Variable oscillator for code practice (CB7317E)

This circuit is from Popular Electronics from the 90s. The integrated circuit is not very common nowadays.

Touch Switch or Water Alarm 4001 (CB16319E)
The presence of a low resistance between the terminals of the sensor causes this modulated...
Multilayer Varistors for Surge Protection - TDK
TDK provides a wide range of EPCOS varistors for surge protection through Mouser Electronics....
Signal injector (CB21649E)
This circuit was taken from a Popular Electronics from January 1967. Transistors are from the...