This constant current charger from 1997 Linear Technology Applications uses common components at the time. The transformer is the critical component, being designed according to the load voltage.
This circuit with 4 transistors can receive signals in 6 shortwave bands. The circuit is from a...
Found in a 90s 73 magazine for radio amateurs, this circuit makes use of common operational...
Found in a 1960's Mullard transistor manual, this circuit has an input current of 4.4 A and an...