Electronic tube difference amplification circuit installation ----- Vacuum Tubes Differential Pre-Amplifier

Keywords: tube, differential amplification circuit Author: Fang Guisen The circuit is not working properly after the access to one 6n8 is driven after the FD422 single-ended line. Check that the voltage on the 12AU7 cathode has 20 volts (the electrical potentiometer is adjusted, there is no decline), and the installation has failed! This blamed me to read this article. Whether the 62kΩ cathode resistor is properly skeptical (usually in the electrical resistance value of the electronic pipe cathode is a few dozen to 2kΩ), it is considered that 62kΩ is too big. After analysis, the reason is that the gate negative pressure failed to adjust the voltage value of the tube to function properly, so it is an article about current negative feedback. In the end, I found the answer in the article published by Mr. Tian Qingsong. After a big realization, then the cathode resistance of 62kΩ was 510Ω + 5l0Ω. After the string is connected, the V1 gate is connected to the V1 gate with a 200kΩ resistor. When the end of the 5L0Ω resistor is supplied, it is used to constitute a current negative feedback and gate negative pressure, and the electrical power is applied to measure the working voltage of each point, the cathode About 8V normal voltage, but not music in the speaker is not a large noise, and the circuit has self-excited. When the V2 gate resistor R5 is disconnected, the speaker will be successfully loaded with a loud music sound. The difference amplification circuit can indeed suppress current noise, and the ear is not heard from the speaker half of the meter (the signal to noise compaction can be fashionable). After actual audition, the sound quality is very good, there is no distortion; the differential amplification circuit of 12au7 assembled the sound quality is clear, the low frequency and the cohesive force are flexible. The circuit is as follows.

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