I am a tube amplifier enthusiast. I have assembled many bile duct amplifiers, such as 6P14 single-ended small tube amplifier, 6L6 and FU-5 (805) single-ended machine, KT88 push-pull machine, etc. It has always been my wish to make 30OB. Therefore, I ordered the kit by mail two years ago. After two years of hard work, I finally made it. Now I share my fun with everyone. The finalized circuit is shown in Figure 1 (with a slight modification on the circuit provided by the manufacturer). 1. About 300B bile duct In 1930, the United States Wester Electric (Western Electric Company, referred to as the West Electric Company) produced the world-famous classic direct-heating triode tube 300 and 300A, at that time the filament current was 1.0A, 1.2A, 1.4A, etc. The power of the electronic tube is also divided into 8W, 10W, 12W and other types. After several years of optimization and improvement, it was set to 300B in 1934 and has been used for about 80 years. Due to the reasonable internal structure of the tube, moderate power, low internal resistance, and excellent linearity, it almost reached the theoretical design limit of flawlessness. The single-ended class A power amplifier assembled with it was used to promote the high-efficiency horn speaker at that time and can play The sound of traveling clouds and waters has poured generation after generation of enthusiasts and lovers. No wonder there are enthusiasts today who describe it as the highest state of fever, a gem inlaid in the crown of audio culture, and assert that "you have not heard the 300B sound and you are not a amputee." Although this statement is somewhat agitated, it also explains The charm of the clear and transparent sound quality and timbre created by the 300B. The exact name of 30OB should be WE300B3, because it is a patented product of Western Electric. Others such as Europe, Russia or China ’s 300B are imitations. Although there are no less than 30 varieties at present, no matter from the technical indicators or from the sense of hearing, compared with WE300B, so far there is no right. WE300B also has twists and turns in its development history. In 1988, when transistors prevailed and replaced tubes all over the country, the world ’s tube development history had been brilliant for nearly 60 years. The WE300B production line was discontinued in Yuannai, and the production was discontinued into the remaining 30,000. The rest of the tubes were quickly sold out by the Japanese and French with deep insights. Due to the decreasing amount of goods, it has become a passive water, causing its price to soar rapidly. In the United States, the WE300B was fired to $ 750 / piece, and in Asia it was as high as $ 1250 / piece. This is still priceless. Even some enthusiasts in the United States who had a high fever who had difficulty retreating had to turn back to the Japanese or the French and buy back at a price that was several times or even more than ten times higher than the original. Until 1992, in the context of the history of the resurgence of electronic tubes, AT & T Group (WE's parent company), and at the request of all audio fans, high-level decision makers who were once super enthusiasts also saw the broad prospects of the market and decided to invest 500 Ten thousand US dollars to rebuild Xidian Company, recalled the chief engineer of WE300B production line and a number of skilled technicians who could be the only ones to regroup. They use new materials and new processes. It is said that 7 new technologies are used, combined with unusually strict or even harsh management methods, to make the new WE3OOB technical indicators to a higher level. For example, the degree of vacuum is increased by 100 times compared with the original. After the degree of vacuum is greatly increased, in order to resist atmospheric pressure, artificial crystals are added to the glass raw materials for the production of the tube shell, which not only makes the bile ducts look more transparent and beautiful, but also makes the sound subtle. Changes, and its service life has miraculously reached an average of 40,000 hours, which can be used for 40 years based on 3 hours of listening per day. It is exciting to see that in the gap between the WE300B production and reproduction of Xidian Corporation, China ’s largest electron tube manufacturer, Changsha Shuguang Factory, cooperated with the British PM company to develop the 300B and quickly adopted the "Dawn" in early 1991. The "Jinlong" brand was officially launched to the market. The new products are of high quality and catch up with the technical indicators of WE300B, which has attracted the attention of the global Hi-Fi community. It was once called the best 300B product on the market besides the original WE300B. Coincidentally, China's Liuzhou Guiguang Electron Tube Factory also launched Guiguang 4300B (another name for 300B). Its sound has a European style, and it also attracts the attention of many enthusiasts. What is even more surprising is that Tianjin, China, also established Quanzhen Electron Tube Factory at this time. It is said that the factory is a private enterprise established in 1998 by several retired engineers from the former Beijing Electron Tube Factory. After Guangguang ceased production, some experienced and skilled The mechanics are also involved, so the Full Music300B tube it produces in many 30OBs in the world is considered to be the only electronic tube that can compete with WE300B. No matter the theoretical parameters or the sense of hearing, it is enough to challenge WE300B, and the price is much lower than that of Xidian products. Therefore, it is highly respected not only in China, but also among senior enthusiasts in Europe, America and Japan. The 300B tubes manufactured by several domestic tube manufacturers not only push China to the throne of the world's largest tube production country, but also provide an excellent choice for the enthusiasts. The domestically produced 300B is inexpensive and affordable, so that ordinary audiophiles can afford to play with it. This is a great blessing in the domestic fever circle. 2. Circuit principle This circuit is both classic and salty, it has the following characteristics: (1) In order to give full play to the excellent potential of the 300B electron tube, the machine adopts a double triode parallel connection method in the pre-stage voltage amplification and driving stage. This connection was once not favored by some audiophiles. It is considered that the sound of a single tube is not clean and the resolution is reduced. But the author does not think so, this is because: the double transistor is the two transistors with the same characteristics are encapsulated in a glass shell, the two tubes have the same geometry and size, the same material, and the vacuum in the tube is shared equally, so the two tubes The consistency can be fully guaranteed. Even if there are any changes in use, such as gradual aging, it is also two tubes that are synchronized, so it can be regarded as a very ideal single triode after the two tubes are connected in parallel, and its technical parameters have been greatly improved. If the internal resistance is reduced by half and the output current is doubled, the electrical performance of the entire circuit is further optimized without increasing the number of amplification stages. If the frequency band is widened, the damping characteristics are greatly improved and the driving force is increased. , Enhance the load capacity and so on. Figure 1 300B single-ended Class A combined amplifier circuit diagram (2) The negative feedback of the big loop is cancelled. The technology of negative feedback has been widely used in analog amplifier circuits, especially in transistor circuits. Due to the insufficiency of transistors (such as sensitivity to temperature changes), the working stability is relatively poor. The characteristics have been greatly improved. However, in the tube analog amplifier circuit, people increasingly feel that adding this technology is too much to add to the picture. Practice has also proved that after canceling the negative feedback of the large loop, the sound becomes extraordinarily fresh, enthusiastic, and has a sense of jumping, especially It is a 300B tube with excellent linearity, and its sound quality and timbre are more vivid and unrestrained. (3) The power circuit has worked hard. The first is that the two channels have two independent power sources, each doing its own job without interfering with each other, which greatly improves the separation of the two channels of the whole machine, making the sound field and positioning more accurate; second, the rectifier tube uses an electronic tube, which not only makes the sound It is more beautiful, the guts are thicker, and the power supply achieves soft start, which plays a vital role in extending the life of the amplifier tube, especially the life of the expensive 300B. Secondly, the filtering part of the two-way power supply uses two low-frequency choke coils of l0H / 150mA regardless of cost, that is, a good-quality L0 filter circuit is used, because the ripple coefficient of the power supply of the A-type single-ended amplifier is extremely strict. It is difficult to use the RC filter circuit. Unlike the push-pull machine, the secondary and upper arms of the output transformer are symmetrical. Even if there is some AC salt in the power supply, they will cancel each other out. Finally, there is the power supply filtering part. It is worth mentioning that the first stage of the filter circuit has added two Kaidou brand 2OuF / 400V high-quality film capacitors. Due to the extremely fast charge and discharge speed of the thin film capacitor, the slow and long-lasting birth defects of the tube amplifier have been improved, so that the sound is clean and clean, and there is no sense of dragging the mud and water, and the resolution has reached the level that only high-end tube amplifiers have. 3. Component selection All the bile ducts are made of domestic tubes, and the power amplifier tubes are selected from the Shuguang 300B-98 export type. A company took it back and put it on the "Golden Dragon" brand, and then sold it as a replacement for WE300B in the world at high prices. The price of the assembled machine was even higher. What is interesting is that some of our enthusiasts are blindly pursuing imported bile ducts. The author believes that China is already the world's largest tube production country. At least three manufacturers are currently producing 300B. After the Liuzhou Guiguang Tube Factory was shut down in 2000, it was purchased and relocated by a person of insight in 2007. To the frontier province of China's reform and opening up-Foshan City, Guangdong Province, the new Guiguang NGG300B was produced at the same time. I haven't seen this tube yet, but I heard that it is good. The 30OB produced in China is inexpensive and has been recognized by the world, and enthusiasts can choose it boldly. The pre-stage bile ducts were selected from Beijing * and Shuguang ’s 12AX7 (both tubes are common); the promotion level chose Nanjing to produce 6H8 in the 1950s. The sound is particularly thick and beautiful, and the new models later are 6N8P and 6SN7. The effect of coupling capacitors between stages on the sound should not be underestimated. The kit provides a red Kaili MKP capacitor. Some enthusiasts have written an article to introduce this capacitor in a journal. Practice has also proved that the capacitor does have a good performance. , And Xindeke capacitors, are among the best in domestic capacitors. However, I have several capacitors on hand, and enthusiasts of the game machine are constantly changing the same model. Bile ducts produced by different manufacturers, different brands, and different periods; playing the same specifications, different brands, different materials, and resistors and capacitors produced in different periods, especially coupling capacitors, have fun. Play with different components and devices. The different timbre trends, training ears, accumulating experience, increasing knowledge, and getting endless fun from it, only the talents in the circle have this deep experience. I have the German WMA (Wima) capacitor on hand, the red one with MKPIO printed is the best, the price is particularly low, the disassembly product is only more than 1 yuan each, and the sound is quite satisfactory. It was speculated for a while many years ago. , Cost-effective, you may wish to buy a few more to try; American VQ0.1 uF / 6OOV Sibi oil-immersed capacitors, disassembled products for 30 ~ 40 yuan / only, heavy in hand, the sound is steady and heavy, high, The extension of the low frequency is also better than other capacitors, but the low frequency is slightly thicker, and it will be obviously sent after a long time. SPRAGUE is a US-made SPRAGUE, which has a more comprehensive performance, balanced high and low frequencies, especially the mid-range and high-end sounds, but the price is higher. The French SSOUEN SCR (Sauron), also known as the big S capacitor, has a good reputation among enthusiasts, and the cost performance is also high, which is worth using. In addition, the author also has other antique capacitors such as the American-made black widow. Due to too many types, different brands have different sound trends, so I will not repeat them here. Here I would like to recommend two domestic capacitors to enthusiasts. One is the CZM-C capacitor, which is the white ceramic tube we often see. The two sides are welded with iron ferrules to wide pins. The condenser sound performance is extremely comprehensive, especially the sweetness of the mid-frequency and the bright high-pitched sound. It is particularly suitable for listening to human voices and string music. The author uses disassembled products and needs to burn a pot, otherwise it will have a little bit of sand. It is impossible to hear without careful taste, but it must be said to be a small flaw. The second is CZM-J, and there are also oil-immersed capacitors marked with JCZM-J. The colors are mostly dark gray or dark green. The appearance of the two capacitors is shown in Figure 2. The capacitor sound bottom is thick, high, and low-frequency extensions are good, especially the bass performance is thick and not fat, which just makes up for the inherent defect of the lack of the bass of the amplifier, it can respond to all kinds of music, and the cost performance is also very high. If you have to find the shortcomings, the volume is slightly larger. In short, the tone of the coupling capacitor is different from others, and the wise sees the wisdom. If you are satisfied with it, it is good. Figure 2 two types of capacitors specifically recommended Assembly and commissioning When I got the kit and opened the back cover of the chassis, I saw that the power supply part was ready for installation and commissioning by the manufacturer. The filament of the 300B power amplifier tube was powered by DC. The 5V filament voltage and the rectification and filtering of the high-voltage power supply were arranged neatly On the printed circuit board, two low-frequency filter chokes, 300B 920Ω / 20W cathode resistance, 200uF / 100V electrolytic capacitor and 1uF / 400V film capacitor are separated on both sides, which are symmetrical design for left and right channels; Shed connection, because there is no dielectric loss in the shed connection, the wiring is better arranged, and the resistance-capacitance element can be directly welded to the pin, so that the pupil line is simple and shortest, so the distributed capacitance is also minimal, and the sound is more beautiful. See Figure 3 for the internal wiring. In order to further improve the signal-to-noise ratio, high-quality Teflon signal shielding wires are used for the connection of the input end. The shielding net of the shielding wire can be grounded at one end, and it must not be grounded at both ends, which may cause hum. The grounding problem of the resistance-capacitance components of the amplification parts at all levels must attract enough attention. One must be welded to the same ground point, which is the star ground that audiophiles often talk about, especially the shed resistance, cathode resistance and cathode bypass capacitor. The grounding is particularly important, there is no wire allowed between the two, and it is directly welded between the pin and the grounding point. Because the input resistance of the shed pole resistance and the cathode resistance are far away, there is a potential difference between the two for the AC signal, that is, an AC signal source is added between the shed and the cathode of the tube, after each The level is placed, and the crying sound displayed in the speaker can be imagined. In order to minimize the distortion of the amplifier and make the two channels more balanced, no bypass capacitor is added to the cathode of the booster amplifier in the input stage, that is, current negative feedback is applied to both stages. At the same time, in order to ensure the transient response characteristics of the whole machine, in addition to eliminating the large loop negative feedback network, only a shallow inter-stage negative feedback network is added between the cathode of the input tube and the screen electrode of the push tube. It can be seen from the figure that the negative feedback resistance is as large as 30OkΩ. The author also tried to cancel the network altogether, but the distortion was significantly increased. Using this resistor to 270k Ω, the sound was still a little dark and tight, and it felt a little inaccessible. Only when it was added to 3OOkΩ, the sound was not obvious. Distorted, and it sounds fresh, atmospheric, and very audible. Figure 3 The internal structure of the power amplifier The specific debugging has been mentioned earlier. Because the circuit is classic and mature, reasonable design is used to ensure the technical specifications of the entire circuit. As long as the selected components are of high quality and are strictly welded according to the drawings, they can work with little adjustment. , But I still carefully adjusted the aircraft. The method of debugging the machine is somewhat special. Of course, adjust the power first, and then adjust it step by step from back to front. This advantage is because the power consumption of the power amplifier stage accounts for more than 80% of the total power of the machine. Only after the power amplifier stage is roughly adjusted, the promotion level And the input level is easy to adjust. Some audiophiles adjust from the front to the back, and some adjust the front stage without plugging in the power amplifier tube. It should be noted that at this time, because the load is too light and the voltage remains high, the working point adjusted at such a voltage will work once the power amplifier tube is plugged in. The point will fall sharply and need to be readjusted, which is more troublesome. For the adjustment of the power amplifier level, considering that most audiophiles (especially the new entry-level fever + IJE) do not have a special dam J test instrument, the author's approach is this: first adjust the machine) so that it can generally work, the ammeter In series with 300B screen electrode, measure quiescent current. After the quiescent current is stabilized, the audio signal is sent to the input terminal. At this time, the screen current becomes larger, indicating that the absolute value of the negative voltage of the grid is too small, otherwise the opposite. Because 300B adopts the self-sufficient gate negative pressure method, the voltage value across the cathode resistance is the gate negative pressure value, and the magnitude of the gate negative pressure depends on the magnitude of the cathode resistance. The resistance value of 300B cathode resistance is generally selected from 880 to 1000 Ω. After fine-tuning, when the cathode resistance is adjusted to 92O Ω, the signal is sent at the input terminal, and the 300B screen current has the smallest amplitude of change. The 30OB screen-to-ground voltage was measured at 400V, the screen current was 70mA, and the cathode voltage was 64V. The tube pressure (voltage between screen and cathode) of 300B is 400-64 = 336 (V); power calculation: 336 × 0.07 = 23.52 (W), the efficiency of single-ended Class A tube amplifier is calculated as 1/3 That is 23.52 ÷ 3≈8 (W). The debugging data of the driving level and the input level are marked on the graph. These data are measured by the author with a 500-type multimeter. If the enthusiasts use other tables to measure, there may be discrepancies, as long as the difference is not large, it can be regarded as normal. Actual listening I use this power amplifier to match the mountain spirit SI00CD machine (after careful polishing and upgrade), three-way frequency floor speaker (10 inches + 65 inches + 1 inch), sensitivity 90dB, frequency response 30Hz ~ 27kHz. The author's listening habits are also somewhat different. I like to soak a cup of Biluochun or West Lake Longjing at night, turn on the system, put on my favorite CD, and sit on the sofa to turn off all the lights and turn off. Eyes, taste carefully. Music needs to be understood with the soul, so whether it is to listen to Deng Lijun's lyricism, or to listen to Cai Qin's confession, the velvety smoothness makes people forget the existence of the speaker, just right to integrate the singer and the listener into one. Teresa Teng ’s famous title “Light and Emotionalâ€, which reduced Li Yu, the last emperor of the Southern Tang Dynasty, from the highest-ranking ruler to a prisoner of the ranks. The lament that "Yijiang Chunshui flows eastwards", this emotionally rich ancient masterpiece can only be shown to listeners through Deng Lijun's singing that highlights the mid-high notes and is good at lyricism. Her magnetic, yet gentle, melodious singing sounds heart-pounding and tearful, and at the same time makes people intoxicated and intoxicated. It is a pity that we have no fate and it is impossible to go to the scene to listen to the singer's original vocals in person. However, the 30OB amplifier showed this dry and ancient sing to the fullest and scored three points. At this time, I could not help bringing people into contact with the singer's superstar's premature death. While making people feel deeply dry, I secretly sighed: time is ruthless, life is short. After the record was finished, people sat on the sofa in a daze and continued to immerse themselves in the charm of music. Returning to the truth, listening to string music such as guzheng or violin can show the inner world of the entertainer in front of you without reservation; listening to string solo, even the orientation of the other instruments accompanying the back can be clearly heard. The author is not good at using words to describe sounds, especially like the sound of nature from 300B, who is known as the king of the gall, I can only say that listening to 300B is the charm, it is this charm that has been dumped for several generations. People are the "lovers" in the dreams of many enthusiasts and philanthropists who have been tirelessly pursuing for 80 years. Twenty years ago, people who heard the 300B sound were cited as Bai Hao. Having a 30OB tube amplifier in the fever circle is a symbol of their identity, status, qualifications and economic strength. But today, the 300B bile duct is not a rare thing in the domestic audio market. It is no wonder that some senior old enthusiasts sigh: The current enthusiasts are both lucky and happy. Why don't we take this opportunity to DIY and add 300B! Product features: Toggle Switch UL,Mini Toggle Switch UL,Waterproof Toggle Switch UL,Electrical Toggle Switch UL Hoojet Electric Appliance Co.,Ltd , https://www.hoojetgfci.com
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â– Grounding.Connection mode
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hard copper wire
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Mechanical characteristics
â– Mechanical life
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