Apparently you can't. I have an Astral country roses push button phone that has a terrible hum whenever you dial a number. As I understant Astral went out of business 20 odd years ago, and now the phones cannot be repaired :-((
samantha fellows
February 2012
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
