Thank you all for your helpful replies.
Firstly, OH 's headphones (after much trial & error & expense) are Sennhieser, stereo & expensive. A unit plugs into the TV while the headphones "pickup' the signals from the unit. OH is free to roam around the house and even water the garden while listening to the TV. The headphones do not cut off the sound to the rest of us. It is his favourite device and he recommends it to anyone with a hearing loss. I sometimes use it - beautiful sound - with the TV sound turned down while the rest of the family sleep. So with any new TV set he buys, he will be testing to see if these headphones work as well.
Our "old" TV was one of the first digital on the market at the time but our local TV digital reception has changed etc. Having a good TV/ headphone system is vital for my OH despite some of the program content being rubbish.
I think we shall be waiting for our son, who has a bit of tech knowledge, to advise us. Best wishes, Gazania
PS My mother was profoundly deaf all her adult life. When TV came, my father learned how to hook up a coil (primitive length of wires at that time) from the TV set to her hearing aid. The TV became her hearing world and she & Dad travelled through the UK & Europe for 2 years and he was able to hook her up to every TV set.