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.
This 6 V battery charger was found on a 1987 Hands On Electronics. Rc determines the charging...
In the figure we have the way to obtain an adjustable 1 to 10 mAconstant current source. The...
This circuit is used to test an inductor (coil) allowing the observation of its opration in an R-L...