Oh yeah, I see. The differing revision number is odd.
Iām more trusting of the Revision B marking myself. And this site I found early on in my research implies that this device was made sometime during or after 1975.
That is a really neat device. I never even knew ESL manufactured something like that. Was that made to be installed on regular NAC circuits, or was it intended to be a remote horn that could connect to one of their smoke detectorās/alarms? Also wonder if thatās a residential or commercial productā¦ Seems more residential to me, but Iām not entirely sure. Pretty neat it uses the same design as their smoke detectors, I guess they did that to cut manufacturing costs.
If I were to guess, it looks like it may have been manufactured in 1987 actually. I see ā87ā stamped in two places, once on the board itself, and the other on that white sticker. I believe the marking on the board says 87ā18, which may possibly mean the 18th week of 1987. Kind of a shot in the dark, but usually printed circuit boards have dates stamped on them like that, same format and all.
I would assume commercial NAC circuit given this comment I got on one of my videos on it.
And for the date of manufacture, that is indeed a helpful detail. But I see both a 87'13C and a 8717C
Wow, fascinating. So it seems like they were manufactured for commercial use after all. Looking at the pictures again, I see what youāre talking about. Itās like the different revisions stamped on it. Very odd for it to have two different revisions and what Iām assuming to be date codesā¦
My guess for the two revisions is while they updated the etching on the PCB, they forgot to update the stamp.
As for the two date codes, I only have a shot-in-the-dark guess that one is the manufacturing date and the other is inspection date. Again this guess is based on nothing and just a guess.