EL34 single-end megaphone, EL34 Vacuum Tube Power Amplifier
Keywords: EL34 single-ended megaphone
EL34 single-ended megaphone EL34 single-end megaphone Author: An Yujing EL34 tube is very high in audio enthusiasts, "the most common 100 kinds of tube rankings" published in "High-fidelity" in April 2000, EL34 collegeders. The famous electronic pipe manufacturers at home and abroad produce a number of tubes made of EL34. However, from the circuit form of the power output stage, there is almost no exception is to push off, the reason is that the maximum screen consumption of EL34 is only 25 watts. When the single-tube single-ended is used, if the single-tube single-ended is enlarged, if it is pressed by five or super Linear connection, the maximum lossless output power does not exceed 12 watts, if it is connected to a triode, there is only about 6 tiles. With the push-pull amplifying circuit, it can easily do three or forty watts. It can be seen that in terms of output power, the push-pull is much larger than the single end, but in terms of sound quality and sound, single-ended machine is better than Push machine. The single-ended electronic tube made by the author, there are 300b, 2A3, EL34, FU15, FU50, FD422, FU7, 6P3P, 6N18P, 6C33C, etc., there are also a lot of buddies to come to the cold house to compare, if you want to ratio from sound quality Measure, the EL34 is undoubtedly the most valueful, because the price of EL34 is lower, almost 300B 1/10, more, this tube is not only dawn, Gui Guang, Beijing several brands, foreign Russia, Czech, etc. Also in production, choose a large room. This article introduces this EL34 single-ended amplifier, with a triode connection, the maximum loss of 6 watts, between the output power of 2A3 and 300B, used to promote the rain, LS 3 / 5A and black granite Made MOREL MW166 + MDT32 self-tukoco, tone is permeable, and the circuit is simple and easy. I. Circuit principle and characteristics The entire circuit uses two levels to enlarge, and it is characterized by negative feedback. The promotion grade is half a 12ax7, and an output stage uses an EL34. After the EL34 is connected to the triode, there are more than 700K Euro, which is comparable to 300b and 2a3. The best load range is 2-4 thousand o'clock, the load impedance is small, but the output is small, the load impedance is small. on the contrary. This circuit uses 3.3 thousand Euro to make both output and distortion. If the EL34 is much smaller than the three-pole connection, the EL34 is much smaller than the five-pole pickup method, but the linear is much better. Linear is still more than direct heat pipes 2A3 and 300B. If you do not use local or large ring negative feedback, the distortion is still relatively large, but this distortion is mainly even harmonic distortion. If this distortion is reduced under conditions without negative feedback? The way is still there, this can be solved by reasonable choice of push tubes and its static work points, load resistance. This machine uses a high amplification of the famous tube 12AX7 to make EL34's push tube, the circuit form of the push-level and output stage is amplified. The input signal of this amplifying circuit is opposite to the output signal, so that the current of the pipe When the output tube is increased; when the current of the push tube is reduced, the current of the output tube increases, because the output characteristic curve when the triode is in small current, is not a straight line, so it produces nonlinear distortion, but this The distortion direction generated by the two tubes is opposite, so it can be canceled with each other. If the push-level distortion is not, the distortion generated by the output stage appears on the load speaker. However, if appropriate, the working point and AC load resistance of the push tube are appropriately selected, deliberately make the distortion of this level are substantially comparable to the output stage, and the distortion of the load speaker can be greatly reduced using his cancellation. The static current of the push-level 12AX7 in this unit is about 0.7mA, enabling it in the curved portion of the output characteristic curve, this level of AC load resistance is its screen resistance (150 thousand) and the next gate resistance ( The parallel value of 82 kWh, about 53 thousand Europe, in this case, the output waveform with an oscilloscope can be seen that when the overload distortion is generated because the input signal is too large, the top of the sine wave is a sleek. This means that the increase in nonlinear distortion is relatively slow when this act is placed, so that the power amplifier is not large, but the sense of hearing is very good. The native output circuit and the push level are used to use a self-biased, which is relatively simple, and a certain protective effect on the output tube, the static operating point of EL34 is as follows: screen scroll voltage: ua = 360V screen current IA = 63mA gate Polar weight gate pressure ug = -27V static screen consumption PA = 360 × 0.063 = 22.6W, less than its maximum screen consumption 25W, the safer power supply circuit is used as a full wavelength rectification, the filter circuit uses CLC-type π-type filtering, this The residual ripple form of the filter method is similar to the sine wave, does not affect the sense of hearing. The rectifier uses the side heat-type 5Z4Pa without using a straight heat 5Z3P or 5Z2P because the tube is particularly fast, and the wireless wire of the el34 is hot. DC high pressure is added to the screen and the cathode. This will affect the service life of the power tube for a long time. Even if it is 5Z4P, its cathode is still faster than EL34, but after all, the time difference is greatly shortened. Don't underestimate this, there are many tube machines that use transistors to rectify, for less than one year, the tube is seriously aging, the cathode launch capacity is greatly reduced, and some radios using electronic tube rectification, it is still not reduced for more than ten years. . Second, the components selection and production preamplifier can use a double tripode such as 12AX7, 6N4, or one 6G2 or 6At6 per channel, but the diode three-pole complex tube used in the tube radio, with the triode part The characteristics are the same as half of 12AX7. The output tube is also called 6ca7, the old model of the former Soviet Union is 6N27C. Now there are many brands to choose from, and their basic structure is the same, and the sound is slightly different. The author uses my country's dawn, and the rectifier uses domestic 5Z4PA, the maximum rectification current is 140mA. The quality of the output transformer determines the advantages and disadvantages of the whole machine, so it is the key to success. Since the unit does not use a negative feedback, the frequency response of the output transformer determines the frequency response of the unit, then how is it simple to determine the frequency of a transformer? We know that determines the main factor of the transformer's frequency of transformers is his primary inductance and leak. For a good output transformer, the ratio between the two should be more than 1000, the author uses DL6423 digital capacitor inductance to measure the OEB 300B Output transformers, its primary inductance is approximately 11h, and the leak is only 10.6MH. The specific measurement method is as follows: First, use a 20h to measure the inductance of the primary coil, write down its value, then use a short wire to talk about the secondary short circuit, then measure the primary inductance, this value is the leak, the ratio of the two Big Better, generally satisfied the requirements when approximately 600. In addition, pay attention to the air gap of the transformer core and the DC resistance of the primary coil. Although the amount of inductance will be larger, it is easy to generate magnetic saturation, and the primary secondary coil DC resistance is too large, and the efficiency is lowered. . If the economic conditions allow, you can buy a regular electronic pipe manufacturer's product. The output transformer of the author is homemade. It uses the transformer core removed from the old instrument, the tongue is 25.4mm, the thickness of 40mm, the primary coil is diameter 0.23mm enameled wire 2400, the secondary is 0.8mm enameled wire 126 (load 8 o'clock) core unilaterally inserted, and the air gap of 0.15 mm. When winding, the primary is divided into 5 sections, the secondary is divided into 4 sections, and the interval is placed. The measurement results are as follows: primary inductance 8.84h, primary coil DC resistance 180 o'clock, leakage 14MH. Finally, you must use it. The filter wave is also self-made, using domestic Kei20 core, 36mm thick, 4000 包 包 线 包 线 线 匝 匝 匝 匝 匝 匝 匝 匝 匝 匝 匝 平 匝 匝 匝 匝 平 匝 平 平 平 平,,,, 130 Euro, also to dry the dip, otherwise communication sound. The power transformer production data is as follows: the iron core width is 35mm, and the stack is 45 mm. 220V primary coil with a diameter of 0.44 mm enameled wire around 880, the secondary 330V windings with 0.21 mm enamel wiring line around 1320, 6.3V winding turns is 27, 3a windings with a diameter of 1.2 mm lacquered line, 0.15a winding. 0.21mm enameled wire. The 5V / 2A windings contain 1.0 mm enameled wire around 21. Iron core is inserted, drying the dip. Third, debugging to test adjustment should start from the high pressure portion, first check if the power supply DC high pressure is 400V, pay attention not to exceed this value, otherwise the EL34 screen is increased, exceeding its limit value parameter 25 watts, the screen will be red , Seriously affect the service life, but also pay attention not to increase the cathode filter capacity of the whole flow tube. When its capacity is too large, it will reduce the life of the rectification tube. The circuit uses the self-bias, which is basically not debugged, and the value is as long as the circuit diagram. It is not a big difference. Measurement index: maximum lossless output power: 6.3W (8 ohms, 1kHz) frequency response: 28Hz-17KHz (-1DB, 1W) voltage amplification: 14 (voltage gain 23dB) sensitivity: 0.5V residual noise: no more than 1mV gall Yixuan Note: The power supply circuit is omitted, the CLC filter circuit, the capacitor is 47 uf and 100uf R4 resistance is two channels.
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