[Andrew2]

OK here we are, Neil.
Test cct consisted of TA7642 with output load res (pin3) of 1.2k, supply 1.5v.
AGC bias res (pin 3 to pin 2) of 120k.
Input from sig gen via 0.1uf to pin 2.
nothing was properly terminated, so levels may be somewhat questionable.

Useful audio (around 100mV p-p) output appears with 70uv p-p input. There is very little AGC action at this point.
AGC starts to cut back the gain at 200uV input, distortion appears on output audio, which is now at around 200mV p-p.
With 400uV p-p input the audio out is slightly over 200 mV p-p and the distortion is worse. Screenshot attached.
I thought the distortion was perhaps caused by audio getting back onto the input pin via the bias resistor, but splitting the 120k into two 56k's and decoupling the junction made no difference.
Hope this helps. It's still all lashed up so let me know if you want any more tests before we start on the wine & crisps!