Continuity test (CB9328E)

This audible continuity test was obtained in a book from the 90's describing simple projects. The feeding is done with a single battery.

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10-minute timer 555 (CB9368E)
Found in a magazine 73 for radio amateurs, this circuit has two settings, one for the interval and the...
1 W Amplifier (CB18192E)
This good quality amplifier found in a 1982 documentation has a traditional complementary output...
Frequency Divider With Unijunction Transistors (CB929E)
A low frequency divider can be made using common unijunction transistors as shown by the figure...