"300B single-ended player, 300B Power Amplifier
Keywords: 300B single-terminal courage
300B single-ended play-up
Simple, as long as the driving force is sufficient, try to reduce the number of amplifiers, which is the basic principle of the author's production line. Speaking of 300B, both playing the tube knows a variety of lines, and has also been used in a variety of routes. After making a variety of routes, the author feels very good to have a line from the active effect or the line structure, so the author writes it, I hope that the readers who love 300B can enjoy the fun.
one. Principle Introduction A single end as an ancient, inefficient, powerful amplifier, still attracts countless audio enthusiasts with its unique and difficult charm. Whether the Aquarium is still a plaque, the author has a unique momentum. everybody knows. An amplifier If it is too much, no matter in any way to reduce distortion, its distortion is definitely more than a small number, and the larger number of magnifications, more, phase shift The larger the possibility, the narrower the pass band. This article describes a two-level single-ended amplifier, which avoids some of the above situations. Everyone is clear that the main role of voltage amplification is to enlarge the audio signal to a sufficient amplitude to achieve the purpose of driving the last level of power, which requires a large number of magnification to enhance the overall audio. The sensitivity required for the amplifier, followed by uniform frequency characteristics, and the signal after the signal is not lost. Since the five tiger has the characteristics of large amplification factor, strong driving force, the motor electrical voltage is selected to select a five-pole. Due to the characteristic curve of 6J4P, the screen pressure, screen stream, and the amplification factor are more compliant with the voltage amplifier level of this unit (Figure 1 is 6J4P characteristic graph), the author selects the push tube of the 6J4P. Generally speaking, the distortion of the five is more than the triode, but through the correct design and necessary measures, the five poles are not inferior to the triode from the test indicators. The power amplification is held by 300B, and the specific circuit principle is shown in Figure 2, Figure 3 is a characteristic graph of 300b. RG1 is the gate resistance of the voltage amplification, RG2 is a gate resistance of the power amplification stage. This gate resistance has two effects: one is to make the next level of electron tube energy to add the gate bias EG to the gate by RG Up to the DC pathway as an EG, the next level of electronic pipe internal electrons from the cathode flow direction, there are more or less some electrons fall to the gate, and RG gives these electrons a DC path, The polar potential is not increasingly negatively affected by the normal operation of the amplifier, so the gate resistance is also called a gate leakage resistance; the second is to send the AC signal voltage output from the screen loop to the next level. The value of the RG resistor should not be too large, and when the resistance is too large, the electrons are difficult to leak to the cathode from the gate, and the gate is prone to the gate stream, because the RG is too large, extremely tiny hierarchy The flow will produce a larger voltage drop at both ends of the RG. Its positive end will be added to the gate. As a result, the gate bias value of the gate loop is small, and it may even make the gate pressure to the positive value. The screen is soaring to damage the tube. When the resistance is too small, it is large to be the score of the electrical tube-screen load resistance RG, which reduces the magnification of the tube. At the same time, if the resistance of the RG is much larger than the impedance of the coupling capacitor C, then the amplified AC signal voltage on the RA will have a large portion directly on the coupling capacitor C, and actually add it to the next gate. The change signal voltage will be reduced. The value of this resistor generally should be 4 to 9 times the screen resistance. At the same time, there are two rigid bias generated by the resistor: one is to cause the electron tube in the process of normal operation, and the gate potential is always below the cathode potential, so that the electrons cannot run to the cathode by the gate, thereby reaching the gate loop. The purpose of no gate; the second is to correctly determine the static work point Q by the gate bias, only when the line waveform is in the case of the position of the power characteristic curve, it will be symmetrical, and only At this time, distortion is the smallest. RK1 is a cathode resistance, its circuit form is a self-bias circuit, and the main function is to generate a stable gate bias. Here we cancel the cathode bypass capacitor CK, the main reason is that the addition of the capacitor has a certain impact on distortion (mainly nonlinear distortion and frequency distortion), and cancels the capacitance within a certain operating voltage range. It is possible to reduce the distortion. Although the increase in capacitance can increase the gain, as a five-pole, its gain is sufficient. From the perspective of pros and cons, we have chosen to cancel the capacitor, of course, this is also based on circuit stability, driving voltage sufficient. superior. Generally speaking, the cathode resistance RK of the five can be calculated using the following formula: RK = EG / (IaO + Ig2O) (IG2O is the DC component of the curtain gate, IAO is the direct current component of the screen, due to the cathode resistance There is also a curtain stream except the current division, so the cathode resistance should be equal to the sum of the curtain stream and the screen stream). Since the value of the RK has a certain impact on the gain, when the value of RK is too large, the gain is small, when the RK is in an hour, the gain is too high, which will cause distortion, so the resistance must be in the above formula. Based on practice. RA is the screen load resistance. When the electronic pipe gate loop adds an AC signal power source, since the control acts of the gate make the original constant anode current becomes a pulsating current which varies with the signal voltage, thereby generates an alternating component, and the AC component on the screen is loaded in the anode load. AC voltage drop is generated on the resistor RA, which is an enlarged signal voltage between the screen and the cathode. Therefore, the resistance has a certain impact on the magnification. The value of this resistance should not be too large and too small. When the resistance is too large, it is lowered to the DC pressure generated by the screen power supply voltage, so that the voltage is too low on the electrical pipe screen, the screen is too small, which makes the position of the operating point of the tube reduction The curved portion of the characteristic curve. At this time, the internal resistance of the tube is increased, and the magnification is reduced, and it will generate severe nonlinear distortion, and the high-frequency characteristics are also impact on the screen resistance. When the power resistance is too small, the splitting effect of the coupling capacitor C is affected, although the magnitude of the high frequency zone can be reduced, but at the same time, the magnification of the intermediate frequency zone is reduced, so the resistance cannot be obtained too small. Therefore, the value of this resistor must be considered to enlarge the multiple of the same time to take into account the magnitude of the work area. In general, the value of the resistor should cause the voltage value of the tube screen equal to about half of the pipe supply voltage. By the curtain bump resistance Rg2, the curtain partial voltage divide resistance RG3, the cantodexial bypass capacitor CG2 composed of step-down, limited flow, and regulatory circuit, which provides a stable DC operation for the curtain gate. Voltage. The main function of the resistor R1 and R5 is to eliminate the energy of parasitic oscillation, so that the amplitude of parasitic oscillation becomes weak, thereby maintaining the normal operation of the amplifier; the other is to have buffer protection and isolation. RK2 is the cathode resistance of the power tube, the CK is the cathode bypass capacitor of the power tube, the main function of RK2, and CK is used to generate a negative gate pressure, and when the DC component IAO of the power tube is over the cathode resistor RK2, it will be generated on RK2. A DC voltage of a size of IaO × RK2, which is a negative gate pressure of the tube gate. The role of the bypass capacitor CK is the AC component of the bypass screen stream so that it does not generate an AC voltage drop on RK2. Therefore, the capacitance value of the bypass capacitor Ck is required to be large, because the capacitance value is, the smaller it on the impedance of the alternating component, that is, CK must be much smaller than the impedance of the audio current. Only in this way can we play a large bypass. W is a 300B filament voltage balanced adjustment resistor, and the potentiometer can reduce the noise of the unit.
two. Output transformer as a very critical ring, the good and bad output cattle directly affects the playback effect, and several main parameters determined by the audio output transformer are self-sensing (inductance), efficiency, leak, magnetic flux density, power And working frequency. The inductor is directly affected and determines the frequency response of the low frequency band and the voltage waveform distortion of the low frequency band, and the output impedance. The efficiency of output cattle not only affects the core size of the output cattle, but also plays an important role in the tone of the output cattle. The magnitude of the leakage is directly determined the frequency response of the high frequency end of the output cattle, but the self-sensing and leakage are proportional to the number of circles, while increasing the amount of inductance, the leakage will increase At this time, it is necessary to use a layer of winding between layered segments. Since the distribution capacitance exists between the layer segment will increase with the increase in the hierarchical segment, the distribution capacitance also directly affects the frequency response of the output cattle high frequency end, so properly handles the relationship between inductance, leak, distribution capacitance. It is an important condition for a good output cattle. Similarly, in the case of a window area, if the amount of large inductance is pursued, a smaller copper wire must be used around the number of turns. Such a result is that the copper resistance of the primary side increases, the efficiency is lowered, and its playback effect will also be affected. But in any case, the design and production of output cattle is mainly for people to listen to music, and the actual test parameters can only be an important basis. Only by continuous practice, experimentation, and listen to can make a good Output cattle. Waveform distortion affects the low frequency band of the audio transformer is not only related to the inductance, air gap, but also related to the magnetic flux density and the non-DC magnetization, and the relationship between the waveform distortion coefficient between the magnetization current is a non-linear relationship. The minimum operating frequency not only determines the size of the core size, but also an important parameter affecting the distortion of low frequency response and voltage waveform. Through multiple experiments, we feel that the imported national standard iron core, the magnetic magnetic rate is output at 16000 ~ 18000 Gaussian Cattle is relatively easy to make. The specific design steps on output cattle have introduced many books, and the author will no longer repeat. The production of the transformer is shown in Figure 4. Be
three. Selecting a good line equivalent to half of a good electronic pipe amplifier. However, although the flowers still need green leaves to set off, a good line is also inseparable from the components, so we must be cautious when choosing components. The quality of domestic big red gun resistors and its playback effect, there is a reputation in the sound industry, plus its price is not expensive, the performance of the tone is quite good, so the heavy responsibility is not it. Capacitor is preferably a non-polar capacitor such as a domestic CZY oil immersion capacitor, CZM metallized paper dielectric capacitor, followed by a polar electrolytic capacitor. This machine has a 0.22uF coupled capacitor, which is an audio signal coupled capacitor, which is more critical. It is recommended to select high quality oil immersion capacitors at home and abroad or use Sibibi VQ oily silver film capacitance. The tube is an important device for the amplification and conversion of the signal, which directly affects the playback effect of the entire amplifier. After our test. 6 ж4c, 6ж8c, OTK produced 6 ж4c, 6J4P, 6J8P, etc. in Nanjing have a good performance, of which Nanjing's product is very cheap, and its performance is quite good in this machine, it is worth a try. Since the tubes produced by each manufacturer have some differences, only the work points of the electronic tube are designed, so that they can work in the best working voltage to exert the best results. At present, there are 3 manufacturers of 300b in China. After testing, the 300B of the 300B appreciated by the author has the 4300b gold gate, 4300B improved black screen, 4300blx, and Changsha Shishuang 300BA. Recently, the performance of the 300BS eggplant produced by Shuguang Factory is also OK, but the overall feeling of people is like a state of modern commercial, and there are less music's charm. After the material is selected, it can be installed according to the drawings we give, or can be installed in a shed installation, or a circuit board of Figure 5 can also be installed. After the component is installed, it can be applied after the check is correct, and it is preferable to add a 2.5A fuse, and high pressure switch K2 before power-on. (1) The first tube is not needed. Plus the first test of the wire voltage of the tube, and can add 6J4P, 274B tube after the filament voltage is correct. Close high pressure switch K2, since the working voltage of 6J4P and 300B is independent of each other, it can be commissioned separately. First add 6J4P, the potential of the voltage A point of the test screen should be 236V. Then then test the binding gate B-point voltage. Should be 115V, at this time, the pressure drop of the cathode resistance should be 1.9V, and the screen flow that flows through the tube should be around 5 mA. The above points are allocated to the ground, and if there is a larger entry with the voltage tested above, it is necessary to cut off check, look at the resistor, and there is no error. If the test voltage is different from the above voltage value, then the stage has been working properly and the debugging is successful. (2) Adjustment of 300B work points. Before the debugging output is added, first add the filament voltage to 3 minutes, then close the high voltage switch K2, test 300B of the screen voltage, is the voltage of D. At this time, the electricity should be 403V, and then the pressure drop of the cathode should be about 70V should be measured. The current flowing through the cathode resistance is calculated from the ohmic to the current flowing through 300b, and the pressure drop of 300b tubes (D point is about 328V of the voltage, the voltage is about 328V) calculates the screen consumption of 300b at this time. This screen should be within 40W. The author recommends that the screen is less than or equal to 36W. 40W is the maximum screen consumption given by the factory. If the voltage and screen consumption at this time are normal, it can be said that the unit has been basically debugged, and the upper voltage is the measured voltage after the loadload. (3) When debugging this machine, since the operating voltage of this machine is high, it must pay attention to personal safety during debugging, and a high-pressure wire is used to use high-pressure wires. Secondary outer layer is to be retrieved. If it is a shed installation, the filament should use dual strand strands during the wiring. That is to closely twisted two wires, when the current is reverse, the radiated alternatives will cancel each other. Thereby achieving the purpose of reducing noise. In the process of wiring, it is necessary to follow a little star ground, that is, the voltage stage is centered on the ground point of the cathode resistance. The other contacts are connected to this point, and the power amplification stage is grounded by the cathode resistance of the power tube. The grounding point is also grounded in this point, and then the two contacts are respectively connected to the center point of the female, i.e., the negative electrode of the filter capacitor, and finally the line is grounded, so that the entire wiring is completed. Since the quality of the wiring directly affects the signal-to-noise ratio of the local machine, it must be strict in the process of the wiring.Follow a little star grounding method. The adjustable resistor W can also adjust the noise of this machine, by adjusting the resistance, the noise of the unit can be lower. In the power supply of the filament, the author uses AC power supply. If DC power supply, noise processing is relatively more than AC power supply, but the author's feeling is inferior to power supply. In summary, the author believes that you must make a 300B amplifier you satisfied with you. "
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