Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime powered by a 6 V continuous voltage. The transistor can be a BD136.
Below are two frequency filters for receivers using crystals. The crystals must have the frequency of...
We found this circuit in a Radio Electronics from December 1963. The circuit combines valves and...
This circuit published in the November 1964 Radio Electronics magazine powers a light bulb but can...