In the circuit exist a simple power amplifier 60W in the 8 ohm and 80W in the 4 ohm, with components that sure exist in big quantities. It can be used in home cinema systems or in other uses. With the TR1 we regulate the DC voltage in the output of amplifier in low levels [±20 until ±50mV it is a good level]. Good also they are the two transistors Q1-2 of differential amplifier, they have matched characteristically. With the TR2 trimmer we regulate the transistors bias current of output power stage, in 50mA roughly for each sector. This regulation become without exist signal in the input, place a digital multimeter in terminal since of the resistors R22-23-24-25 and regulating him TR2 should we have clue, roughly 25mV DC, that corresponds in current 50mA.
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We leave the amplifier to work for few hour and if it needs we regulate again. Transistors Q6 until Q12, should be placed on a good heatsink, with attention so that insulation well from the heatsink and the support screws.
Part List
R1=1.5Kohm R21=10ohm 1W D1=5V6 0.4W zener
R2-9=10Kohm R22-23-24-25=0.47ohm 5W Q1-2-3=BC557
R3=2.7Kohm TR1=100ohm trimmer Q4-8=BD140
R4=5.6Kohm TR2=470ohm trimmer Q5-7=BD139
R5=3.3Kohm C1=2.2uF 100V MKT Q6=BC549
R6-12=470ohm C2=330pF Q9-10=TIP2955 [MJE2955]
R7-11=1.2Kohm C3=100uF 16V Q11-12=TIP3055 [MJ3055]
R8=560ohm C4=100pF
R10=220ohm C5=27pF F1-2= 3A slow Fuse 5X20mm
R13-14=47ohm C6=3.3nF 100V MKT
R15-16=33ohm 1W C7-8-9-10-13-14=100nF 100V MKT All resistors is 1/2W 1% metal film except for announce differently
R17-18-19-20=220ohm 1W C11-12=220uF 63V
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