This stereo meter-indicator was found in the August 1971 issue of Radio Electronics magazine. The transistors are known types and BC548 equivalents can be used.
The automatic modulated siren circuit shown in the figure really produces an interesting sound...
This circuit was found in the August 1973 issue of Radio Electronics magazine. The Darlington...
This circuit has three settings, central sound frequency, modulation speed and modulation depth. The...