 The Reisong A10 vacuum tube amplifier is a stereo class-A ultra lineair audio amplifier. The amplifier looks like the Boyuu A9 amplifier. The schematics are also very similar. The main difference is that the A9 amplifier is a do it yourself kit amplifier and the A10 amplifier is a factory made amplifier. So the A10 amplifier is a plug and play device. This amplifier is an affordable amplifier that is a good start for tube amplifier enthusiasts. Although is it's a plug and play amplifier, the amplifier is also great for modifying to your personal 'taste'. Remind that the amplifier contains lethal voltages and can kill you. So don't start tinkering with the amplifier unless you're very sure about what you're doing!
specifications
 Maximum output power: 12 Watts per channel
Frequency response: 20...28.000 Hz
Output impedance: 4 or 8 Ohms
Total harmonic distortion: ? 1 % @ 1 kHz
Signal to noise ratio (SNR): 88 dB
Preamplifier tube: 2x 6N2J (one per channel)
Power output tube: 2x EL34 (one per channel)
Rectifier tube: 1x 5Z4PJ
Input sensitivity: 750 mV
Input impedance: 100 K?
Dimensions (W × D × H): 310 × 268 × 165 mm
Power Supply Voltage: 100...240VAC (depending on the model) / 50Hz...60Hz
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The design is rather straight forward. There's a transformer power supply for feeding both amplifiers (left and right channel). The power supply is equipped with a large inductor instead of a resistor. The inductor is a positive quality choice in the design. Each channel amplifier has a Chinese 6N2J double triode preamplifier tube. Per channel are both triode sections linked parallel. The preamp design is rather straight forward. The output section is designed with an EL34 power output tube. The output tube is 'cathode biassed' by using a resistor between the cathode and the common ground. The output amplifier is a class-A design. This means that the output tube is always 'on' and loaded halfway. The result is that the output quality is good since there's no crossover distortion (what can occur at a more powerfull push-pull configuration) but the efficiency is lower compared to a push-pull final stage. The overal power consumption is therefore also constant and is not affected by the set audio level.
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There's a 5Z4PJ tube used for rectification. This tube makes that the amplifier is 'all tube' that is appreciated by audiophiles. The downside is that the voltage drop is significant that results in less audio output power. The voltage drop lowered the supply voltage to the final tubes. The result is that the produces audio level is lower. It's also possible to replace the 5Z4PJ rectifier tube by two 1N4007 general purpose diodes. The result is that the power loss for filament heating is gone and the supply voltage is much higher that results in more audio output. This difference can clearly be heard.
As shown on the image there are already two diodes installed. This is a 'trick' to obtain a 'ground' then there's no center tap on the power supply transformer. Usually there are two high voltage windings on the power transformer there the center tap is connected to the ground and the two other winding ends are connected to the tube rectifier. But since a power transformer with a double windings is more expensive, a single winding with two additional semiconductor diodes can be used to obtain a artificial ground. The result is rather similar, but technically the amplifier is not 'all tube' to begin with.
I always replaced the tube rectifier with two semiconductor 1N4007 diodes since the load on the power transformer is less since there's no rectifier tube filament to power, the audio output level is much higher and I don't hear the difference between a rectifier tube and semiconductor rectifiers. But that's also a matter of 'taste'.
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