This signal injector and tracer (follower) was found in an old American documentation. The transistors can be general use and power is made with one or two common cells.
This circuit is from a 1967 RCA documentation. Components can be replaced with modern equivalents. The...
This two stages amplifier is used with high impedance earphones. The transistors are very old...
The oscillator of the figure has its frequency determined by the crystal. The indicated value is...