Quote:
Originally Posted by mhennessy
But the quiescent point is around 8.4 volts, so isn't there a danger of the positive half-cycle might be clipping before over-mod is detected? Presumably it's slightly lower - things don't always follow the theory
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Thanks for comments and interest, Mark.
The quiescent point is around 7.5V and with a sinewave input gives symmetric clipping as it approaches overload. So, there's no danger of the positive half-cycle clipping before the negative.
The reason that the quiescent point is 7.5 not 8.4V is, the emitter current of Q1 flows through R7 (and similarly Q3 and R13), so each stage's DC feedback drops the quiescent output voltage by a small amount to give the requisite DC voltage across the feedback resistors.
Hope you had a good dinner and chat about modulation! This stage is straightforward if you bear in mind that the Q13/D4 pair is either 'on' or 'off', with no linear region at all. Then, all voltages are proportional to the supply voltage at the top of L4, which varies at an audio frequency rate.