Concord Telephone Exchange Inc.

   The Concord Telephone Exchange Inc.  in Farragut Tn. had a receiver off hook tone that was a medium pitch sound that went like a horn. I lived there back in 1980 to 1981. does anyone have any idea what kind of off hook tone that was? Was it a howler tone or high tone? was the concord Telephone Exchange Inc. a G.T.D.-5 E.A.X. system or a P.B.X. system or a P.A.B.X. system or a P.A.X. system or a ROLM C.B.X. system? Please let me know. Thank you.