Hi Sean, the aerial and all cabling is indoors, in bone dry conditions and has never been wetted at all. You are quite right, I had to fit adapters to go from the Belling Lee connectors on the cabling to the F type sockets on the new amp. But this determination led me to try refitting the old amp and sure enough,m the problem immediately returned. I again checked its internal PSU and from just over 12V AC from its little mains transformer it gives about 16V DC. This comes out of the little single package full wave bridge rectifier into a 330uF cap, then through a dropper resistor (current limiting?) of 47 Ohms into another 330uF cap and this feeds the circuitry of the amp. The output looked clean earlier, but after it had been on a while I was seeing the attached on my scope on AC setting. Could that ripple be affecting things? The two 330uF electrolytics checked out OK out of circuit. It's all pretty academic, now a new unit has fixed this, but I am stubborn and rather than bin it would like to learn from this a bit more. Thanks!