555 Code Oscillator (CB26324E)

Found in a 1990s Popular Electronics, this circuit produces a tone on a small speaker. The keyer directly controls the power supply.

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Wien Bridge Oscillator (CB8089E)
This circuit generates sinusoidal signals between 300 and 3000 Hz. We find a 303 Circuits from the 90's....
Line Amplifier (CB19052E)
This amplifier for audio transmission lines was found in a 1961 American publication. The critical...
Intercom with telephone (CB7829E)
Old phones with dials can be used in a simple home intercom system, as this circuit from Popular...