I used to work for Sears in their service department, 25+ years ago. Check to see if there is a switch on the back of the cabinet marked "Vacation"; this disables the instant-on feature. Some sets had this switch. If the switch isn't there, the set could be modified to defeat the feature, or you could operate the set from a switched power strip. The instant-on feature went by the wayside around 1973 or so.