Practice code oscillator (CB21090E)

Found in Popular Electronics from the 90's, this circuit consists of an audio oscillator for Morse code practice.

LM3914 Audio Level Meter (CB24606E)
This circuit was found in the February 1980 issue of Radio Electronics magazine. The digital...
Capacitive Ignition (CB6380E)
We found this circuit in a Motorola manual. The circuit has the capacitor charging at 15 to 30 V,...
Impedance Adapter (CB15044E)
This circuit has a high input impedance and low output impedance, serving as an adapter for...