Simplex 4246-2 SU?

So i got this new panel off facebook today and what appears to be different from the SU model to the typical 4246 is that it has this timer mounted in the middle. I havent had time yet to plug it in and test it but does anyone have any info about these SU models and what the timer does?

That’s an AC klaxon panel. If I had to hazard a guess, that timer may have to do with setting the code pattern for the horns. We have some experienced Simplex guys here, if I’m wrong hopefully they will correct me.
Have you ever worked with an AC panel before? They are very different from the 24VDC panels we use today. These AC panels are extremely dangerous if you do not possess the tools, documentation, and technical skills needed to work on them safely.

This is my first AC panel im working on. I have found a diagram and have familiarized myself with the wiring setup as well as how to make some of the adjustments needed for supervision. I have wired a pull station to it and the timer seems to count down once activated. I wonder if its a timer to auto silence the bells because i didnt hear any clicking that would come from a march time circuit. However i havent tested any horns on it yet so i still have to see what that timer actually does.

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Do the NAC relay(s) click on/off as the timer goes? Some of the really old AC panels do indeed only do a certain number of repetitions, others will pulse out a 4-n code (4 blasts for the really old signal H-E-L-P, n blasts to indicate the zone that tripped.

There are a few guys around here that know quite a bit about the AC panels, maybe they’ll chime in as they’ll be able to tell you a lot more than I could.

I actually managed to figure out the purpose of the timer. Its an adjustable auto silence timer that can go up to 5 minutes. But im still figuring out of the “SU” in the model number coresponds with the timer, or if it is for something else.