Practice code oscillator (CB21696E)

In the figure we have an astable multivibrator driving a speaker to produce audio signals for Morse code practice.

Signal Compressor and Expander (CB20310E)
This circuit acts on the dynamic range of an audio signal, which can be useful for recording,...
Stepper Motor Control UCN4202 (CB4860E)
This is the conventional application of the UCN4202 to control a 12 V stepper motor with current...
10 V Transformerless Power Supply (CB23987E)
Described in the December 1969 Radio Electronics magazine, this circuit is intended to supply the...