Tonora, it's not the ringing tone I need to hear better but the caller's voice. Sorry - should have made that clearer. Have tested volume of a few at my local phone shop (very obliging people) but none can be put high enough for me.
Clubman, thanks for that thoughful suggestion and link. My present "personal stereo system" is too small to have a T-switch - they tend to be standard on larger aids; witness the need to have loud volume as I take the aid out on one side to use the phone without a hum.
Reckon it's time to upgrade my stuff to something a bit larger with room for a telecoil. Oh well.....