In December last year, I bought a 6N13P amplifier kit for 1,400 yuan. Although it had a "bile taste" after it was assembled, it had insufficient power reserve and seemed to be less powerful. The reason for the analysis is that the total gain of the circuit is not enough, and the output excitation voltage of the driving stage is small.
In order to pursue better results, I designed the circuit by myself to increase the gain of the front stage so that the driving stage has a large enough distortion-free output voltage; I designed the output transformer myself and spent only 800 yuan to design and produce a Class A analog Amplifier.
6N13P is a high power, low internal resistance dual triode, the foreign model is 6AS7, which was originally used in stabilized power supply and TV vertical circuit. It can be seen from this tube screen pole characteristic curve that 6N13P is also suitable for audio power output. A 6N13P dual triode is used as a push-pull output to obtain 12-15W of power. If two 6N13P tubes are used for parallel push-pull, there will be more than 25W output, which is suitable for general household use.
Line introduction
The circuit diagram of 6N13P Class A push-pull tube amplifier is shown in the attached drawings. This machine adopts four domestically produced bipolar transistors to form a four-stage amplifier circuit. Among them, the front stage is made up of 6N11, 6N9, and 6N8 bipolar transistors for diode voltage amplification, one-stage inversion, and one-stage push; All levels are biased by the cathode self-sufficient gate, and the use of capacitive inter-level coupling is conducive to the adjustment of static operating points at all levels. After canceling the overall large loop negative feedback circuit, the output circuit is very stable and the audition effect is also good.
The screen-to-ground and cathode-to-ground voltages of all levels are marked on the circuit diagrams in the drawings. As long as it is adjusted according to the marked voltage, the machine can work in Class A working state.
In the drawing, the first stage is a voltage amplifier circuit, which uses a low-noise bipolar transistor 6N11 (6N4, E88CC and other bipolar transistors are also available).
The second stage is an ordinary voltage amplifying circuit, which uses high μ bipolar transistor 6N9. The purpose is to make this stage have sufficient voltage amplification.
The third stage is a load-sharing inverter circuit, which uses a high μ bipolar transistor 6N9. The inverter circuit has no voltage amplification function, and mainly plays the role of inverter.
The fourth level is the driving level, which uses 6N8P dual transistors with low and medium μ and low internal resistance. The push-level circuit is mainly to provide a sufficiently high excitation voltage for the final push-pull output tube. This stage uses common cathode voltage amplification connection. When the screen voltage of about 190V is added, and the appropriate load resistors R17 and R18 are selected, it can meet the drive signal requirements of the final power tube gate.
In order for the final stage push-pull output circuit to obtain input signal voltages of equal magnitude and opposite phases, the gate-drain resistors R17 and R18 of the upper and lower tubes of the driving stage must be paired with a resistance value within 5%. This machine selects a metal film precision resistor with 0 ~ 5% error.
The last stage uses a class A push-pull power amplifier circuit, which differs from the previous stage in voltage amplification. The voltage amplification requires low noise and a first-class output voltage, while the power amplification circuit is different. It requires large signals, large dynamics, and large currents. Therefore, the unit is connected to a common cathode push-pull output circuit, and the gate resistors R21 and R22 are 470Ω resistors, which are high-frequency self-excited resistors. The resistance on the cathode has three functions:
1? Adjust the static working point so that the straight line of the 6N13P screen pole characteristic curve is at the midpoint, which is in the class A working state;
2? A voltage drop is generated by the cathode resistors R23 and R24 to provide the grid bias voltage for the push-pull tube;
3? Protect the 6N13P high power tube.
The power transformer adopts the design of 250WC iron core, and the primary is divided into two sets of coils of 240V and 220V. The secondary requirements have a center tap, 240V and 240V + 60V coils with the same number of turns, and use 1N4007 crystal rectifier diodes to form two full-wave rectifier filter circuits to provide DC power supply voltage as the DC high voltage of each tube screen. The filament coil winding design is 6? 3V 5A, 6? 3V 5A, 6? 3V 3A, and has a center tap to ground the center point of the filament supply coil, so that the AC voltage phase formed by the other ends of the filament to other electrodes On the contrary, the leakage currents generated in the filament and grid circuits (or filament and cathode circuits) cancel each other out.
After the full-wave rectification and filtering of this machine, high voltage switches B + 450V and B + 360V are set. Because this machine is a transistor rectifier, tube circuit amplifier, high and low voltage must be turned on separately.
The low-pressure switch is set on the left side of the panel of the amplifier, and the high-pressure switch is set on the right side. When starting up, be sure to turn on the low voltage switch first, and then turn on the high voltage switch. After turning on the low voltage, the filament is preheated for a period of time, usually about 15 minutes in winter and 3 to 5 minutes in summer. When shutting down, be sure to turn off the high voltage, wait a few minutes, or wait for no music, then turn off the low voltage. In places where the power supply voltage is unstable, always pay attention to adjust the power supply voltage so that it can be maintained at about 220V.
In order to pursue better results, I designed the circuit by myself to increase the gain of the front stage so that the driving stage has a large enough distortion-free output voltage; I designed the output transformer myself and spent only 800 yuan to design and produce a Class A analog Amplifier.
6N13P is a high power, low internal resistance dual triode, the foreign model is 6AS7, which was originally used in stabilized power supply and TV vertical circuit. It can be seen from this tube screen pole characteristic curve that 6N13P is also suitable for audio power output. A 6N13P dual triode is used as a push-pull output to obtain 12-15W of power. If two 6N13P tubes are used for parallel push-pull, there will be more than 25W output, which is suitable for general household use.
Line introduction
The circuit diagram of 6N13P Class A push-pull tube amplifier is shown in the attached drawings. This machine adopts four domestically produced bipolar transistors to form a four-stage amplifier circuit. Among them, the front stage is made up of 6N11, 6N9, and 6N8 bipolar transistors for diode voltage amplification, one-stage inversion, and one-stage push; All levels are biased by the cathode self-sufficient gate, and the use of capacitive inter-level coupling is conducive to the adjustment of static operating points at all levels. After canceling the overall large loop negative feedback circuit, the output circuit is very stable and the audition effect is also good.
The screen-to-ground and cathode-to-ground voltages of all levels are marked on the circuit diagrams in the drawings. As long as it is adjusted according to the marked voltage, the machine can work in Class A working state.
In the drawing, the first stage is a voltage amplifier circuit, which uses a low-noise bipolar transistor 6N11 (6N4, E88CC and other bipolar transistors are also available).
The second stage is an ordinary voltage amplifying circuit, which uses high μ bipolar transistor 6N9. The purpose is to make this stage have sufficient voltage amplification.
The third stage is a load-sharing inverter circuit, which uses a high μ bipolar transistor 6N9. The inverter circuit has no voltage amplification function, and mainly plays the role of inverter.
The fourth level is the driving level, which uses 6N8P dual transistors with low and medium μ and low internal resistance. The push-level circuit is mainly to provide a sufficiently high excitation voltage for the final push-pull output tube. This stage uses common cathode voltage amplification connection. When the screen voltage of about 190V is added, and the appropriate load resistors R17 and R18 are selected, it can meet the drive signal requirements of the final power tube gate.
In order for the final stage push-pull output circuit to obtain input signal voltages of equal magnitude and opposite phases, the gate-drain resistors R17 and R18 of the upper and lower tubes of the driving stage must be paired with a resistance value within 5%. This machine selects a metal film precision resistor with 0 ~ 5% error.
The last stage uses a class A push-pull power amplifier circuit, which differs from the previous stage in voltage amplification. The voltage amplification requires low noise and a first-class output voltage, while the power amplification circuit is different. It requires large signals, large dynamics, and large currents. Therefore, the unit is connected to a common cathode push-pull output circuit, and the gate resistors R21 and R22 are 470Ω resistors, which are high-frequency self-excited resistors. The resistance on the cathode has three functions:
1? Adjust the static working point so that the straight line of the 6N13P screen pole characteristic curve is at the midpoint, which is in the class A working state;
2? A voltage drop is generated by the cathode resistors R23 and R24 to provide the grid bias voltage for the push-pull tube;
3? Protect the 6N13P high power tube.
The power transformer adopts the design of 250WC iron core, and the primary is divided into two sets of coils of 240V and 220V. The secondary requirements have a center tap, 240V and 240V + 60V coils with the same number of turns, and use 1N4007 crystal rectifier diodes to form two full-wave rectifier filter circuits to provide DC power supply voltage as the DC high voltage of each tube screen. The filament coil winding design is 6? 3V 5A, 6? 3V 5A, 6? 3V 3A, and has a center tap to ground the center point of the filament supply coil, so that the AC voltage phase formed by the other ends of the filament to other electrodes On the contrary, the leakage currents generated in the filament and grid circuits (or filament and cathode circuits) cancel each other out.
After the full-wave rectification and filtering of this machine, high voltage switches B + 450V and B + 360V are set. Because this machine is a transistor rectifier, tube circuit amplifier, high and low voltage must be turned on separately.
The low-pressure switch is set on the left side of the panel of the amplifier, and the high-pressure switch is set on the right side. When starting up, be sure to turn on the low voltage switch first, and then turn on the high voltage switch. After turning on the low voltage, the filament is preheated for a period of time, usually about 15 minutes in winter and 3 to 5 minutes in summer. When shutting down, be sure to turn off the high voltage, wait a few minutes, or wait for no music, then turn off the low voltage. In places where the power supply voltage is unstable, always pay attention to adjust the power supply voltage so that it can be maintained at about 220V.
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