I have searched so many sites and have managed to duplicate the fire truck and ambulance siren, but does anyone have the schematics for the yelp, and the hail 1 and hail 2 for the US police sirens? With 2 lm555 timers in a sweeping output frequency schematic I was able to emulate a realistic sounding slow siren and up and down ambulance but I cannot get it to do the fast smooth rotating police sound. The only yelp schematic I have found uses unijunction transistors and I cannot find those anywhere.

 

Jameco ( www.jameco.com ) carries 2N2646 @ $3.99.

 

Digikey carries 2N6027 and 2N6028 UJT's (PUT's, actually - Programmable UJT's) for $0.48/ea. The 2N6028's carry more current [eta] than the 2N2607's do.

[eta]
Newark carries a few different UJT's:
http://www.newark.com/jsp/search/br...e=en_US&catalogId=&prevNValues=500003+1001821

Avoid NTE parts unless you like spending far more than you should.

I don't know what Newark's handling/shipping charges are lately, and I don't know if they'll ship USPS 1st Class like Digikey will.

 

A really old design I copied when I was a teen.

 

Amazing - somebody still carries some of those old Motorola HEP's - http://www.talonix.com/shop/category.aspx?catid=10

 

I have another sheet with a very similar schematic, that has a list of substitutes I tried. To be honest I thought that was the one I used in the original forum long long ago (this was a recycled picture).