In the figure we have a simple way to produce tone in a piezoelectric transducer. The frequency depends on the capacitors and the supply can be done with voltages from 1.5 to 6 V.
This single transistor radio without a power supply was found in documentation from the 1960s. The...
T1 and T2 can be BC557 and T3 a TIP32 for lamps up to 3 A. The supply is made by voltage of 12 V...
This circuit is from the time of the tubes, being indicated to operate with transmitters turning off...