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Introduction In general, the radio is constructed by mechanical devices, electronic devices, magnets, etc. It receives the audio signals emitted by broadcasting stations through converting electric wave signals. After the invention of the vacuum tube, the circuit and receiving performance of the radio had undergone revolutionary progress and improvement, that is valve radio. Later, with the development of technology, radios with transistors as the core gradually became popular. It's what we know as a transistor radio. Radios are still widely used for many functions. Here two main radios will be described in detail below. Catalog Introduction Ⅰ Valve Tube Radio 1.1 Vacuum Tube Radio Classifications 1.2 Advantages and Disadvantages of Valve Radio 1.3 German Vintage Valve Radio Models for Sale Ⅱ Transistor Radio 2.1 Transistor Radio Overview 2.2 Transistor Radio Selection Matters 2.3 Transistor Radio Brands for Sale Ⅲ Radio Further Development Ⅳ FAQ Ⅰ Valve Tube Radio The valve radio, also known as the vacuum tube radio, was a product of the early 20th century, and immediately became the new favorite of that era with the launch of the broadcasting station. By the late 1920s, vacuum tube radio equipment replaced the primitive spark-gap systems on most merchant ships. This new equipment could send and receive signals virtually worldwide, by using high frequency or "short-wave" bands. Tube technology allowed radio signals to be tuned with much greater precision than spark-gap. The basic design for tube radio was perfected by the 1930s and continued in use on merchant vessels into the 1980s. 1.1 Vacuum Tube Radio Classifications 🔺AM (Amplitude Modulation) RadioIn the era when tube radios were popular, AM radios were the mainstream products. Amplitude modulation wave modulates the high-frequency carrier with audio signal. Its waveform is symmetrical, the amplitude is the same as that of the modulated signal, and then obtain the audio signal after high-frequency component is filtered out. In addition, the frequency of the carrier signal (the frequency of the broadcasting station) is the carrier frequency.AM radios can receive medium-wave and short-wave broadcasts, and some can receive long-wave broadcasts. Since the mid-band frequency interval has been unified to 9KHz, its highest audio frequency is only 4KHz. So the sound quality is affected because of large electromagnetic interference.There are two main types of AM radios: direct-amplifier type and external (self) differential type1) Direct-amp radio, also called high-amp radio, its typical circuit structure is as follows:High Amplifier—Detection—Low Amplifier—Power AmplifierA circuit that uses a grid detector circuit and high-frequency positive feedback is called a regenerative radio, which can obtain higher sensitivity and amplitude selectivity. A regenerative radio with high amplifier and short wave can receive AM telegraph signals. Most of the old Japanese-made radios have such circuits. Direct-amp radios are prone to self-excitation of high-frequency signals, high-end and low-end gains are uneven, and regenerative radios without high-amplification have poor selectivity. In addition, the reed speakers with poor sound quality are generally used, so they are gradually replaced by superheterodyne radios.Simple regenerative radios mostly use reed speakers, which have high impedance (about 10K) and high sensitivity. It can be directly used as the load of the power amplifier tube, but the frequency range is only 350~3000Hz, so the sound quality is poor. Later regenerative radios applied moving coil speakers, and the sound quality was better. However, because of low impedance, an output transformer is required, and its primary impedance must match the load impedance of the power amplifier tube. Moving coil speakers are divided into permanent magnets, constant magnets and excitation. Among them, excitation horns are used in AC electronic tube radios, and their excitation coils can also be used as filter chokes. 2) Heterodyne RadioThe heterodyne radio adopts a frequency conversion circuit. The signal generated by its high-frequency oscillation circuit and the input signal have a certain frequency difference. After the two are mixed, a fixed intermediate frequency signal (455~465KHz) is generated. Some people call the oscillation frequency higher than the signal frequency a heterodyne type, and vice versa.Heterodyne plus intermediate frequency amplifier circuit is called superheterodyne. This type of circuit requires a single electron tube to oscillate, and later a multi-pole or composite tube dedicated to frequency conversion appears. The superheterodyne type is the most common circuit of commercial radios. It has an automatic volume control circuit and can add tuning instructions. The circuit principle will be described in detail later. The superheterodyne radio can obtain more stable and higher gain due to amplifying the fixed frequency. The disadvantage is that there is image frequency interference.The circuit structure of a typical superheterodyne radio is as follows:Frequency Conversion—Middle Amplification—Detection—Low Amplification—Power Amplification 3) Autodyne Frequency Conversion RadioUsing ordinary pentodes for frequency conversion is only suitable for the mid-band, and the middle frequency is 175KHz. Due to the popularization of special frequency conversion tubes, it is rarely used now. Figure 1. Vintage AM Radio 🔺FM (Frequency Modulation) RadioFM radio is a radio that transmits radio signals through the use of FM frequency modulation carrier. Due to the shorter wavelength, the signal transmitted is much better than that of the radio that uses the AM wavelength. However, due to the short wave, the transmission distance is relatively short.FM wave is to use audio signal to modulate the frequency of high frequency carrier. Its advantages include strong anti-interference ability, high signal-to-noise ratio, good frequency bandwidth and sound quality, in addition, the audio frequency can reach 20Hz~15000Hz. Because the FM wave works in the ultra-high frequency band, it can accommodate many radio stations. With its linear propagation characteristics, the same frequency can be reused at a distance of hundreds of kilometers, which can effectively solve the problem of congestion of medium and short wave radio stations.Modern FM broadcasting is compatible with stereo and mono channels(in the early days of stereo broadcasting, two frequencies were used and two radios for reception). Some hobbyists are likely to use a simple super-regenerative circuit to receive FM broadcasts. Because it works in a self-oscillation state, the work is unstable and has strong super-noise. 1.2 Advantages and Disadvantages of Valve Radio Advantages of Valve Radio 1) The valve tube circuit has a simple structure and good anti-overload performance.2) The characteristics of the power amplifier circuit of the tube radio are better than those of the transistor or integrated circuit power amplifier. The screen current of the Class A power amplifier circuit with an output transformer for output impedance matching has little change at zero signal and full signal. So the performance is stable, the distortion of the line work area is very small, and the harmonic content is very rich .3) The speakers used in valve radios are generally larger in diameter than those of transistor or integrated circuit radios.4) The IF circuit characteristics of tube radios are better than those of transistor or integrated circuit radios.5) Have collection value. Disadvantages of Valve Radio As for the shortcomings, valve tubes that are large in size and used as basic components, built-in accessories are also bulky, power consumption has also increased, the overall quality has become poor, inconvenient to carry, and poor seismic performance. In addition, it is very difficult to make FM stereo radio devices, because early tube radios can only receive shortwave and medium waves. These shortcomings eventually led to the replacement of tube radios by transistor radios. Vintage Valve Radios - Will they work? 1.3 German Vintage Valve Radio Models for Sale AEG RadioBlaupunktGerman EMUDGraetz Vintage RadioGrundig Vintage RadioHornyphon Vintage RadioVintage Koerting RadioGerman Metz Vintage RadioVintage Nordmende RadioPhilips Vintage RadioVintage Saba RadioVintage Siemens RadioTelefunken Radio Figure 2. Vintage Valve Radio Ⅱ Transistor Radio 2.1 Transistor Radio Overview The transistor radio is the second generation radio after the valve radio. Compared with vacuum tubes, transistors are small in size, light in weight, resistant to vibration, long in life, and low in power consumption. This kind of radios can be made compact and have relatively stable performance. Therefore, after the advent of transistor radios, a large number of portable radios and pocket radios have emerged. They are very convenient for daily use. The Regency TR-1 was the first commercially manufactured transistor radio by developed by Texas Instruments and IDEA Inc., introduced in 1954.Transistor radios use transistors to process and amplify signals. Simple to use, it is a small transistor-based radio receiver. 2.2 Transistor Radio Selection Matters To choose a good transistor radio, you must first understand four basic relationships:1) The larger the chassis volume, the better the sound quality.2) The larger the horn diameter, the better the sound quality.3) The larger the battery volume, the longer the relative service life of the battery.4) The longer the magnetic bar, the higher the sensitivity.Secondly, we should also pay attention to five points when selecting:1) The change after the power supply voltage is reduced should be small. When selecting, you can have listening trial, because the impact on a high-quality radio should not be significant.2) The distortion of the offset radio should be small. After finding a radio station, having the left and right adjustments, the distortion should be small. In addition, there should be no whistling sound, otherwise, the frequency characteristics of the intermediate frequency part are poor.3) The volume change should be small when turning the button.4) Human body induction has little influence. When a person's body is close to the radio, it will have a certain impact on the work of the radio. This situation is particularly obvious for shortwave.5) The noise should be small. Noise generally includes electrical noise and mechanical noise. Turn the radio to a place where there is no station, and turn on the volume to the maximum. At this time, the minimum sound is better. Listen to a program to check whether there are noises caused by resonance of certain components when the volume is loud. Finally, you should also pay attention to whether the tuning knobs and buttons are coordinated and effective, and whether the shell of the radio is damaged or not. Vintage Transistor Radios Show And Tell 2.3 Transistor Radio Brands for Sale EdifierGAORUI HOME TEXTILESONYRoltonHALFSUNPandaSoaiyNintaus Figure 3. Regency tr-1 Transistor Radio Ⅲ Radio Further Development With the advent and development of integrated circuits, transistors have been replaced by integrated circuits, that is the third-generation radios invention, sometimes also known as semiconductor radios.After the radio uses integrated circuits, not only the size can be made smaller, but also the reliability is high. As the number of integrated circuit components is getting larger and larger, radios made with it have better performance and more functions. The integration of radios has become an inevitable trend.   Ⅳ FAQ 1. What is a vacuum tube radio?A vacuum tube, also called a valve in British English, is an electronic device used in many older model radios, television sets, and amplifiers to control electric current flow. The cathode is heated, as in a light bulb, so it will emit electrons. ... The anode is the part that accepts the emitted electrons. 2. Do valve radios still work?A valve radio will never be as reliable as a transistor set, and short of ripping out the chassis and replacing it with a transistor circuit, we aren't going to make it that reliable. However, some designs of valve set are more unreliable than others, and the main factor seems to be heat. 3. What did valves do in radios?The valve was useful as an electronic switch and its first use was in radio circuits detecting signals. The valve has two elements - a wire and a metal plate surrounded by a vacuum. The electricity flows between them. 4. How does a tube radio work?The basic working principle of a vacuum tube is a phenomenon called thermionic emission. It works like this: you heat up a metal, and the thermal energy knocks some electrons loose. 5. When did radios stop using vacuum tubes?1950s-60s - Most vacuum tubes were replaced by transistors in the west. 1970s-80s Tubes are still used in many specialized applications like broadcast television and radio. 6. Why did we stop using vacuum tubes?Vacuum tubes suffered a slow death during the 1950s and '60s thanks to the invention of the transistor—specifically, the ability to mass-produce transistors by chemically engraving, or etching, pieces of silicon. Transistors were smaller, cheaper, and longer lasting.A transistor is a semiconductor device used in electronic circuits as to function as "on" and "off" switching and amplifying device in the electronic circuits. ... Radio is a device which transmit and amplifies signals. The modern radio uses transistor since it is smaller in size. 7. Are transistor radios still being made?Transistor radio is an obsolete term now, carried over from when having transistors rather than tubes made small radios possible. It has come to be analogous to a portable, battery-powered radio, so while I will be making some recommendations, they likely will have integrated circuits, rather than transistors.It is a radio receiver which uses transistors to amplify the sound. Transistor radios can be cheap and small and some use very little electric power. Some can amplify the weak radio waves that are usually not picked up by weaker vacuum tube radios. 8. What does a transistor radio do?The function of transistors in radios is straightforward. Sounds are recorded through a microphone and turned into electrical signals. Those signals travel through a circuit, and the transistor amplifies the signal, which is subsequently much louder when it reaches a speaker. 9. Why was the transistor radio invented?One goal was to find a replacement for fragile and energy-wasting vacuum tubes. Building on war-time research, John Bardeen and Walter Brattain, working with group leader William Shockley, developed a device they called a transistor. 10. Where was the transistor radio invented?There was a tremendous push during the war to reduce the size and power consumption of vacuum tubes, particularly because the receivers used in radio-controlled bombs depended on vacuum tube technology. “Not long after the war ended, the transistor was developed at Bell Labs, in 1947. 11. What is the name of first transistor radio?Regency TR-1In July 1954 the Texas Instruments and Industrial Development Engineering Associates (I.D.E.A.) companies embarked on a six month project to produce a pocket-sized radio for the Christmas market. The result was the Regency TR-1, the world's first pocket transistor radio.

Introduction A resistor is a passive two-terminal electrical component. After it is connected to the circuit, the resistance is fixed, which can limit the current through the branch connected to it. On one hand, the resistance that cannot be changed is called a fixed resistor, on the other hand, the resistances of potentiometers or variable resistors are changeable. The main physical characteristic of a resistor is to transform electrical energy into thermal energy. It can also be said that it is an energy-consuming element, because internal energy is generated when current passes through it. Figure 1. Use Resistor in Circuit Catalog Introduction Ⅰ Functions of Resistor Ⅱ Three Basic Principles for Resistor Selection Ⅲ The Role of Resistors in Transistor Circuits 3.1 Why Should a Resistor Be Added to the Base of the Transistor? 3.2 Pull-down Resistor in Transistor Circuits Ⅳ FAQ Ⅰ Functions of Resistor In short, the function of resistance is to limit current, divide current, divide voltage, and convert electric energy into internal energy (heating) in the circuit. According to Ohm's law, through calculations, resistors in parallel and series connections can be used to achieve the desired current and voltage. Also there are different resistors and switches combined to produce voice-activated switches, photosensitive switches, infrared switches and so on. How to Use Resistors in circuits? 1) Limit CurrentIn order to prevent the components connected in series from being burnt out by the excessive current and to ensure the normal operation of the electrical appliances, a variable resistor can usually be connected in series in the circuit.2) Current DiversionThe resistor is connected in parallel to the component or circuit that needs to be shunted, and the voltage does not change. The function of this resistor is to divide current.3) Voltage DiversionGenerally, electrical appliances are marked with a rated voltage value. If the power supply is higher than it, the electrical appliance cannot be directly connected to the power supply for a normal operation. In this case, a resistor with suitable resistance can be connected in series in the circuit to share a part of the voltage, therefore the electrical appliance can work at the rated voltage. At this time, the role of the resistor is to divide the voltage.4) Provide Bias VoltageIn the transistor circuit, the resistor is connected between the base of it and the working voltage. At this time, the power supply provides a bias voltage to the base through the resistor, and the resistance can determine the bias voltage. The role of the resistor in the circuit at this time is to provide a bias voltage.5) Negative FeedbackUsed in the resistance between the base and collector of the transistor, then the feedback branch of the negative feedback circuit is formed in the circuit. At this time, the resistor plays a negative feedback role in the circuit.6) OscillationResistor and capacitor form an RC circuit, which can be combined in parallel and in series.7) Damping EffectConnecting a resistor in parallel in the LC resonant circuit can reduce the Q value, at this time, resistor plays a damping effect.8) DecouplingThe use of resistors in multi-stage amplifier circuits can prevent harmful low-frequency interference, which play a decoupling effect.9) Convert Electrical Energy into Internal Energy (Heating)When the current passes through the resistor, it will convert all (or part) of the electrical energy into internal energy, which will generate heat. This principle is often used in electric stoves and heaters in our lives.10) Convert Current into VoltageWhen current flows through the resistor, a voltage will be generated across the resistor. As shown in the figure below, the collector load resistor R2 plays this role, converting the current flowing through the resistor R2 into a voltage and outputting it from U0. Figure 2. Resistor Circuit   Ⅱ Three Basic Principles for Resistor Selection 1) Choose resistors that are manufactured by a certification body that implement high-level standards.2) Choose resistors produced by manufacturers with functional advantages, quality advantages, efficiency advantages, price advantages, and service advantages.3) Choose a manufacturer that can meet the above-mentioned requirements in the model catalog.   Ⅲ The Role of Resistors in Transistor Circuits 3.1 Why Should a Resistor Be Added to the Base of the Transistor? First of all, we must understand the basic principle of the transistor. It is a current-controlled element, which is different from the MOFET, a voltage-controlled element. The transistor has three working areas: cut-off area, amplification area and saturation area. Take NPN transistor as an example, the voltage difference（UBE）of BE is about 0.6V (the actual size depends on the model of the component). When UBE＜0.6V , the transistor is off; when UBE=0.6V, the transistor is in the amplification or saturation region. Figure 3. Schematic Diagram of the NPN Transistor Current When the transistor is in the amplification area, the added resistance between the base and VCC is a bias resistance. The following explains why the base should be added when the transistor is used as a switch. What is the difference between transistor and MOSFET circuits when adding a resistor.The following figure is the most commonly used circuit diagram of NPN transistors. The common input terminal is the I/O port of the microprocessor (microcontroller, DSP, ARM, etc.). Figure 4.  NPN Transistor Take the microcontroller I/O port with 0/5V input as an example. Why must a resistor be connected in series with the base? Can it work without a resistor? Here the resistor is a current control element. When the transistor is in an amplified or saturated state, the voltage of the UBE is 0.6V, and the base current can be calculated according to the input voltage U. The calculation formula is Ib=(U-0.6 )/R1. It can also be seen from the formula that if the current limiting resistor R1 is not connected, when the input voltage is greater than 0.6V, the base current will be very large to burn the tube.Moreover, the resistor cannot be used casually. It needs to be calculated according to the input voltage and the characteristics of the tube. For example, the amplification factor β of the transistor is 50, the maximum current of the collector is 500mA, and the input voltage is 5V. If the design requires the transistor to be in a saturated state, then Ic=500mA, Ib=Ic/β=10M=mA, where the current-limiting resistance R1=(5V-0.6V)/Ib=430Ω. If it is required to input 5V, the collector current is about 200mA, then Ib=Ic/β=200mA/50=4mA can be calculated, finally the current-limiting resistance R1=(5V-0.6V)/Ib=1075Ω (1K can be selected Standard resistance). Note: The above figure is used to explain the example, but it is not very reliable. A more reliable connection method should be to connect a large resistor (such as 10K, or 20K) between the base and the ground. When there is no input, pull the base down quickly to ensure that the tube is in a stable cut-off state.If the NPN transistor in the figure above is replaced with an N-channel MOS tube, the principle is the same. When a high level is input, the tube is turned on, and when a low level is input, the tube is turned off. Figure 5. MOSFET Circuit Since the MOSFET is a voltage-controlled device, the current of the gate (G) is very small and can be ignored, so it can work normally without connecting the resistor R1.The figure after remove the resistor is shown in the below: Figure 6. MOSFET Circuit without Resistor Note: In actual applications, a resistor is generally connected in series to improve reliability. The product reliability is very important. Without current-limiting resistor, when the MOS is   damaged by voltage breakdown, the components on the control terminal will be affected easily, especially the processor, is easily damaged by high current. 3.2 Pull-down Resistor in Transistor Circuits 🔺For TransistorsThe transistor is a current-type driving component, so a current-limiting resistor is connected to the base, generally less than 10K, and the typical values are 3.3K, 4.7K, 5.1K, 6.8K, etc. What is the function of this pull-down resistor?The following figure shows the transistor 8050 switching circuit. The transistor will be turned on when the I/O port outputs a high level, and the transistor will not be turned on. If the I/O port does not output a high level, the base will always be pulled low without a 68K pull-down resistor, that is to say it is in the cut-off state. The circuit may be in an unstable state, especially when it is initialized at the moment of power-on. It is easy to generate noise and easily cause the transistor to malfunction, especially for some general input/output ports. Therefore, this resistor is actually a bias resistor, which makes the base to be pulled down when there is no driving signal, making the circuit more reliable. Figure 7.  Pull-down Resistor in Transistor Circuit Although the pull-down resistor can make the circuit more reliable, tit cannot be too large or too small. If the resistance too large, the base current will not be enough to drive the transistor. On the contrary, if it is too small, the bias voltage will be less than the transistor conduction voltage. In general, this resistance is not more than 100K.Sometimes we see that a capacitor is connected in parallel with this resistor. In fact, this is generally designed in high-speed signal switching circuits. Adding a capacitor can improve performance, as shown below: Figure 8.  RC Circuit 🔺For MOSFETUnlike transistors, MOS transistors are voltage-controlled components, which are driven by voltage. We all know that there is parasitic capacitance between the two pins of MOS transistors. In fact, the key of MOS transistors’ conduction is the charging and discharging of capacitors. Therefore, for the N-type MOS, it will be turned on when Vgs is greater than a certain value, but for the P-type MOS, it will be turned on when the value of Vgs is less than a certain value.Therefore, due to the capacitive effect between the three pins, when the MOS is constantly turned off, the parasitic capacitance voltage can be properly discharged, which is similar to the role of a bleeder resistor and is a kind of protection for the MOS. Figure 9.  MOSFET Circuit Ⅳ FAQ 1. What is the function of the resistor?A resistor has the ability to reduce voltage and current when used in a circuit. The main function of a resistor is to limit current flow. Ohm's law tells us that an increase in a resistors value will see a decrease in current.   2. How do resistors work?A conductor has low resistance, while an insulator has much higher resistance. Devices called resistors let us introduce precisely controlled amounts of resistance into electrical circuits. ... A resistor works by converting electrical energy into heat, which is dissipated into the air.   3. Why do you need resistors?A resistor controls the flow of the electrical current within a circuit. ... Resistors are essential to many electoral circuits, and they can be applied to a myriad of different applications. Protect against voltage spikes. Resistors also protect components against voltage spikes.   4. What role do resistors play in electronic devices?A resistor is a passive two-terminal electrical device that resists the flow of current. It is probably the simplest element in an electronic circuit. It is also one of the most common components as resistance is an inherent element of nearly all electronic circuits. They are usually color-coded.   5. What is a good example of a resistor?A few examples include limiting electric current, voltage division, heat generation, matching and loading circuits, gain control, and setting time constants. They are commercially available with resistance values over a range of more than nine orders of magnitude.   6. What happens if I use a higher ohm resistor?The cases where using a higher value resistor will damage a circuit exist, but are a bit less usual than the cases where it may simply produce a weaker result than desired, or a different frequency response than desired.   7. What is a resistor simple explanation?A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor. ... The most common type in electronic devices and systems is the carbon-composition resistor.   8. What happens when a resistor blows?Blowing Up a Resistor. By applying too high a voltage to a resistor, the resistor will draw too much current. This causes excessive power to be dissipated in the resistor which makes it go up in flames and a cloud of smoke as this video shows.   9. How is a resistor connected in a circuit?Resistors are said to be connected in “Series”, when they are daisy chained together in a single line. Since all the current flowing through the first resistor has no other way to go it must also pass through the second resistor and the third and so on.   10. Do resistors change voltage?The larger the resistor, the more energy used by that resistor, and the bigger the voltage drop across that resistor. Ohm's Law can be used to verify voltage drop. In a DC circuit, voltage equals current multiplied by resistance. V = I R.

IntroductionThe transistor is one of the basic semiconductor components, which has the function of current amplification in electronic circuit. It is made of two PN junctions very close to each other on a semiconductor substrate. Two PN junctions divide the entire semiconductor into three parts: The middle part is the base area, and the two sides are the emitter and the collector. What is NPN Transistor? For BeginnerCatalogIntroductionⅠ NPN Transistor Arrangement and SymbolⅡ How Do NPN Transistors Work?Ⅲ NPN Transistor Uses: A Controllable ValveⅠ NPN Transistor Arrangement and SymbolBefore explaining the principle, let's first understand the basic structure and symbols of the NPN transistor. To identify the NPN transistor pins, it will be Collector (c), Base (b) and Emitter (e).Figure 1. NPN Transistor Structure and SymbolNPN transistor is composed of two N-type semiconductors and one P-type semiconductor. Generally, an NPN transistor has a piece of P-type silicon (the base) sandwiched between two pieces of N-type (the collector and emitter). The arrangement is shown in the Figure 1. Ⅱ How Do NPN Transistors Work?Here is the main description to illustrate the basic principle and function of NPN transistors.1) Current AmplificationThe following analysis is only for NPN silicon transistors. As shown in the figure above, we call the current flowing from the base B to the emitter E the base current Ib; the current flowing from the collector C to the emitter E is called the collector current Ic. The directions of these two currents are both flowing out of the emitter, so an arrow is used on the emitter E to indicate the current direction.The amplification function of the transistor is: the collector current is controlled by the base current (assuming that the power supply can provide a large enough current to the collector), and a small change in the base current will cause a large change in the collector current: the change in the collector current is β times the change in the base current, that is, the current change is amplified by β times, so we call β the magnification of the transistor (β is generally much larger than 1). If we add a changing small signal between the base and the emitter, it will cause a change in the base current Ib. After the change in Ib is amplified, it leads to a big change in Ic. If the collector current Ic flows through a resistor R, it can be calculated according to the Ohm's Law formula U=R*I, and the voltage on this resistor will change greatly. According to the voltage on this resistor, so we can get the amplified voltage signal. In short, the change satisfies a certain proportional relationship.2) Bias CircuitWhen the transistor is used in the actual amplifier circuit, it is also necessary to add a suitable bias circuit. There are several reasons for this. First of all, due to the non-linearity of the transistor's BE junction (equivalent to a diode), the base current must be generated after the input voltage reaches a certain level (for silicon tubes, 0.7V is often used). When the voltage between the base and the emitter is less than 0.7V, the base current can be considered as zero. However, in practice, the signal to be amplified is often much smaller than 0.7V. If no bias is applied, such a small signal is not enough to cause a change in the base current (because when it is less than 0.7V, the base current is all 0).Add a suitable current to the base of the transistor (called the bias current, and the resistor in the figure used to provide this current, is called the base bias resistor). When a small signal follows this bias current are superimposed together, a small signal will cause a change in the base current, and the change in the base current will be amplified and output on the collector. Another reason is meeting the requirement of the output signal range. If there is no bias, then only those increased signals will be amplified, but the decreased signals will be invalid (because the collector current is 0 when there is no bias, and it cannot be reduced). With bias, let the collector have a certain current in advance. When the input base current becomes smaller, the collector current can be reduced; when the input base current increases, the collector current increases. Both the reduced signal and the increased signal can be amplified.3) NPN Transistor SwitchLet's talk about the saturation mode of the transistor. As shown in the figure above, because of the limitation of resistance Rc (Rc is a fixed value, then the maximum current is U/Rc, where U is the power supply voltage), the collector current cannot increase indefinitely. When the base current increases and the collector current cannot continue to increase, the transistor enters a saturated state. The general criterion for judging whether the transistor is saturated is: Ib*β>Ic.In a saturation state, the voltage between the collector and the emitter of the transistor will be very small, which can be understood as a switch. In this way, when the base current is 0, the collector current is 0 (this is called the triode cut-off), which is equivalent to the switch off; when the base current is large, it is equivalent to the switch on. In cut-off and saturation state, a transistor is equal to a switch.4) Operational StateIf we replace the resistor Rc with a bulb in the above figure, then when the base current is 0, the collector current is 0, so the bulb is off. If the base current is relatively large (greater than the current flowing through the bulb divided by the magnification β), the transistor will saturate, and the bulb will light up. Since the control current only needs to be a little larger than β of the bulb current, a small current can be used to control the on and off of a large current. If the base current increases slowly, the brightness of the bulb will also increase (which is a saturation process).The figure below is a basic transistor switch circuit. The base should connect a base resistor (R2), and the collector connects with a load resistor (R1).Operational ModeNPNCut-offUne<UonUc>UbActiveUbe>UonUc>UbSaturationUbe>UonUc<UbNPN transistor uses the B-E current (IB) to control the C-E current (IC). The E pole has the lowest potential, and usually the C pole has the highest potential during normal amplification, that is, VC>VB>VE.NPN base extremely high voltage, the collector and emitter are short-circuit and low-voltage, and the collector and emitter are open-circuit.NPN is suitable for two situations:If the input is a high level and the output needs a low level, NPN is better.If the input is a low level and the output needs a high level, NPN is better.2N2222 NPN Transistor PinoutⅢ NPN Transistor Uses: A Controllable ValveNPN is a component that uses b (base) current Ib to drive the current Ic flowing through CE, and its working principle is much like a controllable valve.Figure 2. A Controllable ValveThe blue water flow in the thin pipe on the left impacts the lever to open the valve of the large water pipe, allowing the larger red water flow to pass through the valve. The larger the blue water flow, the greater the red water flow in the big pipe. If the magnification is 100, then when the blue water flow is 1 kg/hour, then 100 kg/hour of water is allowed to flow through the large pipe. The principle of the transistor is the same. When Ib (base current) is 1mA, a current of 100mA is allowed to pass through Ice.Figure 3. NPN Transistor DiagramLet's analyze this circuit. If its magnification is 100, and ignore the base voltage. The base current is 10V÷10K=1mA, so the collector current should be 100mA. According to Ohm's law, the voltage on Rc is 0.1A×50Ω=5V. Then the remaining 5V is on the C and E poles of the transistor. Now if we let Rb be 1K, then the base current is 10V÷1K=10mA, according to the magnification of 100, is Ic 1000mA? If it is really 1A, then the voltage on Rc is 1A×50Ω=50V. The power supply voltage has been exceeded, and the transistors have become generators? This is not the case. See below:Figure 4. NPN Transistor Compared to A ValveContinue the metaphor. When the control current is 10mA, the valve on the main water pipe is opened to allow 1A current to flow, but can 1A be realized? No, because there is a resistor on it, it is equivalent to a fixed valve. It is stringed on top of the main water pipe. When the opening of the lower controllable valve is greater than the opening of the upper fixed resistor, the water flow will not increase any more, but will be equal to the water flow passing through the fixed valve opening above. Therefore, it is useless to open the lower transistor to a large opening. Therefore, we can calculate the maximum current of the fixed resistor 10V÷50Ω=0.2A, which is 200mA. That is to say, in the circuit, the base current increases and the collector current also increases. When the base current Ib increases to 2mA, the collector current increases to 200mA. When the base current increases again, the collector current will no longer increase, and it will not move at 200mA. At this time, the upper resistor also acts as a current limiter.  Let us understand the status of the IO in the microcontroller.Figure 5. AT89S51/52 The circuits with 24 IO ports of P1-P3 in the single-chip microcomputer are as shown in the figure above. Usually the purpose of using electronic circuits is to allow devices to obtain a certain current to make them work. For example, to make light-emitting diodes bright, a current of more than 1mA is generally required. However, the single-chip microcomputer is a smart chip. It can make logical analysis and judgments by detecting the voltage value of each IO port, and outputs high or low voltage as the result signal. Therefore, it can be seen that the IO ports of the single-chip microcomputer focus on voltage, not the current flowing through R and the transistor. Here what is the relationship between the voltage and current of the IO port in the single-chip microcomputer?  Continue the water pipe example.Suppose we let the valve of R open larger and let the control valve below be fully closed. At this time, as shown in Figure 6, it can be seen that the pressure at point P is the same as the water tank. When we fully open the following control valve, as shown in Figure 7, the water will flow through the pipeline with a large flow, and the pressure at point P is 0 at this time. This principle is very similar to electronic circuits. The logic quantity measured at the output point P is 1 (power supply voltage) or 0 (0 potential) by transistor turning off or on. However, there is a problem with this process, that is, when the output of point P is required to be 0, the transistor will be turned on very large, and the current flowing through it will be very large. There are 32 IO ports on the single-chip microcomputer, which consumes a lot of power. Look at Figure 8. If we close the upper valve R very small and close the lower control valve fully, then the pressure at point P will still the same as the water tank, which is the same as in Figure 6 above. When we open the control valve greatly, as shown in Figure 9, although the pressure at point P is also 0, the flow of water passing through at this time is greatly reduced. In this way, we can either output 1 or 0. So very little water is consumed. The circuit in the single-chip microcomputer does exactly this. The resistance R on it is about 50K, and the maximum current is 5V÷50K=0.1mA. In other words, when P outputs 1, no current is consumed, and when P outputs 0, the current consumed is 0.1mA. Because of its large pull-up resistance R, for beginners, it is necessary to have certain methods to directly drive LEDs or other loads. Here to share the various situations when the IO port is connected to the load.Figure 10. AT89S51/52 & 74HC373Let's take a look at the situation of connecting TTL devices first. When P1.0 is connected to an input pin of 74HC373, and the input impedance of TTL is very high, about a few hundred K to M ohm level. We assume 500K resistor to P1.0 to ground. In this way, when the transistor is turned on, the P1.0 point is at a low level, and a current of 0.1mA flows through Rc and then through the transistor to the ground, and no current flows through Ri. When the transistor is cut off, the current flows through Rc and then flows to the ground through Ri. Due to the resistor voltage divider effect, there are partial voltages on Rc and Ri, and the voltage at point P1.0 is the divided voltage of Rc and Ri. Total current is 5V÷(50K＋500K)=0.009mA, then the voltage at point P1.0 is 0.009mA×500K=4.5V. TTL stipulates that output 2.4~5V is high level. So this connection is correct. Now let's take a look at the situation of using S51 to drive the LED.AT89S51 Correct ConnectionLet’s take a look at the situation in Figure 11. Obviously, only P1.0 is a high potential to light the luminous tube, so the transistor must be cut off. In this case, the current flows through Rc to the luminous tube and then to the ground. To make the luminous tube turn on, there must be a threshold voltage exceeding 2.1V at both ends of the luminous tube. Therefore, the current flowing through the luminous tube is (5V-2.1V)÷50K=0.058mA, which is too weak to conduct.Look at Figure 12. It can be seen from the figure that P1.0 must be at a low potential if the luminous tube turned on. The transistor of the P1.0 port must be turned on. At this time, the current flows all the way through Rc to the transistor and then to the ground. The other way consumes 2.1V on the luminous tube. Then current flows through with almost no resistance, but the maximum current of the triode of the IO port cannot exceed 15mA. If it exceeds, the triode will be burned out, so this connection method is incorrect. So how can these two connections be able to drive the light-emitting tube? See below: AT89S51 Incorrect ConnectionLooking at Figure 13, a resistor Ri is connected between P1.0 and Vcc. When the transistor is turned on, two currents will flow through its c, e pole, one is the 0.1mA current on the internal R, and the other is the current on Ri. In order to prevent the transistor from over-current and burn out, we must make sure the resistance value, Ri=5V÷15mA=0.333K, which is about 330 ohms. At this time, the current flowing through the transistor is about 15mA, and the light-emitting tube is not bright at this time. When the transistor is turned off, both currents will flow through the luminous tube. The current flowing through the internal resistance of S51 is (5V-2.1V)÷50K=0.06mA, which is so small that we can ignore it. The current flowing through Ri is (5V-2.1V)÷330Ω=0.0087A, which is 8.7mA. However, the current consumed when the luminous tube is off is greater than the current consumed when the luminous tube is on. If many IO ports are used to light up many LEDs, such a circuit is not economical.Look at Figure 14, after connecting a resistor in series with the luminous tube between Vcc and P1.0. When the transistor is turned on, the two currents will flow through the c, e after confluence. The current on the internal resistance is still 0.1mA. The current on the ce should be less 15mA. If exceeds 15mA, the resistance is determined as (5V-2.1V) ÷ 15mA = 0.193K, which is about 200 ohms. In this way, the current flowing through the luminous tube is about 15mA, and the luminous tube is on. When the transistor is cut off, it blocks the paths of these two currents, so no current is consumed. Low level P1.0 directly drives the light-emitting tube. It can be seen that this circuit consumes 15mA of current when the light-emitting tube is on, and does not consume current when it is off, so this circuit is effective. S51 direct drive digital tube generally also uses this principle. Frequently Asked Questions about NPN Transistor1. What is meant by NPN transistor?An NPN transistor is the most commonly used bipolar junction transistor, and is constructed by sandwiching a P-type semiconductor between two N-type semiconductors. An NPN transistor has three terminals– a collector, emitter and base. The NPN transistor behaves like two PN junctions diodes connected back to back. 2. How do NPN transistors work?The NPN transistor is designed to pass electrons from the emitter to the collector (so conventional current flows from collector to emitter). The emitter "emits" electrons into the base, which controls the number of electrons the emitter emits. ... The transistor is kind of like an electron valve. 3. What is a NPN transistor used for?NPN transistors are mainly used in switching applications. Used in amplifying circuit applications. Used in the Darlington pair circuits to amplify weak signals. NPN transistors are used in the applications where there is a need to sink a current. 4. Which is better PNP or NPN transistor?A NPN transistor has electrons as majority charge carriers whereas the PNP transistor has holes as majority charge carrier. ... mobility of electrons is more than hole,so as a result npn transistor are faster than pnp that's why they are preferred. 5. What does NPN mean?NPN stands for Negative, Positive, Negative. Also known as sinking.

For so many years, tube amplifier has always been a “controversial” component in the electronic field, people are attracted by its premium sound quality but discouraged by its price.   Today we are going to talk about tube amplifiers, to understand what this device is, why its price is so much higher than other amplifiers, what are its advantages and disadvantages compared with other amplifiers, and so on. Catalog I. What is a Tube Amplifier? II. Pros and Cons of Tube Amplifier? III. How Does the Tube Amplifier Work? IV. Tube Amplifier VS Solid State Amplifier? V. Tube Amplifier VS Transistor Amplifier? VI. Things Needing Attention While Using a Tube Amplifier VII. Why is Tube Amplifier So Expensive? Is It Worth It? VIII. How to Extend the Life of   the Tube Amplifier?    FAQ I. What is a Tube Amplifier? The tube amplifier is one of the earliest electrical signal amplifiers.   The cathode electron emission part, the control grid, the acceleration grid, and the anode (panel) lead enclosed in a glass container (generally a glass tube) are welded to the tube base.   The electric field is used to inject an electronic modulation signal into the control grid in the vacuum, and the signal data of different parameters after signal amplification or feedback oscillation is obtained at the anode.   Tube amplifiers were used in electronic products such as televisions and radio amplifiers in the early days. In recent years, they have been gradually replaced by amplifiers and integrated circuits made of semiconductor materials. However, in some high-fidelity audio equipment, tube amplifiers with low noise and high stability coefficient are still used. II. Pros and Cons of Tube Amplifier? Pros: 1. The tube amplifier has a large input dynamic range and a fast conversion rate.   2. Electronic tube amplifiers mostly use discrete components, manual wiring, and welding, which are low in efficiency and high in cost. This is especially obvious in developed countries.   3. The open loop index of the tube amplifier is better than that of the transistor amplifier. It does not need deep negative feedback and can work stably without adding phase compensation capacitors, so its dynamic index is better.   4. The sound quality of the tube amplifier is generally soft and pleasant. More specifically, the low-frequency sound of the tube amplifier is soft and clear, and the high-frequency sound is slender and clean. The performance of human voice is its strong point.   5. The treble of the tube amplifier is smoother, has enough air, and has a sound coloring that quite a few people like. The soft and slightly fuzzy sound is very beautiful.   6. The tube amplifier mainly causes even-numbered second harmonics. This harmonic component is very pleasing, just like adding rich overtones and beautifying the sound.   Cons: 1. The service life of the tube amplifier is relatively low, and some technical indicators will drop significantly after one to two thousand hours of use.   2. The tube amplifier consumes high power and often works in Class A state, which reduces the efficiency. However, there are basically no harmful sound quality factors such as transient intermodulation distortion, switching distortion and crossover distortion.   3. The tube amplifier is not at all superior to the transistor amplifier in terms of weight, efficiency, and lifespan.   4. In use, the tube amplifier should have good ventilation and heat dissipation. Overheating of the temperature will inevitably shorten the life of the tube amplifier, so it is necessary to keep the temperature of the tube amplifier as low as possible.   5. Vibration is not good for tube amplifiers, so it is important to take anti-vibration measures to avoid vibration as much as possible. III. How Does the Tube Amplifier Work? This is a basic overview of some of the components of a tube guitar amp and how they work, without getting too technical. IV. Tube Amplifier VS Solid State Amplifier? A solid-state amplifier converts an electrical signal into an audio wave using transistor circuitry. Instrumental amplifiers have two amplification stages: the preamp stage at the beginning of the circuit and the power amp stage at the end.    The physical difference between a solid-state amp and a tube amp is that a solid-state machine employs electronic transistors for amplification, whereas a tube amp employs vacuum tubes (also known as valves). Transistors differ from tubes in that they do not deform pleasantly when pushed to their limits.   The key difference between tube amplifier and solid state amplifier is: solid-state amplifiers are ideal for guitarists that require a lot of power (a.k.a a loud, clean, undistorted signal). However, without any natural distortion, an electric guitar can sound brittle. As a result, solid-state amplifiers are more popular among bassists and keyboard players than guitarists. Compared with tube amp, solid-state amp has several advantages: 1.    They are less expensive. Almost all solid-state amplifiers are less expensive than tube amplifiers. They have fewer parts and the ones they do have are reasonably inexpensive.  2.    They are less bulky. Weight can be an issue if you're a gigging musician who needs to transport an amp around town. Tube amplifiers are almost always heavier than solid-state amplifiers. This is due to the circuitry necessary to operate the glass tubes, not the glass tubes themselves (which are hollow). 3.    They require less maintenance. Tube amplifiers need routine maintenance. Most gigging guitarists replace their power tubes once a year and their preamp tubes every two years. Solid-state amplifiers, on the other hand, do not require part switching. They can function for decades with all of their original components. V. Tube Amplifier VS Transistor Amplifier? A transistor amplifier, as the name implies, is used to amplify power, voltage, or current signals. It has a common emitter amplifier, a common collector amplifier, and a common base amplifier. This is the most basic. There are also differential, push-pull, and so on. The audio is actually a power (transistor) amplifier. The difference between transistor amplifier and tube amplifier: 1. Working characteristics and circuit structures are different Transistor amplifiers work under low voltage and high currents. The working voltage of transistor power amplifiers is within tens of volts, and the current reaches several amperes or tens of amperes. In the circuit design, direct-coupled (OCL, BTL, etc.) non-output transformer circuits are mostly used. The output power can be very large, up to several hundred watts, and the various electrical properties are very high. The tube amplifier works under high voltage and low current conditions. The screen voltage of the final power amplifier tube can reach 400-500V or even thousands of volts, and the current flowing through the electron tube is only tens of milliamps to hundreds of milliamps. The input range is too large and the conversion rate is fast. Most of the tube amplifiers use discrete components, manual wiring, and welding, which are low in efficiency and high in cost. Transistor amplifiers mostly use a combination of transistors and integrated circuits, and printed circuit boards are widely used, with high efficiency, stable soldering quality, and high electrical performance indicators. 2. Power reserve and anti-overload ability are different The dynamic range of the high-fidelity amplifier should be 120dB, so as to meet the needs of the sound from the slightest to the peak of the climax, the amplifier output is not clipped, so the amplifier must have sufficient power reserve. If the dynamic range of the audio voltage is 3:1, since the power is proportional to the square of the voltage, the power dynamic range is 9:1. That is to say, a power amplifier with a power of 90W can only be turned on to 10W to achieve high-fidelity playback. Therefore, the transistor amplifier needs a large power reserve to avoid overload distortion. Once the ground is loaded, its distortion will almost rise in a vertical line, which can damage the transistor in severe cases. The anti-overload capability of the tube amplifier is far stronger than that of the transistor amplifier. In case of overload, the peak of the music signal only becomes slippery than the normal waveform, and the sound is not deformed much. For transistor amplifiers, clipping will occur at this time, and the sound quality will deteriorate significantly. 3. Efficiency, life, and cost are different Tube amplifiers are not superior to transistor amplifiers in terms of weight, efficiency, and lifespan. The service life of the electron tube is relatively low, and some technical indicators will drop significantly after one to two thousand hours of use. The lifetime of transistors and integrated circuits is much longer. In addition, the tube amplifier consumes high power and often works in the Class A state, which reduces the efficiency. However, there are no harmful sound quality factors such as transient intermodulation distortion, switching distortion, and crossover distortion. In terms of cost, for the same grade of amplifiers, tube amplifiers are generally significantly higher than transistor amplifiers. The main reasons are the high cost of electronic tubes and output transformers, and the production process of electronic tube power amplifiers is not easy to automate, and the production efficiency is low. 4. Different sound quality The sound quality of the tube amplifier is significantly better than that of the transistor amplifier. Transistor power amplifiers have a sense of overwhelming when listening to high and medium and high frequencies, and less low frequencies. Transistor power amplifiers sound hard, especially low-frequency sounds are not soft enough, and high-frequency sounds are sharp and dry. Sometimes it sounds like there is crossover distortion in the high-frequency range. These phenomena become more obvious when the frequency increases and the volume is louder. However, the transistor amplifier has large dynamics and high speed, which is especially suitable for music with greater dynamics. As for the sound effects of guns and lightning, it is certainly better than a tube amplifier. Generally speaking, the sound quality of the tube amplifier is soft and pleasant. Specifically, the low-frequency sound of the tube amplifier is soft and clear, and the high-frequency sound is slender and clean. The performance of the human voice is its strong point, and therefore it is more valuable. All in all, the choice of amplifier varies from person to person. If you like orchestral music, especially chamber music and vocals, then tube amplifiers should be your first choice. If you like jazz, rock, and modern music, then transistor amplifiers are the choice. VI. Things Needing Attention While Using a Tube Amplifier? 1.    The tube amplifier must be used under the limit parameters. Although it can still work normally under the limit parameters, the life of the tube amplifier will be shortened quickly. Therefore, the tube should be used under the rated parameters. 2.    The location of the components in the device should be conducive to the heat dissipation of the tube amplifier. To control the temperature of the tube case of the tube amplifier, the allowable temperature of the glass case of various tube amplifiers is different. For example, the allowable limit temperature of the power output tube during operation does not exceed 90°C in principle. 3.    Except for the high-reliability tube amplifier with a special structure that can work at higher accelerations, other receiver amplifier tubes can only withstand small shocks for a short time. Therefore, pay attention to the shock absorption of the tube when using it. 4.    When using small tubes (thumb-finger type) and other tubes without tube bases (but with tube needles), use tube sockets specified by the Ministry of Electronics Industry. Prevent cracking or damage to the glass shell. When plugging and unplugging the tube, its direction should be perpendicular to the plane of the tube base. When inserting an electronic tube, prevent damage to the normal position of the contact reed in the socket socket of the tube socket, and avoid using the empty foot of the tube socket as a connecting pad. 5.    When using an indirectly heated tube amplifier, the potential difference between the cathode and the filament must not exceed the specified limit. For this reason, a dedicated filament transformer is often used for power supply. In order to eliminate the effect of leakage current instability, under the condition of not hindering the operation of the circuit, a shunt resistance of about several ohms can be connected between the cathode and the filament. VII. Why is Tube Amplifier So Expensive? Is It Worth It? In short, tube amplifiers are costly because they use pre and power tubes as their primary amplification source. Each tube costs approximately $50 and can have up to four of them in a single unit. Second, these amplifiers have more expensive components, larger casings, and more complicated circuitry than solid-state amplifiers.   Whether tube amplifiers are "worth it” or not, well, that’s more of a subjective question.   If your goal is to build a pristine audio chain that cleanly reproduces the input signal you give it, a tube amplifier is definitely not worth it. By spending extra money to put a tube in your signal chain, you are intentionally distorting the sound.   Note that modern high end A/D/A conversion equipment (which aims for perfect signal reproduction) never uses tubes. The marketing pitch on tube equipment is that it does change the sound that you give it. Don't buy a tube amplifier unless that is what you want.   Now, if your goal is not to amplify signal accurately, but rather to make a sound that you personally find pleasing, a tube may yield some benefits.   You can listen to some tube amps at different levels to decide what you personally prefer. Does this make a tube amp worth it? Bear in mind that there are many ways of creating harmonic distortion (in the analog domain, or emulated with digital techniques), and many are cheaper than tubes, which are expensive to produce.   The high cost of tubes is not a function of the fact that it was difficult to engineer their particular audio qualities. The way tube amplifiers color audio is a historical function of the fact that engineers were not able to compensate for the changes they introduce.   Many people have now decided that this is a valuable property - but the production of tubes is becoming relatively more expensive as demand for them diminishes and they require specialty, limited-run manufacturing (compared to transistors, demand for which is growing).   In all, thinking from your practical needs before jump into any conclusion, whether tube amplifier is worth it or not, there’s no absolute answer to this question. VIII. How to Extend the Life of the Tube Amplifier?    The problem of short life of the tube amplifier is often criticized, but this is often not a problem of the tube amplifier itself, but a defect in the circuit design and a problem in use. It should be noted that a good quality tube amplifier must have a correctly designed circuit, sufficient heat dissipation, and thoughtful shock absorption.   In use, the tube amplifier must have good ventilation and heat dissipation. Overheating of the temperature will inevitably shorten the life of the tube, so the tube amplifier should be kept as low as possible.   Vibration is not good for tube amplifiers, so it is important to take anti-vibration measures to avoid vibration as much as possible. If these two can be achieved, the service life of the tube amplifier can be at least doubled. For this reason, there should be a proper space around the tube amplifier equipment, especially above it, in order to have good convection ventilation, if possible, a fan can be used to help dissipate heat.   When the cathode of the tube amplifier has not reached the required temperature, the high-voltage power supply is immediately applied, and its cathode will be damaged, which will also shorten the life of the tube amplifier.   Therefore, if the tube amplifier equipment has a preheating device, it must be used. For example, first turn on the filament low-voltage power supply to preheat, and then turn on the high-voltage power supply. If there is no preheating device, don't rush to connect the input signal, you can turn the volume down to the minimum, wait for 20-30 minutes to warm up the machine before using it.   If the indirectly heated rectifier tube is used to supply the high voltage of the whole machine, it just provides a simple and effective high voltage delay. In addition, do not switch the power supply frequently during normal use.   Of course, if the tube amplifier circuit is designed correctly and the wrong use is avoided, the tube amplifier will not "die young". It should be normal for the tube amplifier to use thousands of listening hours.   The most common mistakes in circuit design are: 1. The potential difference between the filament and the cathode of the tube amplifier is too high 2. The screen or screen grid voltage of the tube amplifier is applied to the maximum value 3. The filament voltage of the tube amplifier is too low or too high 4. Improper installation position of the tube amplifier causes the electrode to overheat and the high-voltage power supply does not have a delay device, etc.   Therefore, these problems should be avoided when designing the circuit to effectively extend the service life of the tube amplifier. FAQ 1. Why is a tube amp better? Tubes, like analog recordings, have a more full-bodied sound than transistor gear. There's a "roundness" to tube sound that solid-state gear never equals. Tubes are less forgiving about mismatches, so to get the best out of a tube amp it must be used with just the right speaker. 2. What is tube amplifier used for? Tube amplifiers, or tube amps as they're commonly called, are tiny electronic or electromagnetic components that are used to boost electric current in devices to improve their performance. It's what makes your hearing aid pick up sounds through a microphone from all around you. 3. Are tube amps worth it? In many cases, tube amps do not require the amount of maintenance that they have a reputation for. As long as you properly take care of your gear, owning a tube amp is simple and very well worth it for the tone. 4. How long should a tube amp warm up? 20 to 30 minutes. As a rule of thumb, your tube amp needs to be warmed up for 20 to 30 minutes at least before you can start playing your guitar. 5. Why are tube amps louder? When tubes are driven outside their linear region, for the first 12db or so of overdrive the harmonics that they produce trick the human ear into thinking that the sounds are getting louder, when in fact the sound is getting progressively more distorted. 6. How does a tube amplifier work? The power transformer and rectifier work together as an electron pump which pulls electrons out of the amp circuit creating a positive voltage (electron scarcity = positive voltage). The amplifier's electronics need DC to amplify. The amp is powered by DC but the guitar signal moving through the amp is AC. 7. What's the difference between a tube amp and a regular amp? The physical difference between a solid-state amp and a tube amp is that a solid-state machine derives amplification from electronic transistors, while a tube amp uses vacuum tubes (also known as valves). ... Solid-state amps are great for players who want maximum headroom (a.k.a a loud, clean, undistorted signal). 8. Which is better tube amp or solid state? Tube amps are generally more expensive in initial cost and to operate (because you need to replace the tubes occasionally), and solid-state amps are generally less delicate and more reliable. Many players, however, feel that tube amps yield a warmer, more musical tone and more musical-sounding distortion. 9. How often should a tube amp be serviced? 15 years. If its a well made amp, recap every 10 or 15 years, retube as needed. Fenders might go many years without needed a power tube replaced. 10. How many watts do I need in a tube amp? 100 watts. You'll need a solid state amp that has around 100 watts, or a valve amp that has around 50 watts. This will usually give you enough volume that you can be heard over the drummer, without having to push your amp's volume too hard so that the distortion becomes overbearing.

IntroductionA p-n junction is an interface or a boundary between n-type and p-type semiconductor materials, inside a semiconductor. One of the crucial keys to solid state electronics is the nature of the P-N junction. For example, a PN Junction Diode is one of the simplest semiconductor devices around, and which has the characteristic of passing current in only one direction only. And the p-side or the positive side of the semiconductor has an excess of holes and the n-side or the negative side has an excess of electrons. Why pn junction exists? and How does it work? What is p-n junction diode?PN Junction IntroductionCatalogIntroductionIntroductionⅠ PN Junction Basic1.1 PN Semiconductor1.2 PN Junction ReviewⅡ PN Junction Characteristic2.1 Unidirectional Conductivity2.2 Reverse Breakdown2.3 Volt-Ampere Characteristic2.4 Capacitance CharacteristicⅢ Typical Example: Transistor PN JunctionⅠ PN Junction Basic1.1 PN SemiconductorN-type SemiconductorIn silicon crystal (or germanium crystal) doped with a small amount of impurity phosphorus element (or antimony element), since semiconductor atoms (such as silicon atoms) are replaced by impurity atoms, among the five outer electrons in the outer layer of phosphorus atoms four of them form covalent bonds with the surrounding atoms, and the extra electron is almost unbound and becomes a free electron more easily. Therefore, the N-type semiconductor has become a semiconductor with a higher concentration of electrons, and its conductivity is mainly due to the conduction of free electrons.P-type SemiconductorIn silicon crystal (or germanium crystal) doped with a small amount of impurity boron element (or indium element), since semiconductor atoms (such as silicon atoms) are replaced by impurity atoms, the three outer electrons in the outer layer of boron atoms and a semiconductor atom form a covalent bond, at this time, a "hole" is generated. This hole may attract bound electrons to "fill", making the boron atom a negatively charged ion. In this way, this type of semiconductor has a higher concentration of "holes" ("corresponding to" positive charges) and becomes a substance capable of conducting electricity.1.2 PN Junction ReviewP-N junction is formed by joining n-type and p-type semiconductor materials, which is a two terminal device that allows electric current in one direction and blocks electric current in another direction.Figure 1. How is PN Junction FormedOn a silicon wafer, different doping processes are used to form an N-type semiconductor on one side and a P-type semiconductor on the other side. We call the area near the interface of the two semiconductors a PN junction.After the P-type semiconductor and the N-type semiconductor are combined, since the free electrons in the N-type region are more and the holes are less, the concentration difference between electrons and holes appears at their junction. Due to the difference in the concentration of free electrons and holes, some electrons will diffuse from the N-type region to the P-type region, and some holes will diffuse from the P-type region to the N-type region. As a result of their diffusion, the P region loses holes, leaving negatively charged impurity ions, and the N region loses electrons, leaving positively charged impurity ions. The ions in the semiconductor cannot move arbitrarily in an open circuit, so they do not participate in conduction. These immovable charged particles form a space charge zone near the interface between the P and N zones. The thickness of the space charge zone is related to the concentration of dopants.After the space charge region is formed, due to the interaction between the positive and negative charges, an internal electric field is formed in the space charge region, the direction of which is from the positively charged N region to the negatively charged P region. Obviously, the direction of this electric field is opposite to the direction of carrier diffusion, which used to prevent diffusion.On the other hand, this electric field will cause the minority carrier holes in the N region to drift to the P region, and the minority carrier electrons in the P region to drift to the N region. The direction of the drift movement is just opposite to the diffusion movement. The holes drifting from the N region to the P region supplement the holes lost in the P region on the original interface, and the electrons drifting from the P region to the N region supplement the electrons lost in the N region on the original interface, which makes the electric charge is reduced and the internal electric field is weakened. Therefore, the result of drift motion is to narrow the space charge region and strengthen the diffusion motion.Finally, the diffusion of multiple carriers and the drift of minority carriers reach a dynamic balance. On both sides of the junction surface of the P-type semiconductor and the N-type semiconductor, a thin ion layer is left. The charge area formed by this thin ion layer is called a PN junction. The direction of the internal electric field of the PN junction points from the N to the P. It is also called the depletion layer, because lack of electrons.Figure 2. PN Junction Depletion RegionⅡ PN Junction Characteristic2.1 Unidirectional Conductivity(1) The PN junction is turned on when the forward voltage is applied.If the positive pole of the power supply is connected to the P area and the negative pole is connected to the N area, a part of the applied forward voltage is in the PN junction area, at this time, the PN junction is in a forward bias. The current flows from the P to the N, and the holes and electrons move to the interface, which narrows the space charge area. In addition, the current can pass smoothly. Its direction is opposite to the direction of the electric field in the PN junction, which weakens the internal electric field. As a result, the resistance of the internal electric field to the diffusion movement of the multitons weakens, and the diffusion current increases. The diffusion current is much larger than the drift current, and the influence of the drift current can be ignored, and the PN junction is in low resistance.(2) PN junction is cut off when reverse voltage is applied.If the positive pole of the power supply is connected to the N zone, the negative pole is connected to the P zone, and a part of the applied reverse voltage applies in the PN junction zone, and it is in reverse bias. Then the holes and electrons move away from the interface, which widens the space charge area, and the current cannot flow. The direction is the same as the direction of the electric field in the PN junction, which strengthens the internal electric field. The resistance of the internal electric field to the multiton diffusion movement is enhanced, and the diffusion current is greatly reduced. At this time, the drift current formed by the minority carriers in the PN junction region under the action of the internal electric field is greater than the diffusion current. The diffusion current can be ignored, and the PN junction exhibits high resistance.2.2 Reverse BreakdownWhen a reverse voltage is applied to the PN junction, the space charge region becomes wider and the electric field in the region strengthens. When the reverse voltage increases to a certain level, the reverse current will suddenly increase. If the external circuit cannot limit the current, the current will be so large that it will burn the PN junction. At this time, it is called the breakdown voltage. There are two basic breakdown ways, namely tunnel breakdown (also called Zener breakdown) and avalanche breakdown. The former has a breakdown voltage of less than 6V and has a negative temperature coefficient, and the latter has a breakdown voltage of greater than 6V and a positive temperature coefficient.2.3 Volt-Ampere CharacteristicThe volt-ampere characteristics of the PN junction are shown in the Figure 3, which visually shows the unidirectional conductivity.Figure 3. Volt-Ampere Curve of the PN JunctionThe volt-ampere characteristic shows by Where iD is the current passing through the PN junction, VD is the applied voltage at both ends of the PN junction, and VT is the voltage equivalent of temperature.2.4 Capacitance CharacteristicWhen a reverse voltage is applied to the PN junction, the positive and negative charges in the space charge region constitute a capacitive device. Its capacitance changes with the applied voltage, mainly including barrier capacitance (CB) and diffusion capacitance (CD). Both of them are non-linear capacitors. Ⅲ Typical Example: Transistor PN JunctionTransistors are one of the basic building blocks of modern electronics. In the diode tutorials we saw that simple diodes are made up from two pieces of semiconductor material to form a simple pn-junction. While the transistor is a three terminal solid state device which is formed by connecting two diodes back to back. Hence it has got two PN junctions.Transistor NPN-Type and PNP-Type JunctionsTransistor Working StateThe transistor works like an electronic switch. It can turn a current ON and OFF. The basic idea behind a transistor is that it lets you control the flow of current through one channel by varying the intensity of a much smaller current that's flowing through a second channel.1) Cut-off State (C): The base current is zero.2) Amplified State (A): The transmitter junction is forward biased (that is, the voltage direction is P->N), and the collector junction is reverse biased.3) Saturation State (S): Both the emitter junction and the collector junction are forward biased.Working StateNPN-Type TransistorPNP-Type TransistorVb<Ve (C)Vc>Vb>Ve (A)Vb>Ve Vb>Vc (S)Vb>Ve (C)Vc<Vb<Ve (A)Vb<Ve Vb<Vc (S)In Figure (a), when there is no voltage input at b of the NPN transistor, no current flows between c and e, and the triode is in the cut-off state.In Figure (b), when a positive voltage is input to b of the NPN transistor, the negative electrons in the N region of e are attracted by the positrons of P region in b. Due to the effect of the power plant, and they rush (diffuse) to the base region, however, only part of the negative electrons collide with the positive electrons (recombination) to generate the base current, and the other part of the negative electrons gather near the collector junction. The negative electrons gathered in the collector junction pass through (drift) the collector junction due to the action of the electric field. After reaching the collector area, it collides with the positrons gathered in c (N-type semiconductor terminal) to generate a collector current.It can be seen from this that the greater the base current, the greater the collector current. That is, when a small current is input to the collector, a large current can be obtained by the collector, and now the transistor is in an amplified state.It should be noted that when the base current reaches a certain level, the collector current no longer rises. At this time, the transistor loses its current amplification effect, and the voltage between the collector and the emitter is very small. The collector and emitter are equivalent to the on-state of the switch. At this moment, the transistor is in a saturated state.The working principle of the PNP transistor is the same as that of the NPN transistor, except that the direction of the bias voltage and the current are opposite, and the roles of electrons and holes are reversed. The PNP transistor uses Veb to control the positrons incident on the collector area from the emitter area through the base area, while the NPN transistor uses Vbe to control the negative electrons that enter the collector area from the emitter area through the base area.In addition, in a low-power design, the transistor control circuit will have a certain impact on the circuit. No matter it is NPN or PNP, there will be leakage current in the PN junction of the transistor. When the I/O controls the base voltage, in order to stabilize the base voltage, a pull-down resistor is generally added to the base of the NPN switch circuit. In the design of the PNP switch circuit, a pull-down resistor is added to the base. The pull-up and pull-down resistors are selected according to the control chip, transistor and circuit voltage. Frequently Asked Questions about PN Junctions Formed1. What is PN junction and how it is formed?P-n junctions are formed by joining n-type and p-type semiconductor materials, as shown below. ... However, in a p-n junction, when the electrons and holes move to the other side of the junction, they leave behind exposed charges on dopant atom sites, which are fixed in the crystal lattice and are unable to move. 2. What is p-type and n-type?In silicon doping, there are two types of impurities: n-type and p-type. In n-type doping, arsenic or phosphorus is added in small quantities to the silicon. ... In p-type doping, boron or gallium is used as the dopant. These elements each have three electrons in their outer orbitals. 3. What is a PN junction diode?A PN Junction Diode is one of the simplest semiconductor devices around, and which has the characteristic of passing current in only one direction only. ... By applying a negative voltage (reverse bias) results in the free charges being pulled away from the junction resulting in the depletion layer width being increased. 4. What happens in a PN junction?A forward-biased PN junction conducts a current once the barrier voltage is overcome. The external applied potential forces majority carriers toward the junction where recombination takes place, allowing current flow. A reverse-biased PN junction conducts almost no current. 5. What is a PN junction used for?A p-n junction diode is a two terminal device that allows electric current in one direction and blocks electric current in another direction. In forward bias condition, the diode allows electric current whereas in reverse bias condition, the diode does not allow electric current.

Introduction Diodes are widely used in electronics, such as rectification in power supply, as detection and mixing, etc. in communications, and are often used in voltage regulation and protection in various circuits (such as freewheeling diodes, TVS and so on). Due to the wide variety and versatility, the following is an analysis of the simple application of Schottky diodes in digital circuits.In this video, the Schottky diode has been explained.CatalogIntroductionⅠ Schottky Diodes CharacteristicsⅡ Schottky Diode Applications2.1 As Dual Power Supply2.2 As AND Gate2.3 As OR GateⅢ Schottky Diode ParametersⅣ Example AnalysisⅠ Schottky Diodes CharacteristicsThe Schottky diode is structurally different from the PN junction diode. It is made of an anode metal (a barrier layer made of a material such as molybdenum or aluminum), SiO2 (electric field eliminating material), and N- epitaxial layer (arsenic material), the N-type silicon substrate, N+ cathode layer, and the cathode metal, which are as shown in the following figure. A Schottky barrier is formed between the N-type substrate and the anode metal. When a forward bias is applied to both ends of the Schottky barrier (anode metal is connected to the positive electrode of the power supply, and the N-type substrate is connected to the negative electrode), the Schottky barrier layer is narrowed, and the internal resistance becomes small. On the contrary, when a reverse bias is applied across the Schottky barrier, it becomes wider and its internal resistance becomes larger. Figure 1. Schottky Diode Structure Ⅱ Schottky Diode ApplicationsThe problem with Schottky diodes is that the withstand voltage is relatively low and the reverse leakage current is large. At present, the general condition of the Schottky diode used in the power conversion circuit is that the withstand voltage is below 150V, the average current is below 100A, and the reverse recovery time is between 10 and 40ns. Therefore, Schottky diodes are ideal device for use in high frequency and low voltage circuits.2.1 As Dual Power SupplyAt present, in the electronic design with the main controller, the real-time clock (RTC) is basically used, and the RTC needs an additional button battery to support, to avoid information lost after the system is powered off. And meanwhile, after the system is started, in order to extend the battery life, the main system is often supplied with power. Therefore, RTC often requires dual power supply, and the diode can be used for power isolation due to its single-conductivity. Taking the small-signal Schottky diode BAT54C as an example, the forward voltage drop is only 0.24v (the forward current is 0.1mA), and the RTC current consumption is uA-level, after adding the Schottky diode to isolate power supply to save info security.2.2 As AND GateAs shown in the figure below, n Schottky diodes form the AND gate of the n input. As long as there is a signal output logic 0 in A1~An, the Output is logic 0, only all signals in A1~An output logic 1, Output can output logic 1. That is, the phase sum of the signals A1~An is realized. Since the chip signal input stage is basically high-resistance in the digital circuit, the overall current of the AND gate circuit composed of the Schottky diode is uA-level, and the Schottky diode voltage drop is extremely small. In the case of it, the flat can still meet the design requirements.  Figure 2. Schottky Diode as AND Gate2.3 As OR GateAs shown in the figure below, n Schottky diodes form an n-input OR gate. As long as there is a signal output logic 1 in A1~An, Output outputs a logic 1. Only all signals in A1~An output logic 0, and Output can output logic 0. That is, the phase sum of the signals A1~An is realized.  Figutre 3. Schottky Diode as OR Gate Ⅲ Schottky Diode ParametersNote: Because Schottky diodes are used differently in different electronic circuits, we also need to consider the following parameters when using them.1）Forward voltage drop VFVF is the forward voltage drop when the diode is forward conducting. The greater the current through the diode, the larger the VF, in addition, the higher the diode temperature, the smaller the VF.2）Reverse saturation drain current IRIR refers to the current flowing through the diode when a reverse voltage is applied to the diode. The Schottky diode has a large reverse leakage current, therefore, selecting a Schottky diode with a smaller IR.3）Rated current IFIt refers to the average current value calculated from the allowable temperature rise when the diode is in a long time operation.4）Maximum surge current IFSMExcessive forward current that is allowed to flow. It is not a normal current, but an instantaneous current, which is quite large.5）Maximum peak inverse voltage VRMEven if there is no reverse current, as long as the reverse voltage is continuously increased, the diode will be damaged sooner or later. This reverse voltage is not the instantaneous voltage, but the reversed voltage that is added repeatedly. Since the rectifier is supplied with an alternating voltage, its maximum value is a specified important factor. And the maximum reverse peak voltage VRM refers to the maximum reverse voltage that can be applied to avoid breakdown. At present, Schottky's highest VRM value is 150V.6）Maximum DC reverse voltage VRVR is the value when the DC voltage is continuously applied. For DC circuits, the maximum DC reverse voltage is important to determine the allowable and upper limits.7）Maximum operating frequency FMDue to the junction capacitance of the PN junction, when the operating frequency exceeds a certain value, its unidirectional conductivity will deteriorate. And Schottky diodes have high FM values up to 100 GHz.8）Reverse recovery time TrrWhen the operating voltage changes from a forward voltage to a reverse voltage, the ideal operation of the diode is that the current can be instantaneously turned off. In fact, it usually takes a little delay. The amount that determines the current cut-off delay is the reverse recovery time. Although it directly affects the switching speed of the diode, it does not mean that this value is small. That is, when the diode is suddenly reversed by conduction, the reverse current is greatly attenuated to a time required to approach IR. This indicator is important when the high-power switch is operating in the high-frequency state.9）Maximum dissipation power PWhen a current flows through the diode, it absorbs heat and raises its temperature. In reality, the external heat dissipation condition also has a great influence on P. Specifically, the voltage applied across the diode is multiplied by the current flowing through and the reverse recovery loss. Schottky Diode Symbols Ⅳ Example AnalysisIn digital circuit design, it is often necessary to make simple phase, or phase inversion of some signals. If the logic chip such as the 74 series is directly used, not only the layout area is greatly increased, but also the wiring is not flexible. The use of small-signal Schottky diodes and OR gates is more flexible and easy to use. The following figure shows a simple two-way reset circuit. JTAG generating a reset signal needs to reset the master, and the external reset button also needs to reset the master when pressed. If the JTAG reset and button reset directly to the reset pin of the master, it may cause damage to the JTAG emulator. For example, when the reset button is pressed, the JTAG output reset pin will be directly lowered. The phase and circuit are formed by the Schottky diode BAT54A , and the signal outputs do not affect each other. The following figure allows the master to reset as long as the JTAG output logic 0 or pressing the button reset output logic 0.Figure 4. Schottky Diode BAT54A ApplicationIf it is to be used as a non-gate, a triode can be used. Of course, the triode is widely used in electronics, such as a switching device in a digital circuit, as a current drive, level shifter, and the like. Frequently Asked Questions about Small Signal Schottky Diodes1. What is the Schottky diode and how it works?A typical diode combines p-type and n-type semiconductors to form a p-n junction. In a Schottky diode metal replaces the p-type semiconductor. This metal can range from platinum to tungsten, molybdenum, gold, etc. When metal is combined with an n-type semiconductor an m-s junction is formed. 2. What does small signal mean?A small signal is an AC signal (more technically, a signal having zero average value) superimposed on a bias signal (or superimposed on a DC constant signal). This resolution of a signal into two components allows the technique of superposition to be used to simplify further analysis. 3. Which statement is correct for Schottky diode?Explanation: The majority charge carriers in a Schottky diode are electrons not holes. Explanation: Due to the metal-silicon junction there are no stored charges hence, no reverse recovery time, due to which the switching is faster. 4. What are the two important features of a Schottky diode?We have seen here that the Schottky Diode also known as a Schottky Barrier Diode is a solid-state semiconductor diode in which a metal electrode and an n-type semiconductor form the diodes ms-junction giving it two major advantages over traditional pn-junction diodes, a faster switching speed, and a low forward bias.