Keywords: FU-50 single-ended power amplifier
The Fu-50 is a high-yang voltage, a low anode current power tube, which is limited to UAMAX € 0V, which can be used in UAMAX € 0V. The UA @ 0V is selected here. One considers that the home audio power is not too high. The two increase the anode voltage in order not to exceed the anode power consumption, and the anode current is reduced. As a result, there is an increase in distortion of the internal resistance of the electronic pipe. The impedance increases, and the output transformer is often expanded. Therefore, in order to take care of the output power and other factors to select 400V anode voltage. The FU-50 UAMAX is 250V, and 150V power is selected here is to take into account the gate control voltage in the anode power consumption zone has a larger linear zone to facilitate the play of the A-class action.
The FU-50 single-ended Class 7W power amplifier circuit is shown in the drawing, the maximum second gate voltage limit is 250V, and the column is selected from the column, but this voltage must not be simply suppressed by resistance, otherwise the power is turned on, FU- The 50 cathode does not reach the emission electron temperature, the second gate is no current, and the voltage is inevitably high, and the FU-50 life will be shortened. At the same time, the second gate current varies with the input signal, and the second gate is not stable and the distortion is increased. Therefore, the second gate voltage is regulated in 150V in the machine in the machine (the same as the domestic WY-4, the former Soviet CT-4C and the same). When the second gate current fluctuates less than 30 mA, this voltage is stable.
FU-50 is an elongated tube, and the side of the glass shell has a long positioning pin. The positioning pin is vertical, the pin is the first foot, and the pin is in the need to 1 ~ 8 foot, the 7th foot For the internal isolation piece, it can be grounded when used. Sera 4, 8 foot is 12.6V filament. Electromechanical
The source portion adopts a semiconductor diode bridge rectification, and the 100Ω resistor can be powered on 400V. The anode internal resistance of the five-pole output tube is high, meaning that the anode voltage on the anode current is extremely small, although a single single end of the A, which does not have significant AC noise with simple RC filter. However, the second gate voltage to the anode current is extremely high, and the power supply ripple must be small, so that the charging regulator tube has excellent filtering, so the machine outputs the static noise voltage of only 20mV below the 8Ω end. Since the VR150 is connected, when the power-on FU-50 filament is preheated (about 35 seconds after the FU-50, the rated electron radiation temperature is reached) The regulator VR150 immediately generates a glow discharge of about 30 mA current, so the semiconductor rectifier is also High-voltage delay circuitry is required, so that the power-on impact voltage is within the limit of the FU-50, once the electron emission temperature, the second gate generates current, and the inflatable regulator current simultaneously increases 6.2 kΩ resistive pressure reduction, maintenance The second gate voltage is 150V unchanged. When it is considered that the glow discharge tube is troublesome, it is also possible to replace the Zener diode, but there should be a high pressure regulator of the 150V Zener voltage and the maximum Zener current of not less than 45mA.
The output transformer primary impedance is high, and the primary inductance must increase, otherwise the low frequency response will be restricted. The E32 high silicon steel sheet is used, the thickness of 50 mm, the EI sheet is single-to-insert, and the air gap is 0.2mm.
The primary winding is 3500 with φ0.17m, the secondary 8Ω winding wire is used with φ0.51mm enamel line 52. Author: Zheng Guichuan
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