Device for tracing a telephone switch train

Claim 1

A self-contained, solid-state device for tracing a telephone switch train in a telephone central office and which is provided with selector contacts, said device being adapted for separable connection to a switch test jack of a telephone central office, said device receiving its power from the switch train, and comprising: line connection means to said train and the power source thereof, the ground of the power source being connected to the emitter of the third transistor, and the collector of the latter transistor being connected to the filament of the lamp, a high-frequency audio oscillator of the phase shift type including a transistor having its emitter connected to the negative of said power source and having its collector connected to receive positive voltage from positive ground of said source to turn on the transistor, two phase shift networks each comprising a resistor and capacitor connected across the emitter and collector of said transistor, the base of said transistor being connected to receive the AC signal developed across the transistor, a low-frequency interrupter oscillator of the phase shift type connected across the high-frequency oscillator and having a transistor, resistor and capacitors in circuit similar to that of said high-frequency oscillator, the AC signal to start the low-frequency oscillator being supplied by the power source and by the surges involved in the partial charging of the latter capacitors, and a lamp-flashing circuit including a series arrangement between the base of the transistor of the low-frequency oscillator and the steering diodes thereof, of a transistorswitching Zener diode, a third transistor, a lamp, and a second Zener diode for limiting lamp voltage and opposed to the first diode, and a ground from said power source connected to the filament of said lamp through said third transistor, a portion of the outlet of the transistor of the low-frequency oscillator being fed through said circuit through the first Zener diode to the base of the third transistor, the latter diode being conductive to the third transistor when the alternations in the low-frequency oscillator swing more negative, the third transistor being switched into conductance, causing the lamp to light and the second Zener diode to limit the voltage to the lamp filament.