Keywords: Fu-50, amplifier circuit diagram
Author: Liu Rui
Be
Recently, the data is found, and the triode approach of the Fu-50-five-pole electron tube is found. Its characteristic curve is similar to 300B, but its output power is about 7W, if used in parallel with the two tubes, it can reach 14W, for 30m2 room is complete enough Use only 1/5 of 300B (including the tube).
The line is as shown in the figure, and 4 tubes per channel. The advantages of the triode approach at all levels, the advantage of the triode connection is that the signal distortion characteristics are basically even harmonic distortion, and the sound is gentle, sweet, very resistant to listening .
The pre-stage voltage amplification is held by 6N11, which is connected to the SRPP circuit, and the magnification is about 29.
Be
The promotion grade is served as the power tube EL-34, which is connected to the triode to do voltage amplification. The tube screen pressure is about 250V, the screen stream is 20mA, the gate negative pressure -20v, the gain is about 7.5. The output voltage amplitude is 20Vx7.5 = 150V.
The output stage is formed by the FU-50 tubes of the two triode connections.
Be
Working in a status. The two tubes are connected in parallel with only 1.25kΩ, which can reduce nonlinear distortion and improve the playback system damping. Strengthen the control of the speaker. FU-50 screen pressure 480V, screen stream 80mA. Grid negative pressure -65V, self-suction, load impedance 2.25kΩ, two tubes, 12W, total output power 14W. A 1kΩ resistor in the gate circuit string to prevent self-excitation.
The promotion level is negatively fed by the RC network to broaden the passband and improve the transient response of the whole machine.
The high-voltage DC circuit is made from diode rectification, and the entire CLC filter is supplied with DC high pressure. With two delay circuits, the delay time is 60 seconds and 70 to 80 seconds, respectively. After booting for 60 seconds, DC high pressure is limited to each filter capacitor, and after 70 ~ 80 seconds, the high voltage circuit is working properly. The high pressure has reached the "soft start" purpose to prevent high voltage impact (power supply circuit slightly).
The windings of each filament are double-wire and in the middle, and this method can significantly reduce communication.
The two channels are made of φ2mm silver-plated copper wire, and they have looped. The grounding wire is as follows: Input Interface - Volume Potentiometer - Pre-Level - Push - Power Level - Load. Finally, with the filter capacitor is approaching the chassis.
Each transformer must add a shield, especially similar to the output transformer similar to the power transformer, which is significant for improving the whole machine signal-to-noise ratio. .
The self-made data of the audio output device is as follows: The core is 40mm wide with high quality silicon steel sheet, and the thickness is 50 mm. The primary winding is 3500 with φ0.31mm high quality enameled wire.
The secondary is φ0.96mm enameled wire around 39 (4Ω) or 323 匝 (8Ω), and the primary is divided into four layers and secondary divided into three layers. Iron hearts, EI middle pad 0.2mm thick sheet of paper.
Our other product:
