This circuit for VCR recording heads was found in the February 1990 issue of Radio Electronics magazine. The circuit is use do observe signal in an oscilloscope.
This circuit with unijunction transistors was found in a documentation from the 80's. The trigger...
In this circuit of an old American documentation, the input impedance is the same as the output...
In the figure we have the way to obtain a voltage of 18 V from a 6.3 V transformer with central...