This filter for receiving audio in telegraphy was found in a magazine 73 for radio amateurs, in an edition of the 80s. The circuit is tuned to 700 Hz and has a 200 Hz bandpass.
Only incandescent lamp can be used in this circuit. The SCR must be mounted on a heatsink and...
This circuit originally appeared in a publication of 1997. With the changes, the circuit can be...
This circuit is from a 1969 Electronics World. The transistors may be modern general-purpose...