This circuit is from a 1968 documentation. It makes use of thermistors (NTC) to indicate overheating of charged batteries. Modern equivalent components can be used.
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
We found this circuit in an 80's Radio Shack publication. The circuit uses a company buzzer, but...
This basic amplifier using complementary transistor in the output sources about 0.5 W of good...