Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime powered by a 6 V continuous voltage. The transistor can be a BD136.
This linear oscillator was found in a 1968 publication. The operational amplifier is from that...
This circuit was found in Radio Electronics from May 1965. The SCRs and transistors are from that...
This Wien bridge circuit, using a 741 operational amplifier, was suggested by Texas Instruments in its 1996...