Worked in a housing for elderly project where 24VAC is used for an emergency call system. All of the Edwards bells which are installed are 24 VDC bells. They all work, although a couple that had to be replaced we replaced with DC bells and they didn't work without fiddling around with the gong for tightness. So what's the actual difference between AC and DC bells...are they interchangeble?
I don't know what type Edwards DC bell you are using without looking however it may be similar to the usual doorbell or buzzer also made by them. They all use an interrupter and will work on AC as well as DC as we all know. The fact that you had to do some adjustments to make them work on AC suggests that they are indeed a DC device. Perhaps the other existing bells had a small rectifier wire nutted in the line ahead of them?