I have a subwoofer in my system that I’ve had for 20 years and it has been fault free til now . It was until I got the BHK 250 which replaced a Sugden IA4 class A integrated , the problem is as stated the sub won’t turn off anymore when used with the BHK , it was intermittently functioning ok initially but then would stay on all the time . I pulled the amp out of the sub and there’s nothing looking cooked or suspect , I did notice though a low level hum . I thought I’d get a bit more serious and cleaned connectors and switches etc pulled the lead from the amp ( high level input on the sub ) and I thought that I had it , after pulling the positive from right hand channel out of the BHK , the sub turned off . But for nought tried it again the next day no luck . Anyway cut to the climax , in the end I got the Sugden out and plugged the sub in and it functions fine , turns off after 5 minutes fires up ok etc . What’s different between the two amps , there’s no standby mode on the Sugden , turn it on it’s on turn it off it’s off . Any suggestions or thoughts . Interestingly when using the low level input on the sub everything is fine .