This audio oscillator is from a 1957 Raytheon publication. The tone generated depends on C2 and C2 and the handset must be high-impedance magnetic. Equivalent transistors can be tested.
This source is indicated for the power of the digital multimeter of the CIR12007, but it can be...
This 1967 Electronics World circuit is suitable for frequencies up to 1 MHz. The setting applies...
This circuit was found in a Popular Electronics from the 90's. The operating curve is given next...