[sdiy] KN-75 optocoupler

[anthony]

I found some more old circuit boards I overlooked in my basement the other 
day that had yet to be desoldered and pilfered of their parts. One caught my 
eye as I was desoldering it from a board from an old telephone answering 
machine (replete with many a solenoid...): a big black tubular thing with 4 
leads, that I at first mistook for a reed switch replay (something I like a 
lot for some reason). But upon removing it, I discovered some circuit 
symbols silk screened unto the top of the pc board. One side was in 
unmistakeable symbol of an LDR and the other was less obvious, but seemed to 
indicate that an AC signal should go there. On the side of the tube is 
printed KN-75 with a directional arrow underneath.

So I was wondering if anyone knows anything about this particular doo-dad, 
since googlling "KN-75" mostly yields hit involving aircraft of some sort or 
random things (as simple part numbers so often do...).

My guess is an incandescent bulb on one end and an LDR on the other. 
N'est-ce pas?


cheers,
aa