Yaqin MC-100B tube amplifier

Grzegorz 'gsmok' Makarewicz (January 8, 2018)

The Yaqin MC-100B is a stereo tube amplifier made in China. Its original name, a registered trademark, contains several strange symbols and cannot be written in the traditional alphabet. Willingly or unwillingly, I am forced to use the name Yaqin in this review. This approach is justified, as even in the user manual, the "worm" designation appears on the cover, but inside the manual, we find the symbol Yaqin MC-100B. The amplifier isn't exactly a refined aesthetic. The distinctive cage covering the tubes reminds me of a bread bin, and I'd prefer to see this amplifier with the cover permanently removed and hidden away somewhere inaccessible.

Yaqin Audio originated from a small family-owned factory, or more precisely, a husband-and-wife (Mr. Liang, the designer, and his wife), located in southern China. By the way, does anyone know of any factories outside of southern China? Within a few years, this "miniature business" has grown into a brand recognized in many countries (including Poland). Yaqin produces amplifiers not only under its own trademark, but also audio equipment commissioned by other "manufacturers," who then sell them as their own products. Yaqin amplifiers offer a good price-performance ratio. You can own a decent tube amplifier without breaking the bank.

Basic parameters of the amplifier

According to the manufacturer's declaration included in the user manual, the Yaqin MC-100B amplifier is characterized by the following parameters:

• Output power:
• 2 x 30W / 8Ω in triode mode (TR),
• 2 x 60W / 8Ω in ultralinear mode (UL).
• Load resistance: 4Ω / 8Ω.
• Input sensitivity:
• 250mV for CD/DVD/Tape/Tuner inputs located on the rear panel,
• 600mV for inputs located on the front panel.
• Harmonic distortion: < 1.5%.
• Frequency response: 5Hz ... 80kHz (-2dB).
• Signal to noise ratio: 90dB (A-weighted).
• Power consumption: 280W.
• AC fuse: 6A (F6A250V).
• Weight: 23kg.
• Electron tubes used:
• KT88-98 x 4 (output stage),
• 6N8P x 4 (driver stages),
• 12AX7B x 2 (voltage gain stages).

A general view of the amplifier is shown in Fig. 1. The four transformer protection boxes suggest that this is a design that houses not only two amplification channels but also two independent power supplies within a single enclosure. This is therefore known as a "dual mono" arrangement.

Fig. 1.

The next two shots show the amplifier fitted with a tube cover. Some of the horizontal rods are a bit loose, allowing you to play them by snapping your fingers.

Fig. 2.

The front panel of the amplifier is not standard, because in addition to the volume control potentiometer and the input selector, it contains two additional inputs and switch that activates:

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

Note: The manufacturer recommends turning the amplifier off when changing the input group switch.

From the side, you can see that the amplifier's base, or chassis, has a large surface area yet is relatively low. Considering the amplifier's considerable weight (23 kg), I began to wonder how such a delicate base could maintain its rigidity and not bend when carrying the amplifier. After all, it's only bent on the sides, and there's only a simple cover on the bottom. The mystery was solved during disassembly. But more on that later.

Fig. 3.

And here's what the amplifier looks like after removing the "bread box lid"—sorry, after removing the tube cover. Doesn't it just get even more beautiful?

Fig. 4.

From above, you can see even more clearly how the amplifier looks without the cover.

Fig. 5.

In Fig. 6, two switches are visible between the output transformers. These switches are designed to change the output tubes' operating mode from triode (TR) to ultralinear (UL). The manufacturer notes that before changing the operating mode, the amplifier should be turned off and both channels should be operating in the same mode. Two critical comments come to mind at this point:

1. If both channels should always work in the same mode (which is perfectly logical and I find it hard to imagine the point of setting one channel in triode mode and the other in ultralinear mode), then why are two independent switches used?
2. Why are the switches placed in such an inaccessible and dangerous place? Even after turning off the amplifier, reaching for them too quickly can result in burning your hand on the output tubes.

Between the output tubes and the output transformers, you'll find four pairs of measuring sockets, which, in conjunction with four potentiometers accessible through holes near the output tubes, allow for adjustment of the output tube current. This is a rare feature in modern tube amplifiers. Typically, the so-called "bias adjustment" requires removing the bottom cover and turning the amplifier upside down (the amplifier has been sold, so let the user worry about adjusting it without suffering a hernia). The Yaqin is a notable exception, comparable to good old classics like the Radford or Ranaissance. A truly significant advantage.

Fig. 6.

Time to reveal the secret behind the metal base's rigidity. We see two additional rubber feet and an impressive set of screws.

Fig. 7.

These screws, 32 in total, are no mere design invention. Along with the two additional feet, they play a crucial role in stiffening the base. Once tightened, the bottom cover acts as if it were literally welded to the chassis.

Fig. 8.

Before looking inside the amplifier, it's worth taking a look at its schematic diagram. A more readable version can be obtained by clicking on Fig. 9. It's worth comparing the elements of the schematic diagram with the actual components shown in the photographs.

Fig. 9.

And now it's time to take a look inside. Be careful not to lift the amplifier carelessly in its current state. Unscrewing the bottom cover causes the base to become "rubbery" and begin to bend in various directions.

Fig. 10.

A top-down view of the entire interior. It feels solid and organized.

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Below are photos of the interior, arranged in such a way that they show the assembly details in greater and greater detail.

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And that's all (for now).

Written by: Grzegorz "gsmok" Makarewicz