Yaqin MS-300C is single-ended tube amplifier working with 2 power tubes 300B (legendary triode directly heated) and tubes: 6SN7 x 2 with 12AT7 x 2. In this system, instead of a silicon diode rectifier uses double diode - tube 274B. This model is equipped with a manual adjustment bias power tubes.
Tubes are protected by High DC voltage delay - about 40s.
The power supply of this amplifier uses a separate power supply transformers, chokes and filters for each grade enable them to complete isolation. Capacitors used are high-capacity for power supply pulsation filtering.
Headphone output, 4 switches of input selector and volume potentiometer are on the front panel. Volume control is possible also with infrared remote. 4 RCA input are on rear panel. There are also power output for 4 and 8 Ohm speakers.
The design uses the transformers from STALLOY company, high-quality metal film resistors, selected electrolytic capacitors.
Amplifire is placed in a rugged aluminium housing. Protective cage at the power tubes is constructed of aluminum.
Remote controller for volme control and input selector is also in alu enclosure.
Amplifier as for a small power plays rather dynamic, with a good deep bass. Quickly resolution can be observed, especially in the midrange and treble. The details are not lost under the onslaught of other sounds. The mids are strong with very good separation of voices, detailed and clear. The nature of the treble is delicate with a lot of detail. Bass can play low and softly but is not spectacular. Microdynamics of the amplifier is quite high. In the whole band you can distinctly hear all the little impact, puffs, jerking.
It’s very important to maintain the stability and accuracy of the operating points of the tube amplifier, especially of the power tubes. When the tube get ageing, or replacing the tube, the screen current changes, break away of the required operating points will influence sound resolution and the stability of the device. So, please check and adjust the screen current after a long time of use, and it is the same when replace the tube.
METHODS of MEASUREMENT of the TUBE SCREEN CURRENT:
Use a multimeter to measure. Adjust the multimeter to volts d.c. 1V range, and the volume of the amplifier the minimum, then insert the anode of the multimeter pen into the positive hole, and the cathode into the negative hole respectively. The screen current is about 0.8V when the standard input voltage is 230V or 115V.