Keywords: 805 single-ended output, amplifier circuit, 805 courage circuit
805 single-ended output 45W × 2 combined courage
805 is an excellent B class power triode. The main purpose is to push-pull audio power. A pair of output tubes can output 300 to 370W audio power; another purpose is RF Class Power amplification. Therefore, the plate is poled by the top of the tube. If it is only for the audio design, the plate should not be taken from the top of the tube, and the other electrodes can be introduced by the pin, such as the US model 838. Since the 805 yield is large, it is widely used for high power megaphones. Therefore, there are more social insurance, and the domestic tube model is Fu-5. Many enthusiasts try to use it to do a single-ended power amplifier, making drawings, but the result is not very satisfactory, the bass is loose, the treble is not resistant, the sound quality is significantly higher than the power ratio of 845 tube A single-ended power difference. However, the enthusiasts are difficult to enter, and they have repeatedly defeated the fight, and the spirit can be pleasing.
First, the poor power tube and the Power tube are very different, and the rigid diode is generally deeper, and the gate pressure is zero when the maximum board flows, and the gate flow is not generated throughout the zone. Theoretically input impedance is infinite. The plate polar internal resistance is small, and the circuit has a large damping coefficient for the speaker. The gate is small to the plate voltage amplification coefficient, which is called low μ tube. Such as 2A3, 300B, 211, 845, etc. The B-based power triode, the gate negative bias is shallow, even the positive gate bias, and the gate pressure is alternated between the positive gate pressure and the negative gate pressure, and is quite in the positive gate pressure range. The amplitude swing produces a gate stream. The gate stream varies with the plate pressure, and is not proportional to the gate pressure, which is a nonlinear state. The internal resistance of the plate is generally large, and the amplifier is small to the speaker's damping coefficient, generally zero. The gate is extremely large, and 60 ~ 200 is often 60 ~ 200, which is a so-called high μ tube. Such as 805, 806, 809, 810, 8L1A, 812A, 833, 838, 572B, and the like. The parameters of the 838 are the same as 805. The only difference is that the plate is poled by the pin, and there is no screen hat, which is a B-like push-pull power amplifier. It is said that the dawn plant also produces the 805 805, which is 538, is a full-class tube of 838. The 805 tube has an 11KΩ panel, and the μ value is about 60.805 pin wiring as shown in Fig. 1 (a), and the panel characteristic curve is shown in Fig. 1 (b). The upper maximum operating voltage is 1500V, and the maximum plate is 125W. There is a 1 (i.e., B1) class and the B2 (B2) class in the B-like push-pull power amplifier circuit, and the maximum gate pressure of the B-1 class is zero volts, and the two category is a positive gate pressure during the dynamic process. The stream is driven, and 805 is a class B2. If used for a single-ended circuit, the driving circuit must provide a certain gate stream, the gate stream and the gate pressure are nonlinear relationships. In order to make the push signals, it must have a very low internal resistance. The 805 gate is working on the positive gate pressure, and when there is a large dynamic, there is a gate stream in half and negative for half a week. Under this condition, it is necessary to do it without distortion (push the signal voltage is not true). The 805-tube amplification coefficient is large, so the driving voltage is not high. The 805-tube plate is large, about 11kΩ, so it is poorly damped in the speaker damping coefficient, and the damping coefficient is about 0.9 for 10kΩ load impedance. This is why the bass is loose, and the treble distortion is true. Obviously don't work on dry high fidelity. This must use negative feedback to reduce its output internal resistance. In summary, it is more difficult to use 805 single-ended amplifiers, which do not exist in 211,845 classic tubes. Therefore, it is easy to use a single-ended machine or use of a dedicated tube.
Second, overcome the measures 805, although there is the above unfavorable conditions, if it takes measures to overcome, it can produce excellent single-ended amplifiers, some aspects can exceed 845 types. The performance of the tube is the purpose of this article. I believe that the reader will look at the 805 tube. One of its main points is pushed, and it is equipped with the second addition of points. Some circuits use low internal resistance triode 300b by push transformers 2: 1 buck, so that the push internal resistance is reduced to 200 Ω, the effect is good, but the promoter is a constraint, high production cost, poor frequency. The 805-board adjustment circuit of the push circuit is also difficult to process. Another solution is that the promotion grade uses a cathode output, which greatly reduces the internal resistance. The cathode output is distorted, the internal resistance is very low, Ri = 1 / s, which is used as a triode as an example, Ri≈1 / 6 (mA / V) = 167 Ω. The output peak current can reach 100mA, while 805 under dynamic US = 150V board pressure, the gate voltage Ug = + 57V, gate stream Ig = 50mA, as shown in Fig. 1 (b), so there is no problem . The cathode outputtor voltage amplification coefficient a ≈1, the gain is 0 dB. The 845-tube internal resistance is Ri = 1.7kΩ. If the 7kΩ load is used, the ratio of load and internal resistance is 4, that is, its damping coefficient of the speaker is 4.805 to achieve and exceed its damping effect, and negative feedback has 12 ~ 18db. 4 to 8 times, at this time, add 805 self-resistant damping coefficient of about 0.9, ie (f-1) +0.9, the damping coefficient is (4-1) + 0.9 = 3.9.18db when negative feedback 12db When a negative feedback, the damping coefficient is (8-1) + 0.9 = 7.9, has reached or exceeded 845 tubes. Such an 805 tube A single-ended power amplifier sound quality is not as good as the problem of a special tube. At the same time, it is required to have a large amount of voltage amplifier, and you must take 4 to 8 times 12 to 18 dB to use dry negative feedback. At the same time, two benefits: 1 reduces the output internal resistance, enhance the amplifier to the speaker damping coefficient; 2 overcome the shortcomings of the distortion coefficient of single-ended output circuits, so that distortion is greatly reduced.
Third, the circuit introduction is based on the above characteristics and requirements. As shown in Figure 2, the input stage high μ tube 1/2 6SL7GT is a typical blocked coupling amplification circuit, and the cathode is negative feedback sampling resistor Ri = 100Ω. Cathode resistor 2.2kΩ, there is a bypass capacitor. Some circuits will not be desirable. First, the current negative feedback is harmful feedback generated by the cathode resistance. It will reduce the circuit voltage gain while increasing the output internal resistance. . The second is that the leakage and distribution capacitance between the cathode and the filament will result in noise, which can be filtered by bypass capacitor. The panel circuit couples the same ultrasonic suppression circuit 100oP capacitor string of the Williamson circuit, which is to prevent the ultrasonic self-excitation oscillation caused by the phase shift when the negative feedback amount is large. The voltage gain of this grade is 40 times (32dB), the filament DC power supply, star ground. The second stage voltage is promoted, using the middle tube 1/2 6SN7GT, the output is large, the distortion is small, and there is a 16-fold (24dB) voltage gain. The output can reach 83V peak when the 300V is powered, and the 805 is sufficient. The cathode resistance also connects to the bypass capacitor. The third stage is a cathode output device, which is connected to a triode with 6L6GC (6P3P), and the cathode output is directly connected to the 805 gate. The output internal resistance is 170 Ω, and the drive current can exceed 100 mA, and the 805 gate stream is only 50 mA, which is also driven. relaxing. The 6L6GC cathode is connected to a 22kΩ electrical pressure-210V power supply, providing 10mA bias. When the 805 gates immediately dry-210V, the board is completely closed, only when the 6L6GC cathode is heated, the 805 gate pressure is normal, this process is approximately 10s, naturally it has reached the delay circuit. Function, the power circuit does not have to delay the circuit, which is a uniform circuit. The 6L6GC gate passes the gate pressure adjustment circuit through the gate leakage, by adjusting the 6L6GC gate pressure, the control cathode voltage is 805 gate pressure, thereby achieving the purpose of adjusting the 805 board. When such a circuit is damaged or removed by 6L6GC, 805 is dry off, so it is also a very safe circuit. The voltage gain of this grade is 1, namely 0dB. The 805 filament is powered by DC and can get as low background noise. In the 100Ω balance potentiometer, the point is 10Ω electrical resistance, and is set to measure the 805 board. If the device current table, the 10Ω resistor is replaced by the current table. The 805 gate is clamped by a 6L6GC cathode output, and does not generate a fixed bias circuit from a power tube flow drift caused by a gate leakage resistance ion-in-gate stream. From low distortion, high-power output and relaxation, etc., it is advantageous to choose higher plate pressure. Negative feedback is completed by the 8Ω output end through the feedback resistor RF. The power supply circuit is shown in Figure 2. The power transformer is 600VA, and the quotation current laid in the figure is a resistive load current. If a rectified capacitance input circuit, the practical current is multiplied by a coefficient of 0.55, such a winding does not have a larger time. Temperature rise. The transformer is stripped in Table 1. Be
Fourth, the working condition calculation 1.805 Calculation Example 1: UA = 1100V PA = 105W (limit value 125W) (1) Board IA = PA / UA = 105/1100 = 0.095a (2) According to Figure 1 b) The plate characteristic curve, static 1100V board pressure, the board flow 95mA, the gate pressure is Ug = 10V. When the dynamic peak board IAM = 2Ia = 190mA, the pipe pressure drop US = 150V, at this time, the gate pressure is UGM = + 57V, the gate stream IgM = 50mA, so the push voltage peak ΔUg = ugm-ug = 57-10 = 47V (3) Output Impedance RO = (UA-US) / IA = (1100-150) / 0.095=10000Ω (4) Output PO = (UA-US) × IA / 2 = (1100-150) × 0.095 / 2 = 45.125W (5) Voltage gain a = △ ua / △ ug = (1100-150) /47=20.2 times Example 2: ua = 800V PA = 105W (1) board IA = PA / UA = 105/800 = 0.131A (2) According to the chalar characteristic curve, as shown in Fig. 1 (b), the static plate pressure 800V board flows 130 mA gate pressure ug = + 26V. When the dynamic maximum board IAM = 2Ia = 260mA, the pipe pressure drop US = 150V, at this time, the gate pressure Ugm = + 70V, the gate stream IgM = 75 mA. Therefore, push voltage peak △ ug = UGM-UG = 70-26 = 44V (3) Output impedance RO = (UA-US) / IA = (800-150) /0.13=5000Ω (4) Output power PO = (UA- US) × IA / 2 = (800-150) × 0.13 / 2 = 42.25W (5) Voltage gain A = △ uA / △ ug = (800-150) /44=14.8 times The above two examples are 10kΩ output transformers, respectively And 5kΩ output transformer application is typical, each has a thousand autumn. From the promotion, the output power is large, the + 10V gate bias is easy to obtain and make full use of high pressure of the 805 tube, the unit selected the former. From the foregoing two cases, it can be seen that when the use of a single-ended single-ended output is used, the efficiency is higher than the special triode power tube of the class A, which is highly promoted, and only 47V peak. 2. Circuit calculates the calculation of the total gain of the circuit's open loop voltage, the total gain, sensitivity, negative feedback circuit, and damping coefficient of the circuit. The input stage 1/2 6SL7GT voltage is placed in a large amount of 40 times (32dB), and the push level 1/2 6SN7GT voltage is placed on a large amount of 16 times (24dB), and the voltage amplifies a large amount of 20.2 times (26dB) under this working condition, and outputs the transformer voltage ratio n. = 34 (-30.5 dB). The open loop voltage gain A = 32dB + 24dB + 26DB-30.5dB = 51.5 dB (approximately 380 times). Take a negative feedback f = -17dB = 7 times, so the whole machine closed loop voltage total gain AS = A / f = 380/7 = 54.3 times, the full power is 45W, the output voltage u = (PO · RL) = (45 × 8 1/2 = 18.97V, so sensitivity Ui = UO / AS = 18.97 / 54.3 = 0.35V (RMS). Negative feedback resistor RF = (A · R1) / (F-1) -R1 = 380 × 100 / (7-11) -100 = 6233 Ω, RF = 6.214 Ω. The damping coefficient of the negative feedback formed is 0.9, the total damping coefficient = F-1 + 0.9 = 7-1 + 0.9 = 6.9, has exceeded 845 tube The amplifier damping coefficient is 72.5%. In addition, the negative feedback on the factor of the single-ended mesh is greatly improved, the overall effect of this machine is really removing the bones compared to the unneedcted feedback 805 single-ended machine. This circuit can be replaced directly from 6SL7GT to 6SN7GT under conditions of the circuit parameter constant, and the amount of negative feedback becomes 3.4, i.e., -11dB, damping coefficient becomes 3.3, and the sensitivity is 0.424V, and the calculation is calculated here. The electron discharge of the voltage amplification factor in front-level voltage amplification factor has little effect on circuit parameters. It is mainly the characteristics of the damping coefficient of the feedback and the circuit's speakers. This is the characteristics of negative feedback amplification circuits. This move can be very convenient to enjoy the sound quality of the power amplifier during different negative refueling.
V. Making detailed 2kv / 1a bridge stacks can also be used to use color TV line damper 2KV / 2A 4 to connect to high pressure bridges, and reliability must be high. High-pressure filter capacitor oil immersed paper dielectric capacitance, high withstand voltage, long life, excellent frequency characteristics. Filter inductance can be used with a megaphone power choke, and the finished product such as a leap is 150, and the specification is 10H / 0.43A, which is mounted on the bottom plate. If the self-made, the data is listed in Table 2. Note that the bottom tube and the outer casing must have high pressure insulation, and it is necessary to have a 1500V voltage for a long time. The low pressure 300V circuit bridge stack 1KV / 1A can be connected by 4 1 n4007, the filter inductance L2, the L3 volume is large, can be mounted under the bottom plate, low pressure filter first choke l2 because of the plates of V1, V2, V3 The stream, but also provides a gate stream in FU-5 dynamics, so the current capacity is slightly larger, which is 100mA. The second stage choke L3 only provides a V1 tube 6SL7GT board, two channels only 2mA, using a specifications of 330h / 10mA. L2, L3 winding data is shown in Table 2.3 100 f / 400V filter capacitor does not have special requirements, but you have to use a better brand, such as Panasonic, Japanese Chemical, etc. The negative pressure rectification and the low pressure 300V circuit use the same bridge heap, 3.9kΩ / 5W resistance is filter, buck, and the capacitance to be used as a π-shaped filter, because the electric capacity of the choke is not used. After filtering, there is 4 channels, and the two 210V is connected to 6L6GC cathode resistance 5W22 kΩ, and the other two step-down to -50V supply two 20 kΩ potentiometers to control.The channel 6L6GC gate pressure reaches the purpose of adjusting the FU-5 gate pressure. The two potentiometer handle is on the bottom plate, and when the FU-5 or 6L6GC is replaced, the FU-5 board is adjusted. The front-level 300V low voltage supply filter circuit and the negative pressure supply filter circuit are concentrated on a small print circuit board, which allows the circuit to be small and clean. At the same time, 6 capacitors are set to facilitate the star ground, the background noise is minimal. As shown in Figure 3, the printed plate is shown in the center of the star ground because it is to be pulled into a plurality of ground wires, the drilling is φ5.5 mm. The circuit board is mounted in the bottom plate between the power transformer and the amplifying circuit by the bracket. FU-5 filament rectifier can be used in general 10A bridge, filter capacitance C ≥ 10 / (Ω · r), R = 10 / 3.985 Ω, so C = 10 / (314 × 2.985) = 0.010669f = 10669 uf, use The 15000 UF capacitor is completed. In the 100 Ω balance potentiometer, the ground resistance 10 Ω should use a 1% error of the five-ring resistance. When there is conditional, the current meter is good, because the FU-5 conversion changes, regardless of the replacement of FU-5 or replace 6L6GC, The board can be easily adjusted when there is a current table. When the signal-to-noise ratio is very high, the importance of the front-level filament DC power is high, but the DC power supply is only available for V1, V2 two-stage voltage amplifier filament, and the cathode outputer 6L6GC is an alternating current, and has nothing to do with signal to noise ratio. . This can reduce the burden of the rectification filter, and then when the 6L6GC is replaced by the EL34 as a cathode output push tube, it does not affect the rectified output voltage due to the filament current. The internal restriction is 100 Ω during the pushing tube with a high cross conduit EL34. Now the enthusiasts are prefers to use the biliary stream, and if the main rectifier in this circuit uses the tube, 4 5Z4P or 4 5AR4 can be used to replace the high-pressure bridge heap because of the internal block of the electronic pipe, to ensure output voltage + 1170V, power transformer The winding voltage is increased from 450V × 2 to 500V × 2. At the same time, there are two groups of 5V / 2A filament windings and 1 group 5V / 4A filament windings. These coils must be insulated enough, and it is necessary to have a high pressure of 1500V for a long time. It is best to use a cable paper to add polyester film to the three-layer structure, and only the two groups can be by. The power supply part of the high-voltage electronic tube rectification is shown in Figure 4, and the input stage high voltage capacitor is replaced with 15UF / AC660V to reduce the surge current, protect the rectification pipe. Although the mercury gas tube has the advantages of high withstand voltage and low pressure drop, it is a 3-minute warm-up time, and a "pass" is generated in the high-pressure connection, and the life is also high, so it is not Use. The power transformer power with a bile current is slightly larger, 700VA, the winding is more, and the production data is shown in Table 3. The front stage circuit input stage 6SL7GT, the promotion grade 6SN7GT and the cathode output promotion level 6L6GC three-tube circuit uses more components, using a handwriting mode, is completed by the three terminals, stronger the components single layer arrangement, smeptive, physical map is shown 5. The container components used are obtained by calculating or checking the application, and has been confirmed. The volume potentiometer uses ALPS100KA × 2, and the resistance is unmarked by 1/2W, 100PF band pass filter capacitor is used in mica media. 4 coupling capacitors use Schbiwei to 0.1 600V oil immersed paper dielectric. 6L6GC cathode resistor 22kΩ / 5W actual power consumption 2.2W Please use heat-resistant metal film resistance, high reliability, once the disc will make the FU-5 board increased red, and endangered the safety amplifier. It is connected to the -210V power supply to provide a 10mA static current to the cathode output, which can push the internal resistance and small distortion. The filament balance potentiometer of the FU-5 is more than 2W of 100 Ω, and the potentiometer handle can only be used on the bottom plate, otherwise a large error will result. The current passed in the current table is gate stream, so that the current table pointer is normal. This is different from the A-output tube, while the medium volume is approximately zero, and the meter indication is a board. Current table Overvisor current can be selected from 125 to 150 mA specifications. This output transformer is a key component, and the primary side is opposite to the secondary side coil, which is a negative feedback request. Of course, when audio shaking occurs, the primary side B + can be invisible to the P joint. The primary side electrical inductance should be greater than 110 h (the test conditions are 220V / 50Hz). Note that the electrical inductance measured by the normal inductance is initial inductance, and its numerical value is generally less than the actual inductance. The output transformers and power transformers used in this machine are customized by Kay Li. If you want to be homemade, Table 4 gives the production data. The one-stage side is surrounded by a layer of 0.08 mm cable paper, and the inter-group is insulated to add polyester film plus cable paper with the cable paper. The secondary side is divided into two sections of one side. The power transformer coil and the output transformer coil must be installed vertically, and the 1.5mm thick iron shielding housing is added to minimize magnetic field coupling. Single-ended output transformers Because the air gaps belong to the magnetic circuit transformer, it is easier to sense external magnetic field interference than the closed magnetic circuit iron core of the push-pull output transformer. Of course, the addition of negative feedback in the circuit significantly reduces the output internal resistance, hinders the core magnetic induction, and output transformers to resist external magnetic field interference capabilities will also increase significantly. There is an interesting phenomenon in the production. After the machine is removed, the circuit does not work, the circuit does not work, the speaker bass horn has a weak communication, and after inserting the high pressure tube, the circuit works normally, and the communication is exhausted. The power transformer core has a thickness of 0.5mm thickness than the iron core-stacked iron 3 layer, and then the outer casing is well made, the magnetic interference can be further reduced to the ear sticker bass horn. Practice proves that this method is the most effective way to eliminate power transformer magnetic leakage. When the test machine, the FU-5 filament voltage was found to be DC 10.8V, which exceeded the error requirements of ± 5% of the tungsten cathode filament, which is the solution to the rectifier bridge stack and filter capacitance. 0.1 Ω / 5W resistance Only, as shown in the power circuit diagram 4. There is three benefits that have increased the internal resistance of the input, and the peak current has dropped sharply and reduces the burden of the rectifier. After the second internal resistance increases, the filtered capacitor charge and discharge angle increases, and the filtering effect is improved. Its three adjustments The resistance value can accurately determine the output voltage, which is a guarantee that makes the FU-5 tube longevity. There is a very simple way, that is, the 0.3mm common wire intercept 1.5M length is 0.1 Ω resistor, and it can be connected to the bridge stack and the filter capacitor, and the length is partially tied, which adjusts the length of the wire, The FU-5 filament voltage is 10V can be adjusted. This resistor cannot be connected in series between the DC output and the filament, otherwise there is no advantage.
Sixth, debugging the on-absissue load, the performance is active, as shown in Figure 6. Adjusting the 20KΩ potentiometer with a 6P3P gate pressure 805 board is very convenient, and it is very stable, and the rear bond stream is not changed. 805 filament balance 100Ω potentiometer adjustment is also very sensitive (no other interference), there is a little near the midpoint, and you can't hear a little snoring in the low sound. Everything is as expected, no suspense, the assembly process is surprising. Description This circuit is an excellent mature circuit, which seems to be a bit complicated, in fact, but not difficult. Inject the sine wave signal in the signal generator, and output the pure resistance load and the output power is measured. Confirm that the output sine wave valid value power is 45W or more, reaches 48W. Estimation is that the saturation pressure drop US is slightly conserved by 150V, and it can reach US = 120V. The boot audition is more unusual, listening to vocals in various discs, such as Luohai Ying's first episode, voice soft and sweet, very resistant. Listen to some light music and symphony, such as Strauss's "family", it is worthy of 45W x 2 output power, magnificent, and the scene is grand. Especially listening to the yellow first drums ", the bass drum is condensed, and the vibration is lung, and there is no feeling of looseness. The bass is significantly lower than the 845-tube. The 4th song "101north) disc in the" 101north) disc is started with the "Textile Niang" in the field, and the sound of the "Textile Niang" in the field is really like a summer and night. People's music, such as "Tieguanyin" in the water, guzheng songs, strings, etc., more pleasant, and the treble feels unconscious. The high and low sound domain expands to both ends. The EL34 is used to transfer 6P3P as a cathode output push tube, adjust the trial after the FU-5 board, the small and medium-sized power can not observe the difference, only when the high power output is, it seems more powerful. The native bile duct is a common tube, so the range of tubes is wide and the cost is not high. This machine is from the pre-stage tube until the output stage and the rectifier tube, all of which are dawn. At this point, the author has never been approved with the proposal of the use of a single-class power tube as a single-ended power amplifier output tube to be completely subversive. The excellent performance of the 805 bile duct of the past day, I really got each other. "
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