Hi Tony
Many thanks for such a detailed and informative reply! I’ve clearly got to be more sure of what I’m doing here, and in answer to Paul’s question the beast I’m making this for is my Tecsun PL-330. I was intending to use this hanging out of my bedroom window, but may now keep it for country trips. I did see this YouTube clip of which I’d appreciate an opinion: https://youtu.be/WjCFLG0DHOo
Am I right in thinking that the lower ‘earth’ lead is connected to the plugs sleeve. If this is clouding the issue please tell me to forget for now, I can take it!
As usual any help greatly appreciated 
Drifter