This multivibrator, whose frequency depends on the capacitors, was found in an Argentine publication from the 1970s. The transistors can be any PNP type of germanium or silicon, such as the BC558. The T2 collector resistor is 1k and the phone must be magnetic with impedance between 1k and 5k. A 1k resistor can be used in parallel with a piezoelectric capsule. 0.04uF capacitors can be replaced by the current values of 47nF.
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