OR port gate relay (CB21030E)

We found this circuit in an American brochure from the 90s. In it we have the way to implement a 4-input OR gate with switches and a relay.

1 to 500 V voltmeter (CB18548E)
The accuracy of this simple circuit depends on the accuracy of the input circuit resistors. Any...
Guitar Tremolo (CB6709E)
This circuit is from an Electronics World of 1964. The circuit can be made with modern...
Semiconductor Tester (CB18739E)
We found this circuit in an old documentation, but the circuit is current due to the components it uses and...