The AA-1 was an early Wabco two-chime airhorn used primarily on interurban equipment and some
early locomotives and railcars. It was presumably a combination of long and short bell A-1 horns
on a single manifold. The AA-1 was still available in 1936 when San Francisco Bay Area transit
operator Key System outfitted its new "bridge unit" articulated cars with the horns. The
horn was presumably phased out with the introduction of the AA-2.
Documentation of the factory tuning of the AA-1 has not yet been uncovered. Surviving horns
on Key System bridge units at the Western Railway Museum at
Rio Vista Junction, CA appear to play E and G#.
A few AA-1's survive on preserved electric interurban equipment.
AA-1 sound samples:
Key System bridge units:
Sample 1...195kB...9 seconds
Sample 2...251kB...11 seconds
Sample 3...252kB...11 seconds