1. About 300B bile duct
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In 1930, Wester Electric (Western Electric Company, referred to as Xidian Company) produced the world-famous classical direct-heating three-pole tubes 300 and 300A. At that time, the filament currents were 1.0A, 1.2A, 1.4A, etc. The power of the electron tube is also divided into several types such as 8W, 10W, and 12W. After several years of optimization and improvement, it was set to 300B in 1934, and it has been used for about 80 years. Due to the reasonable internal structure design, moderate power, low internal resistance and excellent linearity, the tube has almost reached the limit of perfect theoretical design. The single-ended Class A power amplifier assembled with it promotes the high-efficiency horn speaker at that time and can play. Traveling like a stream of water, dumping generations of enthusiasts and hobbyists. It’s no wonder that today’s enthusiasts call it the highest level of fever, a gemstone set in the crown of the audio culture, and assert that “there is no amp to the enthusiast if you haven’t heard the 300B sound.†This is a bit of a stoppage, but it also shows The 300B creates a clear, transparent, sweet, true sound and timbre.
The exact name of 30OB should be WE300B3, because it is a patented product of Xidian, and other products such as Europe, Russia or China 300B are imitations. Although there are no fewer than 30 varieties at present, no matter from the technical indicators or from the sense of hearing, compared with the WE300B, there is no such thing as the right one. WE300B is also full of twists and turns in its development history. In 1988, when the transistor was popular and replaced the tube in the country, the world's electronic tube development history has been brilliant for nearly 60 years. The WE300B production line Yuannai has been discontinued, and the remaining 30,000 is suspended. The only electronic tubes were quickly snapped up by Japanese and French people who had a deep eye. Due to the decreasing cargo, it became a passive water, causing its price to soar. In the United States, the WE300B was fired at $750/only, and in Asia it was as high as $1,250/only. This is still priceless. Even some American enthusiasts who have a hard time to retreat have to go back and turn to the Japanese or the French, and buy back at a price that is several times higher than the original ten times. Until 1992, AT&T Group (the parent company of WE) under the background of the history of the resurgence of electronic tubes, at the request of all the audio fans, the top decision-makers who used to be 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 many skilled technicians who can be independent, and regrouped. They use new materials and new processes. It is said that they have used seven new technologies, combined with extremely strict and even harsh management methods, to make the new WE3OOB technical indicators even higher. If the degree of vacuum is increased by 100 times, the vacuum is greatly increased. In order to resist atmospheric pressure, artificial crystals are added to the glass material of the production of the shell, which not only makes the bile duct look more transparent and beautiful, but also makes the sound subtle. The change, and its service life has also miraculously reached an average of 40,000 hours, with a daily listening experience of 3 hours available for 40 years.
What is exciting is that in the few years of the discontinuation of the WE300B of Xidian Company to the reproduction, Changsha Shuguang Factory, the largest electronic tube manufacturer in China, lost no time in cooperating with PM Company of the United Kingdom to develop 300B and quickly became the dawn of 1991. The Jinlong brand was officially launched to the market. The new product quality and direct tracking of WE300B's various technical indicators, the attention of the global Hi-Fi industry, was once known as the best 300B products on the market outside the original WE300B. Coincidentally, China's Liuzhou Guiguang Electronic Tube Factory also launched the Guiguang 4300B (another name for the 300B), which has a European style and attracts the attention of many enthusiasts. What is even more surprising is that Tianjin, China, also established the Quanzhen Electronic Tube Factory at this time. It is said that the factory was a private enterprise established in 1998 by several former retired engineers of Beijing Electronic Tube Factory. Some experienced and experienced after Guiguang stopped production. The mechanics are also involved, so the Full Music 300B tube produced in many 30OBs around the world is considered to be the only tube that can compete with the WE300B. Whether it is theoretical parameters or sense of hearing, it is enough to call the WE300B, and the price is much lower than the Xidian products. Therefore, it is highly praised not only in China but also in senior enthusiasts in Europe, America and Japan.
The 300B pipe manufactured by several domestic electronic tube manufacturers not only pushes China to the throne of the world's largest electronic tube production country, but also provides an excellent choice for the majority of enthusiasts. The domestic 300B is inexpensive, so that ordinary enthusiasts can afford to play, and it is a great blessing in the domestic fever circle.
2. Circuit principle
The circuit is both classic and salty, and it has the following features:
(1) In order to give full play to the outstanding potential of the 300B electron tube, the machine uses a parallel connection of double triodes in the voltage amplification of the front stage and the push stage. This connection was once not optimistic by some enthusiasts. It is considered that the sound of two tubes is not clean and the resolution is reduced. But I don't think so. This is because the double triode is a diode filled with two identical characteristics in a glass case. The two tubes have the same geometry and size. The materials used are the same, and the vacuum in the tube is equally shared. The consistency is fully guaranteed. Even if there is any change in use, such as gradual aging, then the two tubes are synchronized, so it can be considered as a very ideal single triode with two tubes connected in parallel, and its technical parameters have been greatly improved. If the internal resistance is reduced by half, the output current is increased by a factor of two, and the electrical performance of the entire circuit is further optimized without increasing the number of amplification stages, such as widening the frequency band, greatly improving the damping characteristics and improving the driving force. , enhanced load capacity and so on.
Figure 1 300B single-ended class A combined power amplifier circuit diagram
(2) The negative feedback of the big loop was cancelled. Negative feedback technology has been widely used in analog amplifier circuits, especially in transistor circuits. Due to the inherent deficiency of transistors (such as sensitivity to temperature changes), the stability of operation is relatively poor. The characteristics are greatly improved. However, in the tube analog amplifying circuit, people are more and more convinced that the addition of this technology has the suspicion of adding a snake. The practice also proves that after canceling the negative feedback of the big loop, the sound becomes extraordinarily fresh, enthusiastic, and has a sense of jumping, especially It is a linear and excellent tube for the 300B. Its sound quality is more vivid and unconstrained.
(3) The power circuit is working hard. First of all, there are two independent power sources for the two channels, each performing their own functions without disturbing each other, greatly improving the two-channel separation of the whole machine, making the sound field and positioning more accurate. Secondly, the rectifier uses the tube, which not only makes the tone More awkward, more daring, and the power supply achieves a soft start, which plays a crucial role in extending the life of the amplifier tube, especially extending the life of the expensive 300B. Secondly, the filtering part of the two-way power supply uses two l0H/150mA low-frequency chokes at a cost, that is, the L0 filter circuit of good quality is adopted, because the class A single-ended amplifier has strict requirements on the ripple coefficient of the power supply. It is difficult to use the RC filter circuit. Unlike the push-pull machine, the upper and lower arms of the output transformer are symmetrical, and even some AC salt in the power supply cancel each other out. Finally, the power supply filtering part, it is worth mentioning that the first stage of the filter circuit has added two high-quality film capacitors of 2Ku brand 2OuF/400V. Due to the extremely fast charging and discharging speed of the film capacitor, the slow and congenital defects of the amplifier have been improved, the sound is clean and neat, and there is no sense of muddy water, and the resolution reaches the level of the high-end amplifier.
3. Component selection
All the bile ducts are made of domestically produced tubes, and the power amplifier tubes are selected from the Shuguang 300B-98 export type. By the way, a few words are passed. In the years when the old version of Xidian 300B was discontinued to reproduce the new version, the 300B of China Shuguang Factory was once the UK. A company took it back to the "Golden Dragon" and then sold it at the high price as a substitute for the WE300B in the world. The price of the assembled machine was even higher. What's interesting is that some of our enthusiasts are blindly pursuing the import of bile ducts. The author believes that China is already a major producer of electronic tubes in the world. At present, at least three manufacturers are producing 300B. After the closure of the Guiguang Electronic Tube Factory in Liuzhou in 2000, it was purchased and relocated by people of insight in 2007. To the frontier province of China's reform and opening up, Foshan City, Guangdong Province, also produced the new Guiguang NGG300B. I have not seen this tube yet. But I heard that it is good. The 30OB produced in China is cheap and has been recognized by the world. Fans can choose it with great enthusiasm. The pre-stage bile ducts were selected by Beijing* and Shuguang's 12AX7 (two tubes are common); the driving level used Nanjing to produce 6H8 in the 1950s, and the sound was particularly thick and beautiful, and the later new models were 6N8P and 6SN7. The effect of the interstage coupling capacitor on the sound can not be underestimated. The kit provides the red Kay Li MKP capacitor. Some enthusiasts have written articles to introduce this capacitor in a publication. The practice also proves that the capacitor does have a good performance. Like Xindak capacitors, they are among the best in domestic capacitors. However, the author has several capacitors on hand, and the fans who play the game are constantly changing the same model. Bile ducts produced by different manufacturers, different brands and different periods; playing with resistors and capacitors of the same specification, different brands, different materials and different periods, especially coupling capacitors, play with enthusiasm. Experience different components and devices Different timbre trends, training ears, accumulating experience, increasing knowledge, and getting endless fun, only the talents in the circle have this deep experience. The author has the German WMA (Wei Ma) capacitor on hand, the red and printed MKPIO type of the best variety, the price is particularly low, the demolition products are more than 1 yuan each, the sound is quite satisfactory, many years ago was speculated for a while , the price is very high, may wish to buy a few more to try; the United States VQ0.1 uF/6OOV Sibi oil-immersed capacitors, disassemble products for 30 ~ 40 yuan / only, in the hands of heavy, sound calm 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 while. Or the American-made SPRAGUE (Spirit), the performance is more comprehensive, high, low frequency is more balanced, especially the middle and high notes are intriguing, but the price is higher. France's SSOUEN SCR (Sorron), also known as the large S capacitor, has a good reputation among enthusiasts, and the price is also high, it is worth using. In addition, the author also has other antique capacitors such as black widows. Because there are too many types, the different voices of the brand are different, so I will not repeat them here.
Here I would like to recommend two domestic capacitors to the enthusiasts. One is the CZM-C capacitor, which is the white ceramic tube we often see, and the type of wide-pin is sealed with iron ferrules on both sides. The performance of this capacitor is extremely comprehensive, especially the mid-range sweet, high-pitched and beautiful, especially suitable for listening to human voices and strings. The author uses the disassembled products, which need to be smashed, otherwise it has a little bit of sand. It is inaudible to not care, but it cannot be said to be a small embarrassment. The second is CZM-J, which also has the oil-immersed capacitor of JCZM-J. The color is mostly dark gray or dark green. The shape of the two capacitors is shown in Figure 2. The bottom of the capacitor has a thick, high and low frequency extension, especially the bass performance is thick and not fat, which just makes up for the congenital defect of the lack of bass of the amplifier. It can handle all kinds of music, and the price is also very high. If you are not looking for shortcomings, it is slightly larger in size. In short, the tone of the coupling capacitor is the benevolent, the wise see wisdom, and you feel satisfied, that is to return.
Figure 2 specifically recommended two capacitors
Assembly and commissioning
When you get the kit and open the back cover of the chassis, you can see that the power supply part has been installed and debugged by the manufacturer. The filament of the 300B power amplifier tube is powered by DC. The 5V filament voltage and the rectified and filtered RC components of the high voltage power supply are neatly arranged. On the printed circuit board, two low-frequency filter choppers, 300B 920Ω/20W cathode resistors, 200uF/100V electrolytic capacitors and 1uF/400V film capacitors are placed on both sides for symmetrical design of the left and right channels; The shed connection, because there is no dielectric loss in the shed connection, the wiring is better arranged, the RC component can be directly soldered on the pin, so that the 瞳 line is simple and shortest, so the distributed capacitance is also the smallest, and the sound is more ambiguous. The internal connection is shown in Figure 3. In order to further improve the signal-to-noise ratio, the input terminal is connected with a high-quality Teflon signal shielding line. The shielded wire of the shielded wire can be grounded at one end, and must not be grounded at both ends, which may cause hum. At all levels, the grounding problem of the RC components must be paid enough attention. One must be soldered at the same grounding point, which is the star grounding that enthusiasts often talk about, especially the slab resistance, cathode resistance and cathode bypass capacitor. The grounding is particularly important. Wires are not allowed between the two and are soldered directly between the pins and the grounding point. Because the input gate resistance and the cathode resistance are far away from each other, there is a potential difference between the two on the AC signal, that is, an AC signal source is added between the shed and the cathode of the tube. The level is placed, and the crying in the speaker can be imagined. In order to minimize the distortion of the amplifier, the two channels are more balanced, and no bypass capacitor is applied to the cathode of the input stage to drive the amplifier tube, that is, the current is negatively 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, a shallow interstage negative feedback network is added only between the cathode of the input tube and the screen of the push tube. As can be seen from the figure, the negative feedback resistor is used up to 30OkΩ. The author has also tried to cancel this network altogether, but the distortion is obviously increased. This resistor is used to 270k Ω. The sound is still slightly darker and tighter. It feels a little unopened. It is only added to 3OOkΩ, and the sound is neither obvious. Distortion, and it sounds fresh, atmospheric, and very resistant.
Figure 3 Internal structure of the amplifier
The specific debugging mentioned earlier, because the circuit is classic and mature, with reasonable design to ensure the technical indicators of the entire circuit, as long as the selected components are of superior quality and strictly welded, almost no adjustment is required to work. However, the author has carefully adjusted the machine. The method of debugging the machine is somewhat special. Of course, the power supply is first adjusted, and then adjusted step by step. This has the advantage that the power consumption of the power amplifier stage accounts for more than 80% of the power of the whole machine, and only the power amplifier level is generally adjusted. And the input level is easy to adjust. Some enthusiasts adjust from front to back, and some adjust the front stage without inserting the power amplifier. It should be noted that the load is too light and the voltage is high. Adjust the working point under such voltage and plug it into the power amplifier tube. The point will fall sharply and need to be re-adjusted, which is more troublesome. For the adjustment of the power amplifier level, considering that most enthusiasts (especially the fever + IJE just getting started) do not have a special dam J test instrument, the author's approach is this: first adjust the machine to make it work, the ammeter String into the 300B screen and measure the quiescent current. After the quiescent current is stabilized, the audio signal is sent to the input terminal. When the screen current becomes large, the absolute value of the gate negative voltage is small, otherwise it is opposite. Since the 300B adopts the self-supplied gate negative voltage mode, the voltage value across the cathode resistor is the gate negative voltage value, and the magnitude of the gate negative voltage depends on the cathode resistance. The resistance of the 300B cathode resistor is generally selected from 880 to 1000 Ω. The author has fine-tuned, when the cathode resistance is adjusted to 92O Ω, the signal is input at the input end, and the variation of the screen flow of 300B is the smallest, indicating that the working point is generally at the midpoint of the straight portion of the screen flow, and the distortion is also minimal. At this time, the voltage of the 30OB screen to ground is 400V, the screen current is 70mA, and the cathode voltage is 64V. The tube pressure of 300B (the voltage between the screen and the screen) is 400-64=336 (V); the power calculation: 336×0. 07=23.52 (W), the efficiency of the single-ended class A tube is calculated by 1/3. That is, 23.52÷3≈8(W). The debug data of the push level and the input level are all marked on the graph. These data are measured by the author using a 500-type multimeter. If the enthusiast uses other meters to measure, there may be discrepancies as long as the difference is not normal.
Actual listening
I use this amplifier with the Shan Ling SI00CD machine (after careful polishing upgrade), three-way floor speaker (10 inches + 65 inches + 1 inch), sensitivity of 90dB, frequency response 30Hz ~ 27kHz. The author's listening habits are also somewhat different. I like to have a cup of Biluochun or West Lake Longjing at night, open the system, put on my favorite CD CD, sit on the sofa and turn off all the lights, close Eyes, taste it carefully. What music needs is to understand it with the heart, so whether it is listening to Teresa Teng's lyrics, or listening to Tsai Chin's confession, the velvety smoothness makes people forget the existence of the speaker, just blending the singer and the listener. Teresa Teng’s famous lyrics, the emperor of the Southern Tang Dynasty, Li Yu, was ruled by the ruler of the highest power as a prisoner. The psychological impact caused by this extraordinary gap was issued from the heart. One river spring water sighs to the east, this emotionally rich masterpiece can only be shown to the listener through the singer of Teresa Teng who highlights the middle and high notes and is good at lyricism. Her magnetic and euphemistic songs screamed and provoked tears, and at the same time made people fascinated and intoxicated. Unfortunately, we have no fate and we can't go to the scene to listen to the singer's original singer. However, the 30OB amp is the best in this singer. At this time, it is impossible to make people contact the superstar of this song superstar, so that when people feel guilty, they sigh secretly: time is ruthless, life is short. After the album was over, people were still sitting on the sofa with dementia and continued to immerse themselves in the charm of music.
Closer to home, listening to strings such as guzheng or violin can show the inner world of the performer unreservedly in front of you; listening to string solo, even the orientation of the other instruments behind the accompaniment can be clearly heard. The author is not good at using words to describe the sound, especially like the 300B, which is known as the voice of the god of the gallbladder. I can only say that listening to the 300B is the charm. It is this charm that has been dumped for generations. People are the "lovers" in the dreams of many enthusiasts and lovers who have been tirelessly pursued for 80 years. Twenty years ago, the 300B sound was quoted by Bai Hao, and the 30OB amplifier was a symbol of his identity, status, qualifications and economic strength in the fever circle. 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 the opportunity to DIY and add 300B to it!
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