Retired STR-SG wrote:I looked at the FWD for 4001 and 4004. I don't see much difference. As far as I can tell 2901 devices are listed as compatible with each panel. Both show "4051 horn (2901)" as compatible. Simplex originally had a 6 digit sales number for devices (####-##) and later converted to an 8 digit system (####-####). All existing devices that were carried over simply switched numbers. Hence the "4051 horn (2901)" designation on the FWD. I think you will be OK as long as you don't use any really old devices that don't have internal suppression in them (usually an MOV across the coil).
There was a learning curve between the older relay operated panels like 4208 and the next generation 2001, 2100, 2120 electronic panels. Older electromechanical horns, bells, chimes, door holders, etc did not have suppression devices in them. They could produce high voltage spikes when the magnetic field collapsed on the coils in them. A similar inductive discharge system fires the spark plugs in your car. The relay operated panels did not have an issue with that. The electronic panels are sensitive to these back EMF spikes so need devices with internal suppression. In the changeover to electronically operated panels while the vendors were adding suppression I added a lot of diodes to door holder circuits.
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