I found tis circuit in na old documentation from 1958. The circuit uses germanium transistor availble that time and hard to obtain today. The circuit is indicated for phono applications using variable reluctance transducer.
Often, unauthorized people use the phone to make improper calls. A control for this is achieved with...
This circuit was obtained in an Electronque Loisirs magazine from France, in a July 1991 edition. It...
This circuit sensor is an NTC with a resistance of the order of 2k. The SCR can be from the TIC...