Tube Amplifier Yaqin MC-100B

Grzegorz "gsmok" Makarewicz, This email address is being protected from spambots. You need JavaScript enabled to view it.

Yaqin MC-100B is a Chinese stereo tube amplifier. It's original name, which is a registered trademark, has some strange symbols and you can not write it using "traditional" alphabet. Willy-nilly, in this relation I am forced to use the Yaquin name. This approach is justified because even in the manual, strange symbol appears on the cover, but in the inside you can find the name Yaqin MC-100B. The amplifier does not has sophisticated look. The distinctive frame constituting the tubes cover reminds me of a container for storing bread  and willingly I would use this amp with a frame permanently dismantled and hidden in some inaccessible place.

The basic parameters of the amplifier

According to the declaration contained in the manufacturer's manual, amplifier Yaqin MC-100B has the following parameters:

  • Maximum output power:
    • 2 x 30W / 8Ω - triode mode (TR),
    • 2 x 60W / 8Ω - ultralinear mode (UL).
  • Output impedance: 4Ω / 8Ω.
  • Input sensitivity:
    • 250mV in integrated mode CD/DVD/Tape/Tuner,
    • 600mV in pure post-stage mode (front input connectors).
  • Harmonic distortions: < 1.5%.
  • Frequency response: 5Hz ... 80kHz (-2dB).
  • Signal to noise radio: 90dB (A - weighted).
  • Power consumption: 280W.
  • AC fuse: 6A (F6A250V).
  • Net weight: 23kg.
  • Tubes:
    • KT88-98 x 4 (output stage),
    • 6N8P x 4 (drivers and cathode followers),
    • 12AX7B x 2 (voltage amplifiers).

General View of the amplifier is shown in Fig. 1. Four cans to protect transformers suggest that this is a design in which in one case not only two reinforcing channels are contained, but also two separate power supplies . So it is a system called the "dual mono".

Fig. 1.

The next two shots show the amplifier equipped with protecting cover. Some of the horizontal rods are a bit loose and you could "play" them snapping your fingers .

Fig. 2.

Front panel is not standard, because in addition to the volume potentiometer and input signal selector, the middle section contains an additional two inputs and the switch activating:

  • inputs located on the front panel (sensitivity: 600mV),
  • the set of inputs located on the rear panel (sensitivity: 250mV).

Note: The manufacturer recommends that you switch off the amplifier when you change the position of the inputs group switch.

From the side it can be seen that the chassis of the amplifier has a large upper surface with a small height. Given the considerable weight of the amplifier (23 kg), I started to wonder how this delicate base is able to maintain rigidity and does not bend when moving the amplifier . The mystery was explained during disassembly. But more on that a bit later.

Fig. 3.

This is how the amplifier looks after removing the flap of the  bread container- the excuse - after removing the protecting cover. Doesn't become beautiful? Evidently .

Fig. 4.

From the top, you can see even more, like an amplifier gains it's look when the cover is removed.

Fig. 5.

In Fig. 6 there are two switches between the output transformers. They are designed to change the operating mode of the amplifier - between triode (TR) on ultralinear (UL) mode. The manufacturer notes that before changing the operating mode, the amplifier has to be turned off and both channels should work in the same mode. Two critical remarks come to my mind at this point :

  1. If both channels should always work in the same way (as indeed is the most logical and it is hard for me to imagine the meaning of the settings of one channel in triode mode and a second in ultralinear mode) why to use two independent switches .
  2. Why switches are located in such inaccessible and "dangerous" (in view of hot output tubes) place?

Between the output tubes and output transformers, you can see four pairs of test sockets, which, in conjunction with four potentiometers accessible through the holes located near the output tubes allow adjustment of the tubes current (biasing). It is rarely seen in today's tube amplifiers. A bias adjustment usually requires removing bottom cover and reverse an amplifier bottom up. Yaqin is a notable exception. It reminds me old good classics like Radford or Ranaissance. Really big plus .

Fig. 6.

Time to reveal the mystery of rigidity of the chassis. You can see two additional rubber feet and an impressive set of screws .

Fig. 7.

These screws, and there are a total of 32 of them , are very important. They serve, in addition to two extra legs, an important role in stiffening the base. After tightening, the lower shield behaves as if it were literally welded to the chassis.

Fig. 8.

Before you look inside the amplifier is worth looking at the schematic diagram. More readable version can be obtained by clicking the mouse on Fig. 9. It is worth to confront elements from the schematic with the elements in the photographs.

Fig. 9.

And it's time to peek inside. I have to warn against careless lifting of the amplifier in that form. Unscrewing the lower cover makes the chassis behaves like a "rubber" and begins to bend in different directions .

Fig. 10.

Top view of the entire interior. It gives the impression of solidity and reliability.

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Below there are photographs of the interior arranged in such a way that they show more and more detailed views.

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And that's it folks  (as yet).

Written by Grzegorz "gsmok" Makarewicz,