Electronic Siren Circuit

[4. The combination of claim 3 further comprising means for electrically biasing the transistors of said first pair of transistors to their threshold of conductivity, said first circuit means rendering said first pair of transistors individually and alternately conductive in proportion to said first and said second audio

• signals in response thereto.] 5. The combination of claim 3 wherein said second circuit means includes means for rendering said transistors of said second pair of transistors individually and alternately conductive in proportion to the degree of conductivity of said first pair of transistors when said output circuit is selectively connected to said audio signal
• means. 6. The combination of claim 1 wherein said square wave generating means comprises an astable multivibrator circuit which includes a pair of switching transistors, said switching transistors each having a similar one of their collector and emitter connected in common, their bases coupled to said time constant determining means, and a pair of capacitors connecting the other of said collector and emitter of each said switching transistor to the base of the mutually opposite one of said switching transistors, the switching frequency of said multivibrator being
• proportional to the voltage applied to said bases. 7. The combination of claim 6 wherein said multivibrator circuit includes an output circuit having a pulse-shaping means for increasing the switching speed of said
• switching transistors. 8. The combination of claim 7 wherein said multivibrator further includes balancing means for rendering said square
• wave symmetrical. 9. The combination of claim 8 wherein said balancing means includes a resistor and a potentiometer connected electrically in series with the collector-emitter circuit of one of said switching
• transistors. 10. The combination of claim 9 wherein said pulse-shaping means is a capacitor connected electrically in series with the
• collector-emitter circuit of the other of said switching transistors. 11. The combination of claim 1 wherein said first circuit means includes means for electrically isolating said power output circuit and said
• multivibrator circuit. 12. The combination of claim 11 wherein said isolating means comprises a Darlington amplifier circuit which includes an
• input terminal coupled to said output circuit. 13. The combination of claim [18] 11 further comprising second isolating means for electrically isolating said square wave generating means from said
• time constant determining means. 14. The combination of claim 13 wherein said second isolating means includes an isolation transistor having a base, and a collector-emitter circuit, said base being connected to said wave form generating means, said collector-emitter circuit being coupled
• to said square wave generating means. 15. The combination of claim 1 wherein said pulse generating means is a [second] multivibrator
• oscillator. 16. The combination of claim 15 wherein said [second] multivibrator oscillator includes a plurality of frequency determining elements and [second] switch means for selectively connecting a predetermined one of said frequency determining elements into said oscillator circuit thereby determining the switching frequency of said
• multivibrator. 17. The combination of claim 16 wherein said selecting
• means includes a multiple pole switch. 18. The combination of claim 16
• wherein said frequency determining elements are capacitors. 19. The combination of claim 1 further comprising means for selectively disabling said pulse generating means and means coupled to said time constant determining means for manually generating a plurality of charging pulses, said time constant determing means being responsive to said manually
• generated pulses to generate one of said wave forms. 20. The combination of claim 14 further comprising means for coupling an auxiliary siren
• circuit to said time constant determining means. 21. The combination of claim 20 wherein said auxiliary siren connecting means is connected to said time constant determining means, said second isolating means being connected between said auxiliary siren connecting means and said square
• wave generator. 22. For use in an electronic siren capable of producing selectively, audio and siren signals, a power output amplifier circuit including
• a. a first pair of [diffused base] transistors connected in a push-pull amplifier circuit configuration having input and output circuits, means for selectively biasing said transistors to the threshold of conductivity whereby audio signals coupled to said input circuit renders said transistors alternately conductive in proportion to the amplitude thereof,
• b. a second pair of [diffused base] transistors connected in a push-pull emitter-follower amplifier configuration having input and output circuits, said second pair of transistors being diffused base transistors, means coupling the first-mentioned output circuit to the second-mentioned input circuit for driving said second pair of transistors alternately into saturation in synchronism with saturation of respective ones of said first pair of transistors,
• c. impedance-matching means for coupling said second pair of transistors to a sound producing device, said impedance matching means having input and output circuits the input circuit of which being connected across the emitters of said second transistors, the last-mentioned input circuit
• having an impedance appearing across said emitters. 23. The circuitry of claim 22 wherein said coupling means includes an auto transformer having a pair of input terminals and a pair of output terminals, said first pair of transistors each having a similar one of the collectors and emitters connected in common and the other connected to said input terminals, respectively, said second pair of transistors having the bases thereof connected respectively individually to different ones of said output
• terminals. 24. The circuitry of claim 23 in which the emitters of said first transistors are connected in common and the collectors thereof are connected, respectively, to said input terminals, said impedance-matching means including a transformer having primary and secondary windings, the primary winding being connected between the emitters of the second transistors, a source of voltage connected between the center of said
• primary winding and the collectors of said second transistors. 25. The circuitry of claim 24 including a square-wave generator and a source of audio signals selectively coupled to said input circuit of the first-mentioned amplifier and switch means for selecting which of said generator or source is applied to said first mentioned input circuit.