Crystal variable oscillator (CB9506E)

Found in Radio Electronics from the 90s, this circuit can vary the frequency in small values around the crystal frequency.

741 RC Oscillator (CB19350E)
This oscillator circuit for sinusoidal audio signals with operational 741 requires a symmetrical power...
Darlington Logic Tester (CB13786E)
Found in a 1974 Radio Shack documentation. This circuit must have a connection to the ground of...
Pole finder (CB5950E)
This sensitive circuit detects the live pole of a power grid or outlet. The circuit makes use of a high...