Amplifiers are cost-effective. A 5,000 yuan combined amplifier or preamp, the sound effect is often better than the transistor machine that is twice as expensive or even more expensive. More importantly, the music of the amplifier is strong and the overtone is heavy. This is more or less due to the addition of second harmonic distortion. Therefore, the listener feels that the sound is smooth and the hall sounds are rich. Live with the player. I like to listen to music with a tube amplifier. Here are some methods and points for playing a tube amplifier. It is suitable for some friends who are new to playing a tube amplifier.
Single-ended push-pull conversion
The smooth, subtle and transparent sound produced by a single-ended Class A circuit is really fascinating when it comes to playing vocals. Of course, it is best to try it yourself. If you want to use 300B, EL34, KL66 single-ended machines, etc., but the production of single-ended machines requires a higher cost, and the output of ordinary cattle is 1,500 pairs; There is no match between six and seven thousand. If you do n’t have enough guidelines and production experience, it is really not suitable to make your own, so as not to waste money. Recently, in foreign audio magazines, I saw some lines that introduced the changeover machine as a single-ended machine with reference value. See Book 1. A strong discharge tube is used for constant current operation to prevent the output transformer from being saturated by DC magnetization. Among them, SA and SB are double-pole double-throw switches, and RX is used as a voltage-reducing purpose to avoid the pitting sound of the boot sound box. The switch is placed at the AL and BL points for single-ended connection. Although the output power is reduced, the screen flow is generally adjusted higher, but the screen consumption should not exceed the allowable safety. Another connection method is shown in Figure 2. It is to connect the two gallbladders in parallel, the switch is placed in AL, A2, etc. is a single-ended connection method, and the B1, B2, etc. are general push-pull connections.
Three, pentode interchange
It is often said that the sound of the triode is clear and transparent and the analysis power is high. Many people will like to change the super-linear connection to the triode connection method. Throw a 100-time resistance, but you should pay attention to increase the negative bias to avoid exceeding the maximum screen consumption value. The general method of measuring screen current is to add a 10 (2 to 5 W) resistor to the cathode to ground to measure the voltage drop across the resistor. For example, when measuring 1V, according to Golden Ohm's law (I = E / R), the screen current is 100 mA. .
In addition, the pentode is switched to the triode output. The output is originally selected for the pentode input and output. After the triode is connected, it does not completely match the best screen shade, which affects the sound quality. The optimal operating point of the triode load is twice the screen resistance, and the pentode requires that it be selected to work between five and one tenth of the screen load. Taking 6l6gc as an example, the triode screen resistance is 1. 7k and the pentode screen resistance is 27k. Therefore, the triode output is suitable for selecting the 3.4k input output cow, and the pentode output is suitable for selecting the output cow above 5k. The 6l6gc pentode amplifier usually uses more than 6k of output, so it is not suitable for triode output. Therefore, amplifiers designed for transistors really have better sound quality than amplifiers with pentodes replaced by transistors. The triode connection method has large distortion in the low range and is affected dynamically. It is suitable for listening to sketches.
Extend the life of gallbladder
The accelerated loss of the lamp bulb is mostly caused by the loss of the filament and cathode. With regard to the filament, cold start (that is, not to gradually pressurize the filament) accelerates the loss of the filament, especially the use of AC ignition filament. Take 6l6gc as an example, the filament generally consumes 66.3v0.9a, but the inrush current reaches 3a at the moment of startup. As for the boldness, because modern models generally use high-voltage commutator, high voltage for the whole Han Dynasty, there is inrush current when starting up, because the high voltage is immediately added to the screen when starting up, but the cathode has not been preheated enough, the screen has appeared Flow, because the cathode emits electrons by a layer of metal oxide coated on the cathode metal barrel, there is a considerable temperature, when the operating temperature is not reached, because there is no heat penetration, the resistivity of each part is different, so the screen flow It is concentrated in the area where the resistance is small. It is also the same when the power is turned off. After the power is turned off, the cathode temperature drops due to the cut off of the filament power, and the capacity of the high-voltage filter capacitor is generally large. The high voltage will be stored for a period of time. The same one accelerates the loss of the cathode.
Therefore, the following methods may be considered for improvement:
1. Light bulb rectification, which is the rectification method used by radio amplifiers in the 1950s and 1960s. This requires that the power flow hydrocarbon compressor have another 5V and standby power consumption. After the rectification, the high voltage can be fully applied to the screen electrode within ten seconds, and the cathode has sufficient time to warm up, so as not to accelerate the lamp consumption. However, the disadvantage is that the internal resistance of the high-voltage power supply is increased by the lamp rectification. For the signal source, it will generate a voltage drop and reduce the gain. The general effect is to slow down the transient and the sound floor is slow. The solution can be considered parallel rectifier to reduce the internal resistance of the power supply.
2. Install a high-voltage switch, see Figure 5. For example, some factory machines have two standby and working switches. The principle is to turn on the filament switch first, and then turn on the high-voltage switch after a certain period of time. Such as adding switches and parallel resistors to the high voltage secondary. s1 parallel connection resistance and series resistance in the future, it is expected that there will be a certain degree of voltage reduction during the preheating time after booting, to eliminate the phenomenon of accelerated bile loss due to inrush current. In terms of high voltage, s2 can be connected after s1 is connected, so that the cathode has enough warm-up time before adding full-scale screen pressure.
3. A delay circuit can also be used, so that the filament and high voltage can be gradually increased, which has the purpose of protecting the lamp. However, the circuit is more complicated, and I do not know the degree of impact on the sound quality. It requires higher production knowledge and technology, so It may not be suitable for ordinary people.
Single-ended push-pull conversion
The smooth, subtle and transparent sound produced by a single-ended Class A circuit is really fascinating when it comes to playing vocals. Of course, it is best to try it yourself. If you want to use 300B, EL34, KL66 single-ended machines, etc., but the production of single-ended machines requires a higher cost, and the output of ordinary cattle is 1,500 pairs; There is no match between six and seven thousand. If you do n’t have enough guidelines and production experience, it is really not suitable to make your own, so as not to waste money. Recently, in foreign audio magazines, I saw some lines that introduced the changeover machine as a single-ended machine with reference value. See Book 1. A strong discharge tube is used for constant current operation to prevent the output transformer from being saturated by DC magnetization. Among them, SA and SB are double-pole double-throw switches, and RX is used as a voltage-reducing purpose to avoid the pitting sound of the boot sound box. The switch is placed at the AL and BL points for single-ended connection. Although the output power is reduced, the screen flow is generally adjusted higher, but the screen consumption should not exceed the allowable safety. Another connection method is shown in Figure 2. It is to connect the two gallbladders in parallel, the switch is placed in AL, A2, etc. is a single-ended connection method, and the B1, B2, etc. are general push-pull connections.
Three, pentode interchange
It is often said that the sound of the triode is clear and transparent and the analysis power is high. Many people will like to change the super-linear connection to the triode connection method. Throw a 100-time resistance, but you should pay attention to increase the negative bias to avoid exceeding the maximum screen consumption value. The general method of measuring screen current is to add a 10 (2 to 5 W) resistor to the cathode to ground to measure the voltage drop across the resistor. For example, when measuring 1V, according to Golden Ohm's law (I = E / R), the screen current is 100 mA. .
In addition, the pentode is switched to the triode output. The output is originally selected for the pentode input and output. After the triode is connected, it does not completely match the best screen shade, which affects the sound quality. The optimal operating point of the triode load is twice the screen resistance, and the pentode requires that it be selected to work between five and one tenth of the screen load. Taking 6l6gc as an example, the triode screen resistance is 1. 7k and the pentode screen resistance is 27k. Therefore, the triode output is suitable for selecting the 3.4k input output cow, and the pentode output is suitable for selecting the output cow above 5k. The 6l6gc pentode amplifier usually uses more than 6k of output, so it is not suitable for triode output. Therefore, amplifiers designed for transistors really have better sound quality than amplifiers with pentodes replaced by transistors. The triode connection method has large distortion in the low range and is affected dynamically. It is suitable for listening to sketches.
Extend the life of gallbladder
The accelerated loss of the lamp bulb is mostly caused by the loss of the filament and cathode. With regard to the filament, cold start (that is, not to gradually pressurize the filament) accelerates the loss of the filament, especially the use of AC ignition filament. Take 6l6gc as an example, the filament generally consumes 66.3v0.9a, but the inrush current reaches 3a at the moment of startup. As for the boldness, because modern models generally use high-voltage commutator, high voltage for the whole Han Dynasty, there is inrush current when starting up, because the high voltage is immediately added to the screen when starting up, but the cathode has not been preheated enough, the screen has appeared Flow, because the cathode emits electrons by a layer of metal oxide coated on the cathode metal barrel, there is a considerable temperature, when the operating temperature is not reached, because there is no heat penetration, the resistivity of each part is different, so the screen flow It is concentrated in the area where the resistance is small. It is also the same when the power is turned off. After the power is turned off, the cathode temperature drops due to the cut off of the filament power, and the capacity of the high-voltage filter capacitor is generally large. The high voltage will be stored for a period of time. The same one accelerates the loss of the cathode.
Therefore, the following methods may be considered for improvement:
1. Light bulb rectification, which is the rectification method used by radio amplifiers in the 1950s and 1960s. This requires that the power flow hydrocarbon compressor have another 5V and standby power consumption. After the rectification, the high voltage can be fully applied to the screen electrode within ten seconds, and the cathode has sufficient time to warm up, so as not to accelerate the lamp consumption. However, the disadvantage is that the internal resistance of the high-voltage power supply is increased by the lamp rectification. For the signal source, it will generate a voltage drop and reduce the gain. The general effect is to slow down the transient and the sound floor is slow. The solution can be considered parallel rectifier to reduce the internal resistance of the power supply.
2. Install a high-voltage switch, see Figure 5. For example, some factory machines have two standby and working switches. The principle is to turn on the filament switch first, and then turn on the high-voltage switch after a certain period of time. Such as adding switches and parallel resistors to the high voltage secondary. s1 parallel connection resistance and series resistance in the future, it is expected that there will be a certain degree of voltage reduction during the preheating time after booting, to eliminate the phenomenon of accelerated bile loss due to inrush current. In terms of high voltage, s2 can be connected after s1 is connected, so that the cathode has enough warm-up time before adding full-scale screen pressure.
3. A delay circuit can also be used, so that the filament and high voltage can be gradually increased, which has the purpose of protecting the lamp. However, the circuit is more complicated, and I do not know the degree of impact on the sound quality. It requires higher production knowledge and technology, so It may not be suitable for ordinary people.
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