This ingenious circuit was found in a 1990s Popular Electronics. The oscillator is a 555 and the keyer uses an optocoupler in the configuration shown.
The CMOS TLC555 can be gated from external CMOS circuits using the configuration shown here. The...
In the figure we have a two-channel preamplifier with two 741 integrated circuits. The circuit is from a...
We found this circuit in a documentation from the 50's. The transistors are germanium types. The...