Quote:
Originally Posted by mhennessy
Um, what has hfe got to do with the gain of the amplifier?...You only need to consider hfe when establishing the biasing circuits.
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Voltage gain is sensibly independent of hfe, agreed, but the input impedance of a common-emitter stage is highly dependent on hfe.
So, if you are using your transistor to amplify the output of a diode detector, having an output impedance of a few kilohms, you want an amplifier with a highish input impedance. Otherwise, it'll load the detector, the AF voltage will drop, the transistor will see a smaller input, and give a smaller output.