I. Design Outline of Tube Preamplifier The tube is an amplifier with high input impedance, high working voltage and easy aging. It is more difficult to design a tube preamplifier with Hi-Fi standard than the crystal preamplifier. Big. Pay special attention to the following points when designing: 1. Reasonable selection of electronic tubes: There are many types and models of electronic tubes. Each type of tube has different performance, structure, working conditions and use occasions, and has certain timbre differences. Because of this, different tubes cannot be used interchangeably. In the preamplifier, the triode should generally be used, because the triode has good linearity, low noise, and the amplification factor is not too high. It can be used for audio amplification to obtain better comprehensive performance and sound quality, and the circuit is relatively simple. There are many types of triodes. Which one is selected depends on the circuit structure and gain. The gain of a triode amplifier is generally about 0.6 μ, and its μ value is mostly between 20 and 100, so the amplification factor generally does not exceed 70. If the circuit only needs to be amplified one step, a triode with a higher μ value can be selected, and a multi-stage amplifier can be selected. It is better to use medium μ or low μ tube to obtain better stability. Some European and American brands of old-fashioned electronic tubes have been heated up by the media, and the prices have been doubling. It seems that only the pipes of these brands are the most popular. In fact, there are many factors for artificial speculation. China has decades of experience in the production of electronic tubes. It is the world's largest producer of electronic tubes. The life of pipes has reached 10,000 or even more than 100,000 hours. Many brands are also regarded as treasures by foreign enthusiasts. Therefore, in the selection, this problem should be viewed scientifically and sensibly, to avoid people's clouds and clouds, and to listen to partial beliefs. As far as the triode is concerned, the domestically produced 6N1, 6N2, 6N3, 6N4, 6N6, 6N11, etc. are very good performance tubes, and as long as the application is reasonable, the same sound quality can be obtained. What's more, the performance of many foreign second-hand pipes that are popular on the Internet is almost at the end of life. This production tube is locked in 6N2, 6N2 is a very good audio amplifier tube, it is basically the same as the 12AX7 parameters, the sound is similar, only the filament pin is different, it is also very simple to replace the 12AX7 in use. 6N2-PDF file 
6N2 pin 6N2 appearance (Shanghai) 6N2 appearance (Dawn) 6N2 appearance (Beijing)
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