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Home Power Amplification Power Output from a ClassA Stage  
See also: ClassB Operation, ClassAB Operation  
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Power Output from a ClassA StageAuthor: N.H. Crowhurst
As an example, suppose that in ordinary pushpull (known as class A, which means that both tubes are conducting current all the time), the operating point for each tube is 250 volts at 30 milliamperes and that the load value presented to each tube is 5000 ohms with pentode operation. Disregarding the curves to make the calculation simpler (if approximate), the audio fluctuation should carry the plate between 100 volts at 60 milliamperes and 400 volts at zero milliamperes. This represents a peak fluctuation from each tube of 150 volts and 30 milliamps in each direction, which is a peak power of (150 X *03) or 4.5 watts per tube or 9 watts for the two tubes in pushpull. The average power, using a sine wave to drive the output, will be just half of this figure or 4.5 watts for the two tubes.


Home Power Amplification Power Output from a ClassA Stage 