Transistor Current Amplifier Circuit | Electronic Project Circuits

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The Class-A 2N3055 Amplifier 20W

care must be taken to ensure that R5 and RV2 are adequately rated. The current through these components is slightly greater than the sum of the output transistor base currents. The output transistor base current is the output transistor quiescent collector current (Ic) divided by the current gain (Hfe) of the device. The current through R5 and RV2 is therefore approximately equal to 4 x Ic / Hfe and this should be calculated for the chosen output transistor quiescent current and output transistor type. It is recommended that output transistors with a gain of 100 or more at the working collector current are used in this design to reduce the power rating requirements for R5 and RV2.

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Categories: Power Amplifier Tags: 2N3055 amplifier, Class a transistor amplifier, Transistor current amplifier circuit

Power Amplifier Class A 25W

Musical Fidelity would let you believe that this is a Class A design. However, in common with most commercial amplifiers, it is a class AB amplifier – it simply has a rather high standing current in the output stage, which results in the first 8 watts or so being class A.
This is a curious design, in my experience at least. It is a symmetrical design, using what appears to be two identical amplifiers – indeed there’s separate feedback paths for each. I guess that you could replace one half of the amplifier with a current source and it would work happily…

Several people have emailed to inform me that Tim de Paravicini designed the circuit – he is more famous for his valve designs, particularly single-ended, I’m told…

Each half is very simple – essentially a long-tailed pair feeding the output device which is connected in a common-emitter configuration. The two intermediate transistors (TR7/8 and TR5/6) are simply emitter-followers, providing current gain…
Source:http://www.mhennessy1.f9.co.uk/mf_a1/technical.htm