This is a battery powered 3W power amplifier using germanium transistors. The circuit is from an English documentation from 1967. The transistors are from the time.
The component used in this regulator is not common today. The switching circuit is from an 80's...
This analog frequency meter for low frequencies was found in Radio Electronics magazine from July...
This circuit was obtained in a 1970 EEE and applies to almost any operational amplifier. The...