300B vacuum tube Hi-Fi amplifier
The direct heat 300b electronic tube has been in the world for more than 70 years. Due to the reasonable internal design, the consumption is moderate, the internal resistance is low, the linear is excellent, and the single-ended power amplifier with its production is pure, clear and transparent. It is known as the highest realm of Hi-Fi sound quality, which is deeply loved by the enthusiastic friends at home and abroad.
The author analyzes the comparison, and finally decided to use the first stage for the triode voltage amplification, and then use the power tube as the promotion stage, and finally the 300b as the power amplified program, the circuit is shown.
Pre-electrical voltage amplification level.
The front voltage amplification larger V1 adopts the domestic medium-magnification low noise double tripod diode 6N10, which is known as the music flavor, which has been used by many mandators in the world.
In the circuit, the double tripode is used in parallel, which can reduce its internal resistance, which is conducive to match the input signal, and the cross guide is doubled than a single triode, ensuring that there is enough voltage amplification in the predecessor.
Intermediate promotion level
The general efficiency of the heated triode power amplifier is less efficient. When the 300b is full of power output, the variation amplitude of the gate is generally 60 to 70 Vpp, so the characteristics of the push tube are more important, and all 6N8P, 12AU7 cannot be satisfactory. To this end, the power amplifier 6P6P is used in this level, low noise, low frequency band, and the effect is better after using the triode connection.
In fact, it is not necessary to push power, which is mainly to solve the voltage amplitude problem of the promotion level. This level is connected to a common cathode amplifying circuit, and the gate is negatively biased in more than 20V, with a wide input range, the voltage amplification is about 6, the maximum non-distortion output voltage peak can reach 200V, not only can drive the input amplitude A 300B of about 70V is required, and even one type of right-characteristic triode such as 211A, 845 can achieve full power output.
Power amplification level
This grade uses a self-supplied bias circuit to a certain extent, to a certain extent, the malignant growth of the screen stream, ensuring expensive 300b security.
There is a 300mA current table on the cathode resistance, just like two eyes monitor the working conditions of the power amplifier 300b.
Cathode resistance uses 900Ω, 40W high-power resistance, cathode capacitor selection 85UF / 230V oil immersion capacitor, and a new leap in the sound quality compared to the electrolytic capacitance.
power supply
High voltage loop
Power transformer secondary side double 360V winding, 1N5408 silicon rectifying diode per arm is connected in series to full-wave rectification, in parallel with a 0.033 uf / 400V organic film in each diode, and prevents electric web electrical clutter The role of interference can also ensure the safety of the rectifier diode. After the rectified pulse DC high pressure is connected in series with two 2000uf / 250V large electrolytic capacitors, and then the two 5Z4P electronic pipes are fed. The filament heating and power amplifier tube filament is heated to synchronize the sudden impact of high-pressure to the electronic tube, in rectification The cathode of the tube has a 100Ω / 15W current-current resistance, from the shock of the filter capacitor wave surge current to the rectifier diode.
2. Filament power supply
The front voltage amplifies, the push-level filament is powered by AC. There is a direct current voltage of about 40V, so that the wire windings are in the cathode, the cathode cannot absorb the wire emission, thereby no AC voltage on the cathode resistance IRK Decrease, the AC voltage drop in (Rg) can be canceled to each other, thereby eliminating the communication caused by the filament power supply circuit.
The filament is powered, the sound is fresh, and the low frequency is more flexible. DC power supply produces some stone, so that the sound quality is hard. The straight-heat 300B power tube cathode (filament) is a equipotentiometric body, which is easy to produce a subtle communication when heating is heated, which is very uncomfortable. To this end, the power amplifier still uses DC power supply. The rectifier circuit uses a bridge heap of 15A, 10 times that of the filament current, the filter capacitor is 27000 uf / 20V Morroli Electrolysis, and the electrically blocking into a balanced bridge at both ends of the filament, so that the current value of the RG circuit is balanced by distributed capacitive coupling. .
Component selection
Transformer
Power transformers, output transformers are ordered from Sichuan Guanghan Kai Li Electric Factory. The cow core section is 35mmX67mm, the secondary high pressure windings are double 320V, 360V, 400V / 0.4A, 40V / 0.2A group, filament winding 5V / 3A, 3.15V-3.15V / 3A group, weight 6.5kg.
The output transformer model is KSC50A, using Japanese imported H10 high silicon press, high purity oxygen-free copper wire, layered, segmentation, grade high-fidelity design, primary impedance 3.5kΩ, secondary tap 4Ω, 8Ω.
The choke is selected to have no two plants in ZL-10-40, 10H100mA, two parallel use.
2. Capacitor
The front stage of the coupling capacitor uses MKP capacitance, and the promotion of the imported blue SIEMENA MKP capacitor is used in parallel, respectively, and a domestic 0.05 ue / 400V MKP capacitor.
The front-level cathodic capacitor uses the Manon 470UF / 50V electrolytic capacitor, and then the ROE 0.1 UF / 100V organic thin film capacitance is connected.
3. Resistance
The resistance does not have to be detained in a brand, mainly considering the resistance, noise, power consumption, stability of the resistance, as long as the quality is good. The resistance of 2 W or less is selected with a domestic large red cannon resistor, and the RX tube type oxide film wire is wound by the RX tube type oxide film. For 300b cathode resistance, RXYD type tide is wound around the glaze, and the required resistance is obtained by the string, and the power is 40W.
4. Other components
Switches, inserts, terminals, etc., as much as possible, the power switch is used to use the old-fashioned KN3 double-throw double-knife switch. Source switching Selects the KCT medium-sized cassette rolling hop structure porcelain band switch, which is strong, and the contact area is large. Connect the cable plug, socket, select CB2 rectangular plug, socket, small contact resistance, long life. The MA table also chooses a professional level 91C4. Although there is no monster, Turlong, the Silver line is such a high-grade line village, but must guarantee enough capacity and intensity. All in all, the components must choose the quality of the formal manufacturer.
Craftsmanship
Production Process () Author: Feng Kaihui
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