Yes, I have 3 of those SA90LT units. I got them from my grandma’s house when I went to replace her detectors. They were all installed in the basement, and were missing their batteries. They now they sit in my collection. They’re from 1993, so I’m not sure if these are older or newer, but here’s the label of one of mine (sorry about the lighting):
That Smokey Stover detector is actually a rebranded SmokeScan 4909 (I think that’s the model #, but can’t be sure). As you can see, it’s 120VAC hardwire with no battery backup.
It’s nice to know that my smoke alarm is made around 1993, but mine isn’t hardwire- ready. Also I don’t understand how holding the light up to the test button puts it into alarm. I tried it and it didn’t work.
There is a photodiode behind the test button on the circuit board. It looks for a flashing light source. That’s why there’s a hole in the test button and why it’s gold- so that light can go down that gold tunnel and reach the photodiode at a bright enough level.
These are kind of finicky to test with a light. You have to first point the flashlight straight at the test button NOT at an angle, then sweep the beam across the button until it goes off.
I thought there was some kind of photocell there! I learned that from when I first tested 1 of mine and the LED didn’t flash. Turns out it wasn’t an LED after all! And yes the Light Test units came out around 1993 or 1992. They use the 2nd generation SA67D cover and base, and have the newer sensor and piezo horn with only one hole. They do the 4/6 alarm pattern.
In related news, I just ordered a New Old Stock 1st Gen SA67D. The one with the bigger ring around it. I will try to post a video of me testing it!
After gorging myself on smoke alarm videos, I found that before the 1st gen 67D, there were other transition models of the early 80’s between the SA76RC and the SA67D. Check it out…
Courtesy of NLind
There was an in-betweener model for the 76RC and the 67D. And as you can see, it is the SA67. It seems to be almost exactly the same as the 76RC, just a little less fancy with the white test button.
Courtesy of NLind
There was also another in-betweener model called the SA80FD! It had a unique design. It looks like a cross between the 80FC and the 67D. It had a hinged cover but had a smaller set of rings like the 80FC, but also had the more modern style cover mounted test button, and the big ring of the 1st gen 67D.
I think I know which ebay listing you’re talking about. I have never seen an SA67 or an SA80FD in real life, BUT I have once seen an 80FC. in an old house when we went to a party. There is also an SA120, which was the first model with the EscapeLight: https://www.youtube.com/watch?v=rvFkTPsDKjg - (NLind/FireAlarmFan’s video)
This alarm has the same base, horn, and test button as the later SA76RC, but a special cover. I have seen one of these in a building, but it looked like it had the white domed test button rather than the clear tier test button. (it was upstairs, and I was downstairs
Okay, I just learned that 12.6 volt batteries are no longer made. I’ve been searching Duracell, Energizer, Eveready, Rayovac, basically every battery company. The detector will come with its original battery, but it is most likely dead, and if it’s not, it still probably isn’t a good idea to use it. What would be a good substitute battery or where can I get a 12.6 volt battery?
A power supply or car battery could very well work, but they are such big batteries for such a sensitive and small circuit board. Replacement batteries are virtually non-existent for this type, but you could use a similar battery. The Energizer A23. It is a 12 volt battery with a more similar size to the type you’d need. Maybe it would work. It would be electrically perfect, but it might be too small.
to the size in this video of the actual battery you’d need:
it became clear that you wouldn’t want an A23 battery. It might not be able to run the mechanical horn on these old smoke alarms for more than seconds. An A23 is more for keyfobs.
Yeah I’ve never seen such a massive and old keyfob that uses an A23. But even still, an A23 would likely not be big enough in size or in current capacity to power one of these old smoke alarms with the mechanical horns. I don’t know how the horns work, but I can take a pretty good guess they work like a mechanical fire alarm horn. They have an electromagnetic coil that pulls up a “clapper” and lets it go onto the metal diaphragm, much like a bell, but way faster, at the frequency you hear the horn sound at.
On another note, that’s why many old AC smoke alarms and AC mechanical fire alarm horns sound so deep at 60 or 120Hz: 60 Hz is the frequency that all AC power is delivered in the United States. So, it becomes really easy to find something to make the clapper go back and forth to make a tone- use the 60Hz from the wall! This produces a characteristic deep sound like the Simplex 4050, or the Firex FXW-1A.
A DC mechanical horn doesn’t have an oscillating power source to make driving the clapper easy… It has to use a switching mechanism. Below is an article on how the same concept of switching mechanism is used to drive a doorbell: http://www.gcsescience.com/pme6.htm
Replace the bell with a metal diaphragm, and you have yourself a DC vibrating horn!
The reason DC horns sound so much higher pitch than AC horns is pretty simple: Because DC horns require a switching mechanism, they operate as fast as the mechanical parts inside the horn will let them run. It just so happens that the maximum speed of the switching mechanism is way higher than 60Hz. This natural frequency is what makes the Simplex 9838 or the 7002T sound at the pitch they do. Now, in the case of a brass “squealer” horn, or the like, the horn is smaller and the parts don’t have to move as much or as far. So, the pitch is even higher on those horns, because they can move faster.
Much the same way that motorcycle engines can reach higher RPM’s than car engines: they are smaller and lighter and can spin faster without self-destructing.
