PH meter (CB20731E)

This circuit was obtained in an old American documentation. The integrated circuit used is uncommon today. Modern equivalents can be searched.

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Blocking oscillator (CB6921E)
This blocking oscillator configuration was found in a 1964 American book. The circuit can be...
Tunnel Diode Listening Transmitter II (CB19426E)
This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is...
FM AC Transmitter (CB20347E)
This transmitter, indicated for espionage applications, is permanently powered by the power grid....