Found in a 1924 publication, this 2-valve receiver has a speaker output. Power comes from several batteries. Information about the coils is given.
This circuit found in a French documentation from 1982 can be applied to any operator. The...
In this circuit of the 1980s, the T1 transformer has 30 turns of 28 primary wire and the secondary...
Found in American documentation from the 90s, this circuit triggers a buzzer with a Sonalert-type...