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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Transistor Flip Flop (CB20130E)
This flip-flop circuit with general purpose transistors was found in American documentation from...
Square oscillator (CB8452E)
This circuit was found in a 90s Popular Electronics. The integrated circuit used is similar to the 741....
Band rejector active filter (CB7405E)
This filter was found in Texas Instruments documentation from the 1980s. The circuit uses a common...