This circuit for monitoring telegraphy transmissions was found in a 1975 CQ magazine. Transistors may be modern equivalents.
This circuit generates trains of pulses in regular intervals determined by R1 and C1. The...
The first transistor can be the BF494 and the other BC548 on this MW radio found in a...
We found this circuit in a Popular Electronics from 1992. It modulates an infrared LED with a...