Keywords: WE350C power amplifier circuit diagram
WE350B is very famous, 350C is the imitation of the famous West Electric WE350B antique beam shot tetles, allowing enthusiasts to meet the pursuit of high quality tubes.
The 350C screen dissipation power is 30W, the filament voltage, current is 6.3V / 1.6A, and the screen is extremely high voltage 400V. Similar to WE350B, 6L6, 6L6G, 6P3P, can be exchanged directly. 350C is much larger than 6P3P, 5881A glass shell, which is conducive to heat dissipation, making it more stable. When the screen voltage is 250V, 15W output power can be obtained. The commonly used 6L6, 5881, KT66, etc. are only a few watts of output power in this state. If the load resistance is reduced to 2kΩ, the gate negative pressure still has a 10W output power at 14V, and the distortion is smaller.
If the enthusiast has 6L6 or 6P3P output, the amplifier power is used, as long as the change is changed, replace 350c. However, proper adjustments should be made according to the situation of the original power supply part. Mainly adjustment screen pressure, gate negative pressure. Because the 350C's screen is large, if the power supply portion of the original machine is not enough, the phenomenon of insufficient power supply will occur, so that the sound of the sound is unstable, and the transformer is too high. Therefore, it is necessary to adjust the specific conditions of the power supply portion. Adjust the cathode resistance value to make 350C to establish a suitable work point.
When using 350C to make the amplifier amplifier, pay attention to the acetonal and rectification tube. 350 Although the output power is large, its tone is very delicate, parsing, music crystal clear, and the compatibility combination with voltage amplifier should be taken seriously, and there will be a more perfect performance.
This machine is shown in Figure 1. The whole machine uses a primary voltage amplification, first-level driving, one-end A1 feces power amplification circuit. In order to improve the performance of the whole machine, the amplifier circuit has a large loop negative feedback.
The input stage V1 is the voltage amplification level of the translucent of the triode Class A, with a high μ dual-triode dawn color version NO: 01 12AX7B, the voltage gain is around 30 dB. The promotion grade is medium μ, high screen stream double tripod 12au7 constitutes an SRPP circuit, and the voltage gain is about 20 dB. V1, V2 is a rich voltage amplifier, complement to 350C. V2 can be used to open the screen 6n1 in Beijing, and the charm is equally rich. If you use 6922, the music will be thicker, but the treble is slightly inferior.
A switching switch K2 is provided at 350c curtains, which can be placed in two working conditions of the triode and standard circuits. When K2 is at 1 point, the cord gate is parallel to the screen, forming the working state of the triode. At this time, due to the negative feedback of the curtain gate, the output power is reduced, but the tone becomes more meticulous, soft, and the fidelity is also higher. If K2 is set 2, it is a standard line operating state. The output power is restored to a rated value. The dynamic will enhance, and the tone will be more consequent. The feedback amount from the output end to the input stage V1 can be adjusted by W2.
The power section uses Nanjing 5u4g to perform full wave rectification. If the power amplifier grade V4 circuit, if you make appropriate changes, you can directly exchange other types of beam tetracy units, such as 6L6, KT66, 6P3P, 5881, 6V6GT, etc., see Figure 2. That is, add one in the cathode loop of V4. Switch switch K1 and a resistor. When K1 is at 1 point, 350C play is applied. After the K1 is set, it can be used for 6L6, KT66, and the like.
This machine is used to have a 150W megaphone EI-shaped power transformer, and the connection line in the machine has a certain impact.
Assembly production processes have a great impact on sound and signal-to-noise ratios, we must take care of it seriously. This machine uses the method of welding, the component layout is rigorous and reasonable, and the component is placed in the front to postpart from the front to the front to post.
When the assembly welding is completed, measure whether the B + high voltage circuit is short-circuited before power-on, the method is to measure the DC resistance of a point to the ground with the multimeter-based DC resistance, which is generally normal in tens of kΩ or more. If the DC resistance is small, there is a case where it is shorted. The cause should be found and eliminated. Then, the speaker is connected, and the measurement can be performed. B + output voltage (A point) should have about 280V to 300V and should be very stable. 350C No. 3 foot voltage 250V ~ 270V, cathode voltage (8th foot) 14V ~ 18V, indicating that the power supply and the power amplifier circuit work are basically normal. The voltage of the 8 foot of V2 is between 3V ~ 4V, 6 foot voltage is about 1 half of the foot, and the cathode voltage (3 foot) of V1 is 1.5V ~ 2V. If the volume potentiometer is properly opened, hold the small screwdriver The metal part touchs the "+" end of the RCA jack, the speaker can issue "beep", and can pick up the bile predetermined amplifier and sound source audition.
Author: Dai Hongzhi
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