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.
We found this telephone amplifier in a European publication from the 1980s. The transistor can be...
This circuit is one of many that we have in our section. It was taken from the Electronics...
This circuit is from a 1980s Motorola documentation. The circuit can be set to fire from 60 to 120...