellent in the transparent feeling.
a film capacitor is so excellent that a charge-and-discharge time is markedly alike, and is excellent compared with a common chemical capacitor and a capacitor's own rate of distortion is not compared, either. Also although it is called the capacitor of a power supply portion, the sound quality appears as a reproduction sound as it is.
this amplifier is clear and adoption of this film capacitor contributes greatly excelling in and the characteristic. Moreover, although 5U4G is adopted as the rectifier tube of the output stage, in order to supply the big current of KT-88/6550 efficiently, it is used, making Para connection of the 2 pcs. also sumptuously. Other portions are also using many highest-class parts for a part. They are Dale's unguided winding resistance, a speaker terminal of pure copper shave out, a power supply input terminal of 3P, a gorgeous champagne gold chassis, and specifications that do not extract a hand at all, such as a transformer cover. Moreover, having banished a magnetic distortion according to the total nonmagnetic material structure by the firm wooden frame and aluminum material made from cherry tree material cannot be overlooked, either. In A-03S, the substrate is adopted for reduction of cost, stabilization of performance, and a structure low price. Although there are the strong point and a fault about adoption of a substrate, in this amplifier, the portion with much current and the high-pressure portion are considered as composition satisfying also in sound quality by making it not send current through a substrate as much as possible, and also adopting the glass epoxy group board of the pole thickness of 2.0mm thickness also as a substrate.

A-03S Specifications
Form: KT-88 / 6550 single stereo power amplifier
Use vacuum tube: KT88 or 6550 2 pcs. 1D5GP 2 pcs. and 5U4G 2 pcs., A standard attached output tube is Tungsol6550.
Maximum output: 12Wx2
Frequency characteristic: 25 to 50 kHz
Input impedance: 200k ohms
Outside dimension: 460(W) x342(D) x190 (H)
Weight: 18kg
In addition, a design, specification, etc. may be changed without a preliminary announcement.