This circuit was found in an Electronic Engineering of the 80s. The circuit indicates when a telephone line is being used, being useful in case of extensions.
In the figure we have a way of obtaining a 13,2 V with current up to 5 A using an integrated 7812...
This broadband amplifier was found in an Elektor from the 90's. The gain is 10 dB with a noise...
Suggested by General Electric in an old documentation, this circuit can use modern SCRs and the...