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High Quality, powerful unit: 90W into 4 Ohm load Also suited as guitar or bass amplifier 60W MosFet Audio Amplifier 60W MosFet Audio Amplifier Description To celebrate the hundredth design posted to this website, and to fulfil the requests of many correspondents wanting an amplifier more powerful than the 25W MosFet, a 60 - 90W High Quality power amplifier design is presented here. Circuit topology is about the same of the above mentioned amplifier, but the extremely rugged IRFP240 and IRFP9240 MosFet devices are used as the output pair, and well renowned high voltage Motorola's transistors are employed in the preceding stages. The supply rails voltage was kept prudentially at the rather low value of + and - 40V. For those wishing to experiment, the supply rails voltage could be raised to + and - 50V maximum, allowing the amplifier to approach the 100W into 8 Ohm target: enjoy! A matching, discrete components, Modular Preamplifier design is available here:Modular Audio Preamplifier...

This is the circuit diagram of 60W transistored power amplifier. This circuit was designed and built during the 80s. From then it works without problem. It does not present a particular construction problem , apart from the known: the attention to the supplied power source, choosing suitable heatsinks and good matching of the driver transistors. The diodes D3..5 should be placed on the heatsinks of power transistors to have thermal coupling with the output transistors.  60W Transistored Power Amplifier Circuit Diagram With the trimmer R15, we regulate the voltage at the output of the amplifier [with long work hours and little heat stabilized]. With the trimmer TR1, we can adjust the bias current of the amplifier at 50 to 100 mA. The bias current can be measured if you measure the voltage drop at the ends of the resistors R36 and R37, for the voltage that are given in the circuit, the current is approximately 75 mA. The voltage indicated in above diagram can be different, but may h...