This relay shield circuit for old computers was found in January 1983 Radio Electronics magazine. The relays are sensitive types with currents up to 200 mA.
This receiver for the mid-wave band was found in a documentation from the 60's. The transistors are made...
In the figure we have a symmetrical power supply stabilized by a zener diode. Transformer and...
This circuit is a digitally controlled variable capacitor. We found it in American documentation from...