Found in a Motorola documentation from the 70s, this circuit makes use of transistors of the time. Modern equivalents can be used. The diode also supports an equivalent.
This circuit is from an Electronics World of 1964. The circuit can be made with modern...
This circuit is from an old American documentation from the 70s. Transistor 2N3904 can be replaced by...
We found this circuit in the March 1980 Radio Electronics magazine. The circuit used is the HA2400...