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.
Found in a magazine 73 for radio amateurs, this circuit has two settings, one for the interval and the...
This good quality amplifier found in a 1982 documentation has a traditional complementary output...
A low frequency divider can be made using common unijunction transistors as shown by the figure...