I was mostly talking about the pre 1950 models.

Is there any way to contact Art Johannes?

It is too bad Federal never documentated each of those early 500 variants.

Interesting to see how the stator is angled at the port ends.

My initial idea was that the eight blade fan spins around with the siren rotor, somehow supercharging the sound.

If only we had better photos of this siren. Then it'd be easier to tell.

Looks like a Darley 5.

Looks more like a Sentry.

Found this a few days ago. Since it is a photo, and I'd prefer to know more about the siren itself, I'll post the link here, for now. http://cgi.ebay.com/Worlds-largest-air-raid-siren-1942-4x5-PHOTO-NEG-/330432755145?cmd=ViewItem&pt=Art_Photo_Images&hash=item4cef53b5c9 I know the user 500AT ...

3. I think the iForce line uses it's own tones. 4. Single tone carried further. 5. May not have worked as well at long distances. 6. Single phase sirens usually have longer wind up and lower peak RPM. Not always, though. 7. 1000T, 2T, 500T, etc. meant the siren was dual tone. 1003 only came in dual ...

Took these today. I will link the county categories from now on, as it's much faster than linking out every town individually. Not all photos in Fond du Lac set were taken today. Fond du Lac county http://www.flickr.com/photos/46180423@N03/sets/72157623457589040/ Columbia County http://www.flickr.co...

with possible exception to the early roundback models

I do not think there are any substantial differences between the roundback 2001, and the earlier 2001-DCs, aside from the intake box shape.