This is a 1960s amplifier setup found in a period publication. The circuit uses a special driver transformer that inverts the phases of the signal to excite the output transistors.
This simple 555 biofeedback circuit was found in the December 1983 issue of Radio Electronics...
This circuit has a programmable alarm that can be triggered with different water levels. The...
Found in a 1991 Hobbyst Handbook, this circuit monitors both battery and alternator voltage. The set...