6J8P curtain gate input timid stage, 6J8P Preamplifier
Keywords: 6J8P curtain gate input timid stage
6J8P curtain gate input timid stage
In view of the higher high-pronged output level, it can directly promote the post-stage (consolidated machine) amplifier. Therefore, the main purpose of the pre-production of the production is to make the sound quality, the sound quality is better, and the sound is more perfect. The big gain, even no gain, also used the electronic pipe 6J8P, ground the gate, and the front stage circuit input by the curtain gate, the circuit is shown (the other is identical).
First, circuit principle and characteristics
1. There is only 2DB-5DB gain, so the volume potentiometer is not set, the volume control is held by the post-level amplifier, which facilitates the amplitude frequency, phase and the displacement of the potentiometer during the impedance of the potentiometer during the impedance of the attenuation. Harmonic distortion, and facilitates the avoidance of the noise generated by the potentiometer.
2. Due to the pre-prodence sensing noise and filament exchange interference, 6J8P is connected to the grid circuit. The cathode is connected to the cathode, which makes the cathode and suppression gates, which make the front-level sound of the front casket. Quiet The operating performance of the gateway is stable and reliable, overcomes the zero drift of the amplifier, and firmly locks the working state of this level.
3. The audio signal is input from 6J8P curtain gate, and its magnification is reduced, and the distortion is also reduced accordingly, in particular, can reduce the zero distortion and harmonic distortion input from the gate. There is a pole capacitance in the electron tube, in particular the cathode capacitance and the input circuit, the parallel resonance is an important factor in which harmonics is generated. Now use the curtain gate as a signal input pole, and the polar capacitance between the curtain gate and the cathode is more than the negative, gate The capacitance is much smaller, even if resonance has entered a super high frequency range, and it is impossible to find the ear.
4. Another advantage of the preamble of the five-pole production is not sensitive to the change in supply voltage.
Second, the component selection
The 6J8P parameter is attached to the table. The power supply transformer power is 100VA, the blocking ring specification is 10h 60mA, the curtain gate pressure potentiometer, requires good contact performance, or after the adjustment tone is completed, change the potentiometer to fixed resistance /)
The two coupling capacitors of this unit use silver film capacitance, and the silver film capacitance frequency is uniform, small loss. 6J8P cathode bypass capacitor selection axial lead tantalum capacitance, resistance is selected for the early production of green carbon film resistance, electrolytic capacitance domestic day and brand aluminum shell large volume electrolytic capacitor.
Third, welding machine debugging
Although the unit is connected to the ground cord gate input circuit, the DC operating circuit is still the same as the traditional 6J8P, so the adjustment is still referred to with a set of classic working values, that is, the 6J8P cathode voltage is 3V, the screen voltage is 180V, curtain gate The extreme voltage is 75V. The specific method is to regulate the cathode resistance and the cord potentiometer.
The curtain gate resistance is both an input resistor and a bias resistor. It is determined that the amplitude frequency characteristics, the value should not be less than 150kΩ, the curtain is high, the gain is low, and the anti-gain is high. The curtain gate resistance size and the curtain bias size affect the performance of the sound, and must be adjusted repeatedly to achieve perfection. When the specific adjustment must be accessed, it can be determined by listening.
Four, listening
Open the power, a little noise, suspected that the circuit has problems, so that the volume is still the same, press the DVD playback button, eat a lot of shock, a "campus" water clear, the sound is very clear, very Condolence, high school low frequency melody is magnificent, and the gallbladder is rich.
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