Zero crossing switch (CB21543E)

Found in a 1964 publication, this circuit makes use of transistors from the time. It operates on frequencies up to 3 kHz.

27 MHz receiver (CB19446E)
This receiver was obtained in a documentation from the 90's and is of the super-regenerative type....
Line Driver (CB24229E)
This circuit couples 600-ohm signals to a line of the same impedance consisting of an amplifier stage....
Tachometer with Direction of Rotation Indicator (CB11572E)
The circuit presented is from an old magazine having been translated and published in a national...