This circuit was obtained from a 1947 amplifier manual. The circuit makes use of a transformer source, but it can also be battery powered.
These optical relays, which can act as a shield, were found in an American documentation from the...
This circuit, suggested by Philips Components, uses as a base a voltage comparator of the type...
This circuit can generate signals from 2 to 15 MHz or 4 to 22 MHz depending on the used components...