This well-known circuit version of the siren was obtained in a Colectro Handbook from the 70s. The transistors are of general use, with Q2 being a BD136 for greater power with power from 6 to 12 V.
The frequency of this circuit depends on the crystal. The transistor supports a modern equivalent. We...
This circuit is from an Argentine publication from the 1970s but can still be assembled with...
This circuit was obtained in an American documentation from the 80's. The transistors can be...