Arthur -
What a memory! I'd completely forgotten about them. I don't think I've installed one in 35 years.
Matt -
BLFs were a stock item in the early '70s. We'd wire a diode into the set and feed the BLF on the receptionist's desk (or wall). The unit could be ordered either -24VDC or 10VAC and it came with a variety of transparent label overlays (depending on which system you might want to use it with) Usually we matched the numbers to the ICM. On a K-10 where the only spare was the Y/O pair we'd use 1 wire for a buzzer and 1 for a blf with a common ground for both.
Sam
Yes that unit which was available in 1,2,3,or 4 lamp models was a standard (small) BLF.
