Total posts : 45366
**edited** Oops, the specified voltage of 7.1 volts is measured at R34’s lead closest to C23, not at TP1 as I wrote. ****
No, I did not look at this, but from previous experience I know this could be an issue. I applied a 1 kHz. sine wave from a HP audio generator and observed the modulated waveform on the scope. I was on the air with a coupled antenna which I have previously described and noted the best looking waveform when R23 was adjusted for a TP1 voltage of 4.7 volts rather than the specified 7.1 volts. This adjustment changes the input power so proceed carefully if you try this.
I did not observe the modulation with a changing load but it would not surprise me if this would affect the quality of the audio as well since it changes the load line for the amplifier. Again, this is just speculation and if I can I will do an experiment.