Variable oscillator for code practice (CB7317E)

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

Intrusion alarm (CB7239E)
This circuit is from a 1965 General Electric manual. It uses components from the time that admit...
Audio Frequency Meter (CB20477E)
Found in a Popular Electronics from 1992, this circuit uses a PLL567 in an audio meter bridge that...
Darlington Photo Amplifier (CB8316E)
Found in General Electric's 1969 documentation, this circuit uses two Foto Darlingtons to control...