The pre-stage voltage amplification tube produced this time was selected from Nanjing 6SQ7, the circuit architecture adopts 6SQ7 level to promote KT66, and the power amplification part of the power tube adopts standard connection method, so that large audio dynamics and power can be obtained (shown in Figure 1). Since the analog output level of modern audio sources is relatively high, it is generally 1~3V. In order to reduce the signal input amplitude and reduce the pre-amplification distortion, a 1 kΩ resistor is inserted in the front input. The power supply part adopts the method of transistor rectification and bile buffer to improve the power efficiency. The 5Z4P is a side-heating rectifier tube, which has a delay buffer protection function for the power tube KT66 during high voltage starting, which can prolong the service life of the electron tube. Negative feedback R5 and screen feedback R4 are added to the circuit. R5 negative feedback is good for suppressing noise and reducing transient distortion during large dynamics. R4 screen feedback helps to suppress noise, but if R4 resistance is too small, it will decrease. The input impedance affects the low frequency response of the amplifier. The power transformer has a power of 20OW, an AC voltage output of 290~0~290V, a current of 2OOmA, an output transformer output power of 13W, a choke coil inductance of 5mH, and a current of 3OOmA. The cathode bypass capacitor and the decoupling capacitor in the circuit are selected as the audio dedicated capacitor, and the coupling capacitor is selected from the red Wei Ma MPK-10 series tantalum capacitor. This capacitor is cheap and has a good sound, volume potentiometer ALPS dual 100kΩffiALPS original potentiometer. The resistance of the signal is made of carbon film resistors, and the other resistors are made of high temperature resistant metal film resistors. This is helpful for the introduction of enamel.
figure 1
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