This circuit was found in a 1967 Raytheon manual. The transistors are from the time. Equivalent modern transistors can be tried out.
This circuit, from the 90's, is intended for operation with vinyl record players of the time, as...
Using a zener diode it is possible to change the linearity of the scale of an analog instrument by...
Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime...