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.
May 2017 - Mouser Electronics already has inventory with ROHM BD570xx integrated circuits for...
This circuit is from an American 1967 documentation and can be implemented with modern equivalent...
This simple low current circuit was found in a Radio Electronics magazine from August 1960. The...