Many Thanks again to all. Especially Guesser who prompted me again to try the analogue route. Using your wisdom , sir I managed to tune the 128 and one of the 48K speccies to my older DVB TV. Results show a kind of output to the TV.
This first image is the output from the 48K spectrum, accompanied by a lot of white noise.
This was what the 128K spectrum + looked like, similarly with white noise.
The 48K spectrum did beep a lot and produced the wail it used to when loading a programme but the plus unit provided no key sound output, even when I tried listening with headphones plugged into the ear socket.
I suspect these are possibly terminal indications for an amateur like me but there seems to be a market on ebay for spares and repairs, and all the software I have to go with them.
Unless you know differently of course.
Again many thanks to all who have contributed to this posting, it has served to illuminate my inadequacies in this field .