Practice code oscillator (CB21090E)

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

Absolute Value Amplifier CA3140 (CB13841E)
This circuit is from the 1977 RCA Linear Integrated Circuits Manual. The circuit has a...
IR remote control emitter (CB7020E)
This circuit was found in 1980's Radio Electronics. The circuit produces a 1500 Hz modulate 35 kHz....
Triac Power Switch (CB25074E)
The maximum power of the controlled load depends on the triac used. The circuit is from a Radio...