Sugon New Tube 2A3C Single-ended Tube Amplifier

Sugon New Tube 2A3C Single-ended Tube Amplifier

The Sugon new 2A3C is an improved version of the factory's 2A3. Its main features are that it adopts some features of the large single screen 300B, and its sound quality is also better than the traditional 2A3.

Through actual measurement and comparison, the data of 2A3C are: screen voltage 320V (including the voltage drop on RK during self-bias), screen current 45~65mA, screen power consumption about 20W, gate negative voltage 45-55V, maximum output 7W, effective output 5W. When the effective value of the screen-to-cathode voltage difference is 275V, the AC load impedance is 2.75kΩ. When the front-stage driver tube is outputting a large current, the gate-leakage resistance is not greater than 300kΩ.

The actual installation adopts the "simple first" two-stage amplification. A 6J4P is used to amplify and drive the input of one channel. The actual screen voltage (Ra lower end) of 6J4P is 130V, and the screen current is 5.5mA, which can obtain a driving power of no less than 0.15W.

It should be noted that this circuit is an "underdamped" design, with an AC effective amplitude of 26V, which is much smaller than the standard input value given by 2A3C, so the front stage must have a certain driving power. If a high μ low current tube is used, it is necessary to increase the AC amplitude or the screen voltage as much as possible to ensure good load characteristics.

Considering the distortion characteristics and noise of the pentode, Ra and RK of the first stage amplifier should be carefully selected. When the voltage drop on RK is about 1.5V, RK should be as small as possible. Ra should not be too large, otherwise the high frequency will deteriorate and the sound quality will also be affected.

The power supply uses the traditional "tube + π type" filter. The capacitor at the front end of the choke is closely related to the "color" tone. The decoupling capacitors of the two channels of the 6J4P have the greatest impact on the sound of the whole machine and are the two key points of the whole machine calibration. Using high-quality oil-immersed electrolytic capacitors is a good way to take both into account.