What to do if the output tube of the amplifier is broken?

by:Gisen     2020-04-03
First, the cause of damage to the power amplifier tube 1. The impedance of the amplifier and the speaker does not match. For example, using a power amplifier with a rated load of 8Ω to drive a 4Ω speaker, the power amplifier tube is easily overloaded and damaged. 2. The main limit parameters of the newly replaced power amplifier tube are lower than the original power amplifier tube. The three main limiting parameters of the BVCEO, PCM, and ICM of the new tube should be greater than or at least equal to the original tube rating. 3. Poor heat dissipation of the power amplifier tube. When replacing the power tube, pay attention to the tight contact between the power amplifier tube and the radiator. Some insulation pads need to be added between the power amplifier tube and the radiator. Polyester film or mica sheet should be selected. Paper or insulating tape cannot be used. The contact surface of the power amplifier tube and the radiator should be coated with thermal grease. 4. Circuit failure. First test whether the positive and negative power supply voltages of the power amplifier are equal, otherwise check the power circuit of the power amplifier. If the power supply voltage is normal, then test whether the static DC voltage at the output end of the power amplifier is 0V, and if it is 0V, then measure whether the static current of the power amplifier tube is too large. If the static DC voltage at the output end of the power amplifier has a certain deviation but is not large, most of the component parameters of the drive stage or the front stage change. You can first observe whether the transistors at all levels have been replaced, and whether the new tube is consistent with the original tube parameters (especially β value), and then refer to the other channel and use the resistance method to measure the on-circuit resistance of each device and key point to find out Abnormal components. Repair methods for damaged amplifier tubes 1. Reduce the power supply voltage of the power amplifier part. For example, if the voltage of the power amplifier part is 45V positive and negative, use a positive and negative 20V for maintenance, which is safer. 2. When repairing the power amplifier circuit, be sure to short the power amplifier signal input to ground. 3. Some power amplifiers cannot remove the power tube for repair. After the power tube is removed, the midpoint voltage cannot be measured. The midpoint voltage is either positive or negative. It is also a positive or negative value of the supply voltage. The relay of the horn protection circuit cannot be closed at the same time. note! Step-down repairs may keep the circuit's relays from closing. this is normal. Do not suspect that protection due to excessive midpoint voltage. 4. If you are afraid of burning the power tube, you can do this: temporarily replace the 2SA940 and 2SC2073 tubes. Because the general home amplifier is not partial. The static current is not large and will not burn the tube, but the tube must be attached to the heat sink. Don't make too loud sounds during the audition. Take a small speaker audition. 5. The component parameters on the bias circuit must be accurate. The offset triode pin position and tube type must be connected and selected. Otherwise, you have suffered. 6. The β of the 'complementary pair' of the tubes used is basically one to one. How to choose a high-quality amplifier 1. Power or quality Many people pay great attention to the output power of the power amplifier when purchasing it, because it is generally believed that the greater the power of the power amplifier, the more powerful it is, the easier it is to push the speaker, and the easier it is to remove the speaker ( Speakers) to get good sound. From this point of view, there is no doubt that it is correct, because the efficiency of the power amplifier is very low after all, and to make the weak signals in the music play out from the speakers without distortion, the power amplifier must also have enough Reserve power. Therefore, a high-power amplifier is undoubtedly its own advantage. Some previous audio manufacturers have competed on the output power of the amplifier. However, is it better to buy more power when purchasing an amplifier? This issue should be viewed from a comprehensive perspective. In terms of power, the relationship between the power amplifier and the speaker is like the generator and the electric load. When the load is very small, you have to use a super generator. The result is that it will not only increase costs and cause waste, but will not bring What benefits come. Besides, the sound pressure that human ears can withstand is limited, and the space for ordinary families to listen to is limited. Therefore, when purchasing an amplifier, it seems to be a bit one-sided to pursue only high power. As far as ordinary families are concerned, a well-designed amplifier with 50W output power is used to drive a pair of speakers with an efficiency of more than 86dB. The sounds of amplifiers produced in different regions are different. People's preferences for the sound in the sound are different. Therefore, if the price is basically the same, let you have a common power amplifier with an output power of 100W and a 50W output power but the sound quality meets your appreciation requirements. Make a choice in the amplifier, then it is recommended that you choose the one with a lower power. 2.Whether the amplifier is heavier is better Many people will weigh the weight of the power amplifier when choosing an amplifier. The practical method is a simple and practical way to judge the quality of the amplifier. Because the light weight amplifier must have omitted some parts of the amplifier or 'shrink' when selecting parts, but the most obvious one is the power supply part. Any power amplifier (or other audio equipment) relies on power to provide energy to work. If the power supply is insufficient, the machine will often not work properly, resulting in deterioration of sound quality. Therefore, in order to make the power amplifier have sufficient energy supply at high power output, good power amplifiers often leave a sufficient amount of DC power in the design. Therefore, the power amplifier must use heavyweight Large-capacity transformers, and some even use double transformers. In order to resist the impact of external vibration and internal noise on the sound quality of the power amplifier, a good power amplifier will also use very thick metal materials to make the chassis, and the weight of a power amplifier depends largely on the transformer and the chassis. weight. Where does the music background come from In many audio review articles, we can see comments such as quiet music backgrounds, clear and transparent audio, but where does this quiet music background come from, and what guarantees it? It can be said with certainty that it depends on the signal-to-noise ratio S / N of the power amplifier (usually expressed in dB). The signal-to-noise ratio is the ratio of the signal amplitude to the noise amplitude. Because this index is inversely proportional to the output noise of the power amplifier. Therefore, the larger the number of signal-to-noise ratios, the smaller the output noise of the power amplifier and the higher the quality. Therefore, when selecting an amplifier, of course, the larger the signal-to-noise ratio, the better. When using the early cassette tape recording, I believe that many people have such an experience. When playing to the blank space between two music, you often hear some 'hissing' noise. This is why this phenomenon occurs. One of the reasons was that the recorder had a low signal-to-noise ratio (generally below 60dB). As for the power amplifier, if there is a quiet music background, the signal-to-noise ratio of the power amplifier must be above 90dB, and the excellent power amplifier will reach more than 100dB. Generally speaking, it is necessary to increase the output power and frequency response of the power amplifier. Range is not so difficult, but it is not so easy to improve the signal-to-noise ratio of a power amplifier. If the signal-to-noise ratio of a power amplifier reaches more than 100dB, he is by no means a 'leisure generation'. If a power amplifier The signal-to-noise ratio of the machine reaches 110dB, so it is not difficult to have a quiet background, transparent, and three-dimensional sound. In addition, when you understand the technical index of the signal-to-noise ratio, you must pay attention to the marked number. Whether there are additional conditions behind it, if so, we must understand the circumstances under which this indicator was reached, otherwise it will be easy to be deceived by some illusions. 4. Tubes and transistors In recent years, the electronic tube power amplifier has regained its momentum. The reason is that in addition to the advancement of technology, the service life of electronic tubes has been extended, and high-quality and inexpensive electronic tubes produced in China and Eastern Europe have also contributed to the situation, such as Japan. Rex, Denmark's LA Audio and other manufacturers of highly acclaimed tube amplifiers are using Chinese-made tubes. Secondly, because of the cold and dry sound of digital audio, people also miss the tube amplifier with the characteristics of warm and sweet sound. Since tube amplifiers have such a great advantage in sound, is it better than transistor amplifiers? Generally speaking, in the mid-priced amplifier, the sound of the tube amplifier is better than the transistor in terms of sound flexibility, but it is not always the case in high-end machines. 5.Combined and split We know that there are several types of control amplifiers (also known as preamps), power amplifiers, and integrated amplifiers in the power amplifier. The main function of the preamp is to amplify weak signals, and at the same time switch functions and control volume, so It is also called control amplifier, and the main role of power amplifier (also called post amplifier) ​​is to supply the power required for the speaker to work. The integrated amplifier is a combination of the first two amplifiers. Because it is a front and rear amplifier installed in a chassis, it is also called a combined power amplifier compared to the first two. Since the Hi-end amplifiers are all made in the body type, it gives us the impression that the split-type power amplifier is an advanced product. But is this actually the case? The answer is of course no. The main purpose of the power amplifier is to prevent the deterioration of sound quality. Because Hi-end machines have very strict requirements for various technical indicators, in order to ensure the quality of the power amplifier, when engineers design the power amplifier, will the large amount of thermal energy generated during the power amplifier work affect the preamp operation? The problem must also be considered. Therefore, in order to ensure that the Hi-end amplifier has a first-class level in sound and quality, it must be designed as a component. But if the quality of the power amplifier does not reach such a high level at all, and it is necessary to design the component form, it is not difficult to infer that this is largely due to commercial reasons. I haven't seen that many cheap Japanese-made kits are also useful for split-type amplifiers, but I believe that the readers with some experience will naturally understand the quality of the split-type amplifiers in these cheap kits. In general, in the Hi-end class power amplifier, the split type has the advantage, but in the low-end products, the combined power amplifier is not worse than the split type. In terms of convenience and space occupied, the combiner is slightly better, but in combination and matching to obtain different reproduction sounds, the split-type amplifier is dominant.
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