When the phone rings, a high-powered incandescent light comes on. This circuit can be interesting to obtain the remote call warning or to assist the hearing impaired.
This telegraph monitor was found in an American documentation for radio amateurs from the 1970s. The...
We found this circuit in a European publication from the 1970s. The transistor is made of...
This adjustable source from 2 to 15 V uses transistors from the 60's, as indicated in the...