Thanks Bruce,
Tend to feel its the output centre voltages sliding about, where eventually OK and the relay clicks in. Had a look on the output panel but see no pots to adjust quiescent things to perfection. Guess wait 'til it goes pouf then sort duff transistors.
Amusingly the amp was to be used over Crimble, where the chap who runs the shop intended to amuse his family singing along to the dancing dots, where he sang for five minutes to total silence.
Admit haven't had the pleasure, as his music isn't quite mine, him being a salesman of considerable repute, where I prefer more reflective stuff whilst replacing current model Sammy Leds by the dozen - Chris.