A 60Hz signal generator can be useful in testing your circuits. You can test your notch filter, simulating hum noise, or you can use it as part of your DC-to-AC inverter design. Here is the schematic diagram of the circuit:

Stable 60 Hz Generator circuit schematic

The circuit consist of twin T network built around 33k resistors  and 0.068uF caps inside a feedback loop. You can see the cross between 6.8k and 33k is dotted, but I think it shouldn’t (it should be disconnected). You can try yourself!  [Circuit’s schematic diagram source: lh-electric.4t.com]