Found in a 1969 Electronics World, this circuit generates low frequency signals with two repetition bands. Transistors support modern equivalents.
The integrated circuit used in this application is no longer common. The circuit is from the...
This circuit makes use of a sensitive 5 mA reed-relay to be driven directly by a phototransistor. The...
This circuit for monitoring telegraphy transmissions was found in a 1975 CQ magazine. Transistors may be...