[thejazzageuk]

Thanks for all this advice. I have now carried out the checks advised on Techman's original post. I have done about 20 cycles of 1 min on then wait 5 mins. The sound from the speaker has improved- got a bit louder and clearer and hum slightly reduced. Removing the input wiring reduces most of the hum, but some still remains.
I'm very happy to be advised about how to diagnose which electrolytics need replacing- still quite new to all this. I will now carry out the checks in your last 2 posts and let you know how I get on. I've attached a copy of the circuit diagram which may be useful.