Found in a 1924 documentation, this circuit is powered by 3 batteries, two of which are high voltage. The output is a high impedance headphone jack.
This 1970 General Electric circuit is an equivalent configuration to the previous one with PNP...
This circuit was obtained in a Texas Instruments 2012 documentation, which consists of a current...
We obtained this circuit in a Maxim documentation from the 90s. The circuit is based on the...