If you check the voltage coming out of an original IVR, you will NOT get 5 volts. The voltage will go up, then off, then up then off. That is how it works, just gets hot and shuts off, then comes back on. primitive but functional.
hmm my digital does that and never makes 5v reading, but my analog meter is a bit faster and hits 5 v to 0v pulsing. one of the reasons I like analog meters a bit better for classic work.