The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
An excellent signal generator for the audio track was found in a 1983 documentation. Its complete...
CMOS inverters can be used as amplifiers, obtaining a flat response up to approximately 20 kHz....
This circuit uses BCD switches to program the frequency to be divided. The circuit is from a Radio...