'70's movie & T.V siren mystery solved (for me at least)

[Unit of Civil Defense]

For the longest time , I have been trying to figure out who made the vehicle siren that was used pretty much exclusively in movies and television in the 1970's. The sound was a very distinct wail and yelp combined together. The Federal Signal PA 300 Interceptor, which I own, has both wail and yelp but not together and no way that I can figure to combine the two. I also looked into Carson and Southern V.P with no luck.

While looking for something else not related to the siren, I stumbled across how it was done....pretty simple for a T.V sound engineer to do in the 70's.
To get sound dub over, the engineer simply recorded 30 seconds or so of wail and 30 seconds or so of wail. and placed one over the other in a recording. The best example that I can think of is any Starsky & Hutch television show , not the 2004 movie.
To achieve this in the real world, one would need two Federal PA-20's or two PA-15's or one of each....one set to wail and one set to yelp with a remote on/off switch verses using the control knob on the siren control unit so that they both come on together at the same time.