This circuit is from a factory manual from the 80s. The circuit can be implemented with modern operationals. The supply must be symmetrical, and the diode is general-purpose.
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...