FU-50 push-pull amplifier production, Fu-50 Power Amplifier
Keywords: FU-50 push-pull amplifier made
FU-50 push-pull amplifier made
FU-50 produced by a single Swiss Class A amplifier, promote low sensitivity speakers powerless feeling, for young people like large dynamic music is not appropriate for this experiment two class AB push-pull amplifier I, to obtain more good results, especially devote myself to readers.
A test circuit shown in Figure 1, the input stage transistor 6N2 as a high-μ, gain of about 78dB. 6N2 added on the whole cathode negative feedback, the feedback amount of -6.6dB. Inverter stage held by 6P1. The 6p1 ratio of the triode approach is used with a lower internal resistance, a larger output current, thereby having a greater dynamic range. A load resistor on the low voltage output higher low distortion, excellent linearity, this gain stage is 0.85dB. Employed between the input stage and the inverter stage direct coupled circuits, to ensure good frequency and phase characteristics.
The output stage working FU-50: for the class AB state. Numerical FIG Press, Po = 39W, Ra = 9kΩ, Ua = 500V, Iao = 63mA, Ug = -30V, Eg = 2x30Vp-p.
Design methods are presented:
FU-50 limit parameters are as follows: Uamax = 800V, Vg2max = 50V, Ikmax = 230mA, Pa-max = 40W. Take Ua = 500V, with the empirical formula Ra = 4 xUa / Ikmax = 4x500V / 230mA≈9kΩ, (see FIG. 2) takes on a characteristic graph coordinates Iamax = 230mA, Ua = OV to point M, Ua = 500V, Ia = 0 is the N-point connection MN. That is, for Ra = dynamic load line when 9kΩ. Ug = MN line of intersection A 0V, the current point is 190mA, Uamin = 85V. Press the AB1 amplifier operating point current to select the principle of the maximum operating current 1/3 ~ 1/4, take IAO = 1/3 IAMAX = 190/3 = 63mA. The x-axis parallel line is intersected by IA = 63mA and the UA = -30V curve, and the intersection is the operating point of the tube. In this state, UA = 500V, IAO = 63mA, Ug = -30V, UG2 = 250V calculates its output power PO = [(uAmax-uamin) × Ia-max] ÷ 2 = [(500V-85V) × 190mA] ÷ 2 = 39.4W.
The audio output transformer is a local key device, and the author is a self-made transformer as an experiment. The effect is also good. Follows, the choice of high-quality silicon 32mm wide tongue, stack thickness 40mm. The primary coil is coordinated with a φ0.18mm oxygen-free copper wire with a coordinated 2 × 1470 turns, double-wire and wound in three sections. Turns around the first section 2 × 370; 2 × 730 turns about the second section; 2 × 370 turns around the third section. The secondary winding 95 turns (8 ohms) or 68 turns (4 ohms) in two steps between the three sections sandwiched around the primary winding. Connection: each of the three sections of each coil in series into A, B two sets of windings. Connected the first end of the A group with the end of the B group, as the center tap of the primary winding. The tail group A and group B are respectively connected to the output end of the first tube panel electrode. Two secondary windings serially connected to the load. Wiring diagram shown in Figure 3. Output transformer interlayer capacitor paper insulation, and cable paper and yellow paint are insulated. Due to the larger terminal, check the method carefully to avoid mistakes. Three sets of cross stacks of iron cores. Impregnation can check and correct processing. The machine elements are arranged, wiring, and other earthing arrangement principle no different amplifiers, omitted here.
Debug: connected to the load, to the minimum volume potentiometer to adjust the gate opposite the gate piezoelectric positioner negative maximum position. Preheat the power for 10 minutes. No abnormalities after ignition, smoke, etc., W1 and W2 of the adjustment, the voltage on the cathode tube is resistance of the output 0.63V, this time of each flow tube panel 63mA. The value of each pole voltage and the values of the 6N2 and 6P1 should be substantially consistent. The big difference of the adjustable resistance R1, so as to meet the requirements.
Soundcheck: The machine output power is strong, good for large dynamic signal performance. Promote low sensitivity speakers effortlessly, details of the performance of the music is quite good. The embodiment of the whole non-linear distortion of 2% (full power), frequency response of 20Hz ~ 55kHz (± 3dB).
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